A semi-automatic computerized method to measure baroreflex-mediated heart rate responses that reduces interobserver variability

Abstract

Arterial baroreflex sensitivity estimated by pharmacological impulse stimuli depends on intrinsic signal variability and usually a subjective choice of blood pressure (BP) and heart rate (HR) values. We propose a semi-automatic method to estimate cardiovascular reflex sensitivity to bolus infusions of phenylephrine and nitroprusside. Beat-to-beat BP and HR time series for male Wistar rats (N = 13) were obtained from the digitized signal (sample frequency = 2 kHz) and analyzed by the proposed method (PRM) developed in Matlab language. In the PRM, time series were lowpass filtered with zero-phase distortion (3rd order Butterworth used in the forward and reverse direction) and presented graphically, and parameters were selected interactively. Differences between basal mean values and peak BP (∆BP) and HR (∆HR) values after drug infusions were used to calculate baroreflex sensitivity indexes, defined as the ∆HR/∆BP ratio. The PRM was compared to the method traditionally (TDM) employed by seven independent observers using files for reflex bradycardia (N = 43) and tachycardia (N = 61). Agreement was assessed by Bland and Altman plots. Dispersion among users, measured as the standard deviation, was higher for TDM for reflex bradycardia (0.60 ± 0.46 vs 0.21 ± 0.26 bpm/mmHg for PRM, P < 0.001) and tachycardia (0.83 ± 0.62 vs 0.28 ± 0.28 bpm/mmHg for PRM, P < 0.001). The advantage of the present method is related to its objectivity, since the routine automatically calculates the desired parameters according to previous software instructions. This is an objective, robust and easy-to-use tool for cardiovascular reflex studies.

Baroreceptor stimulation enhanced nitric oxide vasodilator responsiveness, a new aspect of baroreflex physiology

“…BRS testing was performed using iv bolus injections of a small dose of a vasoactive drug (Soares et al, 2005). To elicit reflex changes in heart rate in response to changes in blood pressure, iv bolus injections of the rapid-acting vascular smooth muscle dilator, sodium nitroprusside (Ni; 1.0, 3.0, 10.0 and 30.0 μg kg −1 ; sodium pentacyanonitrosylferrate (III) dihydrate; Wako Pure Chemical Industries Co., Ltd, Osaka, Japan), and the vasopressor phenylephrine (Ph; 0.3, 1.0, 3.0 and 10.0 μg kg −1 ; neo-synesin; Kowa Pharmaceutical Co., Ltd, Tokyo, Japan) were performed.…”

“…After each bolus, the arterial blood pressure was allowed to return to its previous resting level before the next dose was given (Hof et al, 1991). The BRS was then calculated as the change in heart rate divided by the change in mean arterial blood pressure (ΔHR / ΔMAP) in response to sodium nitroprusside (3.0, 10.0 and 30.0 μg kg −1 ) and phenylephrine (1.0, 3.0 and 10.0 μg kg − 1 ) administration (Omoniyi et al, 2000;Soares et al, 2005). Data were used only when the animals were calm, resting, and undisturbed during the entire experimental run.…”

Cardiovascular and Autonomic Responses after a Single Bout of Resistance Exercise in Men with Untreated Stage 2 Hypertension

“…[25]. Moreover, HRV time-domain indexes were analyzed by standard statistics by means of an algorithm developed in Matlab (Matlab 6.0, MathWorks Inc., USA) [26]: standard deviation of normal-to-normal (SDNN), the proportion of differences in successive NN intervals >50 ms (PNN50), and square root of the mean squared successive differences in pulse interval (RMSSD).…”