Hemodynamic determinants of chronic hypotension and their modification through vasopressor application

Abstract

Chronic low blood pressure is typically accompanied by symptoms such as fatigue, reduced drive, dizziness, headaches and cold limbs. Reduced cognitive performance, diminished cerebral blood flow and autonomic dysregulation have been furthermore documented in this condition. The present contribution reports two studies exploring systemic hemodynamics in chronic hypotension and their modification through vasopressor application. In study I, effects of the alpha-sympathomimetic midodrine were examined in 54 hypotensive individuals using a placebo-controlled double-blind design. Hemodynamic parameters were assessed at rest and during mental stress. They were derived from continuous blood pressure recordings using Modelflow analysis. The drug led to marked increases in blood pressure, total peripheral resistance and stroke volume. However, due to strong heart rate deceleration, cardiac output remained virtually unchanged. In study II, 40 hypotensive and 40 normotensive control persons were compared with respect to hemodynamics. While groups did not differ in total peripheral resistance, hypotensives exhibited markedly diminished stroke volume and heart rate, resulting in a reduction in cardiac output of 25% at rest and of 33% during mental stress. The data provide relevant knowledge about the hemodynamic mediation of chronic hypotension. In contrast to elevated blood pressure, which is mainly determined by increased peripheral resistance, reduced cardiac output may be the cardinal hemodynamic aberration in chronic hypotension. Midodrine proved to be effective in elevating blood pressure. However, given the cardiac origin of chronic hypotension and the lack of drug effect on cardiac output, alpha-sympathomimetic treatment may be suboptimal.

A prospective report on the prevalence of heart rate and blood pressure abnormalities in veterans with spinal cord injuries

“…37 Compared to the prevalence of a BP ≤90/60 mmHg, the prevalence of hypotension by the WHO criteria was significantly increased in the T and HP groups. Importantly, several investigators report significant adverse effects on mood, 21 quality of life, 38 and cognitive function [39][40][41] in asymptomatic non-SCI individuals with a SBP below the WHO hypotensive thresholds. Further, we recently reported significant deficits in memory and attention and processing speed in males with SCI with a SBP ≤110 mmHg compared to a normotensive SCI cohort.…”

The utility of low frequency heart rate variability as an index of sympathetic cardiac tone: A review with emphasis on a reanalysis of previous studies

“…Our research on pharmacological treatment of chronically low blood pressure yielded information about effects of drugs that affect cardiovascular regulation of HRV (Duschek, Heiss, et al., ; Duschek, Heiss, Schandry, & Reyes del Paso, ). The α ‐adrenergic agonist midodrine, which is frequently used in antihypotensive treatment, causes vasoconstriction and thus increases of total peripheral resistance and blood pressure.…”

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

“…As an a-receptor agonist, midodrine induces arterial and venous vasoconstriction leading to increased peripheral resistance, which, in turn, causes blood pressure elevation. 19,21 In this state, counter-regulatory processes are initiated to return blood pressure to the initial value or to an individual set point. The observed sympathetic inhibition and parasympathetic activation may be regarded as parts of this compensatory mechanism.…”

“…As previously reported, midodrine application leads to a marked increase in stroke volume and total peripheral resistance, but, due to heart deceleration, it does not cause an increase in cardiac output. 21 Therefore, the drug's efficiency in improving organ perfusion is possibly less than ideal. One should, however, not overlook the fact that the effects of a single application of the drug observed in this study may not be generalized to clinical conditions.…”

“…19,20 In participants with chronic low blood pressure, midodrine yielded positive hemodynamic effects in terms of raising blood pressure, vascular resistance and stroke volume. 21 Furthermore, it proved effective in increasing both cerebral blood flow and mental performance in this population. 22 Knowledge about possible effects of a-adrenergic treatment on autonomic cardiovascular regulation, however, remains sparse.…”