JOURNAL OF APPLIED PHYSIOLOGY Vol. 41, No. 1, July 1976. Printed in U.S.A.

Sex and age differences in normal nonsmoking

in pulmonary subjects

mechanics

G. J. GIBSON, N. B. PRIDE, C. O’CAIN, AND R. QUAGLIATO Department of Medicine, Royal Postgraduate Medical School, Hummer-smith Hospital, London W 12, England

GIBSON,G.J.,N.B. PRIDE,C. @CAIN, AND R. QUAGLIATO. Sex and age differences in pulmonary mechanics in normal nonsmoking subjects, J. Physiol. 41(l): 20APPl* 25. 1976. -Maximum flow-volume, static pressure-volume, and maximum flow static recoil curves of three groups of nonsmoking, normal subjects (young men, young women, elderly women) were used to assess age and sex differences in pulmonary mechanics. No significant sex differences in maximum flow were seen but the young men showed higher lung recoil pressures at full inflation. When the influence of the inspiratory muscles and chest wall was excluded by exponential extrapolation of the pressure-volume curves to a maximum volume the bulk elastic properties of the lungs of young men and women appeared identical. Loss of maximum expiratory flow at low lung volumes and of lung recoil pressure occurred with age in nonsmoking women in whom emphysema should be minimal and therefore indicate true physiological effects of aging. The changes in pulmonary mechanics with age are consistent with an increase in unstressed dimensions and loss of elastic recoil of both alveoli and airways.

pressure-volume curves; lung recoil; flow-volume nential functions

MOST

STUDIES

OF

THE

EFFECTS

OF

AGE

on

curves; expo-

pUh0nary

mechanics have been performed in predominantly male populations and the subjects’ smoking habits have been variable or ignored. It is known that the incidence of emphysema at autopsy increases with age and, even in nonsmokers, is greater in men than in women (I). Many of the changes described with increasing age could be due to smoking or unsuspected emphysema, but their effects should be minimized by studying nonsmoking women in whom any true physiological effect of aging should be apparent. Even in young subjects, however, there appears to be a sex difference in that, after standardizing for height, young women have a smaller total lung capacity than men (8). Men can generate greater respiratory pressures than women (29), but it is not clear whether a greater degree of lung distension could alone account for the sex difference in lung volumes. In the present study, we have compared the respiratory mechanics of three small groups of nonsmoking subjects: young men, young women, and elderly women. We wished to assess whether the changes described with increasing age occurred in subjects in whom emphysema should be minimal and to explore possible causes and implications of the sex differences in lung mechanics.

SUBJECTS

AND

METHODS

The subjects studied were all healthy nonsmokers with no history of significant respiratory disease. A group of ten young women aged 21-31 yr was compared with six older women aged 60-69 and with six young men aged 24-29, Forced expiratory volume in 1 s (FE&) and vital capacity (VC) were measured with a dry spirometer (17) and total lung capacity (TLC) by plethysmography (10). Maximum expiratory flow-volume (MEFV) curves were obtained using a pressure-corrected variable volume plethysmograph (18) in which the seated subject performed a forced expiration from TLC through a Fleisch no. 3 or 4 pneumotachograph; the pressure drop across the flowmeter was measured by a Sanborn 270 transducer, recorded on a Sanborn pen recorder and displayed against change in thoracic gas volume (TGV) on a storage oscilloscope from which repeatable MEFV curves were copied. Transpulmonary pressure was estimated by the esophageal balloon method (23) using a balloon volume of 0.4-0.5 ml; a lo-cm balloon was passed to a standard distance with the tip 45 cm from the nostrils and connected to a Sanborn 267 differential transducer, the other side of which recorded mouth pressure. Transpulmonary pressure and change in TGV were recorded simultaneously on the Sanborn recorder. Absolute values of TGV were obtained by relating volume measurements to TLC. After checking for tracheal artifact, the subject was asked to take a series of three full inspirations. After the third inspiration, measurements were made of the transient peak transpulmonary pressure at TLC and of static transpulmonary pressure (Pst(L)) after volume had been maintained for 2-3 s as close as possible to TLC. Further readings of Pst(L) were made during the subsequent expiration as the mouthpiece was obstructed for periods of 2-3 s at volume decrements of approximately 0.5 liter. Several expiratory maneuvers were performed in each subject and a line of best fit drawn by eye through at least three sets of pressurevolume (PV) data which agreed to 21 cmH,O. Static expiratory lung compliance was measured as the slope of the PV curve over the 0.5 liter above functional residual capacity (FRC). -Maximum flow static recoil (MFSR) curves were plotted for volumes b&ween 70% and 30% VC by reading off corresponditig values of maximum expiratory flow (%z,~~) and Pst(lt) from the

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SEX

AND

AGE

DIFFERENCES

IN

PULMONARY

MECHANICS

MEFV and PV curves, respectively, and curves were fitted by eye. Statistical comparisons were made by the Student ttest. RESULTS

The results of spirometry and lung volumes for the three groups are shown in Table 1. The young men were on average 12 cm taller than the young women who in turn were 6 cm taller than the old women. Mean MEFV curves, static expiratory PV curves, and MFSR curves are shown in Figs. 1-3. Flow rate is plotted in TLC l s-l and volume as %VC (Fig. 1) or %TLC (Fig. 2) to standardize for lung size between the subjects. Information derived from the PV and MEFV curves is given in Table 2 where all the measurements are expressed in size-corrected terms. Comparison of the results between young women and young

men

showed

no

difference

in

FEWVC,

or in

the

ratios of residual volume (RV) and functi.onal residual capacity (FRC) t.o TLC. Although mean peak expiratory flow (PEF) was higher in the men, the difference was not statistically significant (0.10 > P > 0.05). The volume (%VC) at which PEF was achieved was, however, significantly higher in the men. The mean PV curves converged as volume decreased (Fig. 2). Recoil pressures at full inflation (Pst(L),,,) were significantly higher in the men; at lower volumes recoil pressures remained higher in the men but the differences were not statistically significant. The MFSR curves between 70 and 30% VC (Fig. 3) showed no significant difference; both mean curves extrapolated to the Pst(L) axis gave intercepts of approximately - 4 cmH20. The elderly women compared to the young wumen showed higher values of RV/TLC and lower FEVJVC with no significant difference in FRC/TLC. The pressure-volume curves showed a lower Pst(L) at all lung volumes in the older subjects (Fig. 2); their static compliance was higher but not significantly so. Comparison of the mean MEFV curves (Fig. I) showed significant differences only at 30% VC and below, where in the older subjects ~~~~~ was lower and the curve became convex to the abscissa. The mean MFSR curves (Fig. 3) showed a higher slope in the elderly subjects; their upstream conductance (Gus) was significantly greater TABLE

volumes subjects

in three groups

1. Lung

of normal

Young

No. of subjects Age, Yr Range Ht, cm FEV,, liters VC, liters FEVJVC, % RV, liters TLC, liters RV/TLC, % FRC/TLC, % Values are means women (P < 0.01). < 0.05).

6 27 k (24-29) 180 k 4.6 t 5.6 2 82 ir 1.6 + 7.2 IL 22 k 54 k

Men

2 6* 0.5* 0.6* 4 0.2 0.7* 3 3

Young

Women

10 25 k (21-31) 168 k 3.4 + 4.0 k 85 + 1.1 k 5.1 + 22 4 52 +

3 4 0.3 0.5 6 0.2 0.6 4 5

VOLUME %VC FIG.

Points SEM.

1. Mean MEFV plotted at PEF

2 80 * g G 6o _

FIG. 2. Mean static expiratory PV curves for 3 groups of normal subjects with volume expressed as %TLC. Points plotted at intervals. of 10% TLC between TLC and FRC and lines drawn by eye. Bars indicate -tl SEM.

TABLE 2. Static compliance, recoil pressures, and maximum expiratury flow rates in three groups of normal subjects Young

k SD. *Significan tlI y different from young Wignificantly different from young women (P

Men

Women

Recoil Peak P&(L) at at at

pressures recoil at TLC, cmH,O at TLC, cmH,O 90% TLC, cmHzO 60% TLC, cmH,O FRC, cmH,O

43.7 36.2 18.8 7.7 6.4

2 2 k 2 rt

7.2* 6.8" 2.2 1.6 2.0

30.9 25.8 16.6 7.4 5.2

in IL 2. t +

8.2 6.2 3.9 2.2 2.6

20.3 16.8 9.9 2.7 1.3

f k f k It

4.1* 2.6' 1.7* 0.7* 1.1*

Maximum flow-volume curves PEF, TLC es-* % VC at PEF VE max 5OS VC, TLC es- ’ Slope 50-25% vc, s-'

1.7 87 0.81 2.10

-5 2 k -t

0.2 3" 0.14 0.36

1.4 78 0.91 2.38

2 i k 2

0.5 5 0.31 0.80

1.2 78 0.75 2.83

+ + k 2

0.2 7 0.21 0.47

are means

+ SD.

* Significantly

different

4.2 4 1.4

Old Women

compliance %TLC - cmHfO-’

Values

3.5 k 0.5

Young

Static

3 St 0.3* 0.2* 5* 0.4* 0.5 6* 8

3 groups of normal subjects. of 10% VC. Bars indicate 2 1

loo

Old Women

6 63 2 (60-69) 162 + 2.3 k 3.1 k 76 k 1.9 2 4.9 4: 38 IL 54 -+

curves for and intervals

from young

5.3 + 1.4

women

(P < 0.01).

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22

GIBSON,

PRIDE,

O’CAIN,

AND

QUAGLIATO

at higher volumes and became lower than that of the young subjects, though not significantly so, at 30% VC. Extrapolation of the curve in the older subjects gave a mean intercept on the Pst(L) axis close to zero.

Comparison of PV curves between subjects. The position of full inflation is set by the balance of the recoil pressure of the total respiratory system and the net maximum inspiratory pressure generated by the inspiratory muscles (Pmus) (19, 28). Alternatively, it may be DISCUSSION considered as a balance of lung recoil pressure and the most negative pleural pressure (Ppl,,,) which can be Possible technical sources oferror. Since the esophagenerated (Ppl,,, = Pmus minus the recoil pressure of geal balloons were introduced to a standard depth, a the chest wall). It is necessary to consider how differsystematic error may occur when subjects of different ences in Pmus between subjects might affect convenheights are compared because of the gravity-dependent tional indices of lung distensibility. Figure 4, left, shows variation of pleural pressure. Using data obtained in the curves of two hypothetical normal subjects whose children by Zapletal (personal communication), the 12- lungs have identical elastic properties but whose inspicm height difference we found between the male and ratory muscle strength is different; the more powerful young female subjects should produce a 2.5~cm differmuscles of subject 2 produce a more negative Ppl,,, a ence in the relative depth of the balloon in the esophagreater TLC, and a greater Pst(L) at full inflation. If the gus. If we assume a pleural pressure gradient in the two PV curves are now replotted with volume expressed upright posture of 0.2 cmH,O per cm height of lung (22) as %TLC (Fig. 4, right,) they diverge as volume inthe resulting error in our estimate of recoil pressure at creases; the recoil pressure at any given %TLC is equivalent levels would amount to only 0.5 cmH,O. greater in subject 2, with the maximum difference at TLC. Any comparison of recoil pressures at a particular percentage of TLC, therefore, may be influenced by factors other than the elastic properties of the lungs. 1.2 r To assess the magnitude of this effect and to remove extrapulmonary influences (respiratory muscle strength, chest wall recoil) it would be desirable to relate lung volume not to TLC, but to the maximum volume (V,,,) which the lungs could contain. One approach to this is to apply an exponential extrapolation to the PV curve; single exponential functions have been shown empirically to fit PV data well (12, 30) and therefore an expression of the form V = V,,, - AeKI’ (where V = TGV, P = Pst(L), A and K are constants) was fitted rYoung 0 to the data of each subject over the volume range from FRC to TLC using an iterative, least mean square technique on a CDC 6400 computer. The computer program . : *

Sex and age differences in pulmonary mechanics in normal nonsmoking subjects.

JOURNAL OF APPLIED PHYSIOLOGY Vol. 41, No. 1, July 1976. Printed in U.S.A. Sex and age differences in normal nonsmoking in pulmonary subjects mecha...
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