Sodium bicarbonate ingestion mitigates the heat-induced hyperventilation and reduction in cerebral blood velocity during exercise in the heat

Abstract

Hyperthermia during exercise in the heat causes minute ventilation (VE) to increase, which leads to reductions in arterial CO2 partial pressure (PaCO2) and cerebral blood flow. On the other hand, sodium bicarbonate ingestion reportedly results in metabolic alkalosis, leading to decreased and increased PaCO2 during prolonged exercise in a thermoneutral environment. Here, we investigated whether sodium bicarbonate ingestion suppresses heat-induced hyperventilation and the resultant hypocapnia and cerebral hypoperfusion during prolonged exercise in the heat. Eleven healthy men ingested a solution of sodium bicarbonate (0.3 g/kg body weight) (NaHCO3 trial) or sodium chloride (0.208 g/kg) (NaCl trial). Ninety minutes after the ingestion, the subjects performed a cycle exercise for 60 min at 50% of peak oxygen uptake in the heat (35°C and 40% relative humidity). Esophageal temperature did not differ between the trials throughout (P = 0.56, main effect of trial). VE gradually increased with exercise duration in the NaCl trial, but the increases in VE were attenuated in the NaHCO3 trial (P = 0.01, main effect of trial). Correspondingly, estimated PaCO2 and middle cerebral artery blood velocity (an index of anterior cerebral blood flow) were higher in the NaHCO3 than the NaCl trial (P = 0.002 and 0.04, main effects of trial). Ratings of perceived exertion were lower in the NaHCO3 than the NaCl trial (P = 0.02, main effect of trial). These results indicate that sodium bicarbonate ingestion mitigates heat-induced hyperventilation and reductions in PaCO2 and cerebral blood velocity during prolonged exercise in the heat.

The effect of diminished metabolic acidosis on thermoregulatory response during exercise

“…Increased body temperature triggers cutaneous vasodilation and sweating, but also causes hyperventilation which reduces arterial carbon dioxide partial pressure (PaCO 2 ) and cerebral blood flow [ 1 ]. Katagiri et al found that metabolic alkalosis produced by sodium bicarbonate ingestion reduced hyperventilation and attenuated hypocapnia-related cerebral hypoperfusion during exercise [ 2 ].…”

Cerebral uptake of microvesicles occurs in normocapnic but not hypocapnic passive hyperthermia in young healthy male adults

“…Respiratory alkalosis and the accompanying reduction in CBF have also been expected to worsen central fatigue, exercise intolerance and cognitive impairments in the heat (Hasegawa & Cheung, 2013). An emerging focus has thus centred on exploring ways of attenuating or offsetting the heat-induced hyperventilation, for example through voluntary suppression of ventilation (Tsuji et al, 2015) or sodium bicarbonate ingestion (Katagiri et al, 2021). Surprisingly, however, most studies have failed to demonstrate any benefit of maintaining eucapnia in hyperthermia, aside from the observation that the CBF is restored.…”

The effect of taurine supplementation on physiological and thermoregulatory responses in humans during rest and exercise in hot environmental conditions

“…In these two studies, the placebo group ingested sodium chloride to match the sodium content of the two conditions, as they were investigating the buffering capacity of the supplement and not its effects on fluid balance (Katagiri et al, 2023;Katagiri et al, 2021). Therefore, it is likely that any potential osmotic effects that could theoretically have aided thermoregulation, would be indistinguishable from the effects in the placebo condition.…”