Hyperthermia modulates regional differences in cerebral blood flow to changes in CO2.
The purpose of this study was to assess blood flow responses to changes in carbon dioxide (CO2) in the internal carotid artery (ICA), external carotid artery (ECA), and vertebral artery (VA) during normothermic and hyperthermic conditions. Eleven healthy subjects aged 22 ± 2 (SD) yr were exposed to passive whole body heating followed by spontaneous hypocapnic and hypercapnic challenges in normothermic and hyperthermic conditions. Right ICA, ECA, and VA blood flows, as well as left middle cerebral artery (MCA) mean blood velocity (Vmean), were measured. Esophageal temperature was elevated by 1.53 ± 0.09°C before hypocapnic and hypercapnic challenges during heat stress. Whole body heating increased ECA blood flow and cardiac output by 130 ± 78 and 47 ± 26%, respectively (P < 0.001), while blood flow (or velocity) in the ICA, MCA, and VA was reduced by 17 ± 14, 24 ± 18, and 12 ± 7%, respectively (P < 0.001). Regardless of the thermal conditions, ICA and VA blood flows and MCA Vmean were decreased by hypocapnic challenges and increased by hypercapnic challenges. Similar responses in ECA blood flow were observed in hyperthermia but not in normothermia. Heat stress did not alter CO2 reactivity in the MCA and VA. However, CO2 reactivity in the ICA was decreased (3.04 ± 1.17 vs. 2.23 ± 1.03%/mmHg; P = 0.039) but that in the ECA was enhanced (0.45 ± 0.47 vs. 0.95 ± 0.61%/mmHg; P = 0.032). These results indicate that hyperthermia is capable of altering dynamic cerebral blood flow regulation.
Department of Biomedical Engineering, Toyo University, Saitama, Japan;
Shigehiko
S
Ogoh
Research Institute of Physical Fitness, Japan Women's College of Physical Education, Tokyo, Japan;
Kohei
K
Sato
Department of Environmental Physiology for Exercise, Osaka City University Graduate School of Medicine, Osaka, Japan;
Kazunobu
K
Okazaki
Morinomiya University of Medical Sciences, Osaka, Japan; and.
Tadayoshi
T
Miyamoto
Department of Biomedical Engineering, Toyo University, Saitama, Japan;
Ai
A
Hirasawa
Department of Environmental Health, Nara Women's University, Nara, Japan shiba@cc.nara-wu.ac.jp.
Manabu
M
Shibasaki
D000328:Adult; D001783:Blood Flow Velocity / Q000502:physiology; D001794:Blood Pressure / Q000502:physiology; D001831:Body Temperature / Q000502:physiology; D001921:Brain / Q000378:metabolism / Q000502:physiology*; D002245:Carbon Dioxide / Q000378:metabolism*; D002302:Cardiac Output / Q000502:physiology; D002342:Carotid Artery, External / Q000378:metabolism / Q000502:physiology; D002343:Carotid Artery, Internal / Q000378:metabolism / Q000502:physiology; D002560:Cerebrovascular Circulation / Q000502:physiology*; D005334:Fever / Q000378:metabolism / Q000503:physiopathology*; D006339:Heart Rate / Q000502:physiology; D006358:Hot Temperature; D006801:Humans; D006935:Hypercapnia / Q000378:metabolism / Q000503:physiopathology; D016857:Hypocapnia / Q000378:metabolism / Q000503:physiopathology; D008297:Male; D020768:Middle Cerebral Artery / Q000378:metabolism / Q000502:physiology; D013312:Stress, Physiological / Q000502:physiology; D014711:Vertebral Artery / Q000378:metabolism / Q000502:physiology; D055815:Young Adult
D002245:Carbon Dioxide
Doppler ultrasound; arterial pressure; cardiac output; humans; hyperthermia