JOURNAL

Vol.

OF

APPLIED

38, No. 4, April

~l~YSIClLOGY

I 975,

Printed

Chest wall

in U.S.A.

mechanics

during

artificial

ventilation

GUNNAR GRIMBY, GijRAN HEDENSTIERNA, AND BERTIL LOFSTRGM Department of Rehabilitution Medicine, Suhlgrenska sjukhuset, Gtiteborg; Departments of Anaesthesiolqy and Clinical Phyiology, Karolinska hstitute at SeruJherlasarettet, Defiartment uf Anaesthesiology, University of Link$ing, Linktiping, Sweden

GRIMBY,

&JNNAR,

&%RAN

HEDENSTIERNA,

AND

BERTIL

STROM. Chest wall mechanics during urtz+fxial vmtilation.

containing thiopentone 1 g and atropine 1 mg in 500 ml)After each set of measurements another OJ mg of fentanyl was given The minute ventilation was measured with pneumotachography (flowhead : Fleisch with a flow range : O-1.3 l/s, Godart Bilthoven, Holland ; differential pressure transducer: EMT 32, amplifier: EMT 3 1, Elema-Schijnander, Stockholm; flow integrator: AN-l, SRA, Kistner & Co, Stockholm) . Anteroposterior diameters of the rib cage and the abdomen were measured at the mamillary and the umbilical levels, respectively. The strengths of magnetic fields generated by electromagnets fixed to the body surface were detected by coils at the opposite surfaces. These signals were displayed on an X-Y storage oscilloscope (564 B with amplifiers 2A 63, Tektronix Inc*, Portland, Oregon), with rib cage diameter on the Y axis and abdominal diameter on the X axis (Fig. 1). The signals are neither scaled nor linear with diameter. But changes in the signals are reasonably linear with the separate volume contributions of each compartment. To calculate the separate contributions of the rib cage and the abdomen to the breathing volume, “isovolume” maneuvers were performed (12). When the subject was awake, he was instructed to contract the abdominal muscles against a closed glottis and, during artii-icial ventilation, the examiner gently pressed .his hand against the patient’s abdomen at different lung volumes, thus displacing volume from the abdomen to the rib cage. In this way, two to three flat loops were registered on the X-Y oscilloscope. The vertical and horizontal distances between the Aat loops on the oscilloscope face were measured, and since the volume changes were known by use of a spirometer (Vitalograph Ltd., Moreton House, Buckingham, England) the deflections on the oscilloscope face could be calibrated in terms of volume changes related to rib cage and abdominal displacements. 1Measures were taken to avoid distorted signals from the magnetometer by pressing over a large area of the abdomen. No obese persons took part in the study, Inspiration and expiration lines coincided fairly closely in most cases. All “isovolume” maneuvers were performed at FKC and within 2 liters above FRC. Tracheal, esophageal, and gastric pressures were recorded. The tracheal pressure was measured with a 65cm long catheter with side holes and an internal bore of 1.4 mm, the tip being located at the distal end of the endotracheal tube. The esophageal pressure was measured with a balloon, 10 cm long with a perimeter of 3 cm. The balloon was sealed over the end of a polyethylene catheter (length

L~F-

J

Appl. Physiol. 38(4) : 576-580. 1975.-Chest wall mechanics were studied in six healthy volunteers before and during anesthesia prior to surgery. The intratracheal, esophageal, and intragastric pressures were measured concurrently. Gas flow was measured by pneumotachography and gas volume was obtained from it by electrical integration. Rib cage and abdomen movements were registered with magnetometers, these being calibrated by ccisovolu me’ ’ maneuvers. During spontaneous breathing in the conscious state, rib cage volume displacement corresponded to 40y0 of the tidal volume. During anesthesia and artificial ventilation, this rose to 7ZLy0 of the tidal volume. The relative contributions of rib cage and abdomen displacements were not influenced by a change in tidal volume. Compliance was higher with a larger tidal volume, a finding which could be due to a curved pressure-volume relationship of the overall chest wall. compliance; rib cage; minute volume

diaphragm;

abdomen;

respiratory

l

frequency;

SINCE THE PRESWTATION of a method for rlleasuring the contribution of the rib cage and abdomen to the tidal volume (I Z), several studies have been performed on healthy and lung-diseased subjects during spontaneous breathing (6, 7, 15). However, there seem to be no reports on the effect of anesthesia and artificial ventilation on partitioning ventilation into rib cage and abdominal components. Since the breathing mechanics of the lung and chest wall may be grossly altered during anesthesia and artificial ventilation (2, 3, 8, 9), we considered it of interest to study the influence of anesthesia and artificial ventilation at different respirator settings on tidal volume partitioning and on chest wall mechanics. MATERIAL

AND

Stockholm; and

METHODS

Six subjects, considered free from respiratory disease on the basis of clinical examination and chest X ray, were selected for the study (Table 1) Studies were performed before and during anesthesia with artificial ventilation prior to abdominal or lower extremity surgery. The subjects were informed of the study and had consented to it. They were premeditated with droperidol 5 mg im. A further 5 mg of this agent were injected during induction along with fentanyl (0.01 mg/kg SW). After endotracheal intubation with a cuffed endotracheal tube, a thiopentone drip was started (0.5 drop/min per kg BW of saline solution (0.9 70) 576

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CHEST

TABLE

WALL

MECHANICS

DURING

ARTIFICIAL

577

VENTILATION

1. Subjects

No.

*f”,“’

SC3

Surgical

1

58

F

Cholelithiasis

23 4 5 6

59 43 62 34 24

F M M M

Cholelithiasis Abdominal hernia Varicose veins Appendectomy

Smokiw, cig/day

Diagnosis

IIt, cm

Symbol Wt, kg in1c4gs.

5

168

66

0

0 5 10 10

163 159 179 175 184

70 68 77 72 69

i a 0 A

k FIG. 1. Rib cage (rc) - abdomen (ab) configuration at two respiratory frequencies during anesthesia. Increase of the anteroposterior diameters is upward for rc and to the right for ab (after Konno and Mead (13)). Two isovolume loops (broken lines) are shown with the spirometrically measured difference in lung volume (1.05 liters). Relative motion during expiration from a higher lung volume is also included.

85 cm, internal diameter 1.4 mm) (cf. 16). The tip of the catheter was located 36-40 cm from the mouth. The balloon was emptied by aspiration to a negative pressure of 20 cmHz0 and then filled with 0.2 ml air (which had been shown to result in volume independent pressure recordings). The gastric pressure was measured with a balloon, 5 cm long, sealed over a polyethylene catheter, 100 cm long, internal diameter 1.4 mm. The balloon was filled with 1 ml of air. All signals were registered on an six-channel ink-jet recorder (Mingograf 8 1, Elema-SchGnander, Stockholm) (Fig. 2). Compliance of the different tissues was calculated according to the following formulas. Thoracic compliance (Ctot)

FIG. 2. Recordings of pressure and volume signals, from top to bottom tracheal (Ptr), esophageal (Pes) and gastric pressure (Pga), tidal volume (VT), rib cage (Vrc), and abdominal (Vab) contribution to tidal breathing. Calibration signals correspond to 10 cmHz0 (square waves) and 500 ml (sine wave and bars). Recordings were also performed with a higher paper speed.

AVrc: rib cage contribution to tidal volume. Diaphragm and abdominal compliance (Cdi

tidal volume; APtr : intratracheal pressure between end inspiration and end expiration. Lung compliance (CL)

CL =

APtr

VT -

APes : esophageal pressure difference tion and end expiration. Chest wall compliance (Cw)

AVab: diaphragm (abdominal) volume. Abdominal compliance (Cab)

cw = -g Rib cage compliance

(Crc) Crc

= ‘2

contribution

to

tidal

Cab = !!vab APga

APga : gastric pressure difference between end inspiration and end expiration. The following relations exist between the various compliances ~1 Ctot

= ;,

+ &

Cw = Crc + Cdi

difference

Statistical analysis of the results Student t-test for paired values.

+ ab was

made

using

the

PROCEDURE

APes between

ab)

Cdi + ab = g

Ctot= APtr Jz VT:

+

end inspira-

The subjects were studied in the supine position. The volume-measurements durinq spontaneous breathing were performed over 2-3 min wirh ;he patient awake diring a period with fairly constant breathing pattern. During the artificial ventilation, the subjects were ventilated by a volumelimited respirator (Engstram 200 and 300, LKB Medical, Stockholm). Volume and pressure (catheters put in location during anesthesia) registrations were performed at three different tidal volumes with the approximate relationship of 1:2: 3 (1 VT, 2 VT, 3 VT in Figs. 3 and 4 and Tables 2

Downloaded from www.physiology.org/journal/jappl by ${individualUser.givenNames} ${individualUser.surname} (128.059.222.107) on January 16, 2019.

578

GRIMBY,

Vrc k+ab 0.9.

I-IEDENSTIERNA,

AND

LijFSTRijM

ml / cmH20

\ ‘di cab a 0.7

0 I

0

l

0.5-

a 0 A

0

0.33

g

0 Artificial 3. Rib cage-to-tidal spontaneous breathing and ventilation. S: spontaneous symbol (see Table 1). FIG.

Ventilation

volume ratio (Vrc/Vrc + ab) during during different conditions of artificial breathing. Each subject has his own

and 3) at either 12 or 24 breaths/min. The order of the respirator settings was varied between the subjects. Ysovolume” maneuvers (described in METHODS) were performed both with the subject awake and anesthetized to get calibration factors for each of these conditions. For calculations the mean value obtained from 10 consecutive breaths were used in each situation. RESULTS

Volume (Figs. I and 3, Table 2). During spontaneous breathing the mean respiratory frequency was 14 (SD + 2) breaths/min. Abdominal breathing predominated with a rib cage-to-tidal volume ratio of 0.40. Artificial ventilation with 12 breaths/min and the medium-sized tidal volume corresponded fairly well with the rate and tidal volume during spontaneous breathing. Thus, at comparable breathing rate and tidal volume (cf. Table 2), anesthesia and artificial ventilation resulted in a significantly greater rib cage contribution to tidal breathing (ratio 0.73). Neither a smaller nor a larger tidal volume nor a change in respiratory frequency a@ected the rib cage-to-tidal volume ratio. The relative configurations of the rib cage and the abdomen during ventilation at the two frequencies coincided with the configuration during relaxed expiration initiated from a higher lung volume (marked with an arrow in Fig. 1). Pressure (Table 2). The pressures registered in trachea, esophagus, and stomach correspond to the end-inspiratory state. During artificial ventilation, there was a slight decline in esophageal pressure during the last part of insuffla-

FIG. 4, Compliance of various parts ing artificial ventilation (for abbreviations his own symbol (see Table I).

at different tidal volumes dursee text). Each subject has

TABLE 2. %%dd, eSo;bha.gt?d, and gastric pressure variations as well as tidal volume, rib cage, and abdominal contribution to tidnl breathing --Ptr, cmHn0

Sponlaneous breathing Artificial ventilation 1 VT

8.8 *I .3 13.0 zt2.1 20.2 ztl1.0

2 VT 3 VT

Signif

Spontaneous breathing lation, P: Artificial ventilntion, 1 VT - 3 VT,

P: Values

Pm

cmH20

3.4 .5 4.8 zt1.8 6.8 It1.5 ItI

- artificial

2.1 zto.5 3.1 zto.7 4.4 Ml.9

ml

vz,

683 zt171

238 zt106

444 +181

386 +29 722

288 h69 523 790 1t78

98 A52 196 *IO2 336 *195