Propranolol and atenolol were used to examine the role of the adrenergic system in the genesis of slow HR variations (waves) in rabbits, the animals characterized by pronounced sympathetic influences. The control experiments were performed with physiological solution and long-term records in intact rabbits. The harmonic (spectrum) analysis was performed with fast Fourier transform. The adrenoblockers produced no decrease in the power of slow waves. The study did not found the sympathetic genesis of slow variations in rabbit HR.

Effects of pentobarbital on spectral characteristics and phase ratios of wave oscillations of the cardiac contraction period (RR interval) and time of atrioventricular conduction (AV interval) were studied in experiments of cats. Pentobarbital moderately reduced the mean values of both intervals and significantly reduced their standard deviations and spectral powers in all frequency bands (high-frequency, low-frequency, and very low-frequency). Pentobarbital treatment led to deceleration of breathing, the frequency range of respiratory oscillations of RR and AV intervals shifted in some cases from high to low frequencies; evaluation of spectral power in the intermittent band corresponding to respiration frequency (instead of standard fixed high-frequency band) showed that pentobarbital suppressed the respiratory oscillations in these bands. Pentobarbital induced inversion of phase ratio between respiratory oscillations of RR and AV intervals: oscillations of both intervals before pentobarbital coincided by phase, while after pentobarbital injection they were in antiphase. The mechanisms of the latter phenomenon deserve further investigation.

The effects of atropine and β-adrenoceptor blockers on mean HR, wave structure of the cardiac rhythm, and chronotropic reaction to noise stress were examined in cats. Atropine (0.5 mg/kg) increased the mean HR and significantly decreased the spectrum power of HF, LF, and VLF oscillations. The decrease in HF power was most pronounced, which enhanced LF/HF ratio. Propranolol (0.5 mg/kg) decreased the mean HR and slightly increased the power of HF, LF, and VLF oscillations. Atenolol (2 mg/kg) exerted similar but more pronounced effects. β-Adrenoceptor blockers increased HF power to a greater extent than LF and VLF power, which led to a decrease in LF/HF ratio. Atropine markedly decreased the chronotropic reaction to stress. β-Adrenoceptor blockers produced no effect on the amplitude of this reaction, but accelerated restoration of initial HR. It is established that the changes in power spectrum of HR and the phase reflex reactions in cats are mediated by parasympathetic influences; the sympathetic system is involved only in the control of mean HR, probably in response to the level of animal activity. The changes in LF/HF ratio during blockade of sympathetic and parasympathetic systems are caused by opposite influences of these systems on HF oscillations, but not by hypothetic “sympathetic” and “parasympathetic” nature of LF and HF oscillations of the heart rhythm.

Cardiac frequency-domain parameters of the left ventricular pressure were studied in acute experiments on cats under conditions of reflex and load stimulation and during maximum inotropic stimulation with epinephrine. A strict correlation was revealed between the upper threshold of the frequency range and the maximum value of pressure first derivative. Without epinephrine infusion, the maximum value of pressure first derivative and the upper threshold of the frequency range attained 9840 mm Hg/sec and 98.4 Hz, correspondingly. During epinephrine infusion, the corresponding values were 12911 mm Hg/sec and 145 Hz. Left ventricular pressure in cats is characterized by high-frequency parameters, which can be measured by special catheter microtransducers and only in some cases by routine pressure gauges.

In acute experiments on cats neural inotropic and lusitropic reactions of the heart to enhancement of pre- and afterload were assessed by changes in contractility and relaxation indices, which were preliminary chosen for their maximum specificity and sensitivity. The control cardiac responses to increased pre- and afterload were measured after treatment with ganglionic blocker arfonad. The myogenic component of these responses assessed under the action of arfonad was highly pronounced, therefore the neural inotropic and lusitropic reactions were measured as the difference between load-induced changes of indices in experiments with and without arfonad. Increased preload produced similar negative inotropic and lusitropic effects, while increased afterload produced a more pronounced negative inotropic effect, which indicated independent regulation of contractility and diastolic relaxation of the heart.

The possibility of using contraction and relaxation indices for evaluation of inotropic and loositropic influences on the heart was studied in experiments on cats. Increased pre- and afterload were used as the stimuli, which are simultaneously loading and reflexogenic. Under conditions of preserved innervation both stimuli elevated the indices selected according to the highest sensitivity/specificity ratio. Ganglionic blocker arfonad potentiated the effects of these stimuli. This attests to a considerable contribution of the myogenic component to the changes in the studied indices in response to increased pre- and afterload and to the existence of negative inotropic and loositropic influences on the heart under conditions of preserved innervation. These conclusions were supported when more specific indices were used: in most cases they decreased during load tests. Thus, when the contraction and relaxation indices are used for evaluation inotropic and loositropic influences on the heart, it seems reasonable either to compare heart responses under conditions of preserved or blocked innervation, or to apply more specific indices. Analysis of changes in most widely used indices (dP/dt)max and t showed that t reliably reflects neural loositropic influences, while the use of (dP/dt)max without proper control can be erroneous.

Sensitivity (response to epinephrine infusion) and specificity (response to changes in pre- and afterload) of some cardiac relaxation indices were compared in acute experiments on cats treated with ganglionic blocker arfonad. Some new indices proposed by us provide better characteristics than widely used relaxation time constant (t) and maximum first derivative of the left ventricular pressure (-dP/dt)(max).

As a result of acute experiments on cats we revealed the approaches to choosing the best indices of the contractility of the left and the right cardiac ventricles in the concrete conditions of the experiment on the basis of the original criterion of optimality. For revealing neural inotropy influences we suggest the index based on the combined changes of optimum indices. A new approach to revealing reflex influences on contractility in the conditions of intact blood circulation is worked out, which is based on the comparison of these influences with the control changes of haemodynamic parameters.

Artifacts which can distort the heart chambers contractility indices and the ways of its prevention are discussed. Changes in the heart pre- and afterload causing an inotropic effects, are analysed. Recommendations on the computer systems for recording and processing of blood pressure parameters in physiological experiment, are given.

In frogs, positive inotropic effects are transmitted catecholaminergically as they have been blocked with propranolol but not with atropine. Positive chronotropic effects were in some experiments blocked with atropine and not with propranolol (a "cholinergic type" of of positive chronotropic effect), the opposite occurred in other experiments (an "adrenergic type"). The cholinergic positive chronotropic effects were observed with the initial slow heart rate and were accompanied by negative inotropic effects; the chronotropic effect itself appeared suddenly (with no gradual acceleration of heart rate) and disappeared just as suddenly. The adrenergic effects, on the contrary, were observed with the initial rapid heart rate; they were accompanied by positive inotropic effects and developed and disappeared gradually.