Alterations in cardiac contractility during classical aversive conditioning in dogs: methodological and theoretical implications

Cardiorespiratory interactions: Noncontact assessment using laser Doppler vibrometry

The application of a noncontact physiological recording technique, based on the method of laser Doppler vibrometry (LDV), is described. The effectiveness of the LDV method as a physiological recording modality lies in the ability to detect very small movements of the skin, associated with internal mechanophysiological activities. The method is validated for a range of cardiovascular variables, extracted from the contour of the carotid pulse waveform as a function of phase of the respiration cycle. Data were obtained from 32 young healthy participants, while resting and breathing spontaneously. Individual beats were assigned to four segments, corresponding with inspiration and expiration peaks and transitional periods. Measures relating to cardiac and vascular dynamics are shown to agree with the pattern of effects seen in the substantial body of literature based on human and animal experiments, and with selected signals recorded simultaneously with conventional sensors. These effects include changes in heart rate, systolic time intervals, and stroke volume. There was also some evidence for vascular adjustments over the respiration cycle. The effectiveness of custom algorithmic approaches for extracting the key signal features was confirmed. The advantages of the LDV method are discussed in terms of the metrological properties and utility in psychophysiological research. Although used here within a suite of conventional sensors and electrodes, the LDV method can be used on a stand-alone, noncontact basis, with no requirement for skin preparation, and can be used in harsh environments including the MR scanner.

The effect of medial frontal cortex lesions on cardiovascular conditioned emotional responses in the rat

The effect of ventral medial frontal cortex (MFC) lesions on heart rate and blood pressure during conditioned emotional responses (CER) was investigated. Male Sprague-Dawley rats were divided into two groups: MFC-lesioned rats (n = 11) sustained bilateral lesions of the infralimbic and ventral prelimbic regions of the MFC via microinjection of the neurotoxin N-methyl-D-aspartate; Controls (n = 13) received sterile saline. Following a 2-week recovery period, all animals were trained; one of two tones served as the conditioned stimulus (CS) and a 2 mA footshock served as the unconditioned stimulus (US). The CS+ tone was consistently paired with the US, while the CS- tone was randomly paired with the US. Heart rate and blood pressure were recorded during CS+ and CS- presentations before and after administration of the following pharmacological agents: atropine, atenolol, and atropine + atenolol. All animals responded to the CS+ with increased BP compared to baseline; the increase was not significantly different between groups. Controls responded to the CS+ with increased HR, while MFC-lesioned animals displayed a bimodal HR response which was not significantly different from baseline, but was significantly different from Controls. Pharmacological blockade of the HR response revealed coactivation of the sympathetic and parasympathetic nervous systems during the CS+, with a significant decrease (52%) in the sympathetic tachycardia component of the CS+ HR response in MFC-lesioned rats as compared to Controls; the parasympathetic bradycardia component was not altered by MFC lesions. In all cases, CS- responses were smaller than the CS+ responses. Pharmacological analysis revealed that the CS- HR response was mediated by the sympathetic component only, which was also significantly reduced in MFC-lesioned animals as compared to Controls. This significant reduction in the sympathetically mediated HR component of both the reinforced CER (CS+) and the unreinforced CER (CS-) following ventral MFC lesions implies that the MFC is necessary for complete sympathetic activation of cardiovascular responses to both severely and mildly stressful stimuli. The role of the MFC in emotion is also discussed.

A comparison of the autonomic nervous control of the heart during classical aversive vs appetitive conditioning in dog

Dogs were trained in either classical (i.e. Pavlovian) appetitive (n = 7) or aversive (n = 7) conditioning by presenting a tone (the conditional stimulus, CS +) that was followed by either food or shock delivery, respectively. In the first case, dog food was given to the animals during the last 30 s of a 1 min CS+. Aversive conditioning was accomplished by giving a 1 s shock at the end of a 30 s CS+. The control consisted of a different tone (CS-) which was never followed by food or shock. A chronically implanted transducer was used to record left ventricular pressure from which its first time derivative was calculated; d(LVP)/dt was used as an index of myocardial inotropic state. Heart rate (HR) was also determined. These data were averaged over the 30 s prior to the CS+, the 30 s of the conditional stimulus tone itself, and the 30 s following shock or during food delivery. Well-trained animals evidenced changes in cardiac inotropism and chronotropism during the CS+ and also in response to unconditional shock or food; these are referred to as the conditional and unconditional cardiovascular responses, respectively. No statistically significant HR or d(LVP)/dt changes were observed during the CS-. The conditional response to food was small: relative to the pre-CS+ interval, average HR increased 11 bpm (P less than 0.05) and average d(LVP)/dt increased 309 mm Hg/s (P less than 0.01). During food delivery, HR increased by additional 23 bpm (P less than 0.01) and d(LVP)/dt increased by another 232 mm Hg/s (P less than 0.01). Beta-adrenergic blockade virtually eliminated the conditional HR and d(LVP)/dt response to food, indicating that both the chronotropic and inotropic changes during CS+ were due to elevated sympathetic drive. beta-blockade did not eliminate the unconditional HR response (+17 bpm, P less than 0.01), indicating that parasympathetic withdrawal has a mediating role in this persisting tachycardia. The conditional response to shock consisted of a 26 bpm increase in HR (P less than 0.01), while d(LVP)/dt increased 998 mm Hg/s (P less than 0.01). The beta-blockade reduced the HR conditional response to +8 bpm (NS) and essentially eliminated the increase in d(LVP)/dt. These data indicate that increases in cardiac sympathetic tone play a primary role in mediating the conditional cardiovascular response for both paradigms. Parasympathetic withdrawal, on the other hand, figures critically in mediating the unconditional response to food.

Intuitive and factual approaches in the comparison of contractility and repolarization measures of sympathetic myocardial activity

Obrist (Cardiovascular Psychophysiology: A Perspective, Plenum Press, New York, 1981) has recently argued for the superiority of contractility (e.g. pulse transit time) over ventricular repolarization (e.g. T-wave amplitude) measures as indices of sympathetic myocardial influences on the grounds that the T-wave occurs during the diastolic portion of the cardiac cycle (in contrast to the systolic temporal locus of contractile-based measures). This note suggests that this argument is intuitively rather than factually based because it lacks both logical and empirical validity.

Psychophysiological and physiological aspects of T-wave amplitude in the objective study of behavior

The objective study of behavior, which is the stated aim of our society, does not impose restrictions on the levels of explanatory constructs that are used. The only restriction is that the evidence concerning those constructs be stated in an objective or scientifically communicable way. Thus the concepts that we employ to explain behavior range from the sociologic to the biochemical. This article's underlying thesis is that behavior needs to be investigated at various levels, and that these levels should be clearly differentiated in order to bring these investigations into a scientifically meaningful relationship. The thesis is here illustrated by examining evidence and arguments concerning the utility and status of a noninvasive index of myocardial performance: T-wave amplitude (TWA). The examination begins at a psychophysiological-index level, wherein TWA is considered in terms of how well this noninvasive physiological index differentiates psychological processes. Secondly, at a lower physiological-index level, we consider the assumption that TWA reflects a relatively unitary physiological process, myocardial beta-adrenergic sympathetic influence. Both the grounds for and implications of this assumption are discussed. Finally, at the physiological-index level of discourse, brief reference is made to the mechanism by which changes in beta-adrenergic sympathetic innervation may produce correlated changes in TWA. The overall aim of the article is to differentiate these three levels of investigation, and yet also to consider the interrelationship among these three levels in order to provide a fuller scientific understanding of the phenomena involved.

Neurophysiology and neuropharmacology of cardiovascular regulation and stress

Evidence has accumulated over the past several years indicating that environmental factors can have a substantial influence on cardiovascular dynamics. It has been hypothesized by many investigators that through these influence environmental stressors may be important to the etiology and maintenance of cardiovascular diseases. Since the nervous system is intimately involved in the regulation of cardiovascular function it may be assumed that environmental influences on cardiovascular dynamics are to a large extent mediated by the nervous system. This assumption is supported by the literature reviewed which indicates that there are many nervous system nuclei and neurotransmitter systems involved in the regulation of cardiovascular dynamics which are also involved in an organisms adjustment to environmental stressors. The conclusion is reached that further multidisciplinary research will reveal underlying neurophysiological and neuropharmacological mechanisms responsible for stress induced cardiovascular disease and lead to new methods of treatment.

Beta-adrenergic influence on cardiac dynamics during shock-avoidance in dogs

The role of beta-adrenergic receptors in the mediation of the cardiodynamic effects of a shock-avoidance task was evaluated in conscious dogs with the cardioselective beta-adrenergic antagonist practolol. The animals were chronically instrumented for the measurement of peak rate of change of left ventricular pressure (LV dP/dt), heart rate (HR), cardiac output (CO), systolic (SPB) and diastolic (DBP) blood pressure and total peripheral resistance (TPR), and were each subjected to brief bouts of shock-avoidance with and without practolol pretreatment (2-4 mg/kg). Shock-avoidance evoked reliable increases of LV dP/dt, HR, CO, SBP and DBP, and decreases of TPR. Beta-adrenergic blockade virtually eliminated LV dP/dt increases, attenuated HR and CO increase as well as the vasodilatation, diminished SBP increases in certain animals but did not affect DBP increases. Stable interindividual differences in the magnitude of LV dP/dt and HR increases during shock-avoidance were demonstrated; these differences were abolished by beta blockade. These findings indicate that a beta-adrenergic mechanism accounted for most of the rise of LV dP/dt during avoidance but contributed proportionally less to the elevations of HR and CO. Inter-individual differences in myocardial reactivity were however completely ascribable to beta-adrenergic factors.

Classically conditioned heart rate responses in Macaca mulatta after beta-adrenergic, vagal and ganglionic blockade

Heart rates of 5 rhesus monkeys (Macaca mulatta) were monitored during classical conditioning trials consisting of a visual conditioned stimulus followed after 10 sec by an electric shock to the tail. Heart rates typically increased at the onset of the visual stimulus, and returned to baseline before shock delivery. Autonomic blocking agents were subsequently administered; their effects on resting heart rates, and on acceleratory and deceleratory phases of the biphasic conditioned heart rate responses were examined, both in the raw data, and with a statistical regression technique. Beta-adrenergic blockade by propranolol lowered resting heart rates and was found, after regression analysis, to reduce the heart rate increase phase, and to weakly enhance the subsequent heart rate decrease phase of the conditioned response. Vagal blockade by atropine sulfate elevated resting heart rate, and markedly reduced both acceleratory and deceleratory heart rate phases of the conditioned responses. Ganglionic blockade by chlorisondamine also elevated resting heart rates (less than atropine), and almost completely eliminated conditioned heart rate changes. Several sources of evidence suggest a predominant vagal tone over resting heart rates, as well as mostly vagal mediation (with some sympathetic contribution) of the biphasic conditioned rate response.

The effects of psychological stress and vagal stimulation with morphine on vulnerability to ventricular fibrillation (VF) in the conscious dog

Ventricular vulnerability to fibrillation was assessed in 12 conscious dogs in aversive and nonaversive environments using the repetitive extrasystole (RE) threshold method. In the average environment, RE threshold was 45 per cent lower than in the nonaversive setting and heart rate and blood pressure were significantly elevated. This decrease in RE threshold occurred within 10 minutes of exposing the animals to stress. In contrast, the recovery in RE threshold in the nonaversive setting occurred over a 40 minute period. When morphine sulfate (MS) 0.25 mg./Kg was administered to dogs in the aversive environment, the RE threshold was significantly increased. Cholinergic blockade of vagal efferent activity with atropine (0.2 mg./Kg) annulled partially the effect of MS on RE threshold MS was without effect in the nonaversive environment. It is concluded that MS exerts a significant protective effect on increased ventricular vulnerability associated with psychological stress. This effect is mediated by the vagotonic and sedative actions of morphine.

Psychological aspects of cardiac arrhythmia

A review of data from a wide spectrum of research studies suggests that psychological-emotional factors can significantly influence and alter the incidence of cardiac arrhythmia. While the existing data are, in many cases, difficult to interpret because of theoretical and methodological problems, sufficient evidence does exist to warrant a concerted investigation into the total involvement of psychological factors in cardiac arrhythmia.

Ventricular electrical instability in the conscious dog: effects of psychologic stress and beta adrenergic blockade

The effect of psychologic stress on cardiac vulnerability was examined in 10 conscious dogs. The repetitive extrasystole threshold was employed as a measure of susceptibility to ventricular fibrillation. Instrumental aversive conditioning constituted a stressful environment. The repetitive extrasystole threshold decreased by nearly 50 percent during 3 days in which the animals were exposed to the stressful environment. When Tolamolol hydrochloride, a cardioselective beta adrenoceptor blocking agent, was administered before a stress session, the repetitive extrasystole threshold was unaltered from the control value. Thus, stress-evoked changes in cardiac vulnerability are mediated through the sympathetic nervous system.

Cardiovascular dynamics during classical appetitive and aversive conditioning in laboratory primates

This report describes changes in the rate of rise of left and right intraventricular pressures during aversive and appetitive conditioning procedures in chair-restrained rhesus monkeys. The conditioning paradigm consisted of a one-minute tone followed, in the one case, by an electric shock, and in the other, by the delivery of Purina monkey pellets. The conditional cardiovascular response was characterized by short latency, highly significant elevations in the derivatives of both ventricular pressures as well as a marked arterial pressor response and tachycardia. The magnitude of the conditional response to the classical aversive procedure was somewhat larger than that to appetitive conditioning. These alterations in the rate of development of intraventricular pressure can be attributed largely to augmentation in the sympathetic neural input to the heart and contribute to an analysis of selective aspects of the nervous regulation of the heart in intact, behaviorally conditioned animals.