assessment-pulmonary-capillary-blood-volume-membrane-diffusing

Assessment of Pulmonary Capillary Blood Volume, Membrane Diffusing Capacity, and Intrapulmonary Arteriovenous Anastomoses During Exercise

Exercise is a stress to the pulmonary vasculature. With incremental exercise, the pulmonary diffusing capacity (DLCO) must increase to meet the increased ...

University of Alberta

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Physical activity, fitness, and vascular health in patients with asthma.

Pulmonary gas exchange, as evaluated by the alveolar-arterial oxygen difference (A-aDO2), is impaired during intense exercise, and has been correlated with recruitment of intrapulmonary arteriovenous anastomoses (IPAVA) as measured by agitated saline contrast echocardiography. Previous work has shown that dopamine (DA) recruits IPAVA and increases venous admixture (Q̇s/Q̇t) at rest. As circulating DA increases during exercise, we hypothesized that A-aDO2 and IPAVA recruitment would be decreased with DA receptor blockade. Twelve healthy males (age: 25 ± 6 years, V̇O2 max : 58.6 ± 6.5 ml kg(-1) min(-1) ) performed two incremental staged cycling exercise sessions after ingestion of either placebo or a DA receptor blocker (metoclopramide 20 mg). Arterial blood gas, cardiorespiratory and IPAVA recruitment (evaluated by agitated saline contrast echocardiography) data were obtained at rest and during exercise up to 85% of V̇O2 max . On different days, participants also completed incremental exercise tests and exercise tolerance (time-to-exhaustion (TTE) at 85% of V̇O2 max ) with or without dopamine blockade. Compared to placebo, DA blockade did not change O2 consumption, CO2 production, or respiratory exchange ratio at any intensity. At 85% V̇O2 max , DA blockade decreased A-aDO2, increased arterial O2 saturation and minute ventilation, but did not reduce IPAVA recruitment, suggesting that positive saline contrast is unrelated to A-aDO2. Compared to placebo, DA blockade decreased maximal cardiac output, V̇O2 max and TTE. Despite improving pulmonary gas exchange, blocking dopamine receptors appears to be detrimental to exercise performance. These findings suggest that endogenous dopamine is important to the normal cardiopulmonary response to exercise and is necessary for optimal high-intensity exercise performance.

Dopamine receptor blockade improves pulmonary gas exchange but decreases exercise performance in healthy humans.

Endurance trained athletes exhibit enhanced cardiovascular function compared to non-athletes, although it is considered that exercise training does not enhance lung structure and function. An increased pulmonary capillary blood volume at rest is associated with a higher V̇O2 max . In the present study, we compared the diffusion capacity, pulmonary capillary blood volume and diffusing membrane capacity responses to exercise in endurance-trained males compared to non-trained males. Exercise diffusion capacity was greater in athletes, secondary to an increased membrane diffusing capacity, and not pulmonary capillary blood volume. Endurance-trained athletes appear to have differences within the pulmonary membrane that facilitate the increased O2 demand needed for high-level exercise.

Effect of aerobic fitness on capillary blood volume and diffusing membrane capacity responses to exercise.

Previous work suggests that women may exhibit a greater respiratory limitation to exercise compared to height-matched men. Diffusion capacity (DLCO) increases with incremental exercise, and the smaller lungs of women may limit membrane diffusing capacity (Dm) and pulmonary capillary blood volume (Vc) in response to the increased oxygen demand. We hypothesized that females would have a lower DLCO, DLCO relative to cardiac output (DLCO/Q), Dm, Vc, and pulmonary transit time, secondary to lower Vc at peak exercise. Sixteen females (112±12% predicted relative VO2peak), and sixteen males (118±22% predicted relative VO2peak) were matched for height and weight. Hemoglobin-corrected diffusing capacity (DLCO), Vc, and Dm were determined via the multiple-FIO2 DLCO technique at rest, and during incremental exercise up to 90% of VO2peak Both groups increased DLCO, Vc, and Dm with exercise intensity, but women had 20% lower DLCO (p<0.001), 18% lower Vc (p=0.002), 22% lower Dm (p<0.001) compared to men across all workloads, and neither group exhibited a plateau in Vc. When expressed relative to alveolar volume (VA), the between-sex difference was eliminated. The drop in DLCO/Q was proportionally less in women than men, and mean pulmonary transit time did not drop below 0.3s in either group. Women demonstrate consistently lower DLCO, Vc, and Dm compared to height-matched men during exercise; however, these differences disappear when corrected for lung size. These results suggest that after accounting for differences in lung volume, there is no intrinsic sex difference in the diffusing capacity, capillary blood volume or diffusion membrane response to exercise.

Article	Year
Comments on point: counterpoint: high altitude is/is not for the birds! Journal of applied physiology (Bethesda, Md. : 1985)\| PubMed ID: 22096211	2011
Physical activity, fitness, and vascular health in patients with asthma. The Journal of allergy and clinical immunology\| PubMed ID: 25913103	2015
Dopamine receptor blockade improves pulmonary gas exchange but decreases exercise performance in healthy humans. The Journal of physiology\| PubMed ID: 25952760	2015
Effect of aerobic fitness on capillary blood volume and diffusing membrane capacity responses to exercise. The Journal of physiology\| PubMed ID: 26959808	2016
Are there sex differences in the capillary blood volume and diffusing capacity response to exercise? Journal of applied physiology (Bethesda, Md. : 1985)\| PubMed ID: 27932673	2016

Vincent Tedjasaputra

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