Determinants of baroreflex sensitivity in health and disease:

Abstract

The baroreflex is a powerful blood pressure regulatory mechanism [1,10]. Baroreceptor nerve endings detect changes in blood pressure and evoke reflex circulatory adjustments that buffer the changes in pressure. By providing moment-to-moment, negative-feedback regulation of blood pressure, the baroreflex reduces blood pressure variability and its adverse consequences.Interest in measuring baroreflex sensitivity (BRS) in human populations is surging [7-9, 11-14, 21, 29]. The increased interest relates, in part, to the now widely recognized association between decreased BRS for control of heart rate and increased risk of arrhythmias and sudden cardiac death in certain pathological states including myocardial infarction [2, 3, 13-15], heart failure [21,22], and possibly diabetes [16]. A large multi-center prospective trial (ATRAMI) recently demonstrated that measures of BRS provide independent prognostic value in predicting total cardiac and arrhythmic mortality after myocardial infarction [13,14]. Attempts are now underway to identify optimal predictors of decreased BRS in healthy subjects [7,8,11] and in patients prior to myocardial infarction or heart failure [9,12].The goal of the study by Yasumasu and colleagues reported in this issue of Clinical Autonomic Research [29], was to identify risk factors of cardiovascular disease that are associated with decreased BRS. The study population was restricted to elderly subjects (40 men and 55 women, 65-69 years old) to take advantage of the prevalence of risk factors in this population and to eliminate the established and possibly confounding effect of age on BRS. BRS was calculated as the transfer function gain between low-frequency fluctuations in R-R interval and mean arterial pressure. Stepwise multiple regression analysis identified only two independent predictors of BRS in this population: heart rate and blood platelet count. These factors together accounted for approximately 20 % of the inter-individual variation in BRS. The finding of an inverse relationship between heart rate and BRS confirms previous studies [8,12].The major new finding of this study is the association of higher platelet counts (within the normal range) with low BRS. The relationship is intriguing given that platelet count in healthy middle-aged men has been shown to be an independent predictor of cardiovascular mortality [28], and that decreased BRS predicts mortality in patients with myocardial infarction [3,[13][14][15].Is platelet count simply a correlate or a cause of decreased BRS?The study by Yasumasu et al. [29] demonstrates an association between platelet count and BRS, but cannot determine causality. Although the inverse relationship between platelet count and BRS may involve an effect of platelets on BRS, platelet count may also simply be a marker of an unidentified determinant of BRS.The authors speculate that factors released from ag-CAR 131

Decreased baroreflex sensitivity in acute schizophrenia

“…In particular, efferent parasympathetic activity has been shown to be decreased in acute (5) and chronic stages (31), possibly increasing the incidence of serious ventricular arrhythmias (30). Such increased risk of arrhythmias and sudden cardiac death has been reported to be associated with decreased baroreflex sensitivity (BRS) in other diseases (11), including myo-cardial infarction (20), heart failure (26), and possibly diabetes (22). Yet BRS has not been examined in schizophrenia to date.…”

Cardiovascular and Cerebral Responses During a Vasovagal Reaction Without Syncope

“…Vaso-vagal events are usually triggered by parasympathetic overactivation associated with a reduced sympathetic response (Gunnar Wallin and Sundlöf, 1982), which in turn causes a reduction in cardiac output, hypotension and cerebral hypoperfusion (Wieling et al, 2016). Arterial blood pressure decreases below the autoregulatory threshold (Van Lieshout et al, 2003) and cannot be compensated for by the delayed normal auto-regulatory reflex-loop blood pressure adjustment of the baroreflex (Chapleau, 2003), leading to cerebral hypoperfusion (Lund et al, 2017). Furthermore, parasympathetic activation corresponds to an increase in heart rate variability and is related with slow alpha power on the electroencephalography (EEG), mainly in the frontal area (Takahashi et al, 2005).…”

Increased neuronal cell number in the dorsal motor nucleus of the vagus in schizophrenia

“…Furthermore, decreased baroreflex sensitivity (BRS) and increased QT variability have been described in the acute state of the disease (4). All autonomic measures altered in schizophrenia have been associated with an increased risk of arrhythmias and sudden cardiac death in other diseases (5,6).…”