Evaluation of the baroreceptor-heart rate reflex by 24-hour intra-arterial blood pressure monitoring in humans.

Abstract

SUMMARYThe baroreceptor control of the sinus node was evaluated in 10 normotensive and 10 age-matched essential hypertensive subjects in whom ambulatory blood pressure was recorded intraarterially for 24 hours and scanned by a computer to identify the sequences of three or more consecutive beats hi which systolic blood pressure (SBP) and pulse interval (PI) progressively rose (+ PI/ + SBP) or fell ( -PI/ -SBP) in a linear fashion, according to a method validated in cats. In normotensive subjects, several hundred +PI/+SBP and -P I / -S B P sequences of 3 beats were found whereas the number of sequences of 4,5, and more than 5 beats showed a progressive drastic reduction. The mean slopes of + PI/ + SBP (7.6 ± 2.0 msec/mm Hg) and -P I / -SBP (6.4 ± 1.5 msec/mm Hg) sequences were similar, but in both instances there was a large scattering of the values around the mean (variation coefficients: 64.2 ± 4.7 and 62.6 ± 2.4%). The slopes decreased as a function of the sequence length and baseline heart rate and increased to a marked extent during the night as compared with daytime values. All sequences were more rare (-33.2% for +PI/ + SBP and -31.7% for -P I / -S B P ) and less steep in hypertensive subjects ( -4 0 . 3 and -3 6 . 2 % , respectively), who failed to show the marked nighttime increase in slope observed in normotensive subjects. To our knowledge, these observations provide the first description in humans of the baroreceptor-heart rate reflex in daily life. This reflex is characterized by marked within-subject variations hi sensitivity due in part to hemodynamic, temporal, and behavioral factors. All features of the baroreceptor-heart rate reflex are unpaired hi essential hypertension. (Hypertension 12: 214-222, 1988) KEY WORDS • baroreceptor reflexes • ambulatory blood pressure monitoring • hypertension sleep • humans • heart rate W E have previously reported 1 -2 that blood pressure in unanesthetized cats exhibits spontaneous rises or falls that are accompanied by linearly related increases or reductions in pulse interval (PI). We have also reported 12 that sinoaortic denervation abolishes these events, which therefore reflect baroreceptor modulation of the sinus node. We have concluded that evaluation of these events by computer analysis of intra-arterial blood pressure tracings represents a powerful tool for studying the baroreceptor-heart rate reflex in daily life.

The effects of acute and chronic dihydropyridine calcium antagonist therapy on baroreflex sensitivity: a re-analysis using the sequence method

“…17 Previous studies using sequence analysis have found that BRS values derived from baroreflex loading were comparable to those derived from unloading. 12 Importantly, in our study the proportion of positive and negative sequences did not change after treatment and thus the differences between positive and negative sequences do not account for the finding that BRS was increased after dihydropyridine therapy.…”

“…Spontaneous BRS was assessed by analysis of the 24-h IABP recordings by an adaptation of the method originally described by Parati et al, 12 as we have previously reported. 13 Each IABP recording was sampled at 125 Hz, digitised into 12 bits and analysed by an Apple Macintosh micro-computer running Lab View software.…”

Nonlinear Methods of Cardiovascular Physics and Their Clinical Applicability

“…There is evidence that a decreased BRS may carry an adverse prognosis in cardiac patients [Osterziel et al, 1995;Mortara et al, 1997;La Rovere et al, 1998]. For several years, the BRS was determined pharmacologically (phenylephrine, nitro-prusside) [McCall & Humphrey, 1983;Vanoli & Adamson, 1994] or mechanically Mancia et al, 1984;Takahashi et al, 1999] until in the 1980s innovative methods for BRS estimation were developed which are based on spontaneous heart rate and blood pressure fluctuations [Di Rienzo et al, 1985;Parati et al, 1988]. These methods evaluate arterial baroreflex function in the absence of external stimulations on the cardiovascular system, therefore defined as spontaneous.…”

“…Di Rienzo and Parati introduced in the 1980s the sequence method [Di Rienzo et al, 1985;Parati et al, 1988] which was the first not requiring drug-injections. This time-domain method scans the beat-to-beat systolic pressure series to identify sequences with monotonic BP increases (or decreases) and synchronous BBI increases (or decreases).…”

Effects of physical training on autonomic cardiac modulation in hypertension: assessment by heart rate variability analysis

“…An example of this is represented by the assessment of HRV along with analysis of BPV from beatto-beat BP recordings, which complements the information provided by HRV analysis (by providing indices of vascular autonomic modulation). In addition, by applying modeling approaches which focus on the relationship between fluctuations of HR and BP (either in time or in the frequency domain), 26,27 it is also possible to assess other mechanisms of major importance for autonomic CV control such as the degree of spontaneous cardiac baroreflex sensitivity. Such an approach may provide a more comprehensive analysis of cardiovascular regulation mechanisms than that represented by the separate analysis of BP and HR variability alone.…”