title: Carotid baroreceptor stimulation alters cutaneous vascular conductance during whole-body heating in humans.
abstract: Prior studies investigating carotid baroreflex control of the cutaneous vasculature have yielded mixed findings. However, previously used methodological and analytical techniques may limit the ability to detect carotid baroreflex-mediated changes in cutaneous vascular conductance (CVC). The aim of this study was to test the hypothesis that dynamic carotid baroreceptor stimulation (i.e. 5 s trials) using neck pressure (NP, simulated carotid hypotension) and neck suction (NS, simulated carotid hypertension) will decrease and increase CVC, respectively, during normothermic and whole-body heating conditions in resting humans. Data were obtained from nine subjects (age, 31 +/- 2 year). The ratio of forearm skin blood flux (laser-Doppler flowmetry) and arterial blood pressure (Finapres) was used as an index of CVC. Multiple 5 s trials of NP (+40(Torr)) and NS (-60(Torr)), as well as breath-hold/airflow control trials, were applied during end-expiratory breath-holds while subjects were normotheric and heat stressed (change in core temperature approximately 0.75 degrees C). CVC responses to each NP and NS trial were averaged into 1 s intervals during the following periods: 3 s prestimulus, 5 s during stimulus, and 5 s poststimulus. Peak CVC responses (3 s average) to NP and NS were compared to prestimulus values using paired t test. During normothermia, NP decreased CVC by 0.032 +/- 0.007 arbitrary units (a.u.) mmHg(-1); (P < 0.05); however, breath-hold/airflow control trials resulted in similar decreases in CVC. NS did not change CVC (Delta = 0.002 +/- 0.005 a.u. mmHg(-1); P = 0.63). During whole-body heating, NP decreased CVC (by 0.16 +/- 0.04 a.u. mmHg(-1); (P < 0.05), whereas NS increased CVC by 0.07 +/- 0.03 a.u. mmHg(-1); (P < 0.05). Furthermore, these changes were greater than, or directionally different from, the breath-hold/airflow control trials. These findings indicate that carotid baroreceptor stimulation elicits dynamic changes in CVC and that these changes are more apparent during whole-body heating.
authors.affiliation: Institute for Exercise and Environmental Medicine, 7232 Greenville Avenue, Dallas, TX 75231, USA.
authors.forename: David M
authors.initials: DM
authors.lastname: Keller
authors.forename: Scott L
authors.initials: SL
authors.lastname: Davis
authors.forename: David A
authors.initials: DA
authors.lastname: Low
authors.forename: Manabu
authors.initials: M
authors.lastname: Shibasaki
authors.forename: Peter B
authors.initials: PB
authors.lastname: Raven
authors.forename: Craig G
authors.initials: CG
authors.lastname: Crandall
mesh_terms: D000328:Adult; D002339:Carotid Arteries / Q000294:innervation*; D005260:Female; D005542:Forearm; D006358:Hot Temperature; D006801:Humans; D008297:Male; D009333:Neck; D010812:Physical Stimulation; D011311:Pressoreceptors / Q000503:physiopathology*; D011312:Pressure; D012123:Pulmonary Ventilation; D012039:Regional Blood Flow / Q000502:physiology; D015656:Respiratory Mechanics; D012867:Skin / Q000098:blood supply*; D013312:Stress, Physiological / Q000209:etiology / Q000503:physiopathology*; D013396:Suction