Identification of low and high frequency ranges for heart rate variability and blood pressure variability analyses using pharmacological autonomic blockade with atropine and propranolol in swine.

Authors: POLETTO, ROSANGELA - Purdue University; JANCZAK, ANDREW - Purdue University; MARCHANT-FORDE, RUTH - Purdue University; Marchant, Jeremy; MATTHEWS, DONALD - Purdue University; DOWELL, CAROL - Purdue University; HOGAN, DANIEL - Purdue University; FREEMAN, LYNETTA - Purdue University; Lay Jr, Donald

Submitted to: Physiology & Behavior
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/20/2011
Publication Date: 1/5/2011
Citation: Poletto, R., Janczak, A.M., Marchant-Forde, R.M., Marchant Forde, J.N., Matthews, D.L., Dowell, C.A., Hogan, D.F., Freeman, L.J., Lay Jr, D.C. 2011. Identification of low and high frequency ranges for heart rate variability and blood pressure variability analyses using pharmacological autonomic blockade with atropine and propranolol in swine. Physiology and Behavior. 103(2):188-196.

Interpretive Summary: Assessment of heart rate variability and blood pressure variability, using time and frequency domain analyses of cardiac activity may provide a sensitive and reliable measure of stress and affective state in farm animals. Analysis of heart rate variability from electrocardiography is a sensitive diagnostic tool for measuring autonomic nervous system activity under conditions of stress, emotional processes, and pathology in humans and other mammalian species. More activity in the low frequency range indicates more sympathetic activity and thus more stress, whereas greater activity in the high frequency range indicates the animal is experiencing less stress. However, the lack of agreement on the cut off for these ranges highlights the need for a controlled study where sympathetic and vagal influences on cardiac activity are pharmacologically controlled. Thus we used atropine to block vagal, and propranolol to block sympathetic control of cardiac activity to elucidate the individual power spectral density within frequency ranges corresponding to the individual branches of the autonomic nervous system. Based on the autonomic blockade outcomes, the optimal frequency ranges for analyses of autonomic modulations in pigs are Low Frequency: 0.0 – 0.09 Hz and High Frequency: 0.09 – 2.0 Hz. These ranges were determined based on best-fit regression line from the power spectral densities between responses to atropine and propranolol treatments. The information generated by the current study may be applied to investigate the pigs’ perception of a stressor under real situations. Further the understanding of autonomic nervous system regulation of heart rate variability and blood pressure variability in domestic swine can facilitate studies on the effects of stressful conditions and affective states, and thus assisting in assessing farm animal welfare.

Technical Abstract: Understanding autonomic nervous system functioning, which mediates behavioral and physiological responses to stress, offers great potential for evaluation of farm animal stress and welfare. Evaluation of heart rate variability (HRV) and blood pressure variability (BPV), using time and frequency domain analyses may provide a sensitive and reliable measure of affective states and stress-mediated changes in sympathetic and vagal tone. The aim of this research was to define low (LF) and high frequency (HF) power spectral ranges using pharmacological autonomic blockade and examine HRV and BPV parameter changes in response to atropine and propranolol in swine. Ten, 13-week old, barrows (n = 6) and gilts (n = 4) underwent surgery to place an intra-cardiac electrocardiogram lead and a blood pressure catheter attached to a biotelemetric transmitter; pigs had a 3-wk recovery period prior to data collection. Each pig was subjected to 4 intravenous (i.v.) drug treatments: a control treatment of i.v. administration of 3 mL of saline, and 3 blockade treatments, 0.1 mg/kg of atropine, 1.0 mg/kg of propranolol, and .1 mg/kg of atropine together with 1.0 mg/kg of propranolol. All treatments were delivered by injection in the jugular vein with a minimum of 48 h between individual treatments. Behavior, ECG and blood pressure data were recorded for a total of 1 h, from 30 minutes pre-injection to 30 minutes post-injection. For data analyses, two 512-beat intervals were selected for each treatment while the pig was lying and inactive. The first interval was selected from the pre-injection period (baseline), and the second was selected between 10 to 30 minutes post-injection. Time and frequency domain (power spectral density) analysis was performed on each data interval. Subsequent, LF and HF bands from the power spectral densities were defined based on general linear and regression analyses. The HRV and BPV were computed with a covariate (baseline) factorial analysis of treatment by sex interaction, and day of injection with mixed models and Tukey’s post-hoc tests. The best-fit range for LF was 0.0 – 0.09 and HF was 0.09 – 2.0 (r2: 0.41 and 0.43, respectively). Propranolol and saline injections led to a greater overall total power and overall higher IBI HF and LF power. Atropine led to a high sympathovagal balance of the cardiac activity in pigs. In addition, atropine led to an increase in LF power of both systolic and diastolic blood pressures in gilts suggesting vagal tone mediation of BPV. The understanding of autonomic regulation of HRV and BPV in domestic swine facilitates our ability to detect and quantify stress responses, broadening its application in assessing farm animal welfare.