Changes in Heart Period, Heart‐Period Variability, and a Spectral Analysis Estimate of Respiratory Sinus Arrhythmia in Response to Pharmacological Manipulations of the Baroreceptor Reflex in Cats

Abstract

The purpose of the present study was to assess changes in heart period, heart‐period variance (HPV), and respiratory sinus arrhythmia (RSA) during manipulations of the baroreceptor reflex in anesthetized cats. Hypertension, induced via phenylephrine infusion, reflexly increases parasym‐pathetic activity and decreases sympathetic activity. Hypotension, produced by infusion of nitroprusside, leads to increased sympathetic activity and an inhibition of vagal influences on the heart. Specific autonomic contributions were assessed following administration of practolol, a β‐adrenergic blocker, or atropine methyl nitrate. Spectral analysis was used to quantify the component of HPV associated with respiration, i.e., RSA, which is proposed to be sensitive to vagal influences on the heart. The respiratory component of HPV is described by a statistic, V̂, which is the sum of the spectral densities of the heart period spectrum across the band of frequencies associated with normal respiration. Hypertension produced an increase in V̂ which was blocked by atropine infusion, but unaltered by beta‐adrenergic blockade. Hypotension decreased V̂ to near‐zero values which persisted after atropine and practolol infusion. These data suggest that V̂ is determined primarily by vagal factors. Correlations between V̂ and a previously used criterion measure of vagal tone further support this hypothesis. In contrast, heart period was sensitive to vagal and sympathetic factors. Heart period increases during hypertension were abolished with atropine and heart period decreases due to hypotension were eliminated by beta‐adrenergic blockade. These responses are consistent with the notion that heart period is under the control of both sympathetic and vagal factors. Since in an anesthetized preparation RSA is the major source of heart‐period variability, HPV responded similarly to V̂. The results suggest that the spectral estimate of RSA, V̂, is particularly sensitive to blood pressure induced reflexive changes in vagal efferent influences on the heart. It also appears that V̂ is less influenced by sympathetic factors than heart period, a commonly used estimate of vagal activity.

Regulation of Heart Rate Variation by the Autonomic Nervous System in Neonatal Lambs

“…baroreflex is weaker than in adults (16). There has been controIn both age groups, the percentage of low frequencies (less than versial information about whether HRV is, as with the sino-atrial six oscillations per m i d , measured as relative Power density, node, under dual autonomic control (17)(18)(19)(20)(21)(22)(23)(24). Our results indicate increased.…”

Time-series analysis of heart rate variability during submaximal exercise. Evidence for reduced cardiac vagal tone in animals susceptible to ventricular fibrillation.

“…The time to onset for ventricular fibrillation was 52.5±3.0 seconds with 12 animals developing ventricular fibrillation shortly after the treadmill was stopped, while the remaining 10 had ventricular fibrillation while running. Ventricular fibrillation could be reproducibly induced in the susceptible animals with each presentation of the exercise plus ischemia test (once a week for a total of 4 weeks).…”

Effect of calcium channel antagonists on the cardiac vagal tone response to submaximal exercise

“…10 Hz) represents a complex combination of sympathetic and parasympathetic activity [Akeslrod et al, 1981;Randall et al, 19911. In an analogous fashion, Porges and coworkers [McCabe et al, 1985;Porges, 1985Porges, , 1986Porges and Bohrer, 19901 developed a time-series analysis technique that accurately evaluates the amplitude of the respiratory sinus arrhythmia (high frequency peak) yet allows for a real-time data analysis over short time intervals. Thus, dynamic changes in autonomic tone in response to physiologic interventions can be evaluated using this technique.…”