Cutaneous vascular responses to hypercapnia during whole-body heating.
BACKGROUND
Hypercapnia may be encountered in lung disease as well as during situations involving rebreathing of previously expired air (e.g., occupational diving). Inhibitory effects of elevated arterial carbon dioxide partial pressure on the central nervous system may result in impaired thermoregulation. This study tested the hypothesis that in heat-stressed subjects, cutaneous vascular responsiveness [expressed as cutaneous vascular conductance (CVC)] would be reduced during hypercapnic exposure.


METHODS
Four men and three women (mean - SD; age: 35 +/- 7 yr) rested supine while wearing a tube-lined suit perfused with 34 degrees C water (normothermia). Following normothermic data collection, 50 degrees C water was perfused through the suit to increase internal temperature approximately 1 degrees C (whole-body heating). In both thermal conditions, a normoxic-hypercapnic (5% CO2, 21% O2, balance N2) gas mixture was inspired while forearm skin blood flux (laser-Doppler flowmetry) was measured continuously and was used for calculation of CVC (skin blood flux/mean arterial pressure).


RESULTS
End-tidal CO2 increased similarly throughout hypercapnic exposure during both normothermic and whole-body heating conditions (7.9 +/- 2.4 and 8.3 +/- 1.9 mmHg, respectively). However, CVC was not different between normocapnia and hypercapnia under either thermal condition (normothermia: 0.42 +/- 0.24 vs. 0.39 +/- 0.21 flux units/mmHg for normocapnia and hypercapnia, respectively; heat stress: 1.89 +/- 0.67 vs. 1.92 +/- 0.63 flux units/ mmHg for normocapnia and hypercapnia, respectively).


CONCLUSIONS
Based on these findings, mild hypercapnia is unlikely to impair heat dissipation by reducing cutaneous vasodilation.
Wingo
Jonathan E
JE
Institute for Exercise and Environmental Medicine, Presbyterian Hospital of Dallas, Texas 75231, USA.
Low
David A
DA
Keller
David M
DM
Crandall
Craig G
CG
D000222:Adaptation, Physiological; D000328:Adult; D001833:Body Temperature Regulation; D002245:Carbon Dioxide / Q000378:metabolism; D005260:Female; D005334:Fever / Q000503:physiopathology; D018882:Heat Stress Disorders / Q000503:physiopathology*; D006358:Hot Temperature; D006801:Humans; D006935:Hypercapnia / Q000503:physiopathology*; D008297:Male; D010865:Pilot Projects; D012119:Respiration; D012867:Skin / Q000098:blood supply*; D012879:Skin Physiological Phenomena
D002245:Carbon Dioxide