Cardiovascular stress responses and their relation to symptoms in Gulf War veterans with fatiguing illness

OBJECTIVE

The objective of this study was to examine whether inappropriate cardiovascular responses to stressors may underlie symptoms in Gulf War veterans with chronic fatigue.

METHODS

Psychophysiological stress testing was performed on 51 Gulf War veterans with chronic fatigue (using the 1994 case definition of the Centers for Disease Control and Prevention) and 42 healthy veterans. Hemodynamic responses to cold pressor, speech, and arithmetic stressors were evaluated using impedance cardiography.

RESULTS

Veterans with chronic fatigue had diminished blood pressure responses during cognitive (speech and arithmetic) stress tests due to unusually small increases in total peripheral resistance. The cold pressor test, however, evoked similar blood pressure responses in the chronic fatigue and control groups. Low reactivity to cognitive stressors was associated with greater fatigue ratings among ill veterans, whereas an opposite relation was observed among healthy veterans. Self-reported neurocognitive decline was associated with low reactivity to the arithmetic task.

CONCLUSIONS

These results suggest a physiological basis for some Gulf War veterans' reports of severe chronic fatigue. A greater deficit with responses processed through cerebral centers, as compared with a sensory stimulus (cold pressor), suggests a defect in cortical control of cardiovascular function. More research is needed to determine the specific mechanisms through which the dissociation between behavioral and cardiovascular activities identified in this study may be contributing to symptoms in Gulf War veterans.

Ethnic variations in the pharmacological and nonpharmacological treatment of hypertension: biopsychosocial perspective

Blood pressure regulation is a complex, dynamic process influenced by psychosocial, behavioral, and cultural factors. Integrative theories of cross-population differences in the prevalence of hypertension and response to treatment include physiological, social, and genetic perspectives. Ethnic differences in salt sensitivity, calcium regulation of sodium flux, vascular reactivity to psychosocial stress, and drug metabolism are integral components of observed cross-cultural variations in hypertension. In general, pharmacological treatment of hypertension in blacks is most consistently achieved through diuretics and calcium-channel blockers; angiotensin-converting enzyme inhibitors and beta-blockers are more efficacious in whites. These stereotypical patterns are consistent with the higher prevalence of salt sensitivity, stress-induced vasoconstriction and slower natriuresis, and alpha-adrenergic receptor mediated vascular reactivity observed in blacks compared with whites. Some antihypertensive agents produce adverse glucose metabolic side effects, thus contraindicating their use in individuals with high sympathetic tone, insulin resistance, or obesity. Cross-population differences in adopted guidelines for treating hypertension exist but are not likely a factor in observed ethnic differences in rate of treatment or control. Attitudes toward nontraditional treatment options (e.g., herbal medicine), political and individual responsibilities in health care, and adaptations to acculturation and urbanization stress differ between and within societies and thus play a role in observed cross-cultural differences in hypertension as well. The value of regular exercise in controlling hypertension is widely recognized, and reductions in blood pressure reactivity to behavioral stress following acute exercise have been documented; however, empirical studies of ethnic differences in exercise-related blood pressure control are lacking. Overall, increased awareness of the multifactorial nature of hypertension by both the physician and the patient will facilitate treatment of this disease on an individual basis.

Cardiovascular and perceptual effects of reporting pain during the foot and forehead cold pressor tests

In research involving the cold pressor test, a tacit presumption is often made that reporting pain during stimulation is not in itself reactive. This study examined whether, for the foot and forehead cold pressor tests, activities involved in reporting pain may affect (a) the evoked pattern of cardiovascular response, and (b) the magnitude of self-perceived pain. In 40 normotensive college men, increases in systolic blood pressure were greater during test sessions that included verbal ratings of pain, as compared to sessions in which pain was not reported. In contrast to its effect on physiological activation, reporting pain did not significantly alter the participant's perception of the painfulness of the lest, on recollection shortly after the test. We conclude, therefore, that reporting pain during the cold pressor test may impose significant additional demands on the cardiovascular system, but it does not interfere significantly with the processing of nociceptive information.

Influence of ethnicity and gender on cardiovascular responses to active coping and inhibitory-passive coping challenges

OBJECTIVE

The goal of this study was to evaluate how black and white men and women responded physiologically to specific laboratory challenges.

METHODS

Hemodynamic responses to an active coping (evaluated speaking) and two inhibitory-passive coping (mirror tracing, cold pressor) tasks were examined in 138 black and white men and women.

RESULTS

Significant ethnicity by gender interactions occurred for the evaluated speaking task. Black men responded with lower blood pressure, cardiac output or heart rate, or both, than black women, white men, and white women, who did not differ from each other. Black men, relative to the other subgroups, also reported more inhibitory-passive coping, hostility, and pessimism, and less social support. Whites also responded with greater increases in systolic blood pressure during mirror tracing than blacks.

CONCLUSIONS

These findings indicate that black-white differences in physiological responsivity obtained for men may have limited generalizability for women. The results also suggest that environmental and social factors rather than genetic or constitutional factors may play a role in black-white reactivity differences.

Stimulus dimensions of the cold pressor test and the associated patterns of cardiovascular response

Hemodynamics of the cold pressor response in relation to its pain and nonpain stimulus components were investigated in normotensive college men using the foot and forehead cold pressor tasks. Mechanisms of pain- and non-pain-related increases in blood pressure were analyzed as residual effects of concurrent changes in total peripheral resistance and cardiac output. The identified partial relationships suggested that the response pattern associated with pain included positive change both in cardiac output and in total peripheral resistance, whereas the nonpain-related response was limited to an increase in total peripheral resistance. Analyses of individual differences in cardiovascular responses to pain further indicated that pain-related increments in blood pressure were mediated by a steeper rise in total peripheral resistance, an increase in heart rate, and an apparent increase in preload. At baseline, high reactors to pain manifested relatively elevated total peripheral resistance, diminished cardiac output, and an indication of a reduced inotropic state, suggesting that altered basal homeostasis may discriminate normotensive individuals displaying heightened cardiovascular reactivity to aversive cold stimulation.

Differential patterns of dynamic cardiovascular regulation as a function of task

In cardiovascular reactivity studies, interpretations of the processes supporting the blood pressure response may become problematic when systolic blood pressure, diastolic blood pressure, and heart rate all increase in response to a behavioral challenge. Therefore, in addition to evaluating these cardiovascular responses, this study examined cardiac output, total peripheral resistance and systolic time intervals derived from impedance cardiogram, electrocardiogram and phonocardiogram recordings during a speech stressor, a mirror tracing task, and a foot cold pressor test. All of the behavioral stressors elicited increases in blood pressure and heart rate, with the largest changes occurring during the overt speech. Based on the examination of the response patterns of the underlying hemodynamic variables it would appear that, in both men and women, the blood pressure increase during the speech preparation period was supported by increased cardiac output; the speech itself resulted in a mixed pattern of increased cardiac output and total peripheral resistance; whereas, the mirror tracing and cold pressor tasks produced increased total peripheral resistance. Although men and women produced similar response patterns to the behavioral challenges, sex differences in the estimates of myocardial contractility were observed during rest. These results provide evidence that different behavioral stressors can produce a distinct yet integrated pattern of responses, whose differences may be revealed, when impedance cardiography is used, to derive sufficient response measures for assessing dynamic cardiovascular processes.

Signal fidelity requirements for deriving impedance cardiographic measures of cardiac function over a broad heart rate range

Our findings indicate that the impedance cardiogram spectrum extends from DC to 50 Hz. Any amplifier with an upper band limit less than 50 Hz can be expected to produce attenuation and distortion of the impedance cardiogram. This signal attenuation may be systematically enhanced under conditions of high heart rate when a greater proportion of signal energy will be in the upper frequency range of the impedance cardiogram spectrum. Therefore, the present study was designed to assess the influence of amplifier bandwidth on dZ/dtmax, stroke volume, and systolic time intervals (LVET, PEP, QZ, QX). Simultaneously measured delta Z and dZ/dt signals from two impedance cardiographs, with corner frequencies of 120 and 60 Hz for the delta Z and 50 and 15 Hz for dZ/dt channels, were contrasted over a broad range of heart rate (70-150 bpm). In addition to the analog dZ/dt signals obtained from the instruments, the delta Z signals were digitally converted to dZ/dt by off-line digital differentiation with a 50 Hz corner frequency. The results demonstrated that the measurements with the 15 Hz corner frequency, when compared with the 50 Hz corner frequency measurements, systematically attenuated the dZ/dtmax amplitude and stroke volume measurements as heart rate increased. The attenuation of dZ/dtmax and stroke volume ranged from about 13% to 26% as heart rate increased from 70 to 150 bpm. When the upper bandlimit was 50 Hz, the dZ/dt signal had greater resolution of waveform events and produced less prolonged systolic time intervals. The 15 Hz amplifier differentially influenced the B point, Z-peak and X minimum, having no apparent effect on the temporal location of the B point, but delaying the Z-peak about 21.7 ms and the X minimum about 7.4 ms. These findings indicate that impedance cardiographs with insufficient upper bandlimits will differentially influence ICG-derived measurements as heart rate varies.

The cold pressor test: vascular and myocardial response patterns and their stability

The purposes of the present study were to compare the cardiovascular response patterns evoked by three versions of the cold pressor test (either forehead stimulation or hand or foot immersion) and to determine the reproducibility of the responses over a 2-week interval. Blood pressure, heart rate, stroke volume, cardiac output, total peripheral resistance, and systolic time intervals were obtained during rest and during the cold pressor test in 42 young men. Across conditions, the pressor response was supported by peripheral resistance increases with concomitant stroke volume decreases. Although the response patterns were generally similar across sites, exceptions were apparent for heart rate. Forehead stimulation was characterized by no significant change in heart rate, whereas limb (hand or foot) immersion was associated with significant heart rate acceleration. The responses elicited by the three cold pressor test conditions were reliable and showed little evidence of attenuation over the test-retest interval.

The stability of cardiovascular parameters under different behavioral challenges: one-year follow-up

The stability of myocardial, peripheral vascular and systolic time-interval measures was assessed over a one-year period in a sample of ten healthy normotensive men. Subjects participated in three laboratory sessions, the first two of which were two weeks apart, and the third approximately one year later. Measures were sampled during the preparation and delivery of a speech, a mirror star tracing task, and the forehead cold pressor test. The results of intraclass correlations computed between the mean of the first two sessions and the third showed that baseline and task levels were highly reproducible across all tasks and most parameters over the one year interval. Results also showed that the long term stability of delta is largely task-dependent.

Myocardial and peripheral vascular responses to behavioral challenges and their stability in black and white Americans

The purpose of this study was to assess the short term stability of myocardial and peripheral vascular responses to behavioral challenges, and to compare the response patterns of Black and White men. Blood pressure and heart rate, as well as stroke volume, cardiac output, total peripheral resistance, and systolic time interval measures derived from the impedance cardiogram were obtained in 12 Black and 12 White men. These measures were taken prior to and during an evaluative speech stressor, a mirror star tracing task, and a forehead cold pressor test presented during two laboratory sessions scheduled two weeks apart. In general, total peripheral resistance and impedance-derived baseline measures showed acceptable reproducibility (G greater than .85). With a few exceptions, adequate reliability was also demonstrated for change (delta) scores. All tasks raised blood pressure responses above resting levels. Blacks demonstrated significantly greater increases in total peripheral resistance responses across tasks. Whites but not Blacks also revealed increases above baseline in cardiac output and contractility as estimated by the Heather Index. These findings are consistent with the view that Blacks show greater vascular responsiveness than Whites across a variety of tasks, but reveal less myocardial responsiveness.

Sensorimotor and cognitive consequences of middle cerebral artery occlusion in rats

Rats were subjected to either right proximal middle cerebral artery (MCA) occlusion or sham operation, and examined for an extended period on a battery of tests designed to measure simple motor function, sensorimotor integration and cognitive function. Rats with MCA occlusion showed extensive neuronal loss in the dorsolateral striatum and variable neuron loss in the parietal, temporal and frontolateral neocortex. MCA occluded animals exhibited significant impairments in tests of postural reflex, visual and tactile forelimb placing, locomotor coordination, and a test of simultaneous bilateral tactile extinction. The reflex and sensorimotor function deficits recovered to pre-operative levels by Day 30 post-ischemia. Five weeks following surgery, rats were tested in 2 versions of the Morris water task. Rats with MCA occlusion demonstrated significant impairments in their ability to navigate to a hidden platform, but were not significantly impaired on the visible (cued) version of the task. This general pattern of transient sensorimotor and reflex deficits, but with more persistent cognitive impairments, is similar to that seen in humans following MCA infarcts.

Amphetamine promotes recovery from sensory-motor integration deficit after thrombotic infarction of the primary somatosensory rat cortex

The present studies were undertaken to examine 1) whether d-amphetamine sulfate administered to rats well after thrombotic infarction of the vibrissal cortical barrel-field within the primary somatosensory cortex affected the rate and completeness of behavioral recovery and 2) whether a dose-response relation exists between d-amphetamine sulfate dose and recovery of function. In a learning task requiring sensory-motor integration, 41 rats were trained to perform a motor response in a T-maze consequent to the detection of a vibrissal deflection cue. Once training was complete, unilateral (n = 29) or sham (n = 12) infarction was produced by a noninvasive photochemical technique. After infarction, T-maze performance was assessed repeatedly in rats receiving 2 (n = 10) or 4 (n = 10) mg/kg d-amphetamine sulfate or saline (n = 9) 24 hours prior to testing on days 4, 6, 9, and 11. The sham-operated control rats received d-amphetamine sulfate (n = 7) or no injections (n = 5). All three infarcted groups displayed a reliable and sustained behavioral deficit in performance that was not present in the sham-operated control animals. Although the performance of each infarcted group improved over the testing sessions after the first injection, the amphetamine-treated groups improved at a faster rate than the saline-injected group. The results further demonstrated a dose-response effect, with the 4 mg/kg amphetamine group recovering to within preinfarction levels 6-8 days earlier than the 2 mg/kg amphetamine and saline-injected groups. Moreover, both amphetamine-treated groups recovered more completely than the saline-injected group. Quantification of the chronic infarct area revealed no differences among the amphetamine-treated and saline-injected groups. These data provide further evidence of the facilitatory effect of d-amphetamine sulfate on recovery from brain injury and extend this effect to the enhancement of recovery subsequent to thrombotic infarction of the primary somatosensory cortex.

Sympathoadrenal preganglionic neurons in the adult rabbit send their dendrites into the contralateral hemicord

Sympathetic preganglionic neurons projecting to the adrenal medulla of the adult rabbit were retrogradely labelled with horseradish peroxidase. Preganglionic neurons were located in thoracic spinal cord segments T3-T12, peaking in number at T8, and only ipsilateral to the side of injections. However, retrogradely labelled dendritic processes of preganglionic neurons in the intercalated nucleus pars paraependimalys, the intercalated nucleus, and possibly even in the intermediolateral cell column, were observed in the contralateral hemicord. This suggests that the activity of sympathoadrenal preganglionic neurons could be modulated by both ipsilaterally and contralaterally descending pathways.

Sensory-motor deficit and recovery from thrombotic infarction of the vibrissal barrel-field cortex

The present studies were undertaken to examine: (1) whether thrombotic infarction of the vibrissal cortical barrel-fields of the primary somatosensory cortex would produce behavioral consequences reflecting a sensory-motor deficit; and (2) whether there was any recovery of function up to two months after infarction. Specifically, in two different learning tasks requiring sensory-motor integration, rats were trained to perform a motor response consequent to the detection of vibrissal cues derived from either active exploration or from passive detection of vibrissal deflection. Once training was complete, unilateral, bilateral or sham-infarction restricted to the region of the primary somatosensory cortex was produced by a non-invasive photochemical technique, which induces platelet-activated vascular occlusion combined with blood-brain barrier changes and subsequent cell death. The results demonstrated that, regardless of the active or passive sensory characteristics of the task, unilateral and bilateral infarction resulted in a reliable performance deficit, which was not present in sham-operated control animals. Thus, the infarct disrupted the ability to integrate passively received or actively acquired vibrissal sensory information with a previously associated motor response. However, unlike the bilaterally infarcted animals, who displayed no recovery of performance level throughout the postinfarction testing sessions, the unilaterally infarcted animals exhibited a gradual improvement in performance beginning in the second or third week postinfarction and recovering to within 10-20% of preinfarction levels between postinfarction days 46-61. The similarity of the temporal pattern of behavioral recovery in the unilateral groups, despite large differences in the sensory-motor demands of the two tasks, may reflect several common underlying mechanisms of recovery. Since similar sensory-motor behavioral deficits and recovery have been described with human stroke, the present model incorporates many of the pathophysiological and behavioral properties present in the clinical situation and may be useful for future investigation of therapeutic intervention.

New signal processing techniques for improved precision of noninvasive impedance cardiography

Impedance cardiographic determination of clinically important cardiac parameters such as systolic time intervals, stroke volume, and related cardiovascular parameters has not yet found adequate application in clinical practice, since its theoretical basis remains controversial, and the precision of beat-to-beat parameter estimation has until recently suffered under severe shortcomings of available signal processing techniques. High levels of noise and motion artifacts deteriorate signal quality and result in poor event detection. To improve the precision of impedance cardiography, new techniques for event detection and parameter estimation have been developed. Specifically, matched filtering and various signal segmentation and decomposition techniques have been tested on impedance signals with various levels of artificially superimposed noise and on actual recordings from subjects in a laboratory study of cardiovascular response to a cognitive challenge. Substantial improvement in the precision of impedance cardiography was obtained using the newly developed signal processing techniques. In addition, some preliminary evidence from comparisons of the impedance cardiogram with invasive aortic electromagnetic flow measurement in anesthetized rabbits is presented to address questions relating to the origin of the impedance signal.

Blood pressure during induction and termination of the dorsal immobility response

Evidence has indicated that afferent baroreceptor input may play a role in the induction of the dorsal and tonic immobility responses, which are behaviorally similar, but involve opposite posture changes upon induction (i.e., upright versus inverted, respectively). Information is lacking on the topography of the blood pressure response during periods of dorsal immobility. The blood pressure response of the adult Wistar rat during induction and termination of dorsal immobility was compared to the blood pressure response during a condition which controlled for posture change. Each animal received two control trials, ten dorsal immobility trials and then two control trials in two successive sessions four and ten days after surgery. A precise second-by-second topographical analysis of the dorsal immobility response revealed a sharp rise in blood pressure at trial onset of 18.4 mmHg, followed by a return below pretrial levels and then subsequent recovery back to pretrial levels by the tenth-trial second. This level was maintained until the last five seconds of immobility when a rapid blood pressure elevation occurred. This terminating elevation correlated highly with the observation of large movement and probably reflected motor activity that eventually culminated in escape from immobility. The vertical posture change of the control condition, on the other hand, resulted in a gradual diminution of blood pressure, which implied that the initial blood pressure elevation during initiation of the dorsal immobility response could not be accounted for simply by posture change.(ABSTRACT TRUNCATED AT 250 WORDS)

The human dive reflex: an experimental, topographical and physiological analysis

This study examined the eliciting conditions, response topography and autonomic nervous system (ANS) control of the dive reflex as evoked in humans. Twenty-four subjects received eight trials in each of the three treatment conditions: breath holding without face immersion (BH); face immersion without breath holding (FI); and the "full dive" FIBH condition. It was the combination of both FI and BH in 23 +/- 0.5 degrees C water that was necessary to elicit the dive reflex. A precise topographical analysis differentiated the FIBH condition from the FI and BH control conditions in terms of the emergence of a secondary component initiated approximately 12 seconds after trial onset. During this secondary component, augmentation of bradycardic (mean = 16.3 bpm) and digital vasoconstrictive (mean = -24.9%) responses were maintained throughout the duration of the 40-second dive. A joint consideration of the heart rate and the T-wave amplitude measures as indices of the action of both branches of the ANS suggested that the dive reflex involves concurrent sympathetic and parasympathetic activation. A potential conditioning application of the dive reflex for countering paroxysmal supraventricular tachycardia was discussed.