Pulmonary gas exchange and acid-base state at 5,260 m in high-altitude Bolivians and acclimatized lowlanders

[EN] Pulmonary gas exchange and acid-base state were compared in nine Danish lowlanders (L) acclimatized to 5,260 m for 9 wk and seven native Bolivian residents (N) of La Paz (altitude 3,600-4,100 m) brought acutely to this altitude. We evaluated normalcy of arterial pH and assessed pulmonary gas exchange and acid-base balance at rest and during peak exercise when breathing room air and 55% O2. Despite 9 wk at 5,260 m and considerable renal bicarbonate excretion (arterial plasma HCO3- concentration = 15.1 meq/l), resting arterial pH in L was 7.48 +/- 0.007 (significantly greater than 7.40). On the other hand, arterial pH in N was only 7.43 +/- 0.004 (despite arterial O2 saturation of 77%) after ascent from 3,600-4,100 to 5,260 m in 2 h. Maximal power output was similar in the two groups breathing air, whereas on 55% O2 only L showed a significant increase. During exercise in air, arterial PCO2 was 8 Torr lower in L than in N (P < 0.001), yet PO2 was the same such that, at maximal O2 uptake, alveolar-arterial PO2 difference was lower in N (5.3 +/- 1.3 Torr) than in L (10.5 +/- 0.8 Torr), P = 0.004. Calculated O2 diffusing capacity was 40% higher in N than in L and, if referenced to maximal hyperoxic work, capacity was 73% greater in N. Buffering of lactic acid was greater in N, with 20% less increase in base deficit per millimole per liter rise in lactate. These data show in L persistent alkalosis even after 9 wk at 5,260 m. In N, the data show 1) insignificant reduction in exercise capacity when breathing air at 5,260 m compared with breathing 55% O2; 2) very little ventilatory response to acute hypoxemia (judged by arterial pH and arterial PCO2 responses to hyperoxia); 3) during exercise, greater pulmonary diffusing capacity than in L, allowing maintenance of arterial PO2 despite lower ventilation; and 4) better buffering of lactic acid. These results support and extend similar observations concerning adaptation in lung function in these and other high-altitude native groups previously performed at much lower altitudes.

The submarine volcano eruption off El Hierro Island: Effects on the scattering migrant biota and the evolution of the pelagic communities

[EN] The submarine volcano eruption off El Hierro Island (Canary Islands) on 10 October 2011 promoted dramatic perturbation of the water column leading to changes in the distribution of pelagic fauna. To study the response of the scattering biota, we combined acoustic data with hydrographic profiles and concurrent sea surface turbidity indexes from satellite imagery. We also monitored changes in the plankton and nekton communities through the eruptive and post-eruptive phases. Decrease of oxygen, acidification, rising temperature and deposition of chemicals in shallow waters resulted in a reduction of epipelagic stocks and a disruption of diel vertical migration (nocturnal ascent) of mesopelagic organisms. Furthermore, decreased light levels at depth caused by extinction in the volcanic plume resulted in a significant shallowing of the deep acoustic scattering layer. Once the eruption ceased, the distribution and abundances of the pelagic biota returned to baseline levels. There was no evidence of a volcano-induced bloom in the plankton community.