Sex and age differences in intrathoracic airways mechanics in normal man JEAN-CLAUDE




Pulmonary and Cardiac Divisions, Department of Internal St. Pierre University Hospital, B-l 070 Brussels, Belgium YERNAULT,JEAN-CLAUDE, ANDRE DE TROYER, AND DANIEL RODENSTEIN. Sex and age differences in intrathoracic airways mechanics in normal man. J. Appl. Physiol.: Respirat. Environ. Exercise Physiol. 46(3): 556-564, 1979.-Expiratory pressure-volume curves and maximal expiratory flow-volume curves were obtained in 74 healthy subjects (49 males 25 females) aged between 20 and 64. Maximal expiratory flowstatic recoil (MEFSR) curves were then constructed. Aging was associated with loss of lung recoil and reduction in maximal expiratory flow measured between 80 and 50% total lung capacity (TLC), in both males and females, with the slope of the MEFSR curve becoming steeper. In subjects less than 40 yr old the conductance of the upstream segment increased from 80 to 50% TLC, whereas in older subjects it decreased. We also studied the effects of alveolar gas compression artifacts on MEFSR curves in 12 additional subjects and 10 patients with chronic obstructive lung disease; consistent changes were found, but the subsequent shift of the MEFSR curve toward the left was only mild. These changes are interpreted as reflecting the net effects of an increase in the unstressed dimensions of the airways together with a decrease in intraparenchymal airways diameter, probably due to loss of parenchymal support. It was also concluded that the analysis of the MEFSR curve did not allow a quantitative estimate of the changes in airways compressibility with aging. static lung recoil pressures; maximal expiratory flow; MEFSR curves; conductance of the upstream segment; Starling’s resistor model; effect of aging

EXPIRATORY FLOW LIMITATION was first clearly demonstrated by Fry et al. (8) and Hyatt et al. (12) with the introduction of the isovolume pressure-flow curves. These observations coupled with measurements of intrabronchial pressures and bronchographic observations generated the concept of dynamic compression of large intrathoracic airways during forced expiration (14, 28). Under conditions of flow limitation, Mead et al. (22) reasoned that, at some point of the airways between the alveoli and the mouth, the pressure drop should be equal to pleural pressure (i.e., the transmural pressure at that equal pressure point (EPP) should be zero), and so for the segment of the airway between alveoli and EPP (called the upstream (us) segment), the driving pressure must be the static recoil pressure of the lung (Pst(L)). They thus proposed to construct the maximal expiratory flow-static recoil pressure (MEFSR) curve of the lung, which allowed calculation of the resistance of the upstream segment at a given volume (Rus = Pst(L)/MEF). 556





Pride et al. (26) analyzed the- relationship between MEF and the driving pressure (which is the alveolar pressure) in terms of the Starling resistor model, assuming that the airway can be represented by two rigid tubes connected in series by a short collapsible segment. The existence of such a flow-limiting segment (FLS) is now well established (14, 28). Two parameters characterize the model of Pride et al. (26): 1) the S segment conductance (Gs), which is the conductance of that segment of the tracheobronchial tree extending from the alveoli to the FLS; and 2) the critical transmural pressure of that collapsible flow-limiting segment (Ptm’). Leaver and coworkers (17) proposed deriving those parameters from the maximum flow-static recoil plot, where Gs is the slope of that curve and Ptm’ is identical with the intercept on the static recoil axis. We shall call this intercept Pnt. A recent study on excised dog and human lungs (28) seems to indicate that the parameters calculated as suggested by Leaver et al. (17) agree well with the values of resistance and transmural pressure of collapse measured directly in the same lungs at a point just upstream from the FLS. The analyses proposed by Mead et al. (22) and Pride et al. (26) have been applied to MEFSR curves obtained in children and adolescents to assessthe effects of growth on the mechanics of the intrathoracic airway (7,20). The effects of other physiological factors such as sex and aging are not well known. The slope of the MEFSR curve tends to increase with aging (9, 10, 22, 25) and the intercept of the curve with the X-axis shifts toward positive values. Such a positive Pnt is also frequently found in disease (17, 34). In patients with asthma this finding had been originally attributed to an increase in the active tension of bronchial smooth muscle (26), which is unlikely to occur in chronic airflow obstruction (17). More recently alveolar gas compression artifact was questioned; although this was felt to be of little importance, its influence was not actually measured (34). The present study was aimed first at characterizing the effects of aging, sex, and smoking on the maximal expiratory flow-static recoil relationships in a group of 74 healthy adults aged 20-64 yr. Second, the role of alveolar gas compression in the analysis of MEFSR curves was evaluated quantitatively both in healthy subjects and in patients with chronic bronchitis and emphysema. The data obtained show that the slope of the MEFSR curve increases systematically with aging both



0 1979 the American Physiological Society

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in males and females, independently of alveolar gas compression; no reliable information has been found on changes in airway compressibility with aging. MATERIALS



Part 1 Subjects. Seventy four subjects (20-64 yr, 49 men and 25 women) were studied; all of them were free of respiratory or cardiac diseases. They were divided into four groups according to age and sex (males and females, more or less than 40 yr old). A further subdivision was made in male groups according to the presence or not of previous history of smoking. Only 3 of the 25 females were smokers. It must be stressed that all nonsmokers had never smoked and that the smokers were totally free of respiratory symptoms. The anthropometric characteristics of those groups are given in Table 1. Methods. Airway resistance and functional residual capacity (FRC) were measured in a constant-volume body plethysmograph. Maximal expiratory flow-volume (MEFV) curves were obtained by measuring flow at the mouth with a Lilly-type pneumotachograph (linear up to 12 l/s) and volume by electric integration of the flow signal. Three curves were obtained in each subject, with the best effort (i.e., with the largest forced vital capacity and the highest peak expiratory flow) being used for calculating the MEF at 80, 70, 60, and 50% total lung capacity (TLC). Expiratory pressure-volume (PV) curves were obtained by a quasi-static method (31)) with a commercially available latex balloon (length 10 cm, perimeter 5 cm) introduced via the nose into the middle third of the esophagus. Air (1 ml) had to be introduced in the balloon to bring the balloon’s transmural pressure to zero. Lung 1. Anthropometric characteristics of subjects __----.--.-.--___________ __I_ _--________ -~- -________--_--. ___-___ ----______~_.__ -___---_-_.________-__-_ __-___ --___~-



~40 Years oZd 26 11 NS 12 S


A& v


28.1 t 4.5 27.2 t, 2.7 29.4 t 5.0

24.6 t, 4.4

1.79 AZ0.07 1.78 t, 0.06 1.80 t 0.08

1.65 -+ 0.08


>40 Years oZd 23 NS 13 S 10

&Y%yr NS S Height,


NS S m



m NS



51.6 k 7.9 53.1 sfr 7.8 49.6 t, 8.0

50.8 t, 7.8

1.72 t, 0.06

1.60 iz 0.02

volume was plotted vs. transpulmonary pressure on a direct-writing X-Y recorder. At least two correctly recorded curves were obtained for each subject. The static recoil pressure of the lung (Pst(L)) was measured on each curve at 100, 90, 80, 70, 60, and 50% TLC, which was calculated by adding to FRC the mean inspiratory capacity measured during the X-Y recording of the PV curves. The reported Pst(L) are thus the means of at least two values. Maximum expiratory-flow-static recoil curves were plotted for volumes between 80 and 50% TLC by reading off corresponding values of MEF and Pst(L) from the MEF and PV curves. A linear fitting of that curve was performed by the least-squares method to calculate Gs and Pnt as suggested by Leaver et al. (17) Y =a+bx with y = MEF, x = Pst(L), Gs = b, Pnt = -a/b For each subject the conductance of the upstream segment (Gus = MEF/Pst(L) according to Mead et al. (22) was also calculated between 80 and 50% TLC.

Part 2 Twenty-two additional subjects were selected for the second part of the investigation. These were six healthy nonsmokers young adults aged 28-33 yr (mean 30.5), six healthy nonsmokers aged 47-66 yr (mean 56.3), eight patients with chronic bronchitis, and two patients with diffuse pulmonary emphysema without history of chronic bronchitis. Airway resistance, FRC, and PV curves were obtained as described above. Flow-volume curves were obtained while the patient was sitting in a flow-corrected plethysmograph. The subject performed a forced expiration from TLC through a Lilly-type pneumotachograph located in the wall of the body box. Flow at the mouth and thoracic flow were measured and integrated. Flow and volumes were recorded on a four-channel magnetic tape recorder; for each maneuver, two flow-volume curves were then displayed on a high speed X-Y recorder plotting flow at the mouth against expired volume (MEFV curve) and against change in the thoracic gas volume (MEF-TGV curve). For each subject, two MEFSR curves were thus constructed, by reading off corresponding values of MEF and Pst(L) from the PV and MEFV curves on the one hand, from the PV and MEF-TGV curves on the other. Each MEFSR relationship was analyzed by linear fitting as reported above. In heal.thy subjects data was analyzed between 70 and 40% TLC, whereas in patien ts the volume range of analysis was narrower (between 80 an.d 60% TLC). An example of the analysi .S performe Id in a 33-yrold man is given in Fig. 1. RESULTS

Part 1

1.70 t 0.04 1.77 t, 0.07

Values are means t SD. n, Number of subjects in each group; nonsmokers; S, smokers (smoking habits were not known in 3 subj


The results of lung recoil pressures measurements are given in Table 2. In young subjects there was no sex difference in Pst(L), whereas older females had lower lung recoil than older males (t test on the means, P

3. Results of maximal

Years old 6.66 -+ 2.25 6.91 t, 2.52 6.33 sf: 1.92

4.82 t 1.27


4.56 Z!I 1.92 4.66 +: 2.23 4.44 k 1.52

3.11 t 1.17


2.50 t 1.34 2.70 zk 1.52 2.24 & 1.11

1.74 t 0.98


1.18 -+ 0.90 1.30 2 1.03 1.03 z!L0.71

0.80 t 0.56


t SD for maximal total lung capacity

expiratory (TLC).


flow (MEF) meaother abbrevia-

increase with aging, whereas at 50% TLC it decreased tion (r”), which lay between 0.98 and 1 (mean 0.993). In significantly (Table 5). There was no change at 70 and the older subjects the curves did not fit as well (mean 0.958; range 0.94-0.98), with the MEFSR curve becoming 60% TLC. convex toward the pressure axis. It was even more so in the patients with a mean r2 of 0.932 (range 0.89-0.96), Part 2 despite the narrower range of analysis. Significant differences in Gs and Pnt were found between the two small groups of healthy subjects in keeping DISCUSSION with the results of Part 1. Gs was 0.65 t 0.10 1. s-’ . Several groups of investigators have recently studied cmHzO-’ (mean t SD) in younger subjects and 1.14 t 0.41 in older subjects (P < 0.02), whereas Pnt was re- sex and age differences in lung elasticity. Most workers spectively -1.6 t 1.0 and +1.6 t 1.5 cmHa0 (P < 0.005), agree that aging is associated with a decrease in lung when MEF was read from the MEFV curves. The indi- recoil pressures (10, 16, 29, 33). However, Bode et al. (2) vidual effects of alveolar gas compression on Gs and Pnt did not find any aging effect in females. Discrepancies also persist concerning the sex differare illustrated in Figs. 6 and 7. For the whole group of healthy subjects Pnt changed ences. In younger subjects we found no sex difference in from a mean value of 0.0 t 2.1 cmHz0 (mean t SD) to Pst(L) at any level of lung volume (32, 33). Gibson et al. -0.7 t 1.9 (P < 0.005) when MEF was read from the (10) reported that the actual values of Pst(L) at TLC achieved by females was lower than that of males, but MEF-TGV curve; in patients Pnt changed from +1.3 t 1.0 cmH20 to -0.1 t 2.3 (P < 0.05). Nevertheless Pnt they attributed this difference to a difference in inspiraremained positi ve in 4 of 6 older healthy subjects and 6 tory muscle strength rather than to a true difference in of 10 patients. Changes in Gs were less marked and the elastic properties of the lungs. On the other hand Bode et al. (2) found at 60 and 50% statistically significant only in healthy subjects (from 0.90 t 0.38 to 0.85 t 0.38 Is-’ cmHzO-‘, P < 0.005). TLC lower Pst(L) in females than in males. MethodologBetween 70 and 40% TLC, the MEFSR curves were well ical problems (i.e., too large volume of air in the esophageal balloon) were advocated by those authors (2) to fitted by linear analysis, with a coefficient of determinal

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4. Changes


flow with

in maximal and aging

height L9ex











MEF, 80% TLC


0.38 -14.73

-0.051 -0.040

+5.11 +13.47

2.03 1.40

0.42 0.68


Sex and age differences in intrathoracic airways mechanics in normal man.

Sex and age differences in intrathoracic airways mechanics in normal man JEAN-CLAUDE YERNAULT, ANDRI? DE TROYER, Pulmonary and Cardiac Divisions,...
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