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Effect of time of day on heat‐induced hyperventilation and cerebrovascular response during exercise in the heat
Author(s) -
Tsuji Bun,
Nakane Akari,
Ohno Mizuki,
Inoue Yukiko
Publication year - 2019
Publication title -
the faseb journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.709
H-Index - 277
eISSN - 1530-6860
pISSN - 0892-6638
DOI - 10.1096/fasebj.2019.33.1_supplement.541.7
Subject(s) - hyperventilation , evening , morning , hyperthermia , medicine , ventilation (architecture) , middle cerebral artery , thermoregulation , anesthesia , respiratory minute volume , blood pressure , cardiology , respiratory system , ischemia , physics , astronomy , mechanical engineering , engineering
Hyperthermia during exercise leads to increases in minute ventilation independently of metabolic factors. This heat‐induced hyperventilation results in excessive elimination of CO 2 from the body, leading to reduced arterial CO 2 pressure (PaCO 2 ) and the resultant cerebral hypoperfusion, which may underlie central fatigue during hyperthermia and impaired exercise performance in the heat. We recently reported that time of day has no effect on time course of hyperventilatory response during exercise in the heat, despite the higher core temperatures in the evening (Tsuji et al. Am J Physiol 2016). This was likely due to diurnal variation in the control of ventilation in response to rising core temperature. However, it remains unclear whether cerebrovascular response during exercise in the heat is affected by time of day. This study thus examined the effect of time of day on respiratory and cerebrovascular responses during prolonged exercise in the heat. Eleven healthy subjects performed a cycle exercise at 50% of peak oxygen uptake in the heat (35°C ambient temperature and 40% relative humidity) in the morning (0830) and evening (1830). The exercise was terminated when the exercise duration reached 60 min, esophageal temperature reached 39.0°C or the subject could no longer pedal at 60 rpm. Esophageal temperature and mean arterial pressure were significantly higher in the evening than morning (both P < 0.01), but time of day had no significant effect on minute ventilation, estimated PaCO 2 , middle cerebral artery blood velocity and cerebral vascular conductance. The ventilatory sensitivity to rising core temperature (i.e., slope of the esophageal temperature‐ventilation relation) was significantly greater in the evening than morning. However, sensitivities of PaCO 2 and cerebrovascular responses to rising core temperature were unaffected by time of day. In conclusion, present results suggest that time of day has no effect on the time course of hyperventilation, PaCO 2 and cerebral blood flow response during prolonged exercise in the heat. This abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal .