Uneven Ventilation of the Lung Following Trauma JEFFREY LOZMAN, M.D., ROBERT E. DUTTON, M.D., JONATHAN NEWELL, PH.D., SAMUEL R. POWERS, JR., M.D.
Ventilatory function of the lungs has been studied in 13 posttrauma patients using a two compartment analysis. The analysis is based upon a model of the lung which describes a nitrogen washout curve in terms of fast and slowly ventilated compartments. Data output from a digital computer provides values that compare the fractions of the alveolar ventilation and volume of the two compartments. All patients on initial investigation had large identifiable slow spaces. Subsequent evaluation at a time of clinical improvement showed that the ventilation of the slow space had increased significantly (P < .003), whereas no change was evident in the volume fraction. The ventilation to volume ratio of the slow space, measured on these two separate occasions increased in twelve of the patients studied. An increase in this ratio correlated with improvement in the patient's clinical condition.
requiring assisted ventilation has improved dramatically over the past several years. The addition of positive end-expiratory ventilation (PEEP) to the armamentarium of treatment protocols and the understanding of its ensuing physiologic consequences has reduced the morbidity and mortality of respiratory complications in post-traumatic patients.20'2125-27 A major problem now is the determination of the end point for decreasing PEEP or of weaning patients away from the respirator. Relapses may occur if PEEP is discontinued or weaning is attempted too early. One method for analyzing the ventilatory functions of the lung is to divide it into two compartments, one rapidly ventilated and the other slowly ventilated.3,4,14>15 23'32 We have adapted this technique for the management of critically ill patients with respiratory complications admitted to the Albany Medical College Trauma Center. This model, describing lung volume and ventilatory distribution as a two compartment system, has been incorporated into on-line computation of respiratory function. The data for the compartment analysis were obtained while measu-ring the Functional Residual Capacity (FRC) by means of a nitrogen washout technique. The fast space has a higher alveolar ventilation (V1) and the slow space has a relatively T HE MANAGEMENT OF PATIENTS
Supported by Grants, GM 15426, HL 12564, and 5MO1RROO094M from the National Institutes of Health, U.S. Public Health Service. Submitted for publication: November 18, 1976.
607
From the Departments of Surgery and Physiology, Albany Medical College of Union University, Albany, New York
slower alveolar ventilation (V2). The total alveolar ventilation is a sum of these two determinations. Nitrogen is washed out of the alveoli in proportion to their individual ventilatory rates. In non-smoking healthy young adults the N2 washout rate of all alveoli are approximately equivalent, whereas in the posttraumatic patients there may be great variations in the washout rates. This report presents data to indicate that patients with post-traumatic respiratory distress syndrome develop substantial regions of their lungs that are more slowly ventilated than normal. Furthermore, an increased ventilation to volume ratio in this slowly ventilated space has been shown to correlate with improvement in the patient's clinical condition and may provide the indication for decreasing the level of PEEP and finally discontinuing ventilatory support. Materials and Methods
Thirteen patients were studied. A radial catheter was inserted and a flowdirected, triple lumen 7F SwanGanz31 catheter was positioned in a pulmonary artery. Pulmonary artery, pulmonary wedge and arterial blood pressures were measured by means of strain gauge transducers. Cardiac output was determined by indocyanine green dye dilution technique. Analog voltages from the densitometer and the output of selected channels of a recorder were transmitted on-line to a medium size digital computer for calculations of cardiac output, cardiac index, and pulmonary vascular resistance. Blood gases were analyzed using Po2, Pco2 and pH electrodes. Mixed venous blood was obtained from the Swan-Ganz catheter. Physiologic shunt fraction of blood through the lung was computed off-line using the Berggrens formula. Oxygen saturation was calculated from hemoglobin content, P02, PCO2 and pH.30 All patients were ventilated by Ohio 560 volume cycled respirators. Functional Residual Capacity was
Ann. Surg. * November 1977
LOZMAN AND OTHERS
608
Per breath nitrogen concentration of less than 2% of the initial breath was used as the end point for the determination. A storage oscilloscope displays the log of the fractional value of the mixed expired nitrogen concentration (Fig. la). This was graphed against time. Analysis was performed by the technique of exponential stripping. 17 During the latter portion of the washout, most of the nitrogen was eliminated from the fast space so that its contribution to the mean expired nitrogen was negligible. The latter points on the plot approach a straight line, representing the exponential washout of the slow space alone. We have developed a computer program which allows the operator to view the graph to determine the time at which the linear portion begins (Fig. lb). This linear portion defines the washout rate of the slow compartment (Fig. Ic). The fast compartment was determined by subtracting the extrapolated slow compartment line from the initial portion of the graph (Fig. ld). The operator sees how well the two compartments chosen fit the actual data when the computer superimposes the derived double exponential curve upon the raw data points (Fig. le). If the curve fit is satisfactory, the computer then determines from
calculated by the nitrogen washout technique using a second volume cycled respirator primed with a mixture of oxygen and argon as the inspired gas. The second respirator was connected with the patient's airway by means of a valve which allowed uninterrupted maintenance of PEEP. Inspired gas from the first respirator was replaced with the non-nitrogen containing gas from the second respirator. Inspired and expired nitrogen concentrations were measured by a mass spectrometer. Expired volume was measured using a wedge spirometer and a bag box arrangement.12 All data were transmitted on-line to a PDP- 15 computer for determination of the FRC and the two compartment analysis. Since each inspired breath dilutes the nitrogen in the lungs, so each successive expired breath contains a decreasing fraction of nitrogen. A computer program for a two compartment analysis of the nitrogen washout begins by setting the quantity of expired nitrogen in the first breath equal to one and each subsequent breath equal to a fraction of one. The program normalizes and corrects for the anatomical and equipment dead space contribution to each expired breath. 100-
50- o ~4
0 o
,
-
0
0S
i,
0 0
o
0
o
o
5-
I
o0 00
oo
20 10
B .oI
0
o o
X
20
1
2 3 TIME (min.)
1
C
2 3 TIME (min.)
0
1
2
3
TIME (min.)
-1 O
50
-4 ~
~
~%200-
5.
?A
-
2-
0
1
2
3
0
TIME (min.) TIME (min.) FIG. 1. Data array necessary for exponential stripping. Logarithms of each breath's nitrogen concentration versus time (A). Portion of the washout representing solely slow compartment contribution is selected (B), and slope and intercept found by least squares analysis is displayed (C). Former portion of washout is examined and fast compartment demarcation is selected. The slow compartment concentration values calculated using the intercept and slope formerly derived are subtracted from the original concentrations located before the newly chosen demarcation. The logarithm of those resultant values which were selected to contribute to the fast space are passed to the least squares routine (D). To attest to the correctness of fit, the derived parameters are now used to calculate the value of concentration at each value of time and these calculated points are superimposed over the actual raw data (E).
Vol. 186 . No. 5
LUNG VENTILATION FOLLOWING TRAUMA
609 tion. Improvement was judged in retrospect by arterial blood gases, and an ability to be permanently weaned from the respirator. Non-survivors were excluded from the analysis since this study was designed to examine V2/V2 in patients who improved sufficiently to be weaned from the respirator and non-survivors at no time were able to be weaned. The V2/V2 ratio of the two groups were compared by the Students' t test for
TABLE 1. Physiologic Shunt, Functional Residual Capacity, Level of Positive Pressure Ventilation and Arterial Pco2 in Thirteen Patients Initial Determination Patient
Age
1 2 3 4 5 6 7 8 9 10 11 12 13
28 17 18 21 18 54
18 21 17 33 49 44 30
Shunt FRC % ml 24 6 32 5 6 17 4 36 14 6 14 16 17
2040 1360 1670 1850 2200 4110 2480 4440 630 3180 2140 2340 3250
Final Determination
PEEP
Pco2
cmH20
mmHg
10 0 10 0 0 0 10 10
42 32 30 31 34 33 35 38 32 25 41 38 38
0 20 15 0 0
Shunt FRC PEEP % ml cmH20 21 10 15 2 18 15 17 12 8 20 14 12
2530 1730 1140 1760 2100 1200 1920 2490 720 1460 890 2800 3000
0 0 5 0 0 0 0 5 0 10 0 0 0
Pco2 mmHg 26 37 29 32 37 30 37 32 30 33
paired variance.
Informed consent for the above procedures was obtained from the patient's legal guardian after the nature, purpose and risks of all procedures to be performed were explained according to the recommendations in the Declaration of Helsinki.
41
30 37
Results
slopes and intercepts of the specified exponentials, the alveolar ventilation (Liters/min) (V) and volume (Liters) (V) of the two spaces. Calculations of the ventilation to volume ratio (V2/V2) for the slow space is then displayed. Lungs were considered to contain two compartments when a fast space was identified having a Vi/V, ratio three times or more than the V2/V2 ratio of the slow space. Furthermore, a compartment with a volume of less than ten per cent of the total FRC falls within the range of error of the calculations and was eliminated. Such a lung was considered a single homogenous compartment with one V/V ratio. This computerized technique allowed frequent repetition of a two compartment analysis. Data sets were selected at a time of the patient's poorest, and at a time of the patient's subsequent improved, ventilatory func-
The physiologic state of the patient represented by physiologic shunt, FRC and arterial PCO2 are shown in Table 1. Arterial Po2 was maintained above 72 mmHg in all except one patient whose Po2 was 55 mmHg on room air ventilation. All 13 patients had an identifiable slow space when initially studied, i.e., the fast space ratio, (V1/Vl) was always at least three times the slow space ratio (V2/V2) (Table 2). On initial determinations, the slow space was 1.45 + 0.22 liters, and the ventilation was 1.25 + 0.20 L/min. At the time of the patients improved ventilatory function, ventilation of the slow space increased significantly to 2.20 + 0.28 L/min (P < .003) whereas the volume fraction did not change significantly. The V2/V2 of the slow space from the two determinations were compared (Fig. 2). If there had been no change in the V2/V2 ratio, then the points would lie on the solid line of the graph, i.e. on the line of iden-
TABLE 2. Fast and Slow Space Data and Ventilation-Volume Ratios in Thirteen Patients
Initial Determination Fast Space
Final Determination
Slow Space
Fast Space
Vol L
Ventil L/min
Vol L
Ventil L/min
V2
VI/V, Fast
Patient
V2
V2/V2 Slow
1 2 3 4 5 6 7 8 9 10 11 12 13
0.55 0.71 0.32 0.77 1.09 0.93 0.45 1.38 0.36 1.55 0.78 1.01 0.78
0.65 3.47 2.00 4.33 4.83 3.47 2.87 6.87 4.27 7.13 4.02 4.01 2.20
1.39 0.54 1.94 0.97 1.00 3.06 1.92 2.13 0.18 1.52 1.42 1.03 2.35
0.46 0.20 1.95 1.53 0.78 2.12 2.43 1.58 0.24 1.59 1.69 0.77 1.56
0.33 0.36 1.00 1.57 0.78 0.69 1.27 0.70 1.37 1.05 0.75 1.66 0.66
Slow Space
V2
V,/V, Fast
Vol L
Ventil L/min
Vol L
Ventil L/min
V2
V2/V2 Slow
3.5 13.5 15.2 3.6 5.7 5.3 5.0
1.13 0.61 0.04* 0.21 0.79 0.83 0.18 0.23 0.62 0.32* 1.47
1.33 1.02 0.99 3.26 1.19 1.00 1.77 1.55 0.45 1.13 1.43 0.46 1.38
2.16 1.06 3.00 4.21 1.61 3.87 2.06 1.73 1.60 2.87 2.12 1.44 0.91
1.66 1.05 3.03 2.92 1.35 3.87 1.16 1.12 3.58 2.54 1.48 2.01 0.68
3.9 3.4
7.1
6.27 2.07 1.34* 1.44 2.43 2.22 1.47* 4.48 3.19 2.94 4.18 5.13* 4.88
8.7 4.4 3.3
3.1 4.2
0.11* 0.05*
5.9 3.9 4.8 5.1 5.1 4.5
4.9
* Lung measurements fulfilled requirements for Homogeneous Single Space Compartment i.e. a single compartment with a volume of less than 10% of the total FRC.
LOZMAN AND OTHERS
610
Ann. Surg. * November 1977
Volume and Ventilation in Each Alveolar Space Volume Ventilation
SLOW SPACE
Fraction
Slow Space Fast Space
Liters
0.767 0.233
3.064 0.929
Fraction
L./Min
0.379 0.621
2.123 3.473
A/V Slow Compartment = 0.69
%IN IN q
'41
14i 14
Q4
t. k ftk.t. Q.
~Nl
114. 4.
V2/V
qz*J
K
SUBSEQUENT DETERMINATION
FIG. 2. Comparison of V2/V2 of the slow space of two determinations. Solid line represents identity. The V2/V2 ratio after the patient's clinical improvement was significantly higher than initial determinations (p < 0.001).
2 3 TIME (min.) FIG. 3a. Patient 6. Initial determination of two compartment analysis. The V,/V2 of the slow compartment is 0.69. Volume and Ventilation in Each Alveolar Space Volume Ventilation Fraction Liters Fraction L./Min
tity. Points on the graph falling below the line of identity indicate improvement in the value of the V2/V2 ratio. The mean of the initial V2/V2 of the slow space was 0.94 + 0.12. After the patients clinical condition improved, there was a significant increase in the V2/V2 ratio of the slow space (p < 0.001). The V2/V2 ratio of the slow space increased from initial determinations in 12 of 13 patients.
Slow Space Fast Space
0.900 0.100
1.003 0.111
0.636 0.364
3.879 2.223
V/V Slow Compartment = 3.87
144 Selected Case Reports Patient 6. A 54-year-old male was involved in an automobile accident sustaining bilateral multiple rib fractures. Paradoxical motion of the chest was observed. There were also fractures of the right clavicle and scapula and a skull fracture. The patient required mechanical ventilatory support and was initially stabilized with an inspired oxygen concentration of 40% and ten centimeters water positive end-expiratory pressure (Table 1). Arterial blood gases, determined after stabilization on the ventilator, were pH 7.47, PCO. 33 mmHg and Pc, 84 mmHg. The pulmonary shunt was 17%, the cardiac index was 3.9 L/min/M2 and the FRC was 4,100 cc. The nitrogen washout was slow and the two compartment analysis demonstrated both a retarded fast space and a very large slow space (Fig. 3a; Table 2). The fast space accounted for 23% of the volume and had 62% of the ventilation. The slow space, consisting of 77% of the total lung volume contributed only 38% of the ventilation. The V2/V2 ratio of the slow space was 0.69. Eighteen hours later, PEEP was discontinued and all studies were repeated. Calculations at the same inspired oxygen concentration of
'44
114j
144
K~
2 3 TIME (min.) FIG. 3b. Patient 6. Second determination of two compartment analysis. The V2/V2 of the slow compartment has increased to 3.87 and the lung now appears to be a single well-ventilated space.
611
LUNG VENTILATION FOLLOWING TRAUMA
Vol. 186 * No. 5
40% showed the pulmonary shunt unchanged, the cardiac index increased to 4.2 I_min/m2 and the FRC dropped to 1200 cc. The FRC was much lower on this determination yet the patient appeared to be clinically improved. Blood gas determinations at this time were pH 7.44, PCO2 30 mmHg and Po, 85 mmHg. Nitrogen washout was very rapid and the two compartment analysis demonstrated a single well-ventilated space (Fig. 3b). The V2/V2 ratio of this space was 3.87 indicating significant improvement over the previously obtained values, consistent with the patient's improvement. The patient was shortly extubated and continued to do well. Patient 12. A 44-year-old male was struck by an automobile, sustaining bilateral lower extremity long bone fractures accompanied by complete disruption of the left femoral artery and vein associated with massive blood loss. After vascular repair and stabilization of the fracture, the patient was admitted to the Trauma Center. On the second day after injury, the patient was alert and cooperative and was maintained on a volume cycled respirator without PEEP at an inspired oxygen concentration of 30%o (Table 1). Arterial blood gas determinations revealed pH 7.42, Po2 100 mmHg, PcO, 30 mmHg. Pulmonary shunt was 16%. Cardiac index was 3.0 L/min/M2 and the FRC was 2340 cc. Weaning of the patient was begun on humidified 40% oxygen delivered to the patient from a Puritan nebulyzer by t-tube. During the weaning period, the two compartment analysis of the previously done FRC, while the patient had still been on the respirator was obtained. These calculations demonstrated two distinct spaces (Fig. 4a) (Table 2). The fast space represented 35% of the total volume accounting for 70% of the ventilation. The slow space represented 65% of the volume and only 30o of the ventilation. The V2/V2 ratio was 1.66 for the slow space. Based upon this low V2/V2 ratio of the slow space, one might have predicted that the patient would not tolerate weaning. Arterial blood gas determinations Volume and Ventilation in Each Alveolar Space Ventilation Volume Fraction L./Min Fraction Liters Slow Space Fast Space
0.648 0.352
0.295 1.685 0.705 4.023
1.445 0.784
V/V Slow Compartment
=
1.66
144
1*44
Volume and Ventilatipn in Each Alveolar Space Ventilation Volume Fraction L./Min Fraction Liters Slow Space Fast Space
0.994 0.006
0.684 0.316
2.671 0.017
Vi/V Slow Compartment
=
5.364 2.479
2.01
C-4
1.44
Kt 14j
0
1
3 2 TIME (min.)
4
FIG. 4b. Patient 12. Second determination of two compartment analysis. V2/V2 of slow space increased to 2.01. The patient was subsequently weaned successfully from the respirator. after 15 minutes off the ventilator confirmed this prediction. Arterial P02 fell to 75 mmHg on 40% oxygen. The patient also became dyspneic. He was returned to the respirator and weaning was discontinued. The following day, arterial blood gases and hemodynamic measurements showed relatively little change. The arterial blood values at an inspired oxygen concentration of 30% were pH 7.50, PO0 100 mmHg and PcO2 30 mmHg. Cardiac index was 3.7 IJminIM2. The pulmonary shunt was 14%. The FRC was now 2,800 cc. In addition to the incresed FRC, the two compartment analysis of the nitrogen washout revealed a single homogenous lung (Fig. 4B). The V/V ratio of this space was 2.01. This improvement in the efficiency of ventilation coincided with successful weaning of the patient. Within one hour, he was extubated and subsequently an arterial PO0 was 143 mmHg with 40%o humidified oxygen delivered from a face mask. The patient continued to do well. Comment
Kl
1
2
3
TIME (min.) FIG. 4a. Patient 12. Initial determination of two compartment analysis. V2/V2 of slow space 1.66.
These two cases illustrate the potential clinical usefulness of compartmental analysis of nitrogen washout data. In the first case, it was possible to safely discontinue ventilatory support at a time when this action was not suggested by routine clinical measurements. In the second case, the two compartment analysis if heeded, might have prevented the initial unsuccessful attempt to discontinue ventilatory support.
Ann. Surg. * November 1977
LOZMAN AND OTHERS
Discussion The concept of uneven ventilation in normal man was suggested as early as 1917 by Krogh and Lindhard,19 who used an inert gas, hydrogen, to measure dead space. They suggested that mixing of gases in alveoli was probably not uniform. The following year, Haldane et al.,13 concluded that ventilation was uneven during shallow breathing in normal man because their subjects had higher expired oxygen concentrations in early expiration than in late expiration. Emphysematous patients demonstrated a sequential decrease in hydrogen concentration during the course of expiration following a single breath of this tracer, indicating a non-uniformity of alveolar ventilation.29 Because of the hazardous nature of hydrogen, helium or nitrogen was substittited in subsequent studies. Christie6 developed a closed circuit technique to measure lung volume utilizing oxygen to dilute nitrogen. Later Darling et al.,7 demonstrated an open circuit nitrogen washout technique. In ensuing decades, the concepts of sequential ventilation as a cause for uneven ventilation were developed and analytical techniques were improved. 10 Darling and co-workers,8 assuming perfect mixing of alveolar gas, developed a formula for predicting the concentration of nitrogen after a period of oxygen breathing. The concept of two lung spaces was introduced by Robertson, Siri, and Jones,28 who used a mass spectrometer as a continuous gas analyzer. Therefore, many investigators demonstrated non-uniformity of ventilation in patients with emphysema and other pulmonary dis-
eases.5'11'16'34'35 Monaco et al.,22 observed that traumatized patients suffering from arterial hypoxemia frequently had a low FRC. Patients with a low Functional Residual Capacity who were ventilated with a high tidal volume by a volume controlled respirator demonstrated a slowed washout of nitrogen from the lungs, suggesting the presence of a slowly ventilated space. One way of determining the ventilatory status of patients was to observe the ventilation to volume ratio of the prolonged nitrogen washout space, designated as the slow space in this study.1 5'9'18 The rate of washout has also been termed the "efficiency" of pulmonary ventilation.2 Thus, this ventilation to volume ratio of the slow space (V21V2) provides an index of efficiency of pulmonary ventilation for comparison between a diseased lung and a healthy lung. New tecniques have enabled investigators to analyze greater numbers of lung compartments.33 However, our data suggest that the biggest gain in information occurs in a move from a single compartment analysis to that of two compartments. The close fit between the derived two compartment washout curve and the actual data in
our patients suggests that little additional information would be obtained by the addition of a third compartment in the nitrogen washout technique. None of these patients developed slow spaces that were as poorly ventilated as the "third" slow space V3/L3 described by Briscoe et al.,5 in emphysematous patients. The patients in this study demonstrated large areas of the lung that were slowly ventilated. An increase in the V2/V2 ratio of the slow space correlated with patient improvement and indicated a lessening dependence on mechanical ventilation in order to maintain adequate pulmonary gas exchange and tissue oxygenation. Thus, an impaired distribution of ventilation in the lung must be added to other physiologic derangements previously recognized in these patients, such as a reduced FRC22 and a shift of the pressure volume curve of the lung to the right.24 References 1. Blair, E. Hickam, J. B.: The Effect of Change in Body Position on Lung Volume and Intrapulmonary Gas Mixing in Normal Subjects. J. Clin. Invest., 34:383, 1955. 2. Bouhuys, A., Hagstom, K. E. and Lundin, G.: Efficiency of Pulmonary Ventilation During Rest and Light Exercise. A
3. 4. 5.
6. 7.
8.
9.
10. 1 1.
12. 13. 14.
Study of Alveolar Nitrogen Washout Curves in Normal Subjects. Acta. Physiol. Scand., 35:289, 1955. Briscoe, W. A.: A Method for Dealing with Data Concerning Uneven Ventilation of the Lung and Its Effects on Blood Gas Transfer. J. Appl. Physiol., 14:291, 1959. Briscoe, W. A. and Cournand, A.: Uneven Ventilation of Normal and Diseased Lungs Studied by An Open-Circuit Method. J. Appl. Physiol., 14:284, 1959. Briscoe, W. A., Cree, E. M., Filler, J., et al.: Lung Volume, Alveolar Ventilation and Perfusion Interrelationships in Chronic Pulmonary Emphysema. J. Appl. Physiol., 15:785, 1960. Christie, R. V.: The Lung Volume and Its Subdivisions. J. Clin. Invest., 11:1099, 1932. Darling, R. C., Courmand, A. and Richards, D. E., Jr.: Studies in Intrapulmonary Mixture of gases: An Open Circuit Method for Measuring Residual Air. J. Clin. Invest., 19:609, 1940. Darling, R. C., Cournand, A., Richards, D. W. and Damonski, B.: Studies on Intrapulmonary Mixture of Gases. V. Formes of Inadequate Ventilation in Normal and Emphysematous Lungs, Analyzed by means of Breathing Pure Oxygen. J. Clin. Invest., 23:55, 1944. Emmanuel, G. E., Smith, W. M. and Briscoe, W. A.: The Effect of Intermittent Positive Pressure Breathing and Voluntary Hyperventilation upon the Distribution of Ventilation and Pulmonary Blood Flow to the Lung in Chronic Obstructive Lung Disease. J. Clin. Invest., 45:1221, 1966. Fowler, W. S.: Intrapulmonary Restriction of Inspired Gas. Physiol. Rev., 32:1, 1952. Fowler, W. S., Comish, E. R., Jr. and Kety, S. S.: Lung Function Studies VIII. Analysis of Alveolar Ventilation by Pulmonary N2 Clearance Curves. J. Clin. Invest., 31:40, 1952. Gisser, D., Newell, J. C. and Powers, S. R., Jr.: A Refined Bag-Box Spriometer. J. Assoc. Advan. Med. Instrum., 6: 167, 1972. Haldane, J. S., Meakins, J. C. and Priestley, J. G.: The Effects of Shallow Breathing. J. Physiol., 52:433, 1918. Hechtman, H. B., Reid, M. H., Dorn, B. C., et al.:
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15.
16.
17.
18.
19.
20. 21.
22.
23.
24.
LUNG VENTILATION FOLLOWING TRAUMA
Shunting in the Lung: A Two-Compartment Model. Surgery, 72:443, 1972. Hickam, J. B., Blair, E. and Frayser, R.: An Open-Circuit Helium Method for Measuring Functional Residual Capacity and Defective Intrapulmonary Gas Mixing. J. Clin. Invest., 33:1277, 1954. Hickam, J. and Frayser, R.: A Comparative Study of Intrapulmonary Gas Mixing and Functional Residual Capacity in Pulmonary Emphysema, Using Helium and Nitrogen as the Test Gases. J. Clin. Invest., 37:567, 1958. Jacquez, J. D.: A First Course in Computing and Numerical Methods. Addison, Wesley Publishing Company, 1970. King, T. K. C. and Briscoe, W. A.: The Distribution of Ventilation, Perfusion, Lung Volume and Transfer Factor (Diffusing Capacity) in Patients with Obstructive Lung Disease. Clin. Sci. 35:153, 1968. Krogh, A. and Lindhard, J.: The Volume of the Dead Space in Breathing and the Mixing of Gases in the Lungs of Man. J. Physiol., 51:59, 1917. Lozman, J. and Powers, S. R., Jr.: The Fat Embolism Syndrome. Resident and Staff., 20:145, 1974. Lozman, J., Powers, S. R., Jr., Older, T., et al.: Correlation of Pulmonary Wedge and Left Atrial Pressures. A study in the Patient Receiving Positive End-Expiratory Pressure Ventilation. Arch. Surg., 109:270, 1974. Monaco, V., Burdge, R., Newell, J., et al.: Pulmonary Venous Admixture In Injured Patients. J. Trauma., 12:15, 1972. Neclario, M. T., Custead, W., Marr, C. and Powers, S. R., Jr.: Compartmental Analysis of Nitrogen Washout Curves by Computer. 1973. N. Engl. Conference on Bioengineering., 1:217, 1973. Newell, J. C., Dutton, R. E. and Powers, S. R., Jr.: Respiratory System Compliance in Conscious Injured Patients. Clin. Res., 20:581, 1972.
613
25. Pontoppidan, H., Geffin, B. and Lowenstein, E.: Acute Respiratory Failure in the Adult. N. Engl. J. Med., 287, 690, 743, 799, 1972. 26. Powers, S. R., Jr., Burdge, R., Leather, R., et al.: Studies of Pulmonary Insufficiency in Non-Thoracic Trauma. J. Trauma, 12:1, 1972. 27. Powers, S. R., Jr., Mannal, R., Neclerio, M., et al.: Physiologic Consequences of Positive End-Expiratory Pressure (PEEP) Ventilation. Ann. Surg., 178:265, 1973. 28. Robertson, J. S., Siri, W. E. and Jones, H. B.: Lung Ventilation Patterns Determined by Analysis of Nitrogen Elimination Rates: Use of the Mass Spectrometer. 29. Roelsen, E.: Functional Analysis of Alveolar Air After Inspiration of Hydrogen as a Method for the Determination of the Distribution of Inspired Air in the Lung. Act. Med. Scand., 95:452, 1938. 30. Severinghaus, J. W.: Blood Gas Calculator. J. Appli. Physiol., 21:1108, 1966. 31. Swan, H. T. C., Ganz, W., Forrester, J., et al.: Catheterization of the Heart in Man with Use of a Flow-Directed-Balloon-Tipped Catheter. N. Engl. J. Med., 283:447, 1970. 32. Torres, G., Lyons, H. A. and Emerson, P.: The Effects of Intermittent Positive Pressure Breathing on the Intrapulmonary Distribution of Inspired Air. Amer. J. Med., 32: 946, 1962. 33. Tsunoda, S., Young, A. C. and Martin, C. T.: Emptying Pattern of Lung Compartments in Normal Man. J. Appl. Physiol., 32:644, 1972. 34. Wagner, P. D., Laravuso, R. B., Uhl, R. R. and West, J. B.: Continuous Distribution of Ventilation Perfusion Ratios in Normal Subjects Breathing Air and 100% 02- J. Clin. Invest., 54:54, 1974. 35. West, J. B.: Pulmonary Gas Exchange in the Critically Ill Patient. Crit. Care Med., 2:171, 1974.
Ventilatory function of the lungs has been studied in 13 posttrauma patients using a two compartment analysis. The analysis is based upon a model of the lung which describes a nitrogen washout curve in terms of fast and slowly ventilated compartments. Data output from a digital computer provides values that compare the fractions of the alveolar ventilation and volume of the two compartments. All patients on initial investigation had large identifiable slow spaces. Subsequent evaluation at a time of clinical improvement showed that the ventilation of the slow space had increased significantly (P < .003), whereas no change was evident in the volume fraction. The ventilation to volume ratio of the slow space, measured on these two separate occasions increased in twelve of the patients studied. An increase in this ratio correlated with improvement in the patient's clinical condition.
requiring assisted ventilation has improved dramatically over the past several years. The addition of positive end-expiratory ventilation (PEEP) to the armamentarium of treatment protocols and the understanding of its ensuing physiologic consequences has reduced the morbidity and mortality of respiratory complications in post-traumatic patients.20'2125-27 A major problem now is the determination of the end point for decreasing PEEP or of weaning patients away from the respirator. Relapses may occur if PEEP is discontinued or weaning is attempted too early. One method for analyzing the ventilatory functions of the lung is to divide it into two compartments, one rapidly ventilated and the other slowly ventilated.3,4,14>15 23'32 We have adapted this technique for the management of critically ill patients with respiratory complications admitted to the Albany Medical College Trauma Center. This model, describing lung volume and ventilatory distribution as a two compartment system, has been incorporated into on-line computation of respiratory function. The data for the compartment analysis were obtained while measu-ring the Functional Residual Capacity (FRC) by means of a nitrogen washout technique. The fast space has a higher alveolar ventilation (V1) and the slow space has a relatively T HE MANAGEMENT OF PATIENTS
Supported by Grants, GM 15426, HL 12564, and 5MO1RROO094M from the National Institutes of Health, U.S. Public Health Service. Submitted for publication: November 18, 1976.
607
From the Departments of Surgery and Physiology, Albany Medical College of Union University, Albany, New York
slower alveolar ventilation (V2). The total alveolar ventilation is a sum of these two determinations. Nitrogen is washed out of the alveoli in proportion to their individual ventilatory rates. In non-smoking healthy young adults the N2 washout rate of all alveoli are approximately equivalent, whereas in the posttraumatic patients there may be great variations in the washout rates. This report presents data to indicate that patients with post-traumatic respiratory distress syndrome develop substantial regions of their lungs that are more slowly ventilated than normal. Furthermore, an increased ventilation to volume ratio in this slowly ventilated space has been shown to correlate with improvement in the patient's clinical condition and may provide the indication for decreasing the level of PEEP and finally discontinuing ventilatory support. Materials and Methods
Thirteen patients were studied. A radial catheter was inserted and a flowdirected, triple lumen 7F SwanGanz31 catheter was positioned in a pulmonary artery. Pulmonary artery, pulmonary wedge and arterial blood pressures were measured by means of strain gauge transducers. Cardiac output was determined by indocyanine green dye dilution technique. Analog voltages from the densitometer and the output of selected channels of a recorder were transmitted on-line to a medium size digital computer for calculations of cardiac output, cardiac index, and pulmonary vascular resistance. Blood gases were analyzed using Po2, Pco2 and pH electrodes. Mixed venous blood was obtained from the Swan-Ganz catheter. Physiologic shunt fraction of blood through the lung was computed off-line using the Berggrens formula. Oxygen saturation was calculated from hemoglobin content, P02, PCO2 and pH.30 All patients were ventilated by Ohio 560 volume cycled respirators. Functional Residual Capacity was
Ann. Surg. * November 1977
LOZMAN AND OTHERS
608
Per breath nitrogen concentration of less than 2% of the initial breath was used as the end point for the determination. A storage oscilloscope displays the log of the fractional value of the mixed expired nitrogen concentration (Fig. la). This was graphed against time. Analysis was performed by the technique of exponential stripping. 17 During the latter portion of the washout, most of the nitrogen was eliminated from the fast space so that its contribution to the mean expired nitrogen was negligible. The latter points on the plot approach a straight line, representing the exponential washout of the slow space alone. We have developed a computer program which allows the operator to view the graph to determine the time at which the linear portion begins (Fig. lb). This linear portion defines the washout rate of the slow compartment (Fig. Ic). The fast compartment was determined by subtracting the extrapolated slow compartment line from the initial portion of the graph (Fig. ld). The operator sees how well the two compartments chosen fit the actual data when the computer superimposes the derived double exponential curve upon the raw data points (Fig. le). If the curve fit is satisfactory, the computer then determines from
calculated by the nitrogen washout technique using a second volume cycled respirator primed with a mixture of oxygen and argon as the inspired gas. The second respirator was connected with the patient's airway by means of a valve which allowed uninterrupted maintenance of PEEP. Inspired gas from the first respirator was replaced with the non-nitrogen containing gas from the second respirator. Inspired and expired nitrogen concentrations were measured by a mass spectrometer. Expired volume was measured using a wedge spirometer and a bag box arrangement.12 All data were transmitted on-line to a PDP- 15 computer for determination of the FRC and the two compartment analysis. Since each inspired breath dilutes the nitrogen in the lungs, so each successive expired breath contains a decreasing fraction of nitrogen. A computer program for a two compartment analysis of the nitrogen washout begins by setting the quantity of expired nitrogen in the first breath equal to one and each subsequent breath equal to a fraction of one. The program normalizes and corrects for the anatomical and equipment dead space contribution to each expired breath. 100-
50- o ~4
0 o
,
-
0
0S
i,
0 0
o
0
o
o
5-
I
o0 00
oo
20 10
B .oI
0
o o
X
20
1
2 3 TIME (min.)
1
C
2 3 TIME (min.)
0
1
2
3
TIME (min.)
-1 O
50
-4 ~
~
~%200-
5.
?A
-
2-
0
1
2
3
0
TIME (min.) TIME (min.) FIG. 1. Data array necessary for exponential stripping. Logarithms of each breath's nitrogen concentration versus time (A). Portion of the washout representing solely slow compartment contribution is selected (B), and slope and intercept found by least squares analysis is displayed (C). Former portion of washout is examined and fast compartment demarcation is selected. The slow compartment concentration values calculated using the intercept and slope formerly derived are subtracted from the original concentrations located before the newly chosen demarcation. The logarithm of those resultant values which were selected to contribute to the fast space are passed to the least squares routine (D). To attest to the correctness of fit, the derived parameters are now used to calculate the value of concentration at each value of time and these calculated points are superimposed over the actual raw data (E).
Vol. 186 . No. 5
LUNG VENTILATION FOLLOWING TRAUMA
609 tion. Improvement was judged in retrospect by arterial blood gases, and an ability to be permanently weaned from the respirator. Non-survivors were excluded from the analysis since this study was designed to examine V2/V2 in patients who improved sufficiently to be weaned from the respirator and non-survivors at no time were able to be weaned. The V2/V2 ratio of the two groups were compared by the Students' t test for
TABLE 1. Physiologic Shunt, Functional Residual Capacity, Level of Positive Pressure Ventilation and Arterial Pco2 in Thirteen Patients Initial Determination Patient
Age
1 2 3 4 5 6 7 8 9 10 11 12 13
28 17 18 21 18 54
18 21 17 33 49 44 30
Shunt FRC % ml 24 6 32 5 6 17 4 36 14 6 14 16 17
2040 1360 1670 1850 2200 4110 2480 4440 630 3180 2140 2340 3250
Final Determination
PEEP
Pco2
cmH20
mmHg
10 0 10 0 0 0 10 10
42 32 30 31 34 33 35 38 32 25 41 38 38
0 20 15 0 0
Shunt FRC PEEP % ml cmH20 21 10 15 2 18 15 17 12 8 20 14 12
2530 1730 1140 1760 2100 1200 1920 2490 720 1460 890 2800 3000
0 0 5 0 0 0 0 5 0 10 0 0 0
Pco2 mmHg 26 37 29 32 37 30 37 32 30 33
paired variance.
Informed consent for the above procedures was obtained from the patient's legal guardian after the nature, purpose and risks of all procedures to be performed were explained according to the recommendations in the Declaration of Helsinki.
41
30 37
Results
slopes and intercepts of the specified exponentials, the alveolar ventilation (Liters/min) (V) and volume (Liters) (V) of the two spaces. Calculations of the ventilation to volume ratio (V2/V2) for the slow space is then displayed. Lungs were considered to contain two compartments when a fast space was identified having a Vi/V, ratio three times or more than the V2/V2 ratio of the slow space. Furthermore, a compartment with a volume of less than ten per cent of the total FRC falls within the range of error of the calculations and was eliminated. Such a lung was considered a single homogenous compartment with one V/V ratio. This computerized technique allowed frequent repetition of a two compartment analysis. Data sets were selected at a time of the patient's poorest, and at a time of the patient's subsequent improved, ventilatory func-
The physiologic state of the patient represented by physiologic shunt, FRC and arterial PCO2 are shown in Table 1. Arterial Po2 was maintained above 72 mmHg in all except one patient whose Po2 was 55 mmHg on room air ventilation. All 13 patients had an identifiable slow space when initially studied, i.e., the fast space ratio, (V1/Vl) was always at least three times the slow space ratio (V2/V2) (Table 2). On initial determinations, the slow space was 1.45 + 0.22 liters, and the ventilation was 1.25 + 0.20 L/min. At the time of the patients improved ventilatory function, ventilation of the slow space increased significantly to 2.20 + 0.28 L/min (P < .003) whereas the volume fraction did not change significantly. The V2/V2 of the slow space from the two determinations were compared (Fig. 2). If there had been no change in the V2/V2 ratio, then the points would lie on the solid line of the graph, i.e. on the line of iden-
TABLE 2. Fast and Slow Space Data and Ventilation-Volume Ratios in Thirteen Patients
Initial Determination Fast Space
Final Determination
Slow Space
Fast Space
Vol L
Ventil L/min
Vol L
Ventil L/min
V2
VI/V, Fast
Patient
V2
V2/V2 Slow
1 2 3 4 5 6 7 8 9 10 11 12 13
0.55 0.71 0.32 0.77 1.09 0.93 0.45 1.38 0.36 1.55 0.78 1.01 0.78
0.65 3.47 2.00 4.33 4.83 3.47 2.87 6.87 4.27 7.13 4.02 4.01 2.20
1.39 0.54 1.94 0.97 1.00 3.06 1.92 2.13 0.18 1.52 1.42 1.03 2.35
0.46 0.20 1.95 1.53 0.78 2.12 2.43 1.58 0.24 1.59 1.69 0.77 1.56
0.33 0.36 1.00 1.57 0.78 0.69 1.27 0.70 1.37 1.05 0.75 1.66 0.66
Slow Space
V2
V,/V, Fast
Vol L
Ventil L/min
Vol L
Ventil L/min
V2
V2/V2 Slow
3.5 13.5 15.2 3.6 5.7 5.3 5.0
1.13 0.61 0.04* 0.21 0.79 0.83 0.18 0.23 0.62 0.32* 1.47
1.33 1.02 0.99 3.26 1.19 1.00 1.77 1.55 0.45 1.13 1.43 0.46 1.38
2.16 1.06 3.00 4.21 1.61 3.87 2.06 1.73 1.60 2.87 2.12 1.44 0.91
1.66 1.05 3.03 2.92 1.35 3.87 1.16 1.12 3.58 2.54 1.48 2.01 0.68
3.9 3.4
7.1
6.27 2.07 1.34* 1.44 2.43 2.22 1.47* 4.48 3.19 2.94 4.18 5.13* 4.88
8.7 4.4 3.3
3.1 4.2
0.11* 0.05*
5.9 3.9 4.8 5.1 5.1 4.5
4.9
* Lung measurements fulfilled requirements for Homogeneous Single Space Compartment i.e. a single compartment with a volume of less than 10% of the total FRC.
LOZMAN AND OTHERS
610
Ann. Surg. * November 1977
Volume and Ventilation in Each Alveolar Space Volume Ventilation
SLOW SPACE
Fraction
Slow Space Fast Space
Liters
0.767 0.233
3.064 0.929
Fraction
L./Min
0.379 0.621
2.123 3.473
A/V Slow Compartment = 0.69
%IN IN q
'41
14i 14
Q4
t. k ftk.t. Q.
~Nl
114. 4.
V2/V
qz*J
K
SUBSEQUENT DETERMINATION
FIG. 2. Comparison of V2/V2 of the slow space of two determinations. Solid line represents identity. The V2/V2 ratio after the patient's clinical improvement was significantly higher than initial determinations (p < 0.001).
2 3 TIME (min.) FIG. 3a. Patient 6. Initial determination of two compartment analysis. The V,/V2 of the slow compartment is 0.69. Volume and Ventilation in Each Alveolar Space Volume Ventilation Fraction Liters Fraction L./Min
tity. Points on the graph falling below the line of identity indicate improvement in the value of the V2/V2 ratio. The mean of the initial V2/V2 of the slow space was 0.94 + 0.12. After the patients clinical condition improved, there was a significant increase in the V2/V2 ratio of the slow space (p < 0.001). The V2/V2 ratio of the slow space increased from initial determinations in 12 of 13 patients.
Slow Space Fast Space
0.900 0.100
1.003 0.111
0.636 0.364
3.879 2.223
V/V Slow Compartment = 3.87
144 Selected Case Reports Patient 6. A 54-year-old male was involved in an automobile accident sustaining bilateral multiple rib fractures. Paradoxical motion of the chest was observed. There were also fractures of the right clavicle and scapula and a skull fracture. The patient required mechanical ventilatory support and was initially stabilized with an inspired oxygen concentration of 40% and ten centimeters water positive end-expiratory pressure (Table 1). Arterial blood gases, determined after stabilization on the ventilator, were pH 7.47, PCO. 33 mmHg and Pc, 84 mmHg. The pulmonary shunt was 17%, the cardiac index was 3.9 L/min/M2 and the FRC was 4,100 cc. The nitrogen washout was slow and the two compartment analysis demonstrated both a retarded fast space and a very large slow space (Fig. 3a; Table 2). The fast space accounted for 23% of the volume and had 62% of the ventilation. The slow space, consisting of 77% of the total lung volume contributed only 38% of the ventilation. The V2/V2 ratio of the slow space was 0.69. Eighteen hours later, PEEP was discontinued and all studies were repeated. Calculations at the same inspired oxygen concentration of
'44
114j
144
K~
2 3 TIME (min.) FIG. 3b. Patient 6. Second determination of two compartment analysis. The V2/V2 of the slow compartment has increased to 3.87 and the lung now appears to be a single well-ventilated space.
611
LUNG VENTILATION FOLLOWING TRAUMA
Vol. 186 * No. 5
40% showed the pulmonary shunt unchanged, the cardiac index increased to 4.2 I_min/m2 and the FRC dropped to 1200 cc. The FRC was much lower on this determination yet the patient appeared to be clinically improved. Blood gas determinations at this time were pH 7.44, PCO2 30 mmHg and Po, 85 mmHg. Nitrogen washout was very rapid and the two compartment analysis demonstrated a single well-ventilated space (Fig. 3b). The V2/V2 ratio of this space was 3.87 indicating significant improvement over the previously obtained values, consistent with the patient's improvement. The patient was shortly extubated and continued to do well. Patient 12. A 44-year-old male was struck by an automobile, sustaining bilateral lower extremity long bone fractures accompanied by complete disruption of the left femoral artery and vein associated with massive blood loss. After vascular repair and stabilization of the fracture, the patient was admitted to the Trauma Center. On the second day after injury, the patient was alert and cooperative and was maintained on a volume cycled respirator without PEEP at an inspired oxygen concentration of 30%o (Table 1). Arterial blood gas determinations revealed pH 7.42, Po2 100 mmHg, PcO, 30 mmHg. Pulmonary shunt was 16%. Cardiac index was 3.0 L/min/M2 and the FRC was 2340 cc. Weaning of the patient was begun on humidified 40% oxygen delivered to the patient from a Puritan nebulyzer by t-tube. During the weaning period, the two compartment analysis of the previously done FRC, while the patient had still been on the respirator was obtained. These calculations demonstrated two distinct spaces (Fig. 4a) (Table 2). The fast space represented 35% of the total volume accounting for 70% of the ventilation. The slow space represented 65% of the volume and only 30o of the ventilation. The V2/V2 ratio was 1.66 for the slow space. Based upon this low V2/V2 ratio of the slow space, one might have predicted that the patient would not tolerate weaning. Arterial blood gas determinations Volume and Ventilation in Each Alveolar Space Ventilation Volume Fraction L./Min Fraction Liters Slow Space Fast Space
0.648 0.352
0.295 1.685 0.705 4.023
1.445 0.784
V/V Slow Compartment
=
1.66
144
1*44
Volume and Ventilatipn in Each Alveolar Space Ventilation Volume Fraction L./Min Fraction Liters Slow Space Fast Space
0.994 0.006
0.684 0.316
2.671 0.017
Vi/V Slow Compartment
=
5.364 2.479
2.01
C-4
1.44
Kt 14j
0
1
3 2 TIME (min.)
4
FIG. 4b. Patient 12. Second determination of two compartment analysis. V2/V2 of slow space increased to 2.01. The patient was subsequently weaned successfully from the respirator. after 15 minutes off the ventilator confirmed this prediction. Arterial P02 fell to 75 mmHg on 40% oxygen. The patient also became dyspneic. He was returned to the respirator and weaning was discontinued. The following day, arterial blood gases and hemodynamic measurements showed relatively little change. The arterial blood values at an inspired oxygen concentration of 30% were pH 7.50, PO0 100 mmHg and PcO2 30 mmHg. Cardiac index was 3.7 IJminIM2. The pulmonary shunt was 14%. The FRC was now 2,800 cc. In addition to the incresed FRC, the two compartment analysis of the nitrogen washout revealed a single homogenous lung (Fig. 4B). The V/V ratio of this space was 2.01. This improvement in the efficiency of ventilation coincided with successful weaning of the patient. Within one hour, he was extubated and subsequently an arterial PO0 was 143 mmHg with 40%o humidified oxygen delivered from a face mask. The patient continued to do well. Comment
Kl
1
2
3
TIME (min.) FIG. 4a. Patient 12. Initial determination of two compartment analysis. V2/V2 of slow space 1.66.
These two cases illustrate the potential clinical usefulness of compartmental analysis of nitrogen washout data. In the first case, it was possible to safely discontinue ventilatory support at a time when this action was not suggested by routine clinical measurements. In the second case, the two compartment analysis if heeded, might have prevented the initial unsuccessful attempt to discontinue ventilatory support.
Ann. Surg. * November 1977
LOZMAN AND OTHERS
Discussion The concept of uneven ventilation in normal man was suggested as early as 1917 by Krogh and Lindhard,19 who used an inert gas, hydrogen, to measure dead space. They suggested that mixing of gases in alveoli was probably not uniform. The following year, Haldane et al.,13 concluded that ventilation was uneven during shallow breathing in normal man because their subjects had higher expired oxygen concentrations in early expiration than in late expiration. Emphysematous patients demonstrated a sequential decrease in hydrogen concentration during the course of expiration following a single breath of this tracer, indicating a non-uniformity of alveolar ventilation.29 Because of the hazardous nature of hydrogen, helium or nitrogen was substittited in subsequent studies. Christie6 developed a closed circuit technique to measure lung volume utilizing oxygen to dilute nitrogen. Later Darling et al.,7 demonstrated an open circuit nitrogen washout technique. In ensuing decades, the concepts of sequential ventilation as a cause for uneven ventilation were developed and analytical techniques were improved. 10 Darling and co-workers,8 assuming perfect mixing of alveolar gas, developed a formula for predicting the concentration of nitrogen after a period of oxygen breathing. The concept of two lung spaces was introduced by Robertson, Siri, and Jones,28 who used a mass spectrometer as a continuous gas analyzer. Therefore, many investigators demonstrated non-uniformity of ventilation in patients with emphysema and other pulmonary dis-
eases.5'11'16'34'35 Monaco et al.,22 observed that traumatized patients suffering from arterial hypoxemia frequently had a low FRC. Patients with a low Functional Residual Capacity who were ventilated with a high tidal volume by a volume controlled respirator demonstrated a slowed washout of nitrogen from the lungs, suggesting the presence of a slowly ventilated space. One way of determining the ventilatory status of patients was to observe the ventilation to volume ratio of the prolonged nitrogen washout space, designated as the slow space in this study.1 5'9'18 The rate of washout has also been termed the "efficiency" of pulmonary ventilation.2 Thus, this ventilation to volume ratio of the slow space (V21V2) provides an index of efficiency of pulmonary ventilation for comparison between a diseased lung and a healthy lung. New tecniques have enabled investigators to analyze greater numbers of lung compartments.33 However, our data suggest that the biggest gain in information occurs in a move from a single compartment analysis to that of two compartments. The close fit between the derived two compartment washout curve and the actual data in
our patients suggests that little additional information would be obtained by the addition of a third compartment in the nitrogen washout technique. None of these patients developed slow spaces that were as poorly ventilated as the "third" slow space V3/L3 described by Briscoe et al.,5 in emphysematous patients. The patients in this study demonstrated large areas of the lung that were slowly ventilated. An increase in the V2/V2 ratio of the slow space correlated with patient improvement and indicated a lessening dependence on mechanical ventilation in order to maintain adequate pulmonary gas exchange and tissue oxygenation. Thus, an impaired distribution of ventilation in the lung must be added to other physiologic derangements previously recognized in these patients, such as a reduced FRC22 and a shift of the pressure volume curve of the lung to the right.24 References 1. Blair, E. Hickam, J. B.: The Effect of Change in Body Position on Lung Volume and Intrapulmonary Gas Mixing in Normal Subjects. J. Clin. Invest., 34:383, 1955. 2. Bouhuys, A., Hagstom, K. E. and Lundin, G.: Efficiency of Pulmonary Ventilation During Rest and Light Exercise. A
3. 4. 5.
6. 7.
8.
9.
10. 1 1.
12. 13. 14.
Study of Alveolar Nitrogen Washout Curves in Normal Subjects. Acta. Physiol. Scand., 35:289, 1955. Briscoe, W. A.: A Method for Dealing with Data Concerning Uneven Ventilation of the Lung and Its Effects on Blood Gas Transfer. J. Appl. Physiol., 14:291, 1959. Briscoe, W. A. and Cournand, A.: Uneven Ventilation of Normal and Diseased Lungs Studied by An Open-Circuit Method. J. Appl. Physiol., 14:284, 1959. Briscoe, W. A., Cree, E. M., Filler, J., et al.: Lung Volume, Alveolar Ventilation and Perfusion Interrelationships in Chronic Pulmonary Emphysema. J. Appl. Physiol., 15:785, 1960. Christie, R. V.: The Lung Volume and Its Subdivisions. J. Clin. Invest., 11:1099, 1932. Darling, R. C., Courmand, A. and Richards, D. E., Jr.: Studies in Intrapulmonary Mixture of gases: An Open Circuit Method for Measuring Residual Air. J. Clin. Invest., 19:609, 1940. Darling, R. C., Cournand, A., Richards, D. W. and Damonski, B.: Studies on Intrapulmonary Mixture of Gases. V. Formes of Inadequate Ventilation in Normal and Emphysematous Lungs, Analyzed by means of Breathing Pure Oxygen. J. Clin. Invest., 23:55, 1944. Emmanuel, G. E., Smith, W. M. and Briscoe, W. A.: The Effect of Intermittent Positive Pressure Breathing and Voluntary Hyperventilation upon the Distribution of Ventilation and Pulmonary Blood Flow to the Lung in Chronic Obstructive Lung Disease. J. Clin. Invest., 45:1221, 1966. Fowler, W. S.: Intrapulmonary Restriction of Inspired Gas. Physiol. Rev., 32:1, 1952. Fowler, W. S., Comish, E. R., Jr. and Kety, S. S.: Lung Function Studies VIII. Analysis of Alveolar Ventilation by Pulmonary N2 Clearance Curves. J. Clin. Invest., 31:40, 1952. Gisser, D., Newell, J. C. and Powers, S. R., Jr.: A Refined Bag-Box Spriometer. J. Assoc. Advan. Med. Instrum., 6: 167, 1972. Haldane, J. S., Meakins, J. C. and Priestley, J. G.: The Effects of Shallow Breathing. J. Physiol., 52:433, 1918. Hechtman, H. B., Reid, M. H., Dorn, B. C., et al.:
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15.
16.
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24.
LUNG VENTILATION FOLLOWING TRAUMA
Shunting in the Lung: A Two-Compartment Model. Surgery, 72:443, 1972. Hickam, J. B., Blair, E. and Frayser, R.: An Open-Circuit Helium Method for Measuring Functional Residual Capacity and Defective Intrapulmonary Gas Mixing. J. Clin. Invest., 33:1277, 1954. Hickam, J. and Frayser, R.: A Comparative Study of Intrapulmonary Gas Mixing and Functional Residual Capacity in Pulmonary Emphysema, Using Helium and Nitrogen as the Test Gases. J. Clin. Invest., 37:567, 1958. Jacquez, J. D.: A First Course in Computing and Numerical Methods. Addison, Wesley Publishing Company, 1970. King, T. K. C. and Briscoe, W. A.: The Distribution of Ventilation, Perfusion, Lung Volume and Transfer Factor (Diffusing Capacity) in Patients with Obstructive Lung Disease. Clin. Sci. 35:153, 1968. Krogh, A. and Lindhard, J.: The Volume of the Dead Space in Breathing and the Mixing of Gases in the Lungs of Man. J. Physiol., 51:59, 1917. Lozman, J. and Powers, S. R., Jr.: The Fat Embolism Syndrome. Resident and Staff., 20:145, 1974. Lozman, J., Powers, S. R., Jr., Older, T., et al.: Correlation of Pulmonary Wedge and Left Atrial Pressures. A study in the Patient Receiving Positive End-Expiratory Pressure Ventilation. Arch. Surg., 109:270, 1974. Monaco, V., Burdge, R., Newell, J., et al.: Pulmonary Venous Admixture In Injured Patients. J. Trauma., 12:15, 1972. Neclario, M. T., Custead, W., Marr, C. and Powers, S. R., Jr.: Compartmental Analysis of Nitrogen Washout Curves by Computer. 1973. N. Engl. Conference on Bioengineering., 1:217, 1973. Newell, J. C., Dutton, R. E. and Powers, S. R., Jr.: Respiratory System Compliance in Conscious Injured Patients. Clin. Res., 20:581, 1972.
613
25. Pontoppidan, H., Geffin, B. and Lowenstein, E.: Acute Respiratory Failure in the Adult. N. Engl. J. Med., 287, 690, 743, 799, 1972. 26. Powers, S. R., Jr., Burdge, R., Leather, R., et al.: Studies of Pulmonary Insufficiency in Non-Thoracic Trauma. J. Trauma, 12:1, 1972. 27. Powers, S. R., Jr., Mannal, R., Neclerio, M., et al.: Physiologic Consequences of Positive End-Expiratory Pressure (PEEP) Ventilation. Ann. Surg., 178:265, 1973. 28. Robertson, J. S., Siri, W. E. and Jones, H. B.: Lung Ventilation Patterns Determined by Analysis of Nitrogen Elimination Rates: Use of the Mass Spectrometer. 29. Roelsen, E.: Functional Analysis of Alveolar Air After Inspiration of Hydrogen as a Method for the Determination of the Distribution of Inspired Air in the Lung. Act. Med. Scand., 95:452, 1938. 30. Severinghaus, J. W.: Blood Gas Calculator. J. Appli. Physiol., 21:1108, 1966. 31. Swan, H. T. C., Ganz, W., Forrester, J., et al.: Catheterization of the Heart in Man with Use of a Flow-Directed-Balloon-Tipped Catheter. N. Engl. J. Med., 283:447, 1970. 32. Torres, G., Lyons, H. A. and Emerson, P.: The Effects of Intermittent Positive Pressure Breathing on the Intrapulmonary Distribution of Inspired Air. Amer. J. Med., 32: 946, 1962. 33. Tsunoda, S., Young, A. C. and Martin, C. T.: Emptying Pattern of Lung Compartments in Normal Man. J. Appl. Physiol., 32:644, 1972. 34. Wagner, P. D., Laravuso, R. B., Uhl, R. R. and West, J. B.: Continuous Distribution of Ventilation Perfusion Ratios in Normal Subjects Breathing Air and 100% 02- J. Clin. Invest., 54:54, 1974. 35. West, J. B.: Pulmonary Gas Exchange in the Critically Ill Patient. Crit. Care Med., 2:171, 1974.
