title: Skin cooling maintains cerebral blood flow velocity and orthostatic tolerance during tilting in heated humans.
abstract: Orthostatic tolerance is reduced in the heat-stressed human. The purpose of this project was to identify whether skin-surface cooling improves orthostatic tolerance. Nine subjects were exposed to 10 min of 60 degrees head-up tilting in each of four conditions: normothermia (NT-tilt), heat stress (HT-tilt), normothermia plus skin-surface cooling 1 min before and throughout tilting (NT-tilt(cool)), and heat stress plus skin-surface cooling 1 min before and throughout tilting (HT-tilt(cool)). Heating and cooling were accomplished by perfusing 46 and 15 degrees C water, respectively, though a tube-lined suit worn by each subject. During HT-tilt, four of nine subjects developed presyncopal symptoms resulting in the termination of the tilt test. In contrast, no subject experienced presyncopal symptoms during NT-tilt, NT-tilt(cool), or HT-tilt(cool). During the HT-tilt procedure, mean arterial blood pressure (MAP) and cerebral blood flow velocity (CBFV) decreased. However, during HT-tilt(cool), MAP, total peripheral resistance, and CBFV were significantly greater relative to HT-tilt (all P < 0.01). No differences were observed in calculated cerebral vascular resistance between the four conditions. These data suggest that skin-surface cooling prevents the fall in CBFV during upright tilting and improves orthostatic tolerance, presumably via maintenance of MAP. Hence, skin-surface cooling may be a potent countermeasure to protect against orthostatic intolerance observed in heat-stressed humans.
authors.affiliation: Institute for Exercise and Environmental Medicine, Presbyterian Hospital of Dallas, Texas 75321, USA.
authors.forename: Thad E
authors.initials: TE
authors.lastname: Wilson
authors.forename: Jian
authors.initials: J
authors.lastname: Cui
authors.forename: Rong
authors.initials: R
authors.lastname: Zhang
authors.forename: Sarah
authors.initials: S
authors.lastname: Witkowski
authors.forename: Craig G
authors.initials: CG
authors.lastname: Crandall
mesh_terms: D000328:Adult; D001794:Blood Pressure / Q000502:physiology; D001831:Body Temperature / Q000502:physiology; D002302:Cardiac Output / Q000502:physiology; D002560:Cerebrovascular Circulation / Q000502:physiology*; D005260:Female; D005712:Galvanic Skin Response; D006339:Heart Rate / Q000502:physiology; D006439:Hemodynamics / Q000502:physiology; D006358:Hot Temperature; D006801:Humans; D007024:Hypotension, Orthostatic / Q000503:physiopathology*; D017078:Laser-Doppler Flowmetry; D008297:Male; D011187:Posture / Q000502:physiology; D012879:Skin Physiological Phenomena; D012881:Skin Temperature / Q000502:physiology*; D013546:Sweating / Q000502:physiology; D017585:Ultrasonography, Doppler, Transcranial; D014655:Vascular Resistance / Q000502:physiology