pH after competitive rowing: the lower physiological range?

At rest, pH is one of the most stable physiological variables with an average of 7.41 (range 7.38±7.44) corresponding to a [H] of 39 nmol kg H2O. Yet, in both health and disease, pH decreases in response to hypoventilation and especially to anaerobic metabolism when `acid production' exceeds the buffer capacity. Thus, blood pH is below 7.1 in diabetic ketoacidosis (Snorgaard et al. 1989) and in response to maximal exercise involving a large muscle mass (Rasmussen et al. 1991), the average value is 7.1. Blood pH may be even lower during a competitive physical effort as blood lactate is higher than during exercise in the laboratory (11 vs. 17 mmol L) (Vaage 1986). However, in healthy humans, the lower physiological limit of pH is not known. This study investigated pH of venous blood immediately after the Danish ergometer rowing championship. Six male oarsmen [age 30  1 year, body weight 78  2 kg, height 186  3 cm, maximal oxygen uptake 5.2  0.2 L min (mean  SEM)] participated in a `2000-m' maximal effort on a rowing ergometer (Concept II, type C; Dreisacker, Morrisville, VT). Two of the oarsmen had won an Olympic gold medal (Atlanta), two were lightweight World champions, and two rowers ranked at the National level. Within 2 min of termination of rowing, a venous puncture was made in an arm vein allowing for free ̄ow. Blood (1 mL) was obtained in a heparinized syringe and measured on a ABL615 apparatus (Radiometer, Copenhagen, Denmark). Plasma lactate was measured in triplicates (YSI 2300; Yellow Springs Instruments, OH, USA) with the average value presented. The concentration of lactate in venous blood was elevated and reached an upper level of 32 mmol L (Table 1). In all rowers, pH was reduced immediately after exercise and the lowest value (6.74) was measured in one of the Olympic gold medalists who won the Danish championship of the lightweight class in a World record time (6 min, 04 s). The second lowest pH (6.76) was measured in one of the rowers who ranked at the National level. Furthermore, base excess and bicarbonate were lowered and in the two subjects with the lowest pH, bicarbonate was not detectable. All oarsmen remained conscious after rowing, and there was no indication for medical interference. A low pH affects the af®nity of haemoglobin to O2. During exercise O2 saturation of haemoglobin (SaO2) decreases to 93% (Nielsen et al. 1998) as arterial O2 tension (PaO2) is reduced (Dempsey et al. 1984) and hypoxaemia hinders O2 uptake (Powers et al. 1989, Nielsen et al. 1998). During competitive exercise, haemoglobin af®nity to O2 may be lower. A pH of 6.74 at the PaO2 obtained during ergometer rowing (Nielsen et al. 1998), SaO2 would be reduced to 78% (Severinghaus 1958). A reduction in SaO2 from 97 to 78% would in turn affect O2 uptake by »15% (Nielsen et al. 1998) as cardiac output does not compensate for a decrease in SaO2. pH was related to a high blood lactate level and a marked reduction in bicarbonate. A pH of 6.74 corresponds to [H] of 182 nmol kg H2O which is more than a fourfold increase compared with the value at rest and twice than that previously reported during maximal exercise (Rasmussen et al. 1991, Nielsen et al. 1998). As bicarbonate was undetectable and lactate twice than