Comments on "carotid dP/dt as a psychophysiological index of sympathetic myocardial effects: some considerations"

Effects of Psychological Stress on Vascular Physiology: Beyond the Current Imaging Signal

PURPOSE OF REVIEW

This review describes the effects of psychological stress on the physiology of the entire vascular system, from individual cellular components to macrovascular and microvascular responses, and highlights the importance of the vascular system in the context of current limitations in cardiac imaging for evaluation of the cardiovascular response to mental stress.

RECENT FINDINGS

The physiological responses that mediate vascular changes are based on evolutionary needs, but there is increasing evidence that the long-term consequences of psychological stress can precipitate the development and progression of cardiovascular disease (CVD). While there is an extensive body of literature describing localized physiological responses or overt cardiovascular manifestations, often framed within the organ-specific scope of cardiovascular imaging, there has not been a comprehensive description of the global vascular effects of psychological stress. Given the global nature of these processes, targeted cardiovascular imaging modalities may be insufficient. Here we approach the vascular response to mental stress systematically, describing the effects on the endothelium, vascular smooth muscle, and adventitia. We then address the mental stress effects on large vessels and the microvascular compartment, with a discussion of the role of microvascular resistance in the pathophysiology of mental stress-induced myocardial ischemia. Vascular responses to psychological stress involve complex physiological processes that are not fully characterized by routine cardiovascular imaging assessments. Future research incorporating standardized psychological assessments targeted toward vascular mechanisms of stress responses is required to guide the development of behavioral and therapeutic interventions.

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.

Sympathetic-parasympathetic mediation of the cardiac defense response in humans

This paper reports an investigation which examined the sympathetic and/or parasympathetic mediation of the heart rate response to intense auditory stimulation - the cardiac defense response (CDR) - by recording cardiac period (CP) and pulse transit time (PTT) simultaneously. Thirteen subjects underwent a physiological reaction test with a single presentation of a distorted 400-Hz sound of 109 dB, instantaneous rise time and 0.5 s duration. The results regarding the form of the CDR replicated the typical pattern with four components: two accelerative and two decelerative in alternating sequence. As regards CP and PTT changes the only coincidences occurred in the second accelerative and second decelerative components of the response. In the first two components the changes in CP and PTT moved in opposite directions. These results support a description and interpretation of the CDR in terms of both accelerative and decelerative components with both vagal and sympathetic mediation.

Cardiac responses to psychological tasks: impedance cardiographic studies

In a series of studies, cardiac activity, assessed with an impedance cardiograph, was monitored as college students performed either a visual search or pursuit rotor task. Heart rate, systolic time intervals, stroke volume, cardiac output and the Heather (1969) index of contractility were measured before, during and after performance. In the first study, visual search did not affect the participants' (N = 44) level of cardiac output or their length of the pre-ejection period. It is likely that the lack of charge in cardiac output resulted from a fall in stroke volume and in the Heather index while the task was performed. Heart rate was most rapid during performance and emerged as the only measure affected by the withdrawal of monetary incentives for failure to solve the visual search problem. In the second study, 40 subjects performed a pursuit rotor task and increases in cardiac output as well as changes in all of the other cardiac measures occurred. The level of task difficulty influenced the extent of heart rate increases and stroke volume decreases during performance. An additional 20 male subjects participated in a third study in which the level of difficulty of the pursuit rotor task was signalled and the order of the levels of difficulty was balanced across trial blocks. Under these conditions, the changes in cardiac activity before, during and after performance were similar to those observed in the first two studies. Heart rate was the only measure sensitive to the level of task difficulty. In general, the findings underscore the sensitivity of heart rate to changes in subtle aspects of psychological situations. To enlist increases in cardiac output and inotropic parameters extensive alterations in behavioral state are required.

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.