Effects of lower body pressure changes on pulmonary function.
OBJECTIVE
During and following exercise there are a number of changes in pulmonary function, among which is a decrease in forced vital capacity (FVC). Several potential mechanisms may explain this decreased FVC, including an exercise-induced increase in thoracic blood volume.


METHODS
We tested the hypothesis that altered thoracic blood volume alone, as produced by the application of 30 mm Hg lower body negative (LBNP) or positive pressure (LBPP) for 5 min, would change FVC and forced expiratory volume in 1 s (FEV1.0). Further, we tested whether the changes in pulmonary function were related to initial lung volume and whether the lower body pressure changes led to an altered lung compliance as measured by static pressure-volume curves.


RESULTS
Results indicated that with LBNP, FVC, and FEV1.0 were significantly increased by approximately 0.15 L and 0.18 L, respectively. When LBPP was applied, FVC and FEV1.0 were decreased by approximately 0.18 and 0.14 L, respectively. The increase in FVC with LBNP was significantly related to the original FVC (r = 0.66, P < 0.05). There was no significant correlation between the increase in FEV1.0 and the original FEV1.0 (r = 0.48, P > 0.05). Pulmonary compliance was not changed significantly by the application of LBPP.


CONCLUSIONS
These results suggest that part of the change in pulmonary function following heavy exercise is related to an increased thoracic blood volume. The lack of change in lung compliance suggests that the effect of altered thoracic blood volume is to displace air and not to change the mechanical properties of the lungs.
Coast
J R
JR
S. A. Rasmussen Exercise Physiology Laboratory, Northern Arizona University, Flagstaff, USA. Richard.Coast@nau.edu
O'Kroy
J A
JA
Akers
F M
FM
Dahl
T
T
D000328:Adult; D000704:Analysis of Variance; D001810:Blood Volume; D015444:Exercise / Q000502:physiology; D005260:Female; D005541:Forced Expiratory Volume; D006801:Humans; D007866:Leg / Q000098:blood supply; D008150:Lower Body Negative Pressure; D008170:Lung Compliance; D008297:Male; D011312:Pressure; D012044:Regression Analysis; D013147:Spirometry; D013909:Thorax / Q000098:blood supply; D014797:Vital Capacity