title: 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 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.
authors.affiliation: Unidade de Hipertensão, Instituto do Coração, Hospital das Clínicas, Faculdade de Medicina, Universidade de São Paulo, SP, Brasil. pedro.soares@incor.usp.br
authors.forename: P P S
authors.initials: PP
authors.lastname: Soares
authors.forename: M R
authors.initials: MR
authors.lastname: Ushizima
authors.forename: E M
authors.initials: EM
authors.lastname: Krieger
authors.forename: M C C
authors.initials: MC
authors.lastname: Irigoyen
mesh_terms: D000818:Animals; D017704:Baroreflex / Q000187:drug effects* / Q000502:physiology; D001794:Blood Pressure / Q000187:drug effects* / Q000502:physiology; D002316:Cardiotonic Agents / Q000494:pharmacology; D006339:Heart Rate / Q000187:drug effects* / Q000502:physiology; D016014:Linear Models; D008297:Male; D009599:Nitroprusside / Q000494:pharmacology; D015588:Observer Variation; D010363:Pattern Recognition, Automated / Q000379:methods*; D010656:Phenylephrine / Q000494:pharmacology; D051381:Rats; D017208:Rats, Wistar; D012815:Signal Processing, Computer-Assisted
chemical_list: D002316:Cardiotonic Agents; D009599:Nitroprusside; D010656:Phenylephrine