title: Forehead versus forearm skin vascular responses at presyncope in humans.
abstract: Facial pallor is commonly observed at presyncope in humans, suggestive of reductions in facial skin blood flow (SkBF). Yet, cutaneous vasoconstriction is usually minimal at presyncope when measured at the forearm. We tested the hypothesis that reductions in forehead SkBF at presyncope are greater than in the forearm. Forehead and forearm SkBF (laser-Doppler) and blood pressure (Finometer or radial artery catheterization) were measured during lower body negative pressure (LBNP) to presyncope in 11 normothermic and 13 heat-stressed subjects (intestinal temperature increased ∼1.4°C). LBNP reduced mean arterial pressure from 91 ± 5 to 57 ± 7 mmHg during normothermia (P ≤ 0.001) and from 82 ± 5 to 57 ± 7 mmHg during heat stress (P ≤ 0.001). During normothermia, LBNP decreased forehead SkBF 55 ± 14% compared with 24 ± 11% at the forearm (P = 0.002), while during heat stress LBNP decreased forehead SkBF 39 ± 11% compared with 28 ± 8% in the forearm (P = 0.007). In both conditions, most (≥68%) of the decreases in SkBF were due to decreases in blood pressure. However, a greater contribution of actively mediated reductions in SkBF was observed at the forehead, relative to the forearm during normothermia (32 ± 13% vs. 11 ± 11%, P = 0.031) and heat stress (30 ± 13% vs. 10 ± 13%, P = 0.004). These data suggest that facial pallor at presyncope is due to a combination of passive decreases in forehead SkBF secondary to reductions in blood pressure and to active decreases in SkBF, the latter of which are relatively greater than in the forearm.
authors.affiliation: Institute for Exercise and Environmental Medicine, Texas Health Presbyterian Hospital Dallas and University of Texas Southwestern Medical Center, Dallas, Texas;
authors.forename: Daniel
authors.initials: D
authors.lastname: Gagnon
authors.affiliation: Environmental and Autonomic Physiology Laboratory, Department of Kinesiology and Health Education, The University of Texas at Austin, Austin, Texas;
authors.forename: R
authors.initials: R
authors.lastname: Matthew Brothers
authors.affiliation: Department of Health, Human Performance and Recreation, University of Arkansas, Fayetteville, Arkansas; and.
authors.forename: Matthew S
authors.initials: MS
authors.lastname: Ganio
authors.affiliation: Institute for Exercise and Environmental Medicine, Texas Health Presbyterian Hospital Dallas and University of Texas Southwestern Medical Center, Dallas, Texas; Veterans Affairs North Texas Health Care System, Dallas, Texas.
authors.forename: Jeffrey L
authors.initials: JL
authors.lastname: Hastings
authors.affiliation: Institute for Exercise and Environmental Medicine, Texas Health Presbyterian Hospital Dallas and University of Texas Southwestern Medical Center, Dallas, Texas; craigcrandall@texashealth.org.
authors.forename: Craig G
authors.initials: CG
authors.lastname: Crandall
mesh_terms: D000328:Adult; D000368:Aged; D001794:Blood Pressure / Q000502:physiology; D005260:Female; D005542:Forearm / Q000098:blood supply*; D005546:Forehead / Q000098:blood supply*; D006801:Humans; D008150:Lower Body Negative Pressure / Q000379:methods; D008297:Male; D008875:Middle Aged; D012039:Regional Blood Flow / Q000502:physiology; D012867:Skin / Q000098:blood supply*; D012881:Skin Temperature / Q000502:physiology; D013575:Syncope / Q000503:physiopathology*; D055815:Young Adult
keywords: heat; lower body negative pressure; skin blood flow; syncope; vasoconstriction
references.citation: Auton Neurosci. 2002 May 31;97(2):122-8
references.pmid: 12132645
references.citation: Circ Res. 1995 Dec;77(6):1222-8
references.pmid: 7586235
references.citation: Eur J Appl Physiol. 2005 Jun;94(3):323-32
references.pmid: 15729550
references.citation: Am J Physiol Regul Integr Comp Physiol. 2012 Nov 1;303(9):R975-83
references.pmid: 22972836
references.citation: J Physiol. 2006 Sep 15;575(Pt 3):953-9
references.pmid: 16793901
references.citation: J Appl Physiol (1985). 2014 Jul 1;117(1):46-52
references.pmid: 24790021
references.citation: Am J Cardiol. 1965 Oct;16(4):506-15
references.pmid: 5319567
references.citation: Am J Physiol Heart Circ Physiol. 2010 Oct;299(4):H1168-73
references.pmid: 20693394
references.citation: J Appl Physiol (1985). 1989 Apr;66(4):1586-92
references.pmid: 2732150
references.citation: Clin Physiol Funct Imaging. 2012 Sep;32(5):361-6
references.pmid: 22856342
references.citation: J Physiol. 2005 Jan 15;562(Pt 2):629-34
references.pmid: 15539401
references.citation: Am J Physiol. 1989 Nov;257(5 Pt 2):H1599-606
references.pmid: 2589514
references.citation: Am J Physiol Regul Integr Comp Physiol. 2014 May 15;306(10):R747-51
references.pmid: 24598464
references.citation: J Cereb Blood Flow Metab. 2013 Dec;33(12):1915-20
references.pmid: 23942362
references.citation: Eur J Appl Physiol Occup Physiol. 1996;74(1-2):78-84
references.pmid: 8891504
references.citation: J Physiol. 1962 May;161:298-312
references.pmid: 13894392
references.citation: J Physiol. 2007 Dec 1;585(Pt 2):627-34
references.pmid: 17947310
references.citation: J Physiol. 1990 Apr;423:241-55
references.pmid: 2388150
references.citation: Exp Physiol. 2013 Jul;98(7):1156-63
references.pmid: 23585326
references.citation: Acta Physiol Scand. 1993 Apr;147(4):431-6
references.pmid: 8493876
references.citation: Clin Sci. 1957 Feb;16(1):67-74
references.pmid: 13414140