Document Detail

Enhanced open-loop but not closed-loop cardiac baroreflex sensitivity during orthostatic stress in humans.
MedLine Citation:
PMID:  21900646     Owner:  NLM     Status:  Publisher    
The neural interaction between the cardiopulmonary and arterial baroreflex may be critical for the regulation of blood pressure during orthostatic stress. However, studies have reported conflicting results with some indicating increases and others decreases in cardiac baroreflex sensitivity (i.e., gain) with cardiopulmonary unloading. Thus, the effect of orthostatic stress induced-central hypovolemia on the regulation of heart rate (HR) via the arterial baroreflex remains unclear. We sought to comprehensively assess baroreflex function during orthostatic stress by identifying and comparing open- and closed-loop dynamic cardiac baroreflex gains at supine rest and during 60 degree head-up tilt (HUT) in ten healthy men. Closed-loop dynamic "spontaneous" cardiac baroreflex sensitivities were calculated by the sequence technique and transfer function, and compared to two open-loop carotid-cardiac baroreflex measures using the neck chamber system: 1) a binary white-noise method and 2) rapid pulse neck pressure-suction technique. The gain from the sequence technique was decreased from -1.19±0.14 at rest to -0.78±0.10 bpm/mmHg during HUT (P=0.005). Similarly, closed-loop low frequency baroreflex transfer function gain was reduced during HUT (P=0.033). In contrast, open-loop low frequency transfer function gain between estimated carotid sinus pressure and HR during white-noise stimulation was augmented during HUT (P=0.01). This result was consistent with the maximal gain of carotid-cardiac baroreflex stimulus-response curve (0.47±0.15 rest to 0.60±0.20 HUT bpm/mmHg; P=0.037). These findings suggest that open-loop cardiac baroreflex gain was enhanced during HUT. Moreover, under closed-loop conditions, spontaneous baroreflex analyses without external stimulation may not represent open-loop cardiac baroreflex characteristics during orthostatic stress.
Toshinari Akimoto; Jun Sugawara; Daisuke Ichikawa; Nobuyuki Terada; Paul J Fadel; Shigehiko Ogoh
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Publication Detail:
Type:  JOURNAL ARTICLE     Date:  2011-9-7
Journal Detail:
Title:  American journal of physiology. Regulatory, integrative and comparative physiology     Volume:  -     ISSN:  1522-1490     ISO Abbreviation:  -     Publication Date:  2011 Sep 
Date Detail:
Created Date:  2011-9-8     Completed Date:  -     Revised Date:  -    
Medline Journal Info:
Nlm Unique ID:  100901230     Medline TA:  Am J Physiol Regul Integr Comp Physiol     Country:  -    
Other Details:
Languages:  ENG     Pagination:  -     Citation Subset:  -    
1Toyo University.
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