Effects of nasal breathing on partial pressure of carbon dioxide in arterial blood during prolonged exercise in a hot environment

Prolonged exercise in a hot environment increases the minute ventilation (VE) and respiratory rate (RR) with an increase core temperature. This hyperthermia-induced hyperventilation decreases partial pressure of arterial blood carbon dioxide (PaCO2). Conversely, nasal breathing during has been reported to produce low VE RR values high PaCO2 values; however, no studies have investigated this environments. Therefore, purpose study was clarify effect on estimated (PaCO2,estimate) prolonged environment. Twelve university endurance athletes participated performed 40-minutes steady-state cycling at intensity 55% peak oxygen uptake (room temperature 35℃, relative humidity 40%). Using randomized crossover design, two experiments were performed—nasal condition (NB) mouth (MB). Moreover, physiological indices measured exercise. Rectal increased both conditions, but there significant difference between these conditions. PaCO2,estimate significantly higher NB 10 minutes 40 (p < 0.05) compared MB, decreased time MB. Compared lower 30 0.05), while 25 0.05). moderate-intensity prevented decrease due hyperventilation.