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%V O 2 max while pulmonary arterial (PAP) and pulmonary artery wedge pressures were measured. Blood samples were obtained from the radial artery, cardiac output (Q) 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 toQ (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),Q (r = 0.76) and PAP (r = 0.73). During exercise, intra-pulmonary shunt always occurred when A-aDO 2 exceeded 12 mmHg andQ 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.

Detection of Intracardiac and Intrapulmonary Shunts at Rest and During Exercise Using Saline Contrast Echocardiography

“…A disadvantage is that it can be difficult to image a patient during exercise in this position if they have abdominal obesity. To date, similar results have been found when comparing right-to-left shunt during recumbent and upright exercise (Stickland et al, 2004;La Gerche et al, 2010;Elliott et al, 2011a). There are no published data examining intrapulmonary shunting during supine exercise.…”

“…In a research setting, subjects can be in a supine, upright or reclined position, however interpretation of the echocardiograms should take into account body positioning during ultrasound imaging. Specifically, there are data suggesting that intrapulmonary arteriovenous anastomoses are patent in the supine position, but not in the upright position (Stickland et al, 2004;Elliott et al, 2011b). Also, Tobin & Zariquiey demonstrated that intrapulmonary arteriovenous anastomoses 20 to 500 m in functional diameter are located in the apex of the human lung (Tobin & Zariquiey, 1950).…”

“…Supine and/or recumbent cycle ergometers are popular in many clinical settings because echocardiographic imaging can be performed during exercise (Stickland et al, 2004). The cycling apparatus is built into an exam table so that an individual is able to exercise while lying in the supine or recumbent position.…”

A case of intrapulmonary transmission of air while transitioning a patient from a sitting to a supine position after venous air embolism during a craniotomy

“…Body positioning can be a factor in recruitment of these transpulmonary pathways, especially in the supine position. 8 Therefore, changing the patient's position from sitting to supine during an interventional procedure under increased pulmonary microvasculature pressure, i.e., when significant venous air emboli are present, may increase the risk for transpulmonary transmission, especially via pathways in the apical lung.…”

“…[4][5][6][7] While these physiological transpulmonary arteriovenous pathways are subclinical in most instances, they have potential to open in up to 90% of individuals during hyperdynamic situations such as exercise. [8][9][10] A recent review of pulmonary pathways and mechanisms pertaining to their autoregulation highlights the interest and importance of this subject. 11 Neuroanesthesiologists are well aware of the multiple pathways for paradoxical air embolism (PAE) to occur.…”