Cardiovagal regulation during combined hypoxic and orthostatic stress: fainters vs. nonfainters. Export

@article{citeulike:1653178, abstract = {We tested the hypothesis that individual differences in the effect of acute hypoxia on the cardiovagal arterial baroreflex would determine individual susceptibility to hypoxic syncope. In 16 healthy, nonsmoking, normotensive subjects (8 women, 8 men, age 20-33 yr), we assessed orthostatic tolerance with a 20-min 60 degrees head-upright tilt during both normoxia and hypoxia (breathing 12\% O(2)). On a separate occasion, we assessed baroreflex control of heart rate (cardiovagal baroreflex gain) using the modified Oxford technique during both normoxia and hypoxia. When subjects were tilted under hypoxic conditions, 5 of the 16 developed presyncopal signs or symptoms, and the 20-min tilt had to be terminated. These "fainters" had comparable cardiovagal baroreflex gain to "nonfainters" under both normoxic and hypoxic conditions (normoxia, fainters: -1.2 +/- 0.2, nonfainters: -1.0 +/- 0.2 beats.min(-1).mmHg(-1), P = 0.252; hypoxia, fainters: -1.3 +/- 0.2, nonfainters: -1.0 +/- 0.1 beats.min(-1).mmHg(-1), P = 0.208). Furthermore, hypoxia did not alter cardiovagal baroreflex gain in either group (both P > 0.8). It appears from these observations that hypoxic syncope results from the superimposed vasodilator effects of hypoxia on the cardiovascular system and not from a hypoxia-induced maladjustment in baroreflex control of heart rate.}, address = {Department of Human Physiology, University of Oregon, Eugene, Oregon, USA. halliwil@uoregon.edu}, author = {Halliwill, J. R. and Minson, C. T.}, citeulike-article-id = {1653178}, citeulike-linkout-0 = {http://dx.doi.org/10.1152/japplphysiol.00871.2004}, citeulike-linkout-1 = {http://view.ncbi.nlm.nih.gov/pubmed/15531565}, citeulike-linkout-2 = {http://www.hubmed.org/display.cgi?uids=15531565}, doi = {10.1152/japplphysiol.00871.2004}, issn = {8750-7587}, journal = {J Appl Physiol}, keywords = {diagnosis, hypoxia, postural, syncope}, month = {March}, number = {3}, pages = {1050--1056}, posted-at = {2007-09-13 23:13:27}, priority = {2}, title = {Cardiovagal regulation during combined hypoxic and orthostatic stress: fainters vs. nonfainters.}, url = {http://dx.doi.org/10.1152/japplphysiol.00871.2004}, volume = {98}, year = {2005} }

TY - JOUR ID - citeulike:1653178 L3 - citeulike-article-id:1653178 N2 - We tested the hypothesis that individual differences in the effect of acute hypoxia on the cardiovagal arterial baroreflex would determine individual susceptibility to hypoxic syncope. In 16 healthy, nonsmoking, normotensive subjects (8 women, 8 men, age 20-33 yr), we assessed orthostatic tolerance with a 20-min 60 degrees head-upright tilt during both normoxia and hypoxia (breathing 12% O(2)). On a separate occasion, we assessed baroreflex control of heart rate (cardiovagal baroreflex gain) using the modified Oxford technique during both normoxia and hypoxia. When subjects were tilted under hypoxic conditions, 5 of the 16 developed presyncopal signs or symptoms, and the 20-min tilt had to be terminated. These "fainters" had comparable cardiovagal baroreflex gain to "nonfainters" under both normoxic and hypoxic conditions (normoxia, fainters: -1.2 +/- 0.2, nonfainters: -1.0 +/- 0.2 beats.min(-1).mmHg(-1), P = 0.252; hypoxia, fainters: -1.3 +/- 0.2, nonfainters: -1.0 +/- 0.1 beats.min(-1).mmHg(-1), P = 0.208). Furthermore, hypoxia did not alter cardiovagal baroreflex gain in either group (both P > 0.8). It appears from these observations that hypoxic syncope results from the superimposed vasodilator effects of hypoxia on the cardiovascular system and not from a hypoxia-induced maladjustment in baroreflex control of heart rate. IS - 3 JF - J Appl Physiol SN - 8750-7587 AD - Department of Human Physiology, University of Oregon, Eugene, Oregon, USA. halliwil@uoregon.edu EP - 1056 TI - Cardiovagal regulation during combined hypoxic and orthostatic stress: fainters vs. nonfainters. VL - 98 SP - 1050 KW - diagnosis KW - hypoxia KW - postural KW - syncope AU - Halliwill, JR AU - Minson, CT PY - 2005/03// UR - http://dx.doi.org/10.1152/japplphysiol.00871.2004 ER -