Abstract
We tested the effect of hypercapnic severity on plasma ammonia (Am) accumulation and respiratory exchange ratio (RER) during incremental exercise. Eight male subjects performed incremental cycle exercise to exhaustion under three conditions: breathing (1) Air, (2) 3% CO2 or (3) 6% CO2. Am in both hypercapnic conditions was lower than Air at 100% 2max O V (P<0.05) without changing Am threshold (AmT). Am for 6% CO 2 was lower than 3% CO 2 immediately after exercise (P<0.05). RER in both hypercapnic conditions was lower than Air throughout the experiment (P<0.05). RER for 6% CO 2
Highlights
Blood lactate (La) and ammonia (Am) concentrations are widely accepted markers of metabolism in clinical studies and during exercise
The primary findings of this study were that: (1) the accumulation of Am due to incremental exercise was inhibited with increasing inhaled CO2 concentration without changing Am threshold (AmT) and (2) respiratory exchange ratio (RER) in both hypercapnic conditions were lower compared with Air, but CO2 storage as indicated by a rise in blood for 6% CO2 occurred at rest, while CO2 storage for 3% CO2 was observed from 60% V O2max
We found that the reduction in HCO3- during incremental exercise decreased with increasing inhaled CO2 concentration (Figure 4), and this result suggests that lactic acidosis decreased with the severity of hypercapnia
Summary
Blood lactate (La) and ammonia (Am) concentrations are widely accepted markers of metabolism in clinical studies and during exercise. A decrease in blood La concentration during exercise under hypercapnic conditions was previously reported [1,2,3,4], and La threshold (LT) was unchanged by hypercapnia [4]. We reported that plasma Am concentration was reduced at maximal exercise in a 6% inhaled CO2 condition [5]. A previous study of exercise under hypercapnic conditions of 2, 4, and 6% CO2 demonstrated that blood La concentration during steady state exercise was the lowest at CO2 concentrations of 6% in inspired gas [2]. It is hypothesized that Am accumulation during exercise may be decreased depending on the severity of hypercapnia. Whether this is true has never been previously explored experimentally
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