Intra-pulmonary shunt and pulmonary gas exchange during exercise in humans.
In young, healthy people the alveolar-arterial P(O(2)) difference (A-aDO(2)) is small at rest, but frequently increases during exercise. Previously, investigators have focused on ventilation/perfusion mismatch and diffusion abnormalities to explain the impairment in gas exchange, as significant physiological intra-pulmonary shunt has not been found. The aim of this study was to use a non-gas exchange method to determine if anatomical intra-pulmonary (I-P) shunts develop during exercise, and, if so, whether there is a relationship between shunt and increased A-aDO(2). Healthy male participants performed graded upright cycling to 90% while pulmonary arterial (PAP) and pulmonary artery wedge pressures were measured. Blood samples were obtained from the radial artery, cardiac output was calculated by the direct Fick method and I-P shunt was determined by administering agitated saline during continuous 2-D echocardiography. A-aDO(2) progressively increased with exercise and was related to (r = 0.86) and PAP (r = 0.75). No evidence of I-P shunt was found at rest in the upright position; however, 7 of 8 subjects developed I-P shunts during exercise. In these subjects, point bi-serial correlations indicated that I-P shunts were related to the increased A-aDO(2) (r = 0.68), (r = 0.76) and PAP (r = 0.73). During exercise, intra-pulmonary shunt always occurred when A-aDO(2) exceeded 12 mmHg and was greater than 24 l min(-1). These results indicate that anatomical I-P shunts develop during exercise and we suggest that shunt recruitment may contribute to the widened A-aDO(2) during exercise.
Stickland
Michael K
MK
Faculty of Physical Education and Recreation, University of Alberta, Edmonton, Alberta, 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; D004452:Echocardiography; D015444:Exercise / Q000502:physiology*; D006801:Humans; D008168:Lung / Q000000981:diagnostic imaging / Q000502:physiology*; D008297:Male; D010100:Oxygen / Q000378:metabolism; D011652:Pulmonary Circulation / Q000502:physiology*; D011659:Pulmonary Gas Exchange / Q000502:physiology*; D011669:Pulmonary Wedge Pressure / Q000502:physiology; D012965:Sodium Chloride; D013318:Stroke Volume / Q000502:physiology; D014692:Ventilation-Perfusion Ratio / Q000502:physiology*
D012965:Sodium Chloride; D010100:Oxygen