Effect of Carotid Sinus Stimulation on Cardiac Output and Peripheral Vascular Resistance during Changes in Blood Volume Distribution in Man

In ten healthy subjects (mean age 29.6 years) the hemodynamic response to carotid sinus stimulation (neck suction - 40 mmHg) was studied under control conditions and during peripheral pooling of blood (lower body negative pressure). Heart rate, arterial and central venous pressure, cardiac output and forearm blood flow were measured. The time sequence of the heart rate response was studied separately in six healthy subjects. During control conditions, carotid sinus stimulation induced a significant decrease in arterial pressure and heart rate. The blood pressure decrease mainly reflected a reduction in cardiac output, total peripheral vascular resistance being essentially unchanged. However, in the skeletal muscle, represented by a forearm segment, vascular resistance decreased significantly. During lower body negative pressure (LBNP) the same stimulation of the carotid sinus induced a significantly greater fall in mean arterial pressure even though the reduction in cardiac output was slightly smaller on the average than in the control condition. The heart rate increased, probably secondary to a time dependent increase in heart rate elicited by the continuous LBNP stimulus. Total peripheral vascular resistance decreased significantly during LBNP, the reaction likewise differing significantly from that in the control condition. Thus the augmented blood pressure response was due to a more pronounced vasodilatation when the carotid sinus was stimulated during lower body negative pressure. The results indicate that the hemodynamic changes elicited by carotid sinus stimulation are modified by changes in the distribution of blood volume and in the tone of resistance vessels.     

Cardiovascular and Neurophysiologic Correlates of Sensory Intake and Rejection. II. Interview Behavior

As part of a three task study of the influence of attentional style on cardiovascular response, 19 normal volunteers were given a 15-min interview during which systolic and diastolic blood pressure, digital pulse volume, heart rate, and forearm blood flow were recorded. At the same time two observers independently assessed five elements of the subjects' interview behavior; arousal, eye contact with the interviewer, self-revelation of interview center, attentiveness to the interviewer, and overall transactional engagement in the interview task. When subjects were divided into groups of interview at tenders and nonattenders on the basis of interviewer ratings, attenders had a mean decrease in forearm blood flow and nonattenders a mean increase. These group differences extended across a word identification (sensory intake) and mental arithmetic (sensory rejection) task as well. When subjects were divided into groups of forearm blood flow increasers and decreasers, increasers displayed less attentiveness to the interviewer, less self-revelation, greater arousal, and less transactional engagement than did decreasers (N=9). Attentiveness to the interviewer and transactional engagement were the two most sensitive behavioral discriminators in comparing the increaser and decreaser groups.     

Caffeine Affects Cardiovascular Responses to Stress

The effects of caffeine on cardiovascular activity at rest and during psychological stress were examined in 33 healthy male college students who did not normally ingest caffeinated products. Caffeine (250 mg) and placebo were administered double-blind in separate sessions. Heart rate, blood pressure, and forearm blood flow and vascular resistance were assessed at rest and during the stressful, competitive performance of a mental arithmetic task. Comparisons of caffeine and placebo sessions revealed that caffeine elevated resting blood pressure 4–6 mmHg, an effect which added to the elevation produced by stress. Caffeine did not affect resting forearm blood flow but potentiated the forearm blood flow response to stress and led to higher levels of flow during stress. No caffeine effects appeared in heart rate or in task performance. Family history of hypertension and Type A behavior were examined as potential modulating factors of caffeine effects but results were generally negative. These results suggest possible mechanisms through which caffeine could enhance the pathogenic effects of stress on the cardiovascular system.     

Exaggerated Sympathetic Nervous System Response to Extended Psychological Stress in Offspring of Hypertensives

The cardiovascular responses of 24 healthy young adult males with a parental history of hypertension and 24 males without a parental history of hypertension to an extended active-coping psychological stressor were compared under three drug conditions: placebo, the beta 1-blocking agent metoprolol, and the alpha 1-blocking agent prazosin. In the placebo condition, offspring of hypertensives exhibited significantly greater heart rate, blood volume pulse, and forearm blood flow responses to the task. They also exhibited a significantly greater initial decrease in forearm vascular resistance, which, in contrast to the offspring of normotensives, was no longer significantly different from baseline levels by the end of the session. No group differences in blood pressure response were observed. Metoprolol eliminated the differences in heart rate and forearm vascular resistance responses. Prazosin eliminated the difference in blood volume pulse response and elicited a sustained group difference in forearm vascular resistance. These results implicate the sympathetic nervous system in the exaggerated cardiovascular responsivity to psychological stress in individuals with a family history of essential hypertension. They also suggest that the pattern of increasing vascular resistance in response to this stressor observed in this and other studies in this laboratory reflects alpha-adrenergic activity and not neurohumorally independent autoregulation.     

Effect of evaluative observation during mental tasks on cardiovascular responses

The effect of evaluative observation on cardiovascular responses was assessed in 20 female undergraduate students. All participants performed a mental arithmetic (MA) task, and a mirror drawing (MD) task, with or without evaluative observation. Heart rate, blood pressure (BP), admittance plethysmography, and task performance were recorded for each task. Both tasks increased blood pressure, but the hemodynamic response patterns were distinct. The MA task induced enhanced cardiac response, whereas the MD task induced a vascular dominant response. Evaluative observation substantially increased BP during both tasks, but it always enhanced cardiac output and reduced total peripheral resistance. The hemodynamic responses changed significantly from vascular dominant to cardiac dominant, particularly during the MD task. The similarity of responses during evaluative and competitive situations is discussed. The significance of interpersonal factors in psychophysiological studies is emphasized.     

Vascular Resistance in Peripheral Blood Vessels at Normotension and at Local Orthostatic Hypertension in Healthy Humans

The effect of changes in orthostatic pressure on vascular resistance in subcutaneous adipose tissue was examined in the forearm at normal tension and in the leg at local orthostatic hypertension in three normal subjects. Blood flow in subcutaneous tissue was measured by the local xenon-133 washout technique. Changes in orthostatic pressure were achieved by postural changes of the extremity. At levels above the heart where venous pressure is constant, there was autoregulation of blood flow over a wider arterial blood pressure range in leg than in forearm. When transmural pressure increased 25 mm Hg or more vascular resistance increased about 50 per cent in the dependent forearm and 300 per cent in the dependent leg. The effect of ischemia on vascular resistance was investigated in cutaneous tissue of hand and foot by means of the ¹³¹I-Antipyrine initial slope technique. Vascular resistance after maximum dilatation achieved after20, 30, and 35 min of ischemia was less in vessels of the hand than in vessels of the foot. Thus, adaptive structural changes of vessels subjected to increased blood pressure are present in cutaneous and subcutaneous adipose tissues in normal subjects.     

Cardiovascular reactivity, Type A behavior, and coronary heart disease: Comparisons between myocardial infarction patients and controls during laboratory-induced stress

Cardiovascular responses to a series of laboratory stressors were examined in middle-aged Type A and Type B men. The subjects were 30 patients with diagnosed myocardial infarction (NYHA Class 1) and 26 age-matched healthy controls. All subjects were nonsmokers in the normotensive range, and none were on medication. Blood pressure, heart rate, forearm blood flow and resistance, and impedance cardiography-determined response variables were obtained during performance and recovery periods of both mental and physical tasks. The patients showed elevated reactivity in systolic blood pressure and cardiac output and prolonged systolic lime ratio during mental stress tasks and elevated total peripheral resistance and lower cardiac output and stroke volume during physical tasks, as compared with control subjects. Thus, the difference in blood pressure reactivity between patients and controls appeared to be primarily dependent on the vascular component during physical tasks, whereas the mental tasks promoted a hemodynamic response pattern more consistent with beta adrenergic activation. Type A men, irrespective of coronary status, showed larger systolic and diastolic blood pressure response to both mental and physical stress than did Type B men.     

Sustained forearm vasodilation in humans during mental stress is not neurogenically mediated

To evaluate the possible neurogenic influence on forearm vasodilation during mental stress (Stroop's colour word conflict test), haemodynamic and catecholamine responses were registered in 12 healthy men after axillary blockade. Forearm blood flow was measured with venous occlusion plethysmography and forearm vascular resistance was calculated, with intra-arterial blood pressure data. Blood samples for arterial and venous adrenaline and noradrenaline determinations were collected. Basal forearm blood flow increased markedly after axillary blockade, but the relative responses of forearm blood flow and forearm vascular resistance to mental stress were the same as in previously studied unblocked individuals (about +125% and about -40%, respectively). There was no increase in noradrenaline overflow from the forearm during mental stress in the nerve blocked arm. Heart rate and arterial systolic pressure responses as well as catecholamine responses to mental stress were augmented in the nerve blocked group, presumably due to a certain arousal caused by the experimental procedure. Increases in forearm blood flow and decreases in forearm vascular resistance during infusion of adrenaline were similar in the nerve blocked and in the control arm. In conclusion, vasodilation in the forearm during mental stress occurs in the absence of nervous control of the vascular bed. The reactivity of the vascular bed to an exogenous vasodilator (adrenaline) remains unchanged after axillary blockade.     

Cardiovascular Effects of Caffeine and Stress in Regular Coffee Drinkers

The effects of caffeine on cardiovascular activity at rest and in response to psychological stress were studied in a group of 30 healthy males who were regular coffee drinkers to replicate caffeine-stress interactions found previously in caffeine-naive subjects. Measures of heart rate, blood pressure, and forearm blood flow were recorded at rest and during the performance of a stressful mental task in two separate sessions. Caffeine (250 mg) or placebo was administered double-blind in a within-subject design. Relative to placebo, caffeine had a pressor effect at rest which persisted during stress and recovery such that blood pressure during stress was higher if caffeine had been consumed. Caffeine also magnified the forearm blood flow and forearm vascular resistance responses to stress, suggestive of a synergistic interaction of caffeine and stress. Analysis of individual difference variables suggested that caffeine effects on the forearm vascular variables were greatest in subjects who were Type B and had a positive family history of hypertension. Results suggest that regular caffeine use does not necessarily lead to tolerance for caffeine-stress interactions and that certain characteristics may be associated with greater sensitivity to caffeine's effects.     

Cardiovascular and Neurophysiologic Correlates of Sensory Intake and Rejection. I. Effect of Cognitive Tasks

In this study of the relationship between sensory processing and cardiovascular function, five cardiovascular parameters were monitored during baseline periods and during tasks requiring either sensory intake or sensory rejection behavior on the part of 19 subjects. Sensory intake behavior was associated with a pattern of response similar lo that seen with activation of peripheral sympathetic nerves-vasoconstriction in both the digit (skin) and forearm (skeletal muscle). In contrast, sensory rejection behavior was associated with vasodilatation in the forearm and vasoconstriction in the digit. Individual differences in an EEG measure of characteristic ways of processing sensory information were predictably associated with differences in resting cardiovascular function. The association of sensory intake with a skeletal muscle vasoconstriction may help to extend our understanding of the physiology of sensory processing, since heretofore only heart rate and somatic motor activity have reliably differentiated sensory intake from sensory rejection behavior.     

Evaluation of Myocardial and Peripheral Vascular Responses During Reaction Time, Mental Arithmetic, and Cold Pressor Tasks

The primary purpose of this study was to examine the covariation of cardiac output and forearm blood flow during reaction time, mental arithmetic, and cold pressor tasks. Cardiac output was indexed using impedance cardiography, whereas impedance venous occlusion plethysmography was used lo index forearm blood flow. Cardiac output increased significantly over resting values in all three tasks, hut the pattern of these increases differed. Large heart rate increases during mental arithmetic and cold pressor tasks more than offset stroke volume decreases; the increases in the reaction time task were due to relatively smaller heart rate increases with stroke volume augmentation. For forearm blood flow, all task levels were higher than resting levels, but only mental arithmetic levels were statistically higher. The correlation between cardiac output and forearm blood flow change was significant for the reaction time task, but not for the mental arithmetic or cold pressor tasks.     

Fatness is related to blunted vascular stress responsivity, independent of cardiorespiratory fitness in normal and overweight men.

Obesity is associated with disturbed cardiovascular responsivity to mental stress, which may mediate psychosocial disease pathways. Whether being aerobically fit is protective against psychophysiological dysfunction in the presence of overweight or obesity is undetermined. Peripheral blood flow, blood pressure, and cardiac responses were measured during a 2-min mental stress task in 48 healthy men (aged 18-32 years). Mental stress-evoked increases in mean arterial pressure and heart rate, forearm vasodilatation, and cardiac parasympathetic withdrawal. Multiple linear regression analyses adjusted for age, peak oxygen uptake, and baseline forearm vascular resistance, revealed that greater fatness was related to a blunted vasodilatation response to mental stress (beta=-.31, p<.05). There were no interactive effects of fitness and fatness. Fitness does not appear to moderate the association between fatness and impaired vascular stress responsivity in normal and overweight men.     

Limb neurovascular control during altered otolithic input in humans

Head-down rotation (HDR), which activates the vestibulosympathetic reflex, increases leg muscle sympathetic nerve activity (MSNA) and produces calf vasoconstriction with no change in either cardiac output or arterial blood pressure. Based on animal studies, it was hypothesized that differential control of arm and leg MSNA explains why HDR does not alter arterial blood pressure. Fifteen healthy subjects were studied. Heart rate, arterial blood pressure, forearm and calf blood flow, and leg MSNA responses were measured during HDR in these subjects. Simultaneous recordings of arm and leg MSNA were obtained from five of the subjects. Forearm and calf blood flow, vascular conductances, and vascular resistances were similar before HDR, as were arm and leg MSNA. HDR elicited similar significant increases in leg (Δ6 ± 1 bursts min⁻¹; 59 ± 16 % from baseline) and arm MSNA (Δ5 ± 1 bursts min⁻¹; 80 ± 28 % from baseline). HDR significantly decreased calf (−19 ± 2 %) and forearm vascular conductance (−12 ± 2 %) and significantly increased calf (25 ± 4 %) and forearm vascular resistance (15 ± 2 %), with ∼60 % greater vasoconstriction in the calf than in the forearm. Arterial blood pressure and heart rate were not altered by HDR. These results indicate that there is no differential control of MSNA in the arm and leg during altered feedback from the otolith organs in humans, but that greater vasoconstriction occurs in the calf than in the forearm. These findings indicate that vasodilatation occurs in other vascular bed(s) to account for the lack of increase in arterial blood pressure during HDR.     

Prenalterol in severe congestive heart failure. I. The immediate haemodynamic effects as compared to nitroglycerine

The immediate haemodynamic effects of prenalterol and nitroglycerine were examined in 15 patients, with severe chronic heart failure. Prenalterol was given intravenously in increasing doses of 2, 4, and 8 mg. Cardiac index increased significantly by 16%, 24%, and 32%, respectively. Heart rate increased by 16%, 19%, and 24%. Stroke volume index, systemic artery pressure, pulmonary artery pressure, and right atrial pressure did not change. Prenalterol reduced systemic vascular resistance by 15%, 17%, and 24%, respectively. Forearm blood flow and forearm vascular resistance was unchanged. Cardiac index and heart rate were not changed by 0.5 mg nitroglycerine, administered sublingually. Systolic and diastolic blood pressure were on average reduced by 14% and 12%, respectively. Systolic and diastolic pulmonary artery pressure and right atrial pressure were similarly reduced by 17%, 31%, and 39%, respectively. Nitroglycerine lowered calculated systemic vascular resistance by 11%, whereas forearm blood flow and forearm vascular resistance was unchanged. The conclusion is that prenalterol acutely increased cardiac index and improved haemodynamics in 14 out of 15 patients, mainly due to an increased heart rate. Nitroglycerine did not change cardiac index in the same group of patients.     

Acute exercise improves endothelial function despite increasing vascular resistance during stress in smokers and nonsmokers

The present study examined the effect of acute exercise on flow mediated dilation (FMD) and reactivity to neurovascular challenges among female smokers and nonsmokers. FMD was determined by arterial diameter, velocity, and blood flow measured by Doppler ultrasonography after forearm occlusion. Those measures and blood pressure and heart rate were also assessed in response to forehead cold and the Stroop Color‐Word Conflict Test (CWT) before and after 30 min of rest or an acute bout of cycling exercise (～50% VO₂peak). Baseline FMD and stress responses were not different between smokers and nonsmokers. Compared to passive rest, exercise increased FMD and decreased arterial velocity and blood flow responses during the Stroop CWT and forehead cold in both groups. Overall, acute exercise improved endothelial function among smokers and nonsmokers despite increasing vascular resistance and reducing limb blood flow during neurovascular stress.     

The effect of calcitonin gene-related peptide (CGRP) on human forearm blood flow

The effect of intravenous and intra-arterially administered calcitonin gene-related peptide (CGRP) on the human forearm blood flow and cutaneous blood flow were investigated by means of venous occlusion plethysmography and laser-Doppler flowmetry, respectively. Infusion of CGRP (11-216 pmol min-1) into the brachial artery resulted in a dose-dependent increase in forearm blood flow and cutaneous blood flow which persisted for up to 90 min after the infusion was stopped. Repeated infusions resulted in an identical response. Systemic intravenous infusion of CGRP (104-520 pmol min-1) resulted in a dose-dependent flush in the face, neck, upper trunck and upper arms, and an increase in the forearm blood flow. The cutaneous blood flow was dramatically increased on the forehead, whereas on the hand only a slight increase was noted. By intravenous infusions a significant drop in blood pressure and increase in heart rate were seen at 520 pmol min-1. Thus, it is possible to give CGRP in doses that increase the blood flow in muscle and skin without resulting in a fall in systemic arterial blood pressure and tachycardia, suggesting that CGRP may be used as a tool for the treatment of various conditions in man with compromised blood flow.     

Individual Differences in Heart Rate and Peripheral Vascular Responses to an Extended Aversive Task

Psychophysiological research on situations requiring active coping has to this point dealt primarily with cardiac responses. Recent studies of vascular responses to such stressors have found conditions in high cardiac reactors that are possible precursors to autoregulatory vasoconstriction. The present study exposed 32 healthy male undergraduates to a one-hour shock avoidance procedure, with avoidance made contingent on video-game performance. Subjects also participated in a separate counterbalanced baseline session. The relationships among individual differences in heart rate, forearm blood flow, forearm vascular resistance, and digital blood volume pulse responses at different points in the stress session were examined. Decreases in forearm vascular resistance were observed only among high and medium heart rate reactors. As the session progressed, however, forearm vascular resistance responses of the medium heart rate reactors were sustained whereas those of the high heart rate reactors habituated despite the fact that heart rate and forearm blood flow responses remained elevated. The potential implications of this pattern of results to an autoregulation theory of hypertension development are discussed. Heart rate reactivity was inversely related to performance on the video-game task but was unrelated to Type A or anxiety.     

Race, Parental History of Hypertension, and Patterns of Cardiovascular Reactivity in Women

This study examined the interaction of race and parental history of hypertension on patterns of cardiovascular responses among women. Two stressors were used that produce different patterns of cardiovascular reactivity: mental arithmetic, primarily a beta-adrenergic stimulus, and the cold face stimulus, which evokes alpha-adrenergic (i.e. vascular) activity. Systolic and diastolic blood pressure, heart rate, forearm blood flow, and forearm vascular resistance were assessed before, during, and after arithmetic and cold face stimulus. Both tasks produced the expected patterns of cardiovascular adjustment, although no Black-White differences occurred during arithmetic. However, Black subjects did show a slower recovery of diastolic blood pressure following arithmetic. The cold face stimulus produced significantly greater changes in systolic blood pressure in the Black than in the White women. Parental history of hypertension did not relate significantly to reactivity. The results provide limited support for the idea that Black females exhibit a greater pressor response than White females to a stimulus that produces primarily vascular rather than cardiac changes. These findings are discussed in relation to previous findings with males and with respect to their implications for the role of reactivity in Black-White differences in hypertension prevalence.     

Attenuation of forearm vasodilator responses to mental stress by regional beta-blockade,but not by atropine

Forearm blood flow during mental stress (Stroop's colour word conflict test) was studied in 18 healthy men before and during regional β-adrenoceptor blockade (propranolol 0.5 mg), muscarinic receptor blockade (atropine 0.2 mg) and combined blockade, and compared with results obtained in untreated controls. Forearm blood flow was measured with venous occlusion plethysmography, and forearm vascular resistance was calculated. Arterial and venous blood sampling was performed for determination of adrenaline and noradrenaline in plasma. Mental stress increased heart rate, systolic and diastolic blood pressures and forearm blood flow, and lowered the forearm vascular resistance, to the same degree as in our previously studied controls. Neither of the intra-arterially administered drugs had any discernible systemic effects. Beta-blockade increased forearm vascular resistance by 32% and decreased forearm blood flow by 21% compared with unblocked levels during mental stress, whereas forearm vasodilation was maintained throughout the stress test in the control group (P < 0.05). Intra-arterial atropine had no certain effects. Arterial adrenaline levels during mental stress were similar in the receptor-blocked and control groups. In conclusion, the sustained forearm vasodilation during mental stress appears to be partly mediated via β₂-adrenoceptor stimulation (i.e. by adrenaline), but we obtained no support for a cholinergic vasodilating mechanism.     

Cardiovascular responses to partial and total immersion in man

1. Short-term cardiovascular effects of partial and total immersion of eighteen human subjects in the horizontal plane have been examined. Brachial arterial pressure, heart rate, forearm blood flow and respiratory movements were monitored simultaneously throughout the experiments. Forearm vascular resistance was calculated from the mean blood pressure and mean flow.2. Total immersion, including the face, with breath-holding resulted in a 61 +/- 43% increase in forearm vascular resistance with an associated 29 +/- 15% reduction in forearm blood flow. The concurrent bradycardia was significantly different from the heart rate changes during breath-holding with the torso only immersed, or during total immersion with snorkel-breathing. Neither breath-holding in air or with only the torso immersed, nor total immersion with snorkel-breathing produced such a diving response.3. Breath-holding, after several minutes of total immersion and snorkel-breathing, produced an attenuated diving response. It therefore appears that a full diving response can be obtained only when the apnoea commences at the moment of face immersion.4. The present investigation supports the concept that in man face immersion is an essential predisposing factor for the diving response, and cortical inhibition of the respiratory centre is important for its initiation and maintenance.