Differences in heartbeat awareness among males with higher and lower levels of systolic blood pressure

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Abstract

Recent empirical findings related to the baroreceptor hypothesis indicate that elevated heart rate, pulse pressure, and blood pressure may dampen exteroception and interoception. We thus predicted that persons with elevated systolic blood pressure would be less able to accurately perceive their heartbeats and profit from feedback training. This study examined the plausibility of this hypothesis by exposing 57 male students (11 with elevated SBP levels and 46 with normotensive SBP levels) to the Whitehead heartbeat perception task with, and without, feedback training. Results indicated that participants with elevated SBP levels were more able to accurately perceive their heartbeats prior to, and after, feedback training. Participants with elevated SBP levels also showed a significant increase in heartbeat perception accuracy when they were provided with feedback training while participants with normotensive blood pressure levels did not show a significant response to feedback training. These findings are interpreted in terms of the ballistic perception model of cardiac awareness.

Introduction

Cardiac perception has been of interest to basic and applied psychophysiologists for at least three reasons. First, based on Jamesian theories of emotion, emotional experiences are at least partially dependent upon perception of visceral and cardiac activity (e.g. Hodapp and Knoll, 1993; Reed et al., 1990). Second, psychophysiologists researching individual differences in symptom perception have argued that increased levels of visceral and cardiac perception may be associated with enhanced symptom recognition among persons with chronic illnesses that have subtle and/or vague manifestations such as hypertension (e.g. Kohlman, 1993; Pennebaker et al., 1985). Third, psychophysiologists investigating biofeedback efficacy have suggested that cardiac perception may be positively associated with responsivity to biofeedback interventions targeting cardiovascular functioning (cf. Brener, 1977, Lacey and Lacey, 1974b, Lacey and Lacey, 1978; Greenstadt et al., 1986).

Two lines of research suggest that elevated blood pressure may be associated with diminished capacities for perceiving cardiac activity and one line of research suggests the opposite — that elevated blood pressure may be associated with an increased ability to perceive cardiac activity. Support for the position that elevated blood pressure may be associated with diminished heartbeat perception capacity can be abstracted from research that has evaluated the baroreceptor hypothesis and differences in nociception among hypertensives and normotensives. Support for the position that elevated blood pressure may be associated with an increased heartbeat perception capacity can be abstracted from research that has evaluated the `ballistic perception model'. In the following introduction, the essential findings from the aforementioned lines of research will be briefly reviewed.

The `baroreceptor hypothesis' essentially posits that there is a direct coupling between the cardiovascular system and cortical processing of external visual and auditory stimuli. This hypothesis descends from the cardiac-somatic coupling model, which was initially proposed by Lacey and Lacey (1974a), Lacey and Lacey (1974b, 1978), and further developed by researchers who investigated relationships between cardiovascular activation levels (e.g. heart rate, pulse pressure, blood pressure, cardiac output, stroke volume, and baroreceptor stimulation) and performance on cognitive tasks (cf. Blumenthal et al., 1993; Coy and O'Brien, 1998; Francheschi et al., 1982; Michael and O'Brien, 1998; Waldstein et al., 1991).

Support for the baroreceptor hypothesis rests on four principal sets of findings. First, increased heart rate which is typically accompanied by increases in pulse pressure, cardiac output, and systolic blood pressure, promotes increased baroreceptor activity along portions of the aortic arch and carotid arteries (cf. Papillo and Shapiro, 1990; Rushmer, 1989). Second, afferent pathways originating in the baroreceptors project to central nervous system areas that are involved in attention (solitary nucleus of the medulla), memory (hypothalamic nuclei and hippocampal formation), and judgement/reasoning (prefrontal area of neocortex) (Campbell et al., 1992; Reed et al., 1990; Skinner, 1988). Third and fourth, experimental manipulations that increase heart rate and/or baroreceptor activity reliably produce (a) poorer performance on cognitive tasks that require attending to, storing, and evaluating external sensory information (e.g. Lacey and Lacey, 1978; Obrist, 1981; Obrist et al., 1970; van der Molen et al., 1985) and (b) EEG waveforms that indicate the presence of reduced cortical processing of sensory stimuli (Elbert et al., 1992; Reed et al., 1990; Rau and Brody, 1994; Rau et al., 1993).

The second line of research supporting an inverse relationship between blood pressure and heartbeat perception is related to observed differences in nociception among persons with higher and lower levels of blood pressure. Specifically, several empirical evaluations of nociception capabilities demonstrated that animals and humans with higher blood pressure levels, relative to animals and humans with lower blood pressure levels, have significantly higher sensory thresholds when exposed to non-painful tactile stimulation and higher pain thresholds when exposed to aversive tactile stimulation (e.g. Maixner and Randich, 1984; Randich and Maixner, 1984; Rau and Brody, 1994; Saavedra, 1981; Sheps et al., 1992; Zamir and Maixner, 1986; Zamir and Segal, 1979; Zamir and Shuber, 1980). Further, these differences in sensory processing can be traced to baroreceptor activity originating in the carotid sinus, cardiopulmonary arteries, and aortic arch (Elbert et al., 1988; Rockstroh et al., 1988; Randich and Maixner, 1986; Rau and Brody, 1994; Zamir and Maixner, 1986).

The `ballistic perception model' is a term we used to represent the third line of research that yields predictions opposite to the two lines of research summarized above. According to the ballistic perception model, increased blood pressure would be associated with more intense pulsations in the peripheral vasculature which, in turn, would make it easier for a person to accurately detect heartbeats. Along these lines, Jones and colleagues (Jones and Hollandsworth, 1981; Jones et al., 1987, Jones et al., 1988) argued that heartbeat perception is at least partially based on sensations associated with the pulsing of blood in the peripheral vasculature. Support for this position was obtained in several studies that demonstrated heartbeat perception varied as a function of body fat, posture, and levels of exercise-induced cardiovascular activation (Jones and Hollandsworth, 1981; Jones et al., 1982Jones et al., 1987; Rouse et al., 1988). Similarly, Schandry et al. (1993) demonstrated that heartbeat perception was significantly correlated with stroke volume, contractility, and a measure of arterial blood momentum.

In summary, the findings from two lines of research provide evidence that elevations in heartbeat, pulse pressure, and blood pressure can dampen processing of both `external' (i.e. visual, auditory) and `internal' (i.e. tactile) sensations. Given that heartbeat perception involves interoception (evaluation of internal sensations), and that the typical heartbeat detection paradigm also requires exteroception (evaluation of the timing of light flashes or auditory tones), it would be reasonable to hypothesize that persons with higher blood pressure levels, relative to persons with lower blood pressure levels, would perform less adequately on a standardized heartbeat detection task. In contrast, findings from a third line of research associated with the ballistic perception model provide evidence that support a hypothesis that persons with higher blood pressure levels, relative to persons with lower blood pressure levels, would perform better on a standardized heartbeat detection task.

In our review of the literature, we could find no studies that had directly evaluated the extent to which persons with higher and lower levels of resting blood pressure differed in their levels of heartbeat awareness. We thus designed a crucial hypothesis test that pitted the hypothesis derived from the baroreceptor hypothesis and the nociception literature against the hypothesis derived from the ballistic perception model.

Section snippets

Participants

Fifty-seven male undergraduate students were recruited through classroom presentations and experimental sign-up sheets. Students who elected to participate in the study were fully informed about the nature of the study through a written consent form. Participants also received research credit and a small monetary reinforcer (described later) for participation. The mean age of the sample was 19.28 (S.D.=1.39 years). Racial characteristics were as follows: Caucasian, 88% (n=50); African American,

Between-group comparisons of demographic and anthropometric characteristics

Demographic and anthropometric variables were compared between the elevated BP and normal BP groups using chi-square analyses and t-tests. Results indicated that the elevated BP participants did not differ from the normal BP participants on any relevant demographic or anthropometric measure.

Blood pressure comparisons

To be assured that the elevated BP and normal BP groups maintained a reliable difference in blood pressure levels across the experiment, a 2 (elevated BP/normal BP)×4 (Condition: baseline, external task,

Discussion

As both hypotheses predicted, the results of this investigation indicated that heartbeat perception varied as a function of systolic blood pressure levels and experimental condition. However, the direction of the relationship between blood pressure levels and heartbeat perception was consistent with the hypothesis derived from the ballistic perception model. Specifically, participants with higher systolic blood pressure levels, relative to participants with lower systolic blood pressure levels,

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