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Effects of systemic hypoxia and lower body negative pressure on heart rate variability and transfer function gain in humans
Author(s) -
Elwood Erik J.,
Lock Michael,
Cui Jian,
Leuenberger Urs A.
Publication year - 2007
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.21.5.a564-d
Subject(s) - baroreflex , medicine , heart rate , blood pressure , hypoxia (environmental) , heart rate variability , cardiology , autonomic nervous system , anesthesia , endocrinology , chemistry , organic chemistry , oxygen
Systemic hypoxia and lower body negative pressure (LBNP) elicit increases in sympathetic vasoconstrictor nerve traffic and heart rate and no change in blood pressure. The effect of hypoxia on baroreflex function is not well known. Analysis of heart rate variability (HRV) has been used to assess changes in autonomic neural tone during physiologic stress. Frequency domain analysis of HRV in the low (LF, 0.05‐0.15 Hz) and high (HF, 0.15–0.5 Hz) frequency ranges can be used to determine “sympathovagal balance” and transfer function (TF) gain between blood pressure and RR‐interval (RRI) can be interpreted as an index of baroreflex gain. To examine the autonomic neural effects of hypoxia and LBNP, we determined finger blood pressure (photo‐plethysmography) and RRI (electrocardiogram) before and during systemic hypoxia (FiO 2 0.1; 15 min) and before and during LBNP (up to −50 mmHg; 15 min) in healthy young humans. Systemic hypoxia (SaO 2 77±1%; n=13) increased the LF/HF ratio of RRI variability substantially ( P <0.01). Similarly, LBNP (n=6) caused a significant increase in the LF/HF ratio ( P <0.05). These responses are consistent with altered autonomic tone and sympathetic predominance. In addition, during hypoxia the TF gain in both the LF and HF ranges decreased significantly (TF LF 19.7±3.1 to 10.7±1.0 ms/mmHg; P =0.01; TF HF 19.3±3.1 to 11.1±1.9 ms/mmHg; P <0.05). Similar decreases of TF LF and TF HF gain were noted during LBNP. These data suggest that systemic hypoxia, a physiologic stressor that elicits sympathetic activation with no change in blood pressure, acutely alters baroreflex gain. Supported by R01 HL068699 , P01 HL077670 and M01 RR010732.