Changes in blood pH, lactate concentration and pulmonary ventilation during incremental testing protocol on cycle ergometer

We investigated mutual changes in the blood lactate concentration ([LA]), blood pH and pulmonary ventilation (VE) to obtain insight into the regulation of pH at different levels of the exercise intensity. For this purpose the ratio VE/[LA] (l/min/mmol/l) was determined at each particular pH corresponding to exercise intensity in seven healthy subjects on the cycle ergometer during incremental exercise test. Changes in VE/[LA] ratio were found to exhibit three phases. In the first phase, the ratio increased without significant changes in [LA] and pH until it reached certain individual peak value. In the second phase, VE/[LA] decreased because increases in [LA] were considerably bigger than those of VE. Decreases in blood pH followed those of VE/[LA], nevertheless differences existed among subjects depending on how successful individual subjects regulated their blood pH. In the third phase with the VE/[LA] values stabilized between 15 and 22 and pH values between 7.32 and 7.26, whereas differences between subjects became negligible. Similar trends to VE/[LA] were observed in case of the Onset of Blood Lactate Accumulation (OBLA) throughout the test at pH values below 7.32, as was manifested by the correlation coefficient. We conclude that blood pH regulation due to respiratory compensation of the lactate acidosis is more successful in subjects with better endurance (higher OBLA), but only when [LA] is slightly increased or at slight acidosis.