Effect of Increased Blood Flow on Pulmonary Circulation Before and During High Altitude Acclimatization.

Matthias Peter Hilty, Andrea Mueller, Daniela Fluck, Christoph Siebenmann, Peter Rasmussen, Stefanie Keiser, Katja Auinger, Carsten Lundby, and Marco Maggiorini. Effect of increased blood flow on the pulmonary circulation before and during high altitude acclimatization. High Alt Med Biol. 17:305-314, 2016.Introduction and Methods: Acute exposure to high altitude increases pulmonary artery pressure (Ppa) and pulmonary vascular resistance (PVR). The evolution of Ppa and PVR with continuous hypoxic exposure remains, however, elusive. To test the hypothesis that altitude exposure leads to a persistent elevation in Ppa and PVR throughout acclimatization in seven healthy male subjects, echocardiography was performed at sea level (SL; 488m) weekly during a 4-week sojourn at 3454m (HA1-HA4) and upon return (SL2). Pulmonary artery catheterization and bilateral thigh cuff release maneuver were performed at SL and HA3 to study the properties of pulmonary circulation after 3 weeks of acclimatization. Results: Pulmonary artery catheter determined that systolic Ppa (mean +/- SEM) was increased from 20 +/- 1 at SL to 27 +/- 2mmHg at HA3 (p<0.01). Echocardiography assessed that systolic Ppa remained equally increased throughout acclimatization (26 +/- 2, 25 +/- 2, 25 +/- 2, and 24 +/- 2mmHg at HA1-HA4; p=0.93) and returned to baseline upon return (17 +/- 2, 18 +/- 1mmHg at SL, SL2; p=0.3). The same was shown for PVR. Right heart function remained unaffected. Thigh cuff release maneuvers at SL and HA3 resulted in similar increase in cardiac output (2.5 +/- 0.5 and 2.2 +/- 0.4L/min; p=0.61) without affecting mean Ppa. Conclusions: Prolonged altitude exposure leads to a persistent increase in Ppa and PVR without affecting right heart function and is fully reversible within 1 week after return to SL. The thigh cuff release maneuver-induced increase in cardiac output suggests a preserved ability of pulmonary circulation to cope with sudden remarkable increase in pulmonary blood flow throughout acclimatization.