Influence of fitness and gender on blood pressure responses during active or passive stress

We examined hemodynamic and autonomic components of blood pressure responses during active and passive stressor tasks in a sample of young, normotensive men and women who were physically active but differed on fitness (i.e., VO2peak). During the hand cold pressor, increases in systolic blood pressure were inversely related to fitness among women but not men. Regardless of gender, fitter participants had a greater increase in cardiac pace during mental arithmetic, coherent with a decreased cardiac-vagal component of heart rate variability, and a greater compensatory reduction in stroke volume. Fitness was otherwise unrelated to changes in cardiac output and vascular resistance during the stressor tasks. Our findings suggest that cardiorespiratory fitness augments the cardiac-vagal withdrawal that is characteristic of mental arithmetic. The blunted systolic blood pressure response to the hand cold pressor among fitter women suggests that cardiorespiratory fitness should be considered as a covariate in studies that examine the hand cold pressor as a predictor of future hypertension among women.     

Augmented limb blood flow during neurovascular stress in physically fit women

The study examined whether cardiorespiratory fitness modifies cardiovascular responses by normotensive men and women during the Stroop color‐word interference test. Independent of age and an estimate of body fatness, fitness level was positively related (R² = .39 and .51) to increases in limb blood flow and vascular conductance, coherent with cardiac‐vagal withdrawal and a decrease in heart period, among women but not men. Fitness was unrelated to changes in systolic and diastolic blood pressures and muscle sympathetic nerve activity. The augmented hemodynamic responses among fitter women were not consistent with passive vasodilation via withdrawal of sympathetic neural tone. The results encourage further gender comparisons testing whether fitness augments limb blood flow during mental stress by neurohumoral and flow‐mediated vasodilatory mechanisms or by increased cardiac output.     

Augmented sympathetic nerve activity in response to stressors in young borderline hypertensive men

To determine whether there may be an abnormality in sympathetic nerve activity in response to physical and psychological stressors, we microneurologically recorded muscle sympathetic nerve activity in 11 normotensive and 9 borderline hypertensive, age-matched men. Supine blood pressure, plasma levels of epinephrine and norepinephrine and muscle sympathetic nerve activity were measured before and during a cold pressor test or a mental arithmetic test. The resting basal values of muscle sympathetic nerve activity, blood pressure and plasma epinephrine were significantly higher in the borderline hypertensives than in the normotensives (P less than 0.05). Plasma norepinephrine levels tended to be higher in the borderline hypertensives than in the normotensives but not to a significant extent (P less than 0.10). The cold test produced significantly exaggerated pressor and muscle sympathetic nerve responses (P less than 0.05) with a trend towards an increase in plasma norepinephrine (P less than 0.10) in the borderline hypertensives as compared with normotensives. The mental arithmetic test produced significantly enhanced pressor and plasma epinephrine responses in the borderline hypertensives as compared with the normotensives (P less than 0.05). During the mental arithmetic test the muscle sympathetic nerve activity decreased significantly in the normotensives (P less than 0.05) but not in the borderline hypertensives. These findings indicate that in people with borderline hypertension an abnormality exists in sympathetic nerve activity at rest and in response to stressors.     

Sympathetic activation during the cold pressor test: influence of stimulus area

The purpose of this study was to determine the effect of the size of the stimulus area on the muscle sympathetic nerve activity (MSNA), systolic arterial blood pressure (SAP), and heart rate responses to the cold pressor test. To accomplish this, these variables were measured before (control), during, and after 1.5 min of ice water immersion of either one or both hands in nine healthy subjects (aged 19-27 years). The cold stimulus elicited significant increases above control levels in all three variables under both conditions (P less than 0.05). Immersion of both hands produced a much greater increase in total MSNA (+366%) than immersion of a single hand (+187%) (P less than 0.05). However, the magnitudes of the increases in SAP and heart rate during two-hand immersion (29 +/- 6 mmHg and 10 +/- 2 beats min-1) were not significantly different from the responses during the one-hand trials (24 +/- 5 mmHg and 6 +/- 2 beats min-1, P greater than 0.05). There was a strong, direct relationship between total MSNA and SAP responses during one-hand immersion (r = 0.93, P less than 0.001) but not during immersion of both hands (r = 0.66, P = 0.08). These findings indicate that during the cold pressor test the magnitude of the increase in sympathetic discharge to skeletal muscle, but not the systolic blood pressure response, is influenced by the size of the tissue area exposed to the stimulus.     

Augmented leg vasoconstriction in dynamically exercising older men during acute sympathetic stimulation

Vasoconstrictor responsiveness to acute sympathetic stimulation declines with advancing age in resting skeletal muscle. The purpose of the present study was to determine if age-related reductions in sympathetic vasoconstrictor responsiveness also occur in exercising skeletal muscle. Thirteen younger (20–30 years) and seven older (62–74 years) healthy non-endurance-trained men performed cycle ergometer exercise at ∼60 % of peak oxygen uptake while leg blood flow (femoral vein thermodilution), mean arterial blood pressure (radial artery catheter), and plasma adrenaline and noradrenaline concentrations were measured. After steady state was reached (i.e. ∼4 min), acute sympathetic stimulation was achieved by immersing a hand in ice water for 2–4 min (cold pressor test, CPT). CPT tended to cause a larger increase in mean arterial blood pressure in older men (older (O): 16 ± 3 mmHg; younger (Y): 10 ± 2 mmHg) during exercise, but increases in arterial noradrenaline were similar (O: 2.56 ± 0.96 nM; Y: 1.98 ± 0.40 nM). However, the older men demonstrated a larger percentage reduction in exercising leg vascular conductance (leg blood flow/mean arterial pressure) during CPT compared to younger men (O: -13.6 ± 3.1%; Y: -1.5 ± 4.3%; P = 0.04). Leg blood flow tended to increase in the younger men, but not in the older men ( P = 0.10). These results suggest, in contrast to what has been observed in resting skeletal muscle, that vasoconstrictor responsiveness to sympathetic stimulation is not reduced, but may be augmented in exercising muscle of healthy older humans. This could reflect a reduced ability of local substances (e.g. nitric oxide) to impair vasoconstriction in response to sympathetic stimulation during exercise in older humans.     

Effect of gastric distension on cardiovascular parameters: gastrovascular reflex is attenuated in the elderly

Stretching the stomach wall in young healthy subjects causes an increase in muscle sympathetic nerve activity and in blood pressure, the gastrovascular reflex. We compared healthy elderly subjects with healthy young subjects to find out whether the gastrovascular reflex attenuates in normal ageing and we studied whether there was a difference in autonomic function or gastric compliance that could explain this possible attenuation. Muscle sympathetic nerve activity, finger blood pressure and heart rate were continuously recorded during stepwise isobaric gastric distension using a barostat in eight healthy young (6 men and 2 women, 27 ± 3.2 years, mean ± s.e.m. ) and eight healthy elderly subjects (7 men and 1 woman, 76 ± 1.5 years). Changes in cardiac output and total peripheral arterial resistance were calculated from the blood pressure signal. The baseline mean arterial pressure and muscle sympathetic nerve activity were higher in the elderly group (both P < 0.05) and muscle sympathetic nerve activity increase during the cold pressor test was lower in the elderly group ( P = 0.005). During stepwise gastric distension, the elderly subjects showed an attenuated increase in muscle sympathetic nerve activity compared to the young subjects ( P < 0.01). The older group tended to show a higher increase in mean arterial pressure ( P = 0.08), heart rate ( P = 0.06) and total peripheral arterial resistance ( P = 0.09) The cardiac output rose slightly in both groups without significant difference between groups. The fundic compliance did not differ between groups. We conclude that stepwise gastric distension caused an increase in muscle sympathetic nerve activity in both groups, but the increase in the elderly was attenuated.     

The combined effect of the cold pressor test and isometric exercise on heart rate and blood pressure

Summary The purpose of this study was to determine if the cold pressor test during isometric knee extension [15% of maximal voluntary contraction (MVC)] could have an additive effect on cardiovascular responses. Systolic and diastolic blood pressures, heart rate and pressure rate product were measured in eight healthy male subjects. The subjects performed the cold pressor tests and isometric leg extensions singly and in combination. The increases of systolic and diastolic blood pressure during isometric exercise were of almost the same magnitude as those during the cold pressor test. The responses of arterial blood pressure, and heart rate to a combination of the cold pressor test and isometric knee extension were greater than for each test separately. It is suggested that this additional effect of cold immersion of one hand during isometric exercise may have been due to vasoconstriction effects in the contralateral unstressed limb. In summary, the circulatory effects of the local application of cold during static exercise at 15% MVC were additive.     

Flow-volume curves during hand immersion in water at 5 degrees C (the cold pressor test)

Seven healthy subjects immersed a hand for 2 min in cold water at 5 degrees C (the standard cold pressor test) with and without beta-adrenoceptor blockade. Control immersions in warm water were also performed. The maximal and partial flow-volume curves as well as the arterial blood pressure, heart rate and body and hand temperatures were recorded before, during and after the hand immersion. The blood pressure rose significantly during the cold pressor test, but the airflow variables did not change significantly, whether or not propranolol had been given. It is concluded that, even though the standard cold pressor test induces sympathetically-mediated cardiovascular responses, it does not produce a bronchodilatation.     

Patterns and stability of cardiovascular responses to variations of the cold pressor test

Test-retest reliabilities and patterns of heart rate and blood pressure responses were examined using variations in the cold pressor test in 113 normotensive white college men. Comparisons were made of stimulus site (forehead vs. foot) and bodily posture (seated vs. supine) across four separate groups of men. The stability of cardiovascular responses was examined over a 2-week test-retest interval. Different cardiovascular response patterns emerged as a function of stimulation site and posture. Systolic and diastolic blood pressure increases were accompanied by bradycardia in the forehead cold pressor task but by tachycardia in the foot cold pressor task. Systolic blood pressure increases were larger for foot than for forehead stimulation. Heart rate increases were larger for supine than for seated men. Effects on response were independent of postural differences at baseline, and there were no stimulation site by posture interactions. The cardiovascular responses to stimulation did not attenuate across sessions in any experimental condition but were more reliable for foot than for forehead stimulation and for supine than for seated posture. Short-term stability for changes to the task approached that for baseline and task and was higher than has been reported elsewhere.     

Blood Pressure Reactivity and Perception of Pain During the Forehead Cold Pressor Test

The relationship between blood pressure reactivity and the perception of pain was examined during a series of three forehead cold pressor tests given every other day to a group of 18 male college students. Subjects classified as high reactors on the basis of peak increases in mean blood pressure during cold pressor tests perceived the cold pressor stimulus as more painful than subjects classified as low reactors. The propensity to rate the cold pressor stimulus as painful was positively correlated with the individual level of blood pressure reactivity (baseline-free partial r = .62). Intra-individual correlations between pain and blood pressure responses were unrelated to subjects' reactivity status. Across the 3-min test, correlations between pain and blood pressure reactivity (with the effects of baseline blood pressure levels partialled out) were significant only during periods when levels of responses were relatively high. The heart rate responses were unrelated to pain ratings. Generalizability theory was applied to the analysis of temporal stability of cold pressor reactions. Both blood pressure and pain responses were highly reproducible across three sessions, appearing to express stable individual differences. The efficacy of 800 mg oral ibuprofen in controlling the cold pressor pain was also tested. Analgesic activity of the drug during the cold pressor test could not be demonstrated.     

Pain perception and cardiovascular responses in men with positive parental history for hypertension

Evidence suggests a reduced pain sensitivity in hypertensive individuals. This study sought to extend this work to normotensive individuals with hypertensive parents. Men with a positive (PH+) or negative (PH?) parental history for hypertension rated their pain every 15 s during a 90-s hand cold pressor test and for 90 s after the cold pressor test. Systolic (SBP) and diastolic (DBP) blood pressures and heart rate were measured throughout. After the cold pressor test, the men recalled their pain using the McGill Pain Questionnaire. PH+ men showed greater SBP and DBP responses to the cold pressor test. Although pain ratings during the cold pressor test did not differ between groups, posttest reported pain receded faster in the PH+ than in the PH? men. The PH+ men also reported less total pain on the McGill. These findings support the hypothesis that risk for hypertension may be associated with attenuated pain responses to nociceptive stimuli.     

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 panerns 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.     

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 test, 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 docs not interfere significantly with the processing of nociceptive information. This research was supported by Grants HL 07426 and HL 36588 from the National Heart, Lung and Blood Institute of the National Institutes of Health     

Melatonin attenuates the sympathetic nerve responses to orthostatic stress in humans

Previous studies have suggested that melatonin alters sympathetic outflow in humans. The purpose of the present study was to determine in humans the effect of melatonin on sympathetic nerve activity and arterial blood pressure during orthostatic stress. Fifty minutes after receiving a 3 mg tablet of melatonin or placebo (different days), muscle sympathetic nerve activity (MSNA), arterial blood pressure, heart rate, forearm blood flow and thoracic impedance were measured for 10 min at rest and during 5 min of lower body negative pressure (LBNP) at -10 and -40 mmHg ( n = 11). During LBNP, MSNA responses were attenuated after melatonin at both -10 and -40 mmHg ( P < 0.03). Specifically, during the placebo trial, MSNA increased by 33 ± 8 and 251 ± 70 % during -10 and -40 mmHg, respectively, but increased by only 8 ± 7 and 111 ± 35 % during -10 and -40 mmHg with melatonin, respectively. However, arterial blood pressure and forearm vascular resistance responses were unchanged by melatonin during LBNP. MSNA responses were not affected by melatonin during an isometric handgrip test (30 % maximum voluntary contraction) and a cold pressor test. Plasma melatonin concentration was measured at 25 min intervals for 125 min in six subjects. Melatonin concentration was 14 ± 11 pg ml⁻¹ before ingestion and was significantly increased at each time point (peaking at 75 min; 1830 ± 848 pg ml⁻¹). These findings indicate that in humans, a high concentration of melatonin can attenuate the reflex sympathetic increases that occur in response to orthostatic stress. These alterations appear to be mediated by melatonin-induced changes to the baroreflexes.     

The cold pressor test: effects on sympathetic nerve activity in human muscle and skin nerve fascicles

Micro-electrode multi-unit recordings of muscle nerve sympathetic activity (MSA) involved in cardiovascular homeostasis or skin nerve sympathetic activity (SSA) involved in thermoregulation were made in the right peroneal nerve of 48 healthy volunteers during performance of the cold pressor test, i.e. immersion of one hand in ice water (2 +/- 0.5 degrees C) for 1 min. Eleven subjects underwent the same procedure on a second MSA recording occasion. As a rule, immersion evoked an increase in MSA, with a gradual decrease on emersion. The response showed a wide range of variation between and within subjects; the intra-individual difference between first and second immersion on the same recording occasion was up to sevenfold, and from first to second recording up to fivefold. The increase in MSA correlated with the degree of discomfort from the ice water. In nine subjects with a large increase in MSA on ice water immersion, intracutaneous painful electrical stimulation to a level equalling the discomfort from the ice water was added, but it was not accompanied by any change in MSA. The increase in MSA was accompanied by and correlated quite well with an increase in blood pressure. Intra-arterial blood pressure recordings showed that MSA occurred at pressure levels normally associated with total inhibition of MSA, and that an inverse linear relationship between diastolic blood pressure and MSA at rest was abolished during the ice water immersion. SSA showed no consistent change with ice water immersion. It is concluded that the cold pressor test is a powerful activator of MSA, i.e. baroreceptor-governed vasoconstrictor outflow; that MSA contributes to the blood pressure elevation with this manoeuvre; that MSA operates at another blood pressure level during the manoeuvre and that the baroreflex inhibitory level consequently is changed; and that the response is not a reaction to pain only.     

Assessment of cardiac contractility during a cold pressor test by using (d<Emphasis Type="Italic">P</Emphasis>/d<Emphasis Type="Italic">t</Emphasis>)/<Emphasis Type="Italic">P</Emphasis> of carotid artery pulses

The ratio of the first derivative (dP/dt) of a carotid artery pulse to the developed pressure (P), (dP/dt)/P, is an easily measurable, noninvasive index of cardiac contractility even in moderate exercise. We examined the effects of transient cold exposure on cardiac contractility in normal reactors (n = 12) and hyperreactors (an increase in systolic or diastolic pressure >15 mm Hg; n = 6) by using this index. Eighteen healthy participants were subjected to the cold pressor test, which required them to immerse the right hand in chilly water (4°C) for 2 min. Although cold stress maximally increased mean blood pressure during the second minute, it maximally increased heart rate and cardiac contractility after 60 s of immersion in both groups of subjects. Comparing normal reactors and hyperreactors by two-way ANOVA revealed a group × time interaction for heart rate but not for cardiac contractility. These findings suggest that the increase in cardiac contractility during cold-water immersion dose not reflect the levels of heart rate and muscle sympathetic nerve activity, and that the specific responses of cardiac function to a cold pressor test in hyperreactors depends on heart rate rather than cardiac contractility.     

Autonomic responses to lateralized cold pressor and facial cooling tasks

Asymmetry in central nervous system (CNS) control of autonomic nervous system (ANS) activity, a widely debated topic, was investigated via lateralized presentation of two ANS challenges: cold pressor, which elicits primarily sympathetic activation, and facial cooling, a predominantly vagal task. Seventy‐three university students (37 female) engaged in these tasks while cardiovascular and electrodermal measures were acquired. Compared to right‐side cold pressor, left cold pressor elicited generally larger cardiac, blood pressure, and skin conductance responses, but did not evoke asymmetric changes in heart rate variability. Facial cooling elicited significant increases in vagally mediated heart rate variability, but they were also not lateralized. These findings are consistent with reports of right hemisphere dominance in sympathetic regulation, but indicate that CNS vagal control is relatively symmetric. These results are framed in terms of polyvagal theory and neurovisceral integration two influential models of CNS‐ANS integration in the service of adaptive environmental engagement.     

Existing and Training Induced Differences in Aerobic Fitness: Their Relationship to Physiological Response Patterns During Different Types of Stress

Aerobic fitness has been associated with various desirable psychological and physiological characteristies. Recently, attenuation of physiological reactivity during stressful situations was added to this list, although comparison of the stress responses of sportsmen and sedentary subjects has yielded equivocal results. The present study examined cardiovascular patterns rather than single variables, and tried to clarify these matters. Tasks were used that were known to increase blood pressure through different combinations of changes in cardiac output and vascular resistance. Autonomic nervous system dynamics underlying these response patterns were studied using preejection period as an index of β-adrenergic activity, and respiratory sinus arrhythmia as an index of vagal activity. Pre-existing differences in aerobic fitness in a sample of sedentary subjects were related to their responses during the stressful tasks and the recovery periods afterwards. This approach prevented confounding of the relationship between fitness and stress-reactivity with the psychological effects of regular exercise. Furthermore, it excluded the bias in psychological makeup that is introduced when subjects spontaneously engaged in sports are compared to non-exercising persons. To rule out a third (hereditary?) factor underlying both stress-reactivity and fitness, physiological responses before and after a seven-week training program were compared to those of subjects in a waiting list control group. Substantial individual differences in aerobic fitness were found in spite of the fact that all subjects reported low levels of habitual activity. During two active coping tasks, diastolic blood pressure reactivity and vagal withdrawal were negatively related to these pre-existing differences in fitness. No such relation was seen during a cold pressor test or during recovery from the tasks. Neither β-adrenergic cardiac reactivity nor heart rate responses were related to fitness, but the absolute heart rate during the tasks was lower in the more fit subjects. Seven weeks of training were not effective in changing either reactivity or recovery of any of the variables. The discrepancy between cross-sectional and longitudinal results in the present study suggests that training of longer duration is necessary to induce the psychological or physiological changes underlying reduced reactivity. The latter may include changes in cardiac vagal/sympathetic balance or in adrenoceptor sensitivity. Alternatively, both psychological and physiological determinants of stress-reactivity may be related to aerobic fitness at a dispositional level.     

Arterial blood pressure and general sympathetic activation in essential hypertension during stimulation

We asked whether exaggerated blood pressure (BP) reactivity in patients with essential hypertension (HT) is a sign of specific activation of the cardiovascular system or of generalized sympathetic activation. Fourteen patients with essential hypertension and 14 matched normotensive (NT) controls were subjected to tasks involving attentional demands, mental arithmetic, a cold pressor test and isometric muscular contraction. Systolic and diastolic BPs, skin and muscle blood flows, heart rate, skin conductance level and fluctuations during each task were recorded. Urine samples for determination of epinephrine and norepinephrine excretion were collected after task completion. All tasks caused BP increases in both groups. HT showed greater absolute and percentage BP reactivity than NT during isometric muscle contraction. Variables for which reactivity differences were observed were poorly correlated across tasks both in HT and NT, whereas resting values prior to each task were highly correlated in both groups. Skin conductance activity, epinephrine and norepinephrine excretion rates being examples of non-cardiovascular sympathetic nervous system (SNS) indicators did not separate HT from NT. Thus, the exaggerated pressor response in HT is not accompanied by signs of generalized SNS activation.     

Increased cardiovascular reactivity to the cold pressor test is not associated with increased reactivity to isometric handgrip exercise

Individuals who respond with a rise of 15 mmHg or more in their systolic and/or diastolic blood pressure to a cold pressor test are called blood pressure hyperreactors. We examined whether hyperreactors (n = 8) showed greater reactivity of arterial stiffness, i.e., pulse wave velocity (PWV) and augmentation index normalized to a heart rate of 75 bpm (AIx@75), to the cold pressor test than normal reactors (n = 15), and whether the former showed larger cardiovascular responses to isometric handgrip exercise. The cold pressor test was performed following Hines–Brown’s method, with subjects immersing their right hand in 4°C water for 2 min. Isometric handgrip exercise was performed at 30% maximal voluntary contraction for 2 min. Comparison between hyperreactors and normal reactors by two-way ANOVA during cold pressor test revealed a group × time interaction for PWV and AIx@75 with a greater increase in hyperreactors. During isometric handgrip exercise, no group × time interactions were detected for all measurements. Blood pressure hyperreactors show larger cardiovascular responses to the cold pressor test, but not to isometric handgrip exercise in comparison to normal blood pressure reactors.