Effect of acute increases in pulmonary vascular pressures on exercise pulmonary gas exchange.
The purpose of this study was to determine the effect of acute increases in pulmonary vascular pressures, caused by the application of lower-body positive pressure (LBPP), on exercise alveolar-to-arterial PO2 difference (A-aDO2), anatomical intrapulmonary (IP) shunt recruitment, and ventilation. Eight healthy men performed graded upright cycling to 90% maximal oxygen uptake under normal conditions and with 52 Torr (1 psi) of LBPP. Pulmonary arterial (PAP) and pulmonary artery wedge pressures (PAWP) were measured with a Swan-Ganz catheter. Arterial blood samples were obtained from a radial artery catheter, cardiac output was calculated by the direct Fick method, and anatomical IP shunt was determined by administering agitated saline during continuous two-dimensional echocardiography. LBPP increased both PAP and PAWP while upright at rest, and at all points during exercise (mean increase in PAP and PAWP 3.7 and 4.0 mmHg, respectively, P<0.05). There were no differences in exercise oxygen uptake or cardiac output between control and LBPP. Despite the increased PAP and PAWP with LBPP, A-aDO2 was not affected. In the upright resting position, there was no evidence of shunt in the control condition, whereas LBPP caused shunt in one subject. At the lowest exercise workload (75 W), shunt occurred in three subjects during control and in four subjects with LBPP. LBPP did not affect IP shunt recruitment during subsequent higher workloads. Minute ventilation and arterial PcO2 were not consistently affected by LBPP. Therefore, small acute increases in pulmonary vascular pressures do not widen exercise A-aDO2 or consistently affect IP shunt recruitment or ventilation.
Stickland
Michael K
MK
Faculty of Physical Education and Recreation, University of Alberta, Edmonton, Canada. stickland@wisc.edu
Welsh
Robert C
RC
Haykowsky
Mark J
MJ
Petersen
Stewart R
SR
Anderson
William D
WD
Taylor
Dylan A
DA
Bouffard
Marcel
M
Jones
Richard L
RL
D000328:Adult; D001163:Arteriovenous Anastomosis / Q000502:physiology; D001794:Blood Pressure / Q000502:physiology*; D015444:Exercise / Q000502:physiology*; D005080:Exercise Test; D006801:Humans; D008150:Lower Body Negative Pressure; D008297:Male; D011652:Pulmonary Circulation / Q000502:physiology*; D011654:Pulmonary Edema / Q000503:physiopathology; D011659:Pulmonary Gas Exchange / Q000502:physiology*; D011669:Pulmonary Wedge Pressure / Q000502:physiology*; D012146:Rest / Q000502:physiology; D014655:Vascular Resistance / Q000502:physiology; D014692:Ventilation-Perfusion Ratio / Q000502:physiology