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 low-pass 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 (deltaBP) and HR (deltaHR) values after drug infusions were used to calculate baroreflex sensitivity indexes, defined as the deltaHR/deltaBP 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.
Highlights
Baroreflex sensitivity has important prognostic value for the stratification of risk for several pathophysiological cardiovascular conditions [1]
The results obtained with the proposed method (PRM) showed higher values for reflex bradycardia when compared to the traditional method (TDM) (PRM = -1.88 ± 0.89 vs TDM = -1.72 ± 0.71 bpm/mmHg, P = 0.005) but did not differ between the two methods for reflex tachycardia (PRM = 3.43 ± 1.42 vs TDM = 3.33 ± 1.32 bpm/mmHg, P = 0.144)
Dispersion among users as measured by the standard deviation was higher when the TDM was used for both reflex bradycardia (PRM = 0.21 ± 0.26 vs TDM = 0.60 ± 0.46 bpm/mmHg, P < 0.001) and reflex tachycardia (PRM = 0.28 ± 0.28 vs TDM = 0.83 ± 0.62 bpm/mmHg, P < 0.001)
Summary
Baroreflex sensitivity has important prognostic value for the stratification of risk for several pathophysiological cardiovascular conditions [1]. Quantitative indexes of baroreflex sensitivity obtained from pharmacologically induced [2] and spontaneous blood pressure (BP) [3] changes have been extensively employed in experimental [4]. Baroreflex indexes are calculated on the basis of these values as the HR/BP ratio This approach has been employed in different protocols in which the BP signals were stored on a sheet of polygraph paper or as digitized signals in a computer. In both situations, subjective criteria are used to select the values used in baroreflex indexes which do not consider the inherent signal variability. Systematic and random errors can occur during parameter selection
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