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. 2004 Nov 15;561(Pt 1):321-9.
doi: 10.1113/jphysiol.2004.069302. Epub 2004 Sep 23.

Intra-pulmonary shunt and pulmonary gas exchange during exercise in humans

Michael K Stickland  1 , Robert C Welsh, Mark J Haykowsky, Stewart R Petersen, William D Anderson, Dylan A Taylor, Marcel Bouffard, Richard L Jones
Affiliations

Intra-pulmonary shunt and pulmonary gas exchange during exercise in humans

Michael K Stickland et al. J Physiol. .

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.

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Figures

Figure 1
Figure 1. Mean (± s.e.m.) pulmonary artery pressure and pulmonary artery wedge pressure at rest (supine and upright) and during graded exercise (n = 8)
PAP, mean pulmonary artery pressure; PAWP, pulmonary artery wedge pressure; SUP, supine; UP, upright; Level I–V, exercise load; *P < 0.05 versus upright at rest.
Figure 2
Figure 2. Mean (± s.e.m.) pulmonary gas exchange at rest (supine and upright) and during graded exercise (n = 8)
SaO2, arterial saturation; PaCO2, arterial PCO2; A-aDO2, alveolar-arterial PO2 difference; SUP, supine; UP, upright; Level I–V, exercise load; *P < 0.05 versus upright at rest.
Figure 3
Figure 3. Individual relationships during upright rest and graded exercise between cardiac output and alveolar-arterial PO2 difference upright at rest and during graded exercise
A-aDO2, alveolar-arterial PO2 difference. Arrow denotes peak work rate for the subject who did not develop I-P shunt during exercise.
Figure 4
Figure 4. Individual relationships during upright rest and graded exercise between mean pulmonary artery pressure and alveolar-arterial PO2 difference
A-aDO2, alveolar-arterial PO2 difference.
Figure 5
Figure 5. Individual relationships during upright rest and graded exercise between cardiac output and mean pulmonary artery pressure
See this image and copyright information in PMC

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