title: Intra-pulmonary shunt and pulmonary gas exchange during exercise in humans.
abstract: 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.
authors.affiliation: Faculty of Physical Education and Recreation, University of Alberta, Edmonton, Alberta, Canada. stickland@wisc.edu
authors.forename: Michael K
authors.initials: MK
authors.lastname: Stickland
authors.forename: Robert C
authors.initials: RC
authors.lastname: Welsh
authors.forename: Mark J
authors.initials: MJ
authors.lastname: Haykowsky
authors.forename: Stewart R
authors.initials: SR
authors.lastname: Petersen
authors.forename: William D
authors.initials: WD
authors.lastname: Anderson
authors.forename: Dylan A
authors.initials: DA
authors.lastname: Taylor
authors.forename: Marcel
authors.initials: M
authors.lastname: Bouffard
authors.forename: Richard L
authors.initials: RL
authors.lastname: Jones
mesh_terms: 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*
chemical_list: D012965:Sodium Chloride; D010100:Oxygen