Acute altitude exposure and altered acid-base states. I. Effects on the exercise ventilation and blood lactate responses.
This study examined the influence of acute altitude (AL) exposure alone or in combination with metabolic acid-base manipulations on the exercise ventilatory and blood lactate responses. Four subjects performed a 4 min, 30 W incremental test to exhaustion at ground level (GL) and a 4 min, 20 W incremental test during three acute exposures to a simulated altitude of 4200 m; (i) normal (NAL), (ii) following 0.2 g.kg-1 ingestion of sodium bicarbonate (BAL), and (iii) following 0.5 g.day-1 ingestion of acetazolamide for 2 days prior to exposure (AAL). VE.VO2-1 increased progressively throughout the incremental tests at AL and the minimum value was not related to a change in the blood lactate response. In contrast, the VE.VCO2-1 decreased initially to reach a minimum value at the same power output for each altitude trial and was related to a lactate threshold defined by a log-log transformation (r = 0.78). This transformation of the blood lactate data was not influenced by the altered acid-base states. The relative exercise intensity corresponding to both a delta lactate of 1 mM and an absolute lactate of 4 mM was significantly increased during the AAL (79.9 +/- 12.9 and 93.9 +/- 13.7% VO2max, respectively) compared with NAL (59.1 +/- 5.5 and 78.0 +/- 5.8% VO2max, respectively). These data suggest that strong relationships exist between the ventilatory and blood lactate response during AL exposure and altered acid-base states. Further, it is concluded that, unless the acid-base status is known, the use of an absolute or delta lactate value to compare submaximal exercise should be interpreted with caution.
D000086:Acetazolamide / Q000494:pharmacology; D000136:Acid-Base Equilibrium; D000328:Adult; D000531:Altitude; D001639:Bicarbonates / Q000494:pharmacology; D002245:Carbon Dioxide; D006801:Humans; D006863:Hydrogen-Ion Concentration; D007773:Lactates / Q000097:blood*; D019344:Lactic Acid; D008297:Male; D010100:Oxygen; D010101:Oxygen Consumption / Q000187:drug effects; D010313:Partial Pressure; D005082:Physical Exertion; D012119:Respiration; D013997:Time Factors
D001639:Bicarbonates; D007773:Lactates; D002245:Carbon Dioxide; D019344:Lactic Acid; D000086:Acetazolamide; D010100:Oxygen