Title

Chronic Intermittent Hypoxia Impairs Baroreflex Control Of Heart Rate But Enhances Heart Rate Responses To Vagal Efferent Stimulation In Anesthetized Mice

Keywords

Cardiac ganglia; Nucleus ambiguus; Obstructive sleep apnea

Abstract

Chronic intermittent hypoxia (CIH) leads to increased sympathetic nerve activity and arterial hypertension. In this study, we tested the hypothesis that CIH impairs baroreflex (BR) control of heart rate (HR) in mice, and that decreased cardiac chronotropic responsiveness to vagal efferent activity contributes to such impairment. C57BL/6J mice were exposed to either room air (RA) or CIH (6-min alternations of 21% O2 and 5.7% O2, 12 h/day) for 90 days. After the treatment period, mice were anesthetized (Avertin) and arterial blood pressure (ABP) was measured from the femoral artery. Mean ABP (MABP) was significantly increased in mice exposed to CIH (98.7 ± 2.5 vs. RA: 78.9 ± 1.4 mmHg, P < 0.001). CIH increased HR significantly (584.7 ± 8.9 beats/min; RA: 518.2 ± 17.9 beats/min, P < 0.05). Sustained infusion of phenylephrine (PE) at different doses (0.1-0.4 μg/min) significantly increased MABP in both CIH and RA mice, but the ABP-mediated decreases in HR were significantly attenuated in mice exposed to CIH (P < 0.001). In contrast, decreases in HR in response to electrical stimulation of the left vagus nerve (30 μA, 2-ms pulses) were significantly enhanced in mice exposed to CIH compared with RA mice at low frequencies. We conclude that CIH elicits a sustained impairment of baroreflex control of HR in mice. The blunted BR-mediated bradycardia occurs despite enhanced cardiac chronotropic responsiveness to vagal efferent stimulation. This suggests that an afferent and/or a central defect is responsible for the baroreflex impairment following CIH.

Publication Date

8-1-2007

Publication Title

American Journal of Physiology - Heart and Circulatory Physiology

Volume

293

Issue

2

Number of Pages

-

Document Type

Article

Personal Identifier

scopus

DOI Link

https://doi.org/10.1152/ajpheart.01124.2006

Socpus ID

34547872784 (Scopus)

Source API URL

https://api.elsevier.com/content/abstract/scopus_id/34547872784

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