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Effect of blood haemoglobin concentration on V̇ o2,max and cardiovascular function in lowlanders acclimatised to 5260 m
Author(s) -
Calbet J. A. L.,
Rådegran G.,
Boushel R.,
Søndergaard H.,
Saltin B.,
Wagner P. D.
Publication year - 2002
Publication title -
the journal of physiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.802
H-Index - 240
eISSN - 1469-7793
pISSN - 0022-3751
DOI - 10.1113/jphysiol.2002.029108
Subject(s) - hyperoxia , cardiac output , effects of high altitude on humans , acclimatization , ventilation (architecture) , altitude (triangle) , zoology , hemoglobin , chemistry , bohr effect , vo2 max , medicine , oxygen , hemodynamics , biology , heart rate , blood pressure , anatomy , biochemistry , mathematics , oxygen–haemoglobin dissociation curve , botany , geometry , mechanical engineering , organic chemistry , engineering
The principal aim of this investigation was to determine the influence of blood haemoglobin concentration ([Hb]) on maximal exercise capacity and maximal O 2 consumption (V̇ O2,max ) in healthy subjects acclimatised to high altitude. Secondarily, we examined the effects of [Hb] on the regulation of cardiac output (CO), blood pressure and muscular blood flow (LBF) during exercise. Eight Danish lowlanders (three females and five males; 24 ± 0.6 years, mean ± s.e.m .) performed submaximal and maximal exercise on a cycle ergometer after 9 weeks at an altitude of 5260 m (Mt Chacaltaya, Bolivia). This was done first with the high [Hb] resulting from acclimatisation and again 2‐4 days later, 1 h after isovolaemic haemodilution with Dextran 70 to near sea level [Hb]. After measurements at maximal exercise while breathing air at each [Hb], subjects were switched to hyperoxia (55 % O 2 in N 2 ) and the measurements were repeated, increasing the work rate as tolerated. Hyperoxia increased maximal power output and leg V̇ O2,max , showing that breathing ambient air at 5260 m, V̇ O2,max is limited by the availability of O 2 rather than by muscular oxidative capacity. Altitude increased [Hb] by 36 % from 136 ± 5 to 185 ± 5 g l −1 ( P < 0.001 ), while haemodilution (replacing 1 l of blood with 1 l of 6 % Dextran) lowered [Hb] by 24 % to 142 ± 6 g l −1 ( P < 0.001 ). Haemodilution had no effect on maximal pulmonary or leg V̇ O2,max , or power output. Despite higher LBF, leg O 2 delivery was reduced and maximal V̇ O2 was thus maintained by higher O 2 extraction. While CO increased linearly with work rate irrespective of [Hb] or inspired oxygen fraction ( F I, O2 ), both LBF and leg vascular conductance were systematically higher when [Hb] was low. Close and significant relationships were seen between LBF (and CO) and both plasma noradrenaline and K + concentrations, independently of [Hb] and F I, O2 . In summary, under conditions where O 2 supply limits maximal exercise, the increase in [Hb] with altitude acclimatisation does not improve maximal exercise capacity or V̇ O2,max , and does not alter peak CO. However, LBF and vascular conductance are higher at altitude when [Hb] is lowered to sea level values, with both relating closely to catecholamine and potassium concentrations. This suggests that the lack of effect of [Hb] on V̇ O2,max may involve reciprocal changes in LBF via local metabolic control of the muscle vasculature.