Is There A Relationship Between Pulmonary Capillary Blood Volume And Intrapulmonary Arteriovenous Anastomosis Recruitment During Exercise?

Abstract

Exercise results in the recruitment of anatomical intrapulmonary arteriovenous anastomoses (IPAVA). There is speculation that IPAVA recruitment may act as a ‘pop‐off’ valve once pulmonary capillaries are fully recruited during exercise to protect the lung from large increases in pulmonary arterial pressure. Recognizing that the pulmonary capillaries are fully recruited in the supine position, we hypothesized that IPAVA recruitment during incremental exercise would initially occur at a pulmonary capillary blood volume (Vc) that approximated the value observed in the supine position. Twenty healthy subjects (9 males, 11 females, means±SD, age: 27±7 yrs, VO2max: 49.9±10.5 mL·kg−1·min−1) performed cycling exercise at 30, 50, 70 and 90% of VO2max. Capillary blood volume (Vc) was determined using the multiple FIO2‐DLCO breath‐hold method in the supine and upright positions at rest, as well as during upright exercise. IPAVA recruitment was evaluated by agitated saline contrast echocardiography. Mean Vc was 80.2±17.2 mL in the resting upright position, which increased to 94.6±24.6 mL when supine (p=0.043). During incremental upright exercise, Vc increased up to 132.9±26.3 mL at peak exercise (p<0.01). IPAVA recruitment was detected in all subjects during exercise, and first occurred at a mean Vc of 93.8±16.0 mL, which is significantly greater than resting upright Vc (p<0.05), but similar to resting supine Vc (p=0.97). Results were similar in men compared to women, and results were consistent when adjusting for alveolar volume. IPAVA recruitment was observed at a capillary blood volume similar to the value observed in the supine position. As the supine position is widely believed to result in the perfusion of all pulmonary capillaries, these data support the hypothesis that recruitment of IPAVAs follows full recruitment of the pulmonary capillaries.Support or Funding InformationProject funding provided by the Natural Sciences and Engineering Research Council (NSERC, PI M. Stickland), and the Canadian Respiratory Research Network (CRRN, PI M. Stickland). V. Tedjasaputra is supported by the The Lung Association of Alberta and NWT graduate studentship. M. Bouwsema was supported by NSERC and Alberta Innovates Health Solutions summer studentships.