Modulations of autonomic cardiovascular control following acute alpha-adrenergic treatment in chronic hypotension

Abstract

Chronic low blood pressure is typically accompanied with symptoms such as fatigue, reduced drive, dizziness, headaches and cold limbs. Alterations in autonomic cardiovascular regulation are assumed to be involved in the etiology of this condition, that is, increased baroreflex sensitivity (BRS) as well as reduced sympathetic and augmented parasympathetic influences on cardiovascular regulation. In this study, the acute effects of the blood pressure-enhancing alpha-adrenergic agonist, midodrine, on autonomic cardiovascular control were investigated in 50 hypotensive persons (mean blood pressure 96/61 mm Hg) based on a placebo-controlled double blind design. BRS was determined using sequence analysis. Spectral analysis of heart rate variability was carried out to quantify sympathetic and parasympathetic cardiac control. Parameters were obtained at rest and during mental stress. Drug application led to marked increases in blood pressure, BRS and respiratory sinus arrhythmia (RSA), whereas heart rate and power in the low frequency (LF) band of the heart rate variability spectrum decreased. The augmentation of RSA and reduction of LF power indicate a shift of the sympathovagal balance toward increased parasympathetic and reduced sympathetic influences on heart rate. Like the increase in BRS, these modulations represent a counter-regulatory autonomic response to the blood pressure elevation, which is initiated to return blood pressure to the initial value or to an individual set point. The finding challenges the use of a-sympathomimetics in the treatment of chronic hypotension as they may not reduce but may instead exacerbate the autonomic dysbalance related to this condition.

Cardiac autonomic profile during rest and working memory load in essential hypotensive women

“…Alterations in autonomic cardiovascular regulation appear to be the cause. A diminished general sympathetic tone and high levels of vagal activity in hypotensives are concepts repeatedly reported in several recent studies (Duschek et al, 2009(Duschek et al, , 2005Schandry, 2006, 2007). To support the role of the Neurovegetative system, these authors mainly referred to studies showing that hypotensives, compared to normotensives, exhibited faster habituation of electrodermal responses to tones (Fredrikson et al, 1990); reduced subjective symptoms and high blood pressure following the administration of substances (Bismarck and Rust, 1982); reduced electrodermal activity (Richter-Heinrich et al, 1971); and augmented respiratory sinus arrhythmia (Cadalbert, 1997).…”

“…Recent intriguing results obtained by Duschek et al (2009), suggested a sympathetic inhibition and a parasympathetic activation after drug application in essential hypotension. However, this data does not directly support a constitutional alteration in autonomic cardiac control, but rather suggests a specific counter-regulatory autonomic response to the application of an alpha-adrenergic drug.…”

The pNNx Heart Rate Variability Statistics: An Application to Neuroautonomic Dysfunction of Clozapine-Treated Subjects

“…Evidence now exists for a strong association between reduced HRV and psychotropic drugs with anticholinergic properties includeing antipsychotics and tricyclic antidepressants 4,8-10,24,31. In addition, the effects of alpha adrenoceptor modulation on HRV via sympathetic and parasympathetic inputs were reported 19,32,33. Therefore, a significant reduction in pNNx statistics is assumed to be explicitly as-sociated with the direct effects of clozapine, although the psychotic symptom itself, might contribute to the decreased heart rate dynamics.…”

Utility of transcranial Doppler ultrasound for the integrative assessment of cerebrovascular function

“…Moreover, Tzeng et al (2010a) showed an inverse relationship between cardiac baroreflex sensitivity and dCA, suggesting the presence of compensatory interactions between peripheral blood pressure and central CBF control mechanisms, directed to optimizing CBF control. Such interactions may account for the divergent changes in CA and baroreflex sensitivity seen with normal aging, and in clinical conditions such as spontaneous hypertension , autonomic failure (Hetzel et al, 2003) and chronic hypotension (Duschek et al, 2009). Some evidence also indicates that free radicals -particularly superoxide anion observed in pathologies such as ischemic and traumatic brain injury -causes impaired CA and increased basal CBF through activation of potassium channels within vascular smooth muscle cells (Zagorac et al, 2005).…”