Acute and chronic effects of a hypocaloric diet on 24-hour blood pressure, heart rate and heart-rate variability in mildly-to-moderately obese patients with essential hypertension

We examined the acute and chronic effects of a nutritionally balanced, moderately hypocaloric diet on 24-hour ambulatory blood pressure, heart rate and heart-rate variability in mildly-to-moderately obese patients with essential hypertension. We enrolled 16 obese patients with essential hypertension [age: 51-76 years, body mass index (BMI): 26-32 kg/m2]. For the initial week, a standard diet of 2,000 kcal/day was given, followed by a 3-week of a hypocaloric diet of 850 kcal/day. In the last period of the standard diet and in the first and the last periods of the hypocaloric diet, each subject's 24-hour ambulatory blood pressure, heart rate and R-R intervals of the electrocardiogram were recorded, and electrolytes and catecholamines in 24-hour urine samples were also measured. A power spectral analysis of the heart-rate variability was performed over a 24-hour period based on the autoregressive method. The subjects lost 3.7+/-0.3 kg (mean +/- s.e.m.) of body weight during the 3-week hypocaloric diet period. The 24-hour blood pressure did not differ between the last period of the standard diet and the first period of the hypocaloric diet; however, it showed a significant reduction after 3 weeks of the hypocaloric diet. The decrease in the 24-hour blood pressure during the study period was 10.5+/-1.5 mm Hg systole and 4.3+/-1.8 mm Hg diastole. In contrast, the 24-hour heart rate was significantly reduced in the first period of the hypocaloric diet, although the body weight and blood pressure did not change, and the rate was maintained even in the last period of the hypocaloric diet. The decrease in the 24-hour heart rate during the study period was 2.8+/-0.9 beats per minute. The hypocaloric diet did not change any autonomic indices obtained from a power spectral analysis of the heart-rate variability. In conclusion, different responses to a hypocaloric diet were observed between the blood pressure and the heart rate in obese hypertensive patients. The changes in power spectral parameters of the heart-rate variability were less apparent than those found with the blood pressure or the heart rate.     

Human obesity is characterized by a selective potentiation of central chemoreflex sensitivity.

The chemoreflexes are an important mechanism for regulation of both breathing and autonomic cardiovascular function. Obesity is associated with an increased risk of alveolar hypoventilation and carbon dioxide retention, suggesting that abnormalities in chemoreflex control mechanisms may be implicated. We tested the hypothesis that chemoreflex function is altered in obesity. We compared ventilatory, sympathetic, heart rate, and blood pressure responses to hypercapnia, hypoxia, and the cold pressor test in 14 obese subjects and 14 normal-weight subjects matched for age and gender. During hypercapnia, the increase in minute ventilation was significantly greater in obese subjects (7.0+/-0.3 L/min) than in normal-weight subjects (3.3+/-1.1 L/min; P=0.03). Despite higher minute ventilation during hypercapnia in obese subjects, the increase in muscle sympathetic nerve activity was similar in obese and normal-weight subjects. When the inhibitory influence of breathing during hypercapnia was eliminated by apnea, the increase in sympathetic nerve activity in obese subjects (99+/-16%) was greater than in normal-weight subjects (44+/-16%; P=0.02). The magnitude of the ventilatory and autonomic responses to hypoxia and the cold pressor test was similar in obese and normal-weight subjects. We conclude that chemoreflex responses to hypercapnia are potentiated in eucapnic obese subjects. In contrast, responses to hypoxia and to the excitatory cold pressor stimulus in obese subjects are similar to those in normal-weight subjects. Thus, obesity is characterized by selective potentiation of central chemoreflex sensitivity.     

Weight reduction lowers blood pressure independently of salt restriction.

The existence of a link between obesity and hypertension is nowadays universally accepted; however, there are still some doubts about the fact that weight reduction induces a significant long-term decrease in blood pressure. This clinical trial aimed at evaluating the effects of marked weight loss (at least 30% of excess body weight) induced by a low-energy (600 Kcal), normal sodium diet in severely obese patients, on blood pressure at rest and during sympathetic stimulation. Eight of the 20 patients initially recruited for the study were able to reach the therapeutical goal and brought their body weight from 107 +/- 6 to 91 +/- 4 kg. Their blood pressure (BP) at rest was at the same time reduced from 137/81 +/- 5/4 to 122/74 +/- 4/4 mmHg. Also, blood pressure measured during three different stimuli (cold pressor test, handgrip and mental arithmetic test) was lowered by this nonpharmacological means. These effects are related solely to weight reduction, since no change in salt intake occurred, as demonstrated by measurements of the 24-h sodium excretion test (191 +/- 13 vs 185 +/- 10 mEq/24 h). In conclusion, these results support the hypothesis that a drastic weight loss, independently of salt restriction, significantly reduces BP at rest and during stimulation of the adrenergic nervous system.     

Primary dysfunction of the afferent limb of the arterial baroreceptor reflex system in a patient with severe supine hypertension and orthostatic hypotension

A 33 year old man with a history of recurrent episodes of orthostatic dizziness since adolescence was noted to have a supine blood pressure of 200/120 mm Hg and a standing blood pressure of 90/60 mm Hg. Results of extensive laboratory studies for secondary hypertension were negative. Studies of the autonomic nervous system function revealed normal plasma catecholamines, cold pressor test and response to 4 minute 30% of maximal static handgrip contraction and an appropriate increase in heart rate on intravenous injection of atropine. In contrast, the heart rate response to phenylephrine and sodium nitroprusside infusion, carotid massage and graded neck suction with an airtight chamber was very abnormal, indicating marked dysfunction of the afferent limb of the arterial baroreceptor reflex system. Methyldopa decreased the supine hypertension and increased the standing blood pressure.     

Weight loss and weight maintenance,ambulatory blood pressure and cardiac autonomic tone in obese persons with the metabolic syndrome

BACKGROUND: Cardiac autonomic function may play a role in obesity-associated hypertension. Most studies on the effects of weight loss on blood pressure and autonomic function do not distinguish between acute or continuing weight loss and steady-state weight maintenance after weight loss. OBJECTIVES: We sought to clarify the changes in ambulatory blood pressure, heart rate and heart rate variability as assessed by spectral analysis during rapid weight loss and extended weight maintenance. PARTICIPANTS: Abdominally obese (body mass index 35.2 +/- 2.1 kg/m2, waist 114.3 +/- 9.0 cm) men and women (n = 41) with the metabolic syndrome. METHODS AND RESULTS: The 34 men and women completing the 1-year weight maintenance period lost 14.6 +/- 3.5 kg during the 9-week very-low-calorie diet and maintained a 12.5 +/- 7.5 kg weight loss to the end of the trial. Ambulatory 24-h blood pressure decreased dramatically during the diet (-9.0 +/- 8.0/-4.6 +/- 4.9 mmHg), but had risen to near baseline levels by the end of weight maintenance (-2.2 +/- 8.2 /-1.2 +/- 6.1 mmHg). Night-time heart rate decreased (-5.5 +/- 9.6 beats/min, P = 0.012), and heart rate variability total and low-frequency power measured during 5 min of controlled breathing increased by 46-56% (P = 0.003-0.09) during rapid weight loss. These changes gradually attenuated during weight maintenance, and only the change in night-time heart rate was still of borderline significance after 1 year of weight maintenance (-3.6 +/- 8.6 beats/min, P = 0.063). Heart rate variability high-frequency power tended to increase during weight loss and weight maintenance. CONCLUSION: Despite successful weight maintenance, the decrease in ambulatory blood pressure after rapid weight loss was largely transient. The increase in parasympathetic tone was more sustained, but also gradually attenuated during 1 year of weight maintenance.     

Autonomic nervous system reactivity in irritable bowel syndrome.

BACKGROUND: Autonomic dysfunction has been implicated as one of the factors involved in the pathogenesis of irritable bowel syndrome (IBS). AIM: To evaluate autonomic function in patients with IBS. METHODS: Thirty-five patients with IBS and thirty healthy controls were evaluated by standard cardiovascular reflex tests. Parasympathetic function was assessed by measuring heart rate responses to deep and slow breathing (E:I ratio), Valsalva maneuver (Valsalva ratio) and head-up tilt tests (30:15 ratio). Sympathetic adrenergic function was assessed by measuring diastolic blood pressure responses to handgrip test at 4 min and cold pressor test at 1 min and also by change in systolic blood pressure in response to head-up tilt. Autonomic functions were tested twice, keeping at least a one-week interval, to find out stability over time. Anxiety status of the subjects was assessed by evaluating responses to a questionnaire. RESULTS: Parasympathetic reactivity was significantly increased in IBS patients as compared to controls during visit 1 (E:I 1.7 [SD 0.2] vs 1.4 [0.1], p < 0.001; Valsalva ratio 2.0 [0.3] vs 1.5 [0.1], p < 0.001; 30:15 ratio 1.2 [0.1] vs 1.1 [0.01], p < 0.001). Similar results were obtained in visit 2. The diastolic blood pressure responses during handgrip and cold pressor tests were not different in comparison to controls during both the visits. However, tilting resulted in less marked rise in diastolic blood pressure (9.1 [4.1] vs 12.1 [6.8] mmHg, p < 0.01) at 0.5 min and less rise in heart rate (6.0 [2.5] vs 10.3 [6.3] per min, p < 0.01) at 1 min in IBS patients during visit 1. The anxiety score of IBS patients was significantly higher (46.2 [3.2] vs 21.6 [1.7], p < 0.001). CONCLUSION: IBS patients have increased parasympathetic reactivity and a high level of anxiety trait.     

Cardiovascular Autonomic Function in Patients with Primary Achalasia

Impaired gastrointestinal function outside the esophagus has been found in achalasic patients. Moreover, achalasia may occur in diseases in which a systemic dysautonomia is evident. These findings raise the question of whether a generalized subclinical alteration of autonomic control is also present in primary achalasia. Cardiovascular reflex tests and power spectral analysis of heart rate variability were studied in patients with primary achalasia to establish whether autonomic nervous system changes are present in districts other than the gastrointestinal tract. Nineteen normotensive patients with untreated primary achalasia and with no history of cardiac, renal, or endocrinological diseases were examined. Cardiovascular reflex tests included: the tilt test (10 min at 65°), Valsalva maneuver (40 mm Hg for 15 sec), deep breathing (6 breaths/min), and sustained handgrip (30% of maximal effort for 5 min). The parameters evaluated were systolic and diastolic blood pressure (continuously recorded), ECG, oronasal and thoracic respiration, tachogram, and plethysmogram. To evaluate the balance between parasympathetic and sympathetic functions, power spectral analysis of the heart rate variability was carried out. Each patient was paired with two sex- and age-matched healthy controls. In achalasic patients the head-up tilt test, Valsalva maneuver, deep breathing test, and sustained handgrip did not show significant differences from the control group. Low-frequency (LF) and high-frequency (HF) spectral powers and the ratio of LF to HF did not differ in both groups. This study failed to disclose impaired cardiovascular autonomic control in achalasic patients. We suggest that in primary achalasia the defect is limited to the gastrointestinal tract.     

Does the autonomic nervous system play a role in the development of insulin resistance? A study on heart rate variability in first‐degree relatives of Type 2 diabetes patients and control subjects

AIMS: To investigate dysregulation of the autonomic nervous system as a potential mechanism for early insulin resistance in the development of Type 2 diabetes. METHODS: Thirteen healthy individuals with first-degree relatives with Type 2 diabetes (R) were compared with 14 control subjects without family history of diabetes (C), matched for age, body mass index and sex. An oral glucose tolerance test and a hyperinsulinaemic euglycaemic clamp were performed. Analysis of heart rate variability during rest, controlled breathing, an orthostatic manoeuvre and a standardized physical stress (cold pressor test (CPT)), were used to evaluate the activity of the autonomic nervous system. RESULTS: Fasting blood glucose, HbA1c and serum insulin were similar in the R and C groups. The M-value, reflecting insulin sensitivity, did not differ significantly between the groups. Total spectral power and high-frequency power were lower in R during controlled breathing (P = 0.05 and P = 0.07, respectively), otherwise there were no significant differences between R and C in heart rate variability. However, low-frequency (LF)/high-frequency (HF) spectral power ratio during CPT, reflecting sympathetic/parasympathetic balance, was negatively associated with insulin sensitivity (r = -0.53, P = 0.006). When all subjects were divided into two groups by the mean M-value, the low M-value group displayed an overall higher LF/HF ratio (P = 0.04). HF power was lower in the low M-value group during controlled breathing and CPT (P = 0.01 and P = 0.03, respectively). CONCLUSION: An altered balance of the parasympathetic and sympathetic nervous activity, mainly explained by an attenuated parasympathetic activity, might contribute to the development of insulin resistance and Type 2 diabetes.     

How useful are the cold pressor test and sustained isometric handgrip exercise with radionuclide ventriculography in the evaluation of patients with coronary artery disease?

The feasibility of using the cold pressor test and the sustained isometric handgrip test as alternatives to dynamic exercise for stressing the heart was investigated. Serial changes in heart rate, blood pressure, and left ventricular performance induced by these tests were studied by radionuclide ventriculography in patients with coronary artery disease and in normal volunteers. Both tests significantly increased heart rate and blood pressure. The reproducibility of serial evaluation of ejection fraction response to cold pressor and isometric handgrip stresses was satisfactory but the sensitivity for detecting coronary artery disease was not. Both stress tests are valuable interventions for the serial evaluation of left ventricular function by radionuclide ventriculography, but they should not be used to detect coronary artery disease.     

How useful are the cold pressor test and sustained isometric handgrip exercise with radionuclide ventriculography in the evaluation of patients with coronary artery disease?

The feasibility of using the cold pressor test and the sustained isometric handgrip test as alternatives to dynamic exercise for stressing the heart was investigated. Serial changes in heart rate, blood pressure, and left ventricular performance induced by these tests were studied by radionuclide ventriculography in patients with coronary artery disease and in normal volunteers. Both tests significantly increased heart rate and blood pressure. The reproducibility of serial evaluation of ejection fraction response to cold pressor and isometric handgrip stresses was satisfactory but the sensitivity for detecting coronary artery disease was not. Both stress tests are valuable interventions for the serial evaluation of left ventricular function by radionuclide ventriculography, but they should not be used to detect coronary artery disease.     

Sympathetic-leptin relationship in obesity: effect of weight loss

Obese patients have high plasma leptin concentrations that do not induce the expected responses on weight regulation, suggesting a leptin resistance in obesity. Elevated leptin levels are also thought to be related to a high sympathetic nervous system (SNS) activity. This effect could be preserved, lowered, or even abolished in obesity. We planned to investigate the possible association in a longitudinal study. Ninety-five normotensive healthy women, aged 40.4 +/- 11.4 years and body mass index of 33.2 +/- 2.3 kg/m(2), were studied. Baseline leptin, fat mass, and heart rate variability were measured and included in a 6-month longitudinal study. Body composition was measured by dual-energy x-ray absorption. Time domain heart rate variability, QT dynamicity, and spectral components on ambulatory electrocardiographs were analyzed. Dietary advice was given by a dietitian to the patient (maximum caloric reduction of 30%), and subjects were randomized in 3 treatment groups: sibutramine 10 mg, sibutramine 20 mg, or placebo. At baseline, low frequencies (LF) and the LF-high frequencies (HF) ratio, mainly related to the SNS, were negatively correlated to leptin concentration (r = -0.30, P = .002 and r = -0.36, P < .001) and to the leptin-fat mass ratio (r = -0.28, P = .004 and r = - 0.33, P = .0007), thus explaining 38% of the LF variance and 33% of the LF/HF variance. Diastolic blood pressure was also negatively correlated to leptin concentrations (-0.20, P = .04) and to the leptin-fat mass ratio (-0.22, P = .022). In contrast, no consistent correlations between leptin and the time domain components related to vagal activity were observed. At 6 months, after completion of the weight loss program, LF significantly decreased (-7.7% +/- 7.9%, P < .001), whereas HF was higher than the initial value (+20% +/- 5.2%). The leptin-fat mass ratio remained negatively correlated to the LF (r = -0.34, P = .030) and to LF/HF (r = -0.35, P = .021) values, explaining 21% of the LF variation. None of the pairwise comparisons between the 2 sibutramine groups and the placebo group were statistically significant for heart rate variability. High leptin concentration is associated with low indexes of cardiac SNS activity and with a lower diastolic blood pressure in normotensive obese women. Our results imply therefore that the relationship between leptin and the autonomic nervous system is disturbed in normotensive obese subjects.     

Changes in short-term variability of blood pressure and heart rate during the development of obesity-associated hypertension in high-fat fed dogs.

OBJECTIVE: To investigate the nature and time course of autonomic nervous system changes elicited by a 21-week ad libitum high-fat diet (HFD) in dogs. RESULTS: The HFD increased body weight (+22.0+/-2.8% at week 21) with an abdominal circumference gain significantly more elevated than the thoracic one. The increases in insulin and free fatty acid plasma levels were correlated with body weight changes. Systolic and diastolic blood pressures and heart rate significantly increased (+23+/-6, +28+/-5 and 19+/-9% respectively). Arterial hypertension was characterized by an increase in cardiac output (+22.3+/-7.7%), in left ventricular mass (+18.1+/-5.0% at week 21) and a decrease in spontaneous baroreflex efficiency (-55+/-6%). The time course of autonomic changes (using spectral analysis of systolic blood pressure and heart rate) showed the existence of time-dependent modifications, which were linked with food intake. The initial rise in arterial blood pressure during body weight increment (observed between the 1st and 8th week of HFD) was associated with a transient increase in the low frequency band of systolic blood pressure variability and noradrenaline plasma levels associated with a long-lasting decrease in the high frequency band of heart rate variability. Early changes in short-term variability were significantly correlated with free fatty acid plasma levels. In contrast, the steady-state of obesity-related hypertension was associated with a decreased high frequency band of heart rate variability, without significant changes in noradrenaline plasma levels. CONCLUSIONS: This study shows that the HFD induces abdominal obesity, hyperinsulinaemia and arterial hypertension, with a left ventricular hypertrophy associated with a biphasic changes in autonomic activity: an early and long-lasting decrease in parasympathetic nervous system activity and an early but transient increase in sympathetic activity. The present data suggest that autonomic nervous system changes are dependent on the time course of obesity development.     

Left ventricular mass predicted by a single reading of ambulatory blood pressure in essential hypertension.

The spectral power of heart rate variability has been shown to be negatively correlated with left ventricular mass (LVM), suggesting the contribution of left ventricular hypertrophy to autonomic dysfunction in essential hypertension. However, a simultaneous assessment of autonomic function and ambulatory blood pressure in relation to LVM has not been carried out. The objective of the present study was to elucidate the synergistic effects of ambulatory blood pressure and autonomic nerve activity on the heart. We enrolled 25 ambulant patients with untreated essential hypertension (9 men and 16 women; mean age 50.6 +/- 2.0 years). The ambulatory blood pressure and heart rate variability were simultaneously monitored every 30 min for 24 h. The spectral power of high-frequency (HF: 0.15 to 0.4 Hz) and low-frequency (LF: 0.05 to 0.15 Hz) bands were measured, and the ratio of LF to HF (LF/HF) was calculated. LF/HF and HF were used as indexes of sympathetic and parasympathetic activities, respectively. LVM was determined by echocardiography. Both the average daytime and nighttime systolic ambulatory blood pressures significantly correlated with the LVM index (r= 0.644, p< 0.001; and r= 0.428, p< 0.05; respectively), although there was no such correlation with the clinic blood pressures. In contrast, a single reading of ambulatory systolic blood pressure measured when LF/HF reached a maximum value was significantly correlated with the LVM index independently of age and sex (partial r= 0.484, p< 0.05). These results suggest that the ambulatory systolic blood pressure during increases in the activity of the sympathetic nervous system is able to infer LVM in essential hypertension.     

Autonomic function in hypertensive patients with neurovascular compression of the ventrolateral medulla oblongata.

OBJECTIVE: To study whether abnormalities of autonomic function exist in patients with essential hypertension and neurovascular compression (NVC) of the medulla oblongata. SUBJECTS AND METHODS: We studied 25 untreated patients with essential hypertension (13 men and 12 women, 27-74 years old). High-resolution magnetic resonance imaging and magnetic resonance angiography were used to detect NVC. Twenty-four-hour ambulatory monitoring of blood pressure and electrocardiogram were performed, and the power spectrum of heart rate variability was analyzed. On a separate day, various autonomic activity tests, including mental stress, hand grip, cold pressor, and Valsalva maneuver were performed. Baroreflex sensitivity was calculated from changes of blood pressure and R-R interval during phenylephrine infusion. A clonidine suppression test was also performed, with measurement of plasma catecholamine levels. RESULTS: Fourteen of 25 patients (56%) had NVC (C group), and 11 patients did not have NVC (NC group). There were no significant differences in age, sex, family history, or duration of hypertension between the C and NC groups. Average 24-h systolic blood pressure was similar between the two groups, although 24-h diastolic blood pressure was higher in the C group than the NC group. Daytime, night-time, and 24-h heart rate was significantly higher in the C group than in the NC group. Night-time low frequency/high frequency ratio was slightly higher in the C group. Plasma norepinephrine levels were significantly higher (467 +/- 217 versus 299 +/- 122 pg/ml), and baroflex sensitivity was slightly lower in the C group than in the NC group. Responses of blood pressure and heart rate to mental stress, cold pressor, hand grip, Valsalva maneuver, phenylephrine infusion, and clonidine tests were not significantly different between the two groups. CONCLUSIONS: NVC of the medulla oblongata was frequently found in patients with essential hypertension. Patients with NVC appeared to have enhanced sympathetic nervous activity compared with those without the compression.     

Effect of diet and weight loss on whole blood filterability and plasma fibrinogen values in hypertensive obese postmenopausal women

Summary The authors evaluated whole blood filterability (V_B) in 29 post-menopausal obese women with (n=14) or without (n=15) hypertension, and in 22 age matched women with normal body weight. After 3 months of a low-calorie (18 kcal/kg IBW) and moderately low-salt (max 6 g NaCl/day) diet, the obese subjects were restudied. In all women plasma fibrinogen values and various indices of metabolic status were evaluated before and after the diet and correlated to V_B values. V_B values and plasma fibrinogen concentrations were similar in normal controls and in women with simple obesity, whereas they were, respectively, significantly lower and higher in obese subjects with hypertension. Three months of diet significantly improved whole blood filterability and decreased fibrinogen levels in these patients. Before the diet a significant negative correlation was found between V_B and plasma fibrinogen values in hypertensive obese patients. Metabolic parameters did not change in the different groups before and after the diet and did not correlate with V_B values. The present sudy indicates that low-calorie, low-salt diet decreases plasma fibrinogen levels and improves whole blood filterability in elderly obese women with hypertension.     

Race and gender influence hemodynamic responses to psychological and physical stimuli

To evaluate factors influencing hemodynamic responses to psychological and physical stress, 117 normotensive college students were studied. The standardized tests included arithmetic, Stroop word-color, mirror draw, isometric handgrip and cold pressor challenges. The responses of blood pressure and pulse during the tests were compared to the baseline measurements. All the challenges produced a significant (P less than 0.01) increase in systolic and diastolic pressure and pulse rate, with the greatest increase being seen with the isometric handgrip test. The increases in the systolic and diastolic pressure and the heart rate to the psychological stressors were highly correlated (P less than 0.001). The responses to the physical stressors were correlated for the diastolic pressure (P less than 0.01) and the heart rate (P less than 0.001), but not for the systolic pressure. The responses of the systolic and diastolic pressure, but not the heart rate, to the isometric handgrip correlated with the responses to the psychological stressors. The responses of the diastolic pressure and the heart rate, but not the systolic pressure, to the cold pressor stimulus correlated with the responses to the psychological stressors. The gender influenced the response to all the stressors with males having a greater (P less than 0.05) blood pressure response and a lesser (P less than 0.001) heart rate response than females. Black subjects had greater blood pressure responses to the cold pressor test and a greater diastolic pressure response to the handgrip, but there were no observed racial differences in the responses to the psychological stressors.(ABSTRACT TRUNCATED AT 250 WORDS)     

Blood pressure reactivity in patients with neurocirculatory asthenia

The hemodynamic reactions of 30 young men with neurocirculatory asthenia (NCA) were compared to those of 30 healthy controls in isometric handgrip test, orthostatic test, and cold pressor test in order to study the regulation of the central circulation of NCA patients. The measurements were made using sphygmomanometry, ECG, and impedance cardiography. In the isometric handgrip test the heart rate and the diastolic and mean blood pressure increased slightly more (P less than 0.05) in the NCA group than in the controls. In the NCA group the blood pressure rise was, on average, due to an increase in the peripheral vascular resistance, while in the control group it was caused by an elevation in the cardiac output. In the orthostatic and cold pressor tests the hemodynamic alterations were quite similar in the two groups. It is concluded that the NCA patients have in the orthostatic and cold pressor tests a normal ability to elevate the blood pressure by increasing the peripheral vascular resistance. The lack of rise in the cardiac output during the isometric handgrip test in the NCA group is an abnormal reaction, the reason of which remains to be studied.     

Comparative plasma catecholamine and hemodynamic responses to handgrip, cold pressor and supine bicycle exercise testing in normal subjects

Serial hemodynamic and plasma catecholamine responses were compared among 10 healthy men (27 +/- 3 years) (+/- 1 standard deviation) during symptom-limited handgrip (33% maximal voluntary contraction for 4.4 +/- 1.8 minutes), cold pressor testing (6 minutes) and symptom-limited supine bicycle exercise (22 +/- 5 minutes). Plasma catecholamine concentrations were measured by radioenzymatic assays: ejection fraction and changes in cardiac volumes were assessed by equilibrium radionuclide angiography. During maximal supine exercise, plasma norepinephrine and epinephrine concentrations increased three to six times more than during either symptom-limited handgrip or cold pressor testing. Additionally, increases in heart rate, systolic blood pressure, rate-pressure product, stroke volume, ejection fraction and cardiac output were significantly greater during bicycle exercise than during the other two tests. A decrease in ejection fraction of 0.05 units or more was common in young normal subjects during the first 2 minutes of cold pressor testing (6 of 10 subjects) or at symptom-limited handgrip (3 of 10), but never occurred during maximal supine bicycle exercise. The magnitude of hemodynamic changes with maximal supine bicycle exercise was greater, more consistent and associated with much higher sympathetic nervous system activation, making this a potentially more useful diagnostic stress than either handgrip exercise or cold pressor testing.     

Comparison of cardiovascular autonomic responses in elderly and young males during head-out water immersion

OBJECTIVES: To investigate the cardiovascular autonomic responses to head-out water immersion in thermoneutral water. The effects of immersion levels (neck, chest, navel) and breathing frequencies (4, 6, 10, 15 times/min) were compared with in ambient air and spontaneous breathing as a control. METHODS: Spectral analysis of heart rate variability was recorded in 11 young (mean age 20 +/- 1 years) and 11 elderly (mean age 68 +/- 6 years) healthy male subjects during water immersion. Modeling was employed to estimate the time course of low-frequency (LF) and high-frequency (HF) power and the ratio of LF to HF power of heart rate variability. RESULTS: In the young group, stroke volume and cardiac output during navel level water immersion manifested a much greater increase than during chest and neck level water immersion. Systolic blood pressure and total peripheral resistance decreased significantly in response to water immersion. The elderly group, however, showed lesser attenuation of stroke volume and cardiac output. Ectopic arrhythmias occurred in only the elderly. The elderly group showed significantly lower and higher amplitudes of HF and LF/HF components of heart rate variability due to water immersion and breathing frequency changes. CONCLUSIONS: These findings suggest differential changes in cardiovascular autonomic responses between the young and elderly groups. These changes in integrative cardiovascular autonomic responses may account for the increased risk of ectopic arrhythmias in elderly people during water immersion. Water immersion model could be utilized to know circulatory regulation during bathing.     

Autonomic imbalance in the recovery period after myocardial infarction

The aim of the study was to evaluate the responses to autonomicfunction tests during the healing period of myocardial infarction(AMI). In 24 patients, at 2 and 6 weeks after the acute event,Valsalva manoeuvre, deep breathing at 6 breaths per min, isometrichandgrip and cold pressor tests were performed. Responses ofarterial blood pressure (BP) and heart rate (HR) were measured.At 2 weeks post AMI a significant decrease in parasympathetictone was noted: HR reduction during deep breathing: 18.5±5.7beats. min^–1 for controls vs 9.7±2.6 beats. min^–1for AMI, P<0.001. Systolic BP response to handgrip and coldpressortest was only slightly (non signflcantly) increased: 30.6±12.9mmHg (controls) vs 40.0±20.5mmHg (AMI) for the handgriptest and 13.8±8.1 mmHg vs 18.0± 10.1 mmHg respectivelyfor the cold pressor test. At 6 weeks post AMI, the responseto the deep breathing test (15.9±5.6 beats. min^–1)nolonger significantly differed from that in controls. In contrast,the sympathetic stressor tests showed a signficant increasein systolic BP response: 63.8±21.9mmHg, P<0.001 and26.1±14.9 mmHg, P<0.05, respectively for the handgripand cold pressor tests. It appeared that infarct localizationhad no effect on autonomic function tests. There is evidence of autonomic imbalance both at 2 and at 6weeks after AMI, with a rapid but transient decrease in vagalactivity and enhancement of orthosympathetic nervous tone; thiswas markedly more pronounced at 6 weeks post AMI despite treatmentwith beta-blocking agents in all patients.