Resting pulmonary haemodynamics and shunting: a comparison of sea‐level inhabitants to high altitude Sherpas

Key points Evolutionary pressure to improve gas exchange and/or resting pulmonary haemodynamics in hypoxic environments may have led to differences in the amount of blood that flows through right‐to‐left shunt pathways between Sherpas and sea‐level inhabitants. We studied sea‐level inhabitants during rest at sea level and acute isocapnic hypoxia and during rest at high altitude following 3 weeks of acclimatization and compared their responses to those of Sherpas during rest at high altitude. Contrary to some previous literature, we found similar resting pulmonary pressure and total pulmonary resistance between acclimatized sea‐level inhabitants and Sherpas at high altitude. We also found a similar number of subjects from each group with intracardiac shunt and intrapulmonary shunt at high altitude. These results help us better understand resting cardiopulmonary adaptations to high altitude by comparing life‐long high altitude residents with sea‐level inhabitants acclimatized to high altitude. The incidence of blood flow through intracardiac shunt and intrapulmonary arteriovenous anastomoses (IPAVA) may differ between Sherpas permanently residing at high altitude (HA) and sea‐level (SL) inhabitants as a result of evolutionary pressure to improve gas exchange and/or resting pulmonary haemodynamics. To test this hypothesis we compared sea‐level inhabitants at SL (SL‐SL; n = 17), during acute isocapnic hypoxia (SL‐HX; n = 7) and following 3 weeks at 5050 m (SL‐HA; n = 8 non‐PFO subjects) to Sherpas at 5050 m (n = 14). S pO 2, heart rate, pulmonary artery systolic pressure (PASP) and cardiac index (Qi) were measured during 5 min of room air breathing at SL and HA, during 20 min of isocapnic hypoxia (SL‐HX; P ETO 2 = 47 mmHg) and during 5 min of hyperoxia (F IO 2 = 1.0; Sherpas only). Intracardiac shunt and IPAVA blood flow was evaluated by agitated saline contrast echocardiography. Although PASP was similar between groups at HA (Sherpas: 30.0 ± 6.0 mmHg; SL‐HA: 32.7 ± 4.2 mmHg; P = 0.27), it was greater than SL‐SL (19.4 ± 2.1 mmHg; P < 0.001). The proportion of subjects with intracardiac shunt was similar between groups (SL‐SL: 41%; Sherpas: 50%). In the remaining subjects, IPAVA blood flow was found in 100% of subjects during acute isocapnic hypoxia at SL, but in only 4 of 7 Sherpas and 1 of 8 SL‐HA subjects at rest. In conclusion, differences in resting pulmonary vascular regulation, intracardiac shunt and IPAVA blood flow do not appear to account for any adap