Exercise-induced VA/Q inequality in subjects with prior high-altitude pulmonary edema

Abstract

Ventilation-perfusion (VA/Q) mismatch has been shown to increase during exercise, especially in hypoxia. A possible explanation is subclinical interstitial edema due to high pulmonary capillary pressures. We hypothesized that this may be pathogenetically similar to high-altitude pulmonary edema (HAPE) so that HAPE-susceptible people with higher vascular pressures would develop more exercise-induced VA/Q mismatch. To examine this, seven healthy people with a history of HAPE and nine with similar altitude exposure but no HAPE history (control) were studied at rest and during exercise at 35, 65, and 85% of maximum 1) at sea level and then 2) after 2 days at altitude (3,810 m) breathing both normoxic (inspired Po2 = 148 Torr) and hypoxic (inspired Po2 = 91 Torr) gas at both locations. We measured cardiac output and respiratory and inert gas exchange. In both groups, VA/Q mismatch (assessed by log standard deviation of the perfusion distribution) increased with exercise. At sea level, log standard deviation of the perfusion distribution was slightly higher in the HAPE-susceptible group than in the control group during heavy exercise. At altitude, these differences disappeared. Because a history of HAPE was associated with greater exercise-induced VA/Q mismatch and higher pulmonary capillary pressures, our findings are consistent with the hypothesis that exercise-induced mismatch is due to a temporary extravascular fluid accumulation.

Pulmonary gas exchange at maximal exercise in Danish lowlanders during 8 wk of acclimatization to 4,100 m and in high-altitude Aymara natives

“…A previous study in conscious dogs concluded that ventilation-perfusion mismatch actually decreased, whereas diffusion limitation increased, during exercise at acute exposure to simulated high altitude (ϳ6,000 m) compared with sea level (22). However, in humans at a more moderate altitude (3,800 m), augmented pulmonary arterial pressure and ventilation-perfusion mismatch (shunting) have been demonstrated in lowlanders during exercise within the first days of acclimatization (15). It is possible that acclimatizing lowlanders during exercise have higher pulmonary arterial pressures than high-altitude natives.…”

Acute high-altitude sickness

“…Increased peripheral hypoxic chemoreceptor sensitivity also appears to reduce the strength of HPV, independent of differences in alveolar ventilation [70]. HAPE-susceptible individuals have slightly lower lung volumes and reduced diffusion capacity [12,71,72].…”

Dexamethasone Improves Maximal Exercise Capacity of Individuals Susceptible to High Altitude Pulmonary Edema at 4559 m

“…Therefore, the lack of a difference in exercise Spo 2 between subject groups in the present study indicates an enhanced pulmonary O 2 diffusion in the dexamethasone group, allowing for Spo 2 to obtain similar levels as in the controls despite higher exercise intensities, an explanation that is supported by the finding of higher resting Spo 2 in the dexamethasone group. An improved pulmonary O 2 diffusion in subjects receiving dexamethasone may have emerged from either an optimized blood distribution over the pulmonary vessels, because subclinical HAPE has been reported to promote ventilation-perfusion inequalities (Podolsky et al, 1996), or from an elevated transpulmonary O 2 diffusion, resulting from a reduction in pulmonary extravascular fluid accumulation (Steinacker et al, 1998). These explanations are supported by the lower Ve/Vco 2 in the dexamethasone group, which indicates a better ventilatory efficiency with dexamethasone.…”

“…Interstitial pulmonary edema elongates the diffusion distance of O 2 from the alveoli into the pulmonary capillaries (Steinacker et al, 1998) and negatively influences ventilation-perfusion matching, thereby deteriorating respiratory efficiency during heavy exercise (Podolsky et al, 1996). All these factors result in a more prominent decrease in Pao 2 .…”