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α‐Adrenergic effects on low‐frequency oscillations in blood pressure and R–R intervals during sympathetic activation
Author(s) -
Kiviniemi Antti M.,
Frances Maria F.,
Tiinanen Suvi,
Craen Rosemary,
Rachinsky Maxim,
Petrella Robert J.,
Seppänen Tapio,
Huikuri Heikki V.,
Tulppo Mikko P.,
Shoemaker J. Kevin
Publication year - 2011
Publication title -
experimental physiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.925
H-Index - 101
eISSN - 1469-445X
pISSN - 0958-0670
DOI - 10.1113/expphysiol.2011.058768
Subject(s) - phentolamine , blood pressure , medicine , endocrinology , adrenergic , sympathetic nervous system , heart rate , chemistry , propranolol , receptor
The present study was designed to address the contribution of α‐adrenergic modulation to the genesis of low‐frequency (LF; 0.04–0.15 Hz) oscillations in R–R interval (RRi), blood pressure (BP) and muscle sympathetic nerve activity (MSNA) during different sympathetic stimuli. Blood pressure and RRi were measured continuously in 12 healthy subjects during 5 min periods each of lower body negative pressure (LBNP; −40 mmHg), static handgrip exercise (HG; 20% of maximal force) and postexercise forearm circulatory occlusion (PECO) with and without α‐adrenergic blockade by phentolamine. Muscle sympathetic nerve activity was recorded in five subjects during LBNP and in six subjects during HG and PECO. Low‐frequency powers and median frequencies of BP, RRi and MSNA were calculated from power spectra. Low‐frequency power during LBNP was lower with phentolamine versus without for both BP and RRi oscillations (1.6 ± 0.6 versus 1.2 ± 0.7 ln mmHg 2 , P = 0.049; and 6.9 ± 0.8 versus 5.4 ± 0.9 ln ms 2 , P = 0.001, respectively). In contrast, the LBNP with phentolamine increased the power of high‐frequency oscillations (0.15–0.4 Hz) in BP and MSNA ( P < 0.01 for both), which was not observed during saline infusion. Phentolamine also blunted the increases in the LBNP‐induced increase in frequency of LF oscillations in BP and RRi. Phentolamine decreased the LF power of RRi during HG ( P = 0.015) but induced no other changes in LF powers or frequencies during HG. Phentolamine resulted in decreased frequency of LF oscillations in RRi ( P = 0.004) during PECO, and a similar tendency was observed in BP and MSNA. The power of LF oscillation in MSNA did not change during any intervention. We conclude that α‐adrenergic modulation contributes to LF oscillations in BP and RRi during baroreceptor unloading (LBNP) but not during static exercise. Also, α‐adrenergic modulation partly explains the shift to a higher frequency of LF oscillations during baroreceptor unloading and muscle metaboreflex activation.