Muscle oxygen saturation increases during head‐up tilt‐induced (pre)syncope. (22nd March 2017)

• Record Type: Journal Article
• Authors: Lund, A.; Sørensen, H.; Jensen, T. W.; Niemann, M. J.; Olesen, N. D.; Nielsen, H. B.; Olsen, N. V.; Secher, N. H.
• Is Part Of: Acta physiologica. Volume 221:Number 1(2017)
• Page Start: 74
• Page End: 80
• Publication Date: 2017-03-22
• Subjects: cerebral blood flow -- head‐up tilt -- muscle oxygenation -- near‐infrared spectroscopy -- skin blood flow -- syncope; Physiology -- Periodicals; Physiology -- Research -- Periodicals; 612
• DOI: 10.1111/apha.12863
• Languages: English
• ISSNs: 1748-1708

Abstract

Abstract: Aim: To evaluate whether muscle vasodilatation plays a role for hypotension developed during central hypovolaemia, muscle oxygenation (Sm O2 ) was examined during (pre)syncope induced by head‐up tilt (HUT). Skin blood flow (SkBF) and oxygenation (Sskin O2 ) were determined because evaluation of Sm O2 may be affected by superficial tissue oxygenation. Furthermore, we evaluated cerebral oxygenation (Sc O2 ) and middle cerebral artery mean blood flow velocity (MCAvmean ). Methods: Twenty healthy male volunteers (median age 24 years; range 19–38) were subjected to passive 50° HUT for 1 h or until (pre)syncope. Sc O2 and Sm O2 (near‐infrared spectroscopy), MCAvmean (transcranial Doppler) along with mean arterial pressure (MAP), heart rate (HR), stroke volume (SV), cardiac output (CO) and total peripheral resistance (TPR) (Modelflow ® ) were determined. Results: (Pre)syncopal symptoms appeared in 17 subjects after 11 min (median; range 2–34) accompanied by a decrease in MAP, SV, CO and TPR, while HR remained elevated. During (pre)syncope, Sc O2 decreased [73% (71–76; mean and 95% CI) to 68% (65–71), P < 0.0001] along with MCAvmean [40 (37–43) to 32 (29–35) cm s −1, P < 0.0001]. In contrast, Sm O2 increased [63 (56–69)% to 71% (65–78), P < 0.0001], while Sskin O2 [64% (58–69) to 53% (47–58), P < 0.0001] and SkBF [71 (44–98) compared to a baseline of 99 (72–125) units, P = 0.020] were reduced. Conclusion: We confirm that the decrease in MAP during HUT is associated with a reduction in indices of cerebral perfusion. (Pre)syncope was associated with an increase in Sm O2 despite reduced Sskin O2 and SkBF, supporting that muscle vasodilation plays an important role in the circulatory events leading to hypotension during HUT.