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Cardiac baroreflex sensitivity during lower body negative pressure and acute hypoxia: fainters vs. nonfainters
Author(s) -
Aarts Hugo M.,
PetersenJones Humphrey G.,
Johnson Blair D.,
Curry Timothy B.,
Joyner Michael J.
Publication year - 2017
Publication title -
the faseb journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.709
H-Index - 277
eISSN - 1530-6860
pISSN - 0892-6638
DOI - 10.1096/fasebj.31.1_supplement.1087.1
Subject(s) - baroreflex , heart rate , blood pressure , medicine , hypovolemia , cardiology , anesthesia , hypoxia (environmental) , chemistry , organic chemistry , oxygen
Background Hypoxia increases susceptibility to syncope during orthostatic stress. Furthermore, cardiac baroreflex sensitivity (cBRS) is attenuated during lower body negative pressure (LBNP). Recent studies suggest that there is cross‐talk between baroreceptors and carotid body chemoreceptors. With this in mind, hypoxia may further blunt cardiac baroreflex sensitivity (cBRS) during central hypovolemia in individuals susceptible to hypoxic syncope. Therefore, we hypothesized that participants susceptible to hypoxic syncope (“fainters”) during progressive central hypovolemia would have lower spontaneous cBRS during LBNP when compared to “nonfainters”. Methods Ten healthy male participants (35 ± 3 yr, BMI 25 ± 1 kg/m 2 ) were exposed to stepwise lower body negative pressure (LBNP, 5 minutes at 0, −15, −30, −45 mmHg) during both normoxia and hypoxia (FiO 2 = 0.12 – 0.15; S p O 2 ~85%). LBNP protocols were terminated early if participants developed presyncopal symptoms. Data from uncompleted stages were excluded. Heart rate (HR, 3 lead electrocardiogram) and mean arterial blood pressure (MAP, brachial arterial catheter) were continuously recorded. Spectral cBRS was calculated from the heart rate and blood pressure signals. Following experimentation, participants were stratified as fainters (developed presyncopal symptoms during hypoxic conditions, n=7) and nonfainters (n=3). Results MAP was lower in fainters than in nonfainters during hypoxia (interaction with LBNP p<0.05) while HR (p=0.38) and cBRS (p=0.43) were similar – Table 1. Hypoxia had a main effect vs normoxia on MAP, HR and cBRS in fainters (all p<0.02). In nonfainters hypoxia had a main effect vs normoxia on HR and cBRS (all p<0.03) and an interaction effect with LBNP on MAP (p<0.01). Conclusion Spontaneous cardiac baroreflex sensitivity is not attenuated in participants susceptible to hypoxic syncope during lower body negative pressure. This suggests that spontaneous cardiac baroreflex sensitivity does not contribute to orthostatic intolerance during hypoxia. Support or Funding Information Funding: W81XWH‐13‐2‐0038 1 Physiological response in fainters and nonfainters to LBNP during hypoxia and normoxiaMAP, mmHg HR, beats·min −1 cBRS, ms·mmHg −1Nonfainters Fainters Nonfainters Fainters Nonfainters FaintersBaseline Normoxia 104 ± 5 102 ± 3 62 ± 5 61 ± 3 13 ± 3 19 ± 2 Hypoxia 106 ± 6 97 ± 4 80 ± 6 72 ± 4 9 ± 3 11 ± 2 LBNP −15 mmHg Normoxia 109 ± 5 103 ± 3 68 ± 5 64 ± 3 11 ± 3 14 ± 2 Hypoxia 106 ± 6 90 ± 4 88 ± 6 72 ± 4 9 ± 3 14 ± 2 LBNP −30 mmHg Normoxia 107 ± 5 98 ± 3 79 ± 5 74 ± 3 8 ± 3 11 ± 2 Hypoxia 103 ± 6 † 82 ± 5 * 95 ± 6 79 ± 5 8 ± 3 9 ± 3 LBNP −45 mmHg Normoxia 101 ± 5 99 ± 3 92 ± 5 84 ± 4 6 ± 2 5 ± 2 Hypoxia 89 ± 6 † N/A 113 ± 6 N/A 3 ± 3 N/A* Different vs. nonfainters p<0.05 † Different vs. normoxia p<0.05