Author(s): MÖLLER, F., FAN, J.L., FUTRAL, E., HODGMAN, C.F., KAYSER, B., LOVERING, A.T., Institution: MASSACHUSETTS INSTITUTE OF TECHNOLOGY, Country: UNITED STATES, Abstract-ID: 661

INTRODUCTION:
Differences in cardiopulmonary hemodynamics of high-altitude and acclimatized sea-level natives might augment exercise performance at altitude and decrease pulmonary artery systolic pressure (PASP) by increased blood flow through intrapulmonary arteriovenous anastomoses (Q̇IPAVA) (1). Although one study reported lower PASP in Tibetans in hypoxia at rest and during exercise (2), most studies have found no differences between populations at rest (3,4), and limited data exist during exercise. We hypothesized that Tibetans would have better exercise capacity at sea level (SL) and 5000 m altitude (ALT) and more favorable cardiopulmonary physiology, such as normal right and left heart function, lower PASP at rest, and greater Q̇IPAVA during exercise.
METHODS:
10 Tibetans and 10 Han Chinese without intracardiac shunts (PFO-negative) cycled stationary from 70 W with stepwise increases of 30 W every 3 min to exhaustion (Wpeak), in a hypo/hyperbaric chamber at SL and ALT. At the end of each step, respiratory variables were averaged over 30 s, and stroke volume (SV) and PASP were determined by ultrasound. Transthoracic saline contrast echocardiography (TTSCE) was used to determine Q̇IPAVA using a bubble scoring system (5). Cardiac output (Q̇T) was calculated as HR x SV and total pulmonary resistance (TPR) as TPR = PASP/Q̇T. Unpaired t-tests compared cardiorespiratory measures at peak workload. Mann-Whitney test compared bubble scores. Significance was set to p < 0.05 a priori, and effect sizes are presented as r2, with r2 > 0.1 indicating small, > 0.25 medium, and > 0.37 large effects.
RESULTS:
Resting cardiac structure and function was not different between groups. Tibetans achieved a higher WPEAK at SL (p = 0.026, r2 = 0.243) and at ALT (p = 0.024, r2 = 0.280), and higher V̇O2PEAK at ALT (p = 0.042, r2 = 0.2340), but not at SL (p = 0.207, r2 = 0.087). No differences were observed in HR, SV, or Q̇T. Q̇IPAVA was only lower in Tibetans during 100 W exercise at ALT (p = 0.039), while the increases in PASP and TPR at ALT were similar between the groups.
CONCLUSION:
Lower Q̇IPAVA in Tibetans during exercise at ALT might support higher WPEAK and V̇O2PEAK. However, no differences were observed in PASP and TPR. Our data suggest that the Tibetans superior aerobic exercise capacity over Han Chinese may be independent of cardiopulmonary features and possibly linked to differences in local muscular oxygen extraction, as previously hypothesized in Sherpas (7).

1 Stickland et al. (2004). DOI: 10.1113/jphysiol.2004.069302
2 Groves et al. (1993). DOI: 10.1152/jappl.1993.74.1.312
3 Foster et al. (2014). DOI: 10.1113/jphysiol.2013.266593
4 Faoro et al. (2014). DOI: 10.1152/japplphysiol.00236.2013
5 Elliot et al. (2011). DOI: 10.1152/japplphysiol.00145.2010
6 Kayser et al. (1991). DOI: 10.1152/jappl.1991.70.5.1938