The association between sympatho-vagal balance and central blood pressures.

PURPOSE: High central blood pressure is more predictive of cardiovascular disease (CVD) versus high peripheral blood pressure. Measures of central pressures (CPs) include, central systolic blood pressure (CSBP) and central diastolic blood pressure. Measures of central pressures augmentation (CPsA) include augmentation pressure (AP) and the augmentation index @ 75 beats·min-1 (AIx@75). Increased sympathetic tone (ST) is also associated with CVD. The low to high frequency ratio (LF/HF) is often used to determine sympatho-vagal balance. Given the association between ST, CPs, CPsA and CVD there is a need to understand the association between these predictors of CVD. The aims of this study were to examine the association between the LF/HF ratio, CPs, and CPsA in men and women collectively and based on gender. METHODS: We measured the LF/HF ratio, CSBP, AP, and AIx@75 in 102 participants (41F/61M). The LF/HF ratio was determined via power spectral density analysis. CSBP, AP, and AIx@75 were determined via applanation tonometry. RESULTS: The LF/HF ratio was inversely associated with AP (r = -0.26) and AIx @75 (r = -0.29) in the combined group of men and women. The LF/HF ratio was inversely associated with CSBP (r = -0.27), AP (r = -0.28), and AIx@75 (r = -0.32) in men, but not in women. CONCLUSION: There is an inverse association between the LF/HF ratio, AP, and AIx@75 in men and women combined. The association between the LF/HF ratio, CSBP, AP, and AIx@75, differs based on gender.

Blood pressure variability responses to tilt are buffered by cardiac autonomic control.

Variability in blood pressure (BPV) is influenced by vascular sympathetic drive as well as autonomic control of the heart. Evidence suggests that elimination of cardiac autonomic control, as measured by heart period variability (HPV), produces a reduction in BPV at rest but an increase in BPV during challenge. We recently showed that the BPV response to psychological challenge, which principally produces cardiac parasympathetic withdrawal, was inversely related to the subject's level of cardiac control. In the current study we examined the BPV response to orthostatic tilt, a sympathetic stressor. Subjects were 22 healthy men and women who differed in cardiac control due in part to differences in aerobic capacity. HPV and BPV were measured noninvasively on a beat-to-beat basis. Tilt produced significant increases in heart rate and diastolic blood pressure and a significant decrease in high frequency HPV. As predicted, changes in BPV in response to tilt were inversely related to resting HPV. Results are interpreted in terms of a model of cardiovascular control which holds that BPV originates from feedforward effects of central control of the heart, feedback effects mediated through the baroreflexes, and direct sympathetic vascular effects.

Cardiac autonomic control is inversely related to blood pressure variability responses to psychological challenge.

Blood pressure exhibits variability (BPV) at low (0.02- to 0.07-Hz), mid (0.07- to 0.15-Hz)-, and high (0.15- to 0.50-Hz) frequencies. Evidence suggests that BPV responses to challenge are inversely related to cardiac autonomic control. We tested this hypothesis by examining the BPV responses to psychological stressors in 22 normal subjects who differed in cardiac control, operationalized as resting heart period variability (HPV). HPV and BPV were measured noninvasively or a beat-to-beat basis. The stressors produced a significant increase in heart rate and a small but significant increase in diastolic blood pressure. As predicted, the changes in BPV in response to the stressors were inversely related to resting HPV. The results are interpreted in terms of a model of cardiovascular control that holds that BPV originates from feedforward effects of central control of the heart, feedback effects mediated through the baroreflexes, and direct sympathetic vascular effects.

QTc interval (cardiac repolarization): lengthening after meals.

Weight reduction, either by dietary or surgical means, is associated with prolongation of the heart rate corrected QT interval (QTc = QT/R-R0.5) and, on occasion, sudden death. Screening subjects with obesity before weight loss for prolonged QTc intervals is an accepted practice, although at present, there are no guidelines for whether subjects should be fasting before electrocardiogram (EKG) evaluation. The aim of this study was to test the hypothesis that EKG QTc interval duration is independent of meal ingestion. The hypothesis was tested in 11 healthy subjects who ingested a 500-kcal formula meal. A small decrease in absolute QT interval and a steady decline in R-R interval were observed for up to 60 minutes after formula ingestion. The QTc interval increased above baseline at 15 minutes (p < 0.007) after meal, a change that persisted for the 1-hour postmeal observation period. Spectral analysis of EKG R-R intervals (low-/high-frequency amplitude ratio) indicated a change in cardiac autonomic flow after meal ingestion. The QTc interval did not lengthen and R-R low-/high-frequency amplitude ratio remained unchanged in eight subjects evaluated in a similar manner but in whom isovolumic amounts of water replaced the meal. These observations suggest that (1) cardiac repolarization changes with fasting and feeding, (2) the QTc interval is influenced by meal intake, and (3) the autonomic nervous system may play a role in meal-related QTc changes. These findings have implications for the evaluation of patients with obesity before starting and during weight loss treatment.

Effect of provocative maneuvers on heart rate variability in subjects with quadriplegia.

This study investigated heart rate variability (HRV) in individuals with quadriplegia who have disruption of autonomic control of the heart. Seven male subjects with neurological complete quadriplegia and seven with incomplete quadriplegia were studied at rest and during provocation. HRV was measured by power spectral analysis using a fast Fourier transform. Two spectral components were generated: 1) the high-frequency (HF) peak, a reflection of parasympathetic activity, and 2) the low-frequency (LF) peak, primarily sympathetic activity with some parasympathetic input. Results of the provocative maneuvers were grouped into one composite variable. Significant differences in the LF spectral component were found between the groups with complete and incomplete lesions in the supine position and after provocation (LF supine: P = 0.01; LF provocation: P = 0.002). After provocation, significant differences were demonstrated in the HF spectral component between these groups (P = 0.005). In contrast to previous findings, a LF component in subjects with complete quadriplegia was observed; this LF component decreased after provocation, suggesting the parasympathetic component withdrew during stressful maneuvers. There also appeared to be general downregulation of parasympathetic activity to the heart in subjects with complete quadriplegia. The presence of an increased LF spectral component during provocation in those with incomplete lesions implies sympathetic stimulation of the heart and may be used as a marker of sympathetic activity in individuals with quadriplegia.

The age-related advancement of arterial disease measured by Doppler ultrasound diastolic flow analysis.

OBJECTIVE: To quantify by A-mode Doppler sonography the age-related progression of arterial disease so that age dependent normal values may be established for the screening Doppler peripheral arterial exam. Arterial distensibility was assessed by A-mode Doppler diastolic flow analysis as a measure of atherogenesis. These values will increase the sensitivity and decrease the incidence of false-positive results when the Doppler exam is utilized to differentially diagnosis vascular and sciatic neurogenic claudication. The relationship between age and results from the standard ankle/arm index ultrasound pneumatic cuff examination was also analyzed. DESIGN: A two by three analysis of variance with orthogonal Helmert contrast codes and simple linear regression analysis was utilized for this cross-sectionally designed investigation. The dependent measures of diastolic flow analysis and ankle/arm pressure index were obtained within three nested successively increasing age groups. SETTING: Chiropractic office. SUBJECTS: Studied were a total of 90 sedentary nonsmoking subjects, aged 23-79 yr, all of whom had normally accepted levels of serum glucose, cholesterol and blood pressure. Subjects were screened for evidence of aortic coarctation, myocardial infarction, tachyarrhythmia, aortic valve stenosis, mitral prolapse, hypertension, hypercholesterolemia, diabetes and peripheral occlusive arterial disease. Anthropometric measurements and percent body fat were obtained. A predictive oxygen consumption bike ergometer test was performed to obtain aerobic capacity. The commonly utilized standard ankle/arm index ultrasound pneumatic cuff examination and arterial diastolic flow analysis were performed with A-mode Doppler ultrasound on all subjects. RESULTS: These results demonstrate that a significant inverse linear relationship exists between aging and arterial compliance (p < .0001) in our population. Diastolic flow analysis had a greater sensitivity to arterial disease than the standard ankle/arm index ultrasound pneumatic cuff procedure. CONCLUSION: When utilizing A-mode Doppler ultrasound diastolic flow analysis as an indicator of early peripheral atherosclerotic arterial disease, increased sensitivity may be obtained when the age-related elevation in atherogenesis is taken into account.

Doppler ultrasound diastolic flow analysis for the early identification of peripheral arterial disease.

OBJECTIVE: The viscoelastic mechanical compliance properties of the human arterial system were examined in 100 subjects with A-mode Doppler ultrasound diastolic flow analysis. This technique of diastolic flow analysis is utilized to identify early atherogenic peripheral arterial disease. The sensitivity of the commonly utilized standard traditional ultrasound pressure-grade pneumatic cuff examination will be increased when accompanied by the diastolic flow analysis technique. SETTING: Diastolic flow analysis will aid in the early identification of lower extremity vascular claudication when lumbar spinal canal stenosis and elevated cardiovascular risk factors are present. This examination may be performed in the office setting with standard A-mode Doppler ultrasound equipment along with the usual pneumatic cuff procedure. The standard ultrasound cuff examinations are based on pressure gradients to identify lower extremity arterial disease. The low level of sensitivity of this test requires arterial obstruction of at least 50% to be present before positive identification is possible. Pathological alterations of the arterial wall occur during the early stages of atherosclerotic disease, are reflected by reduced wall distensibility and may be quantified by Doppler ultrasound. SUBJECTS: Studied were a total of 100 subjects, 50 with arterial disease risk factors and 50 normal controls. All subjects were screened for aortic coarctation, myocardial infarction, tachyarrhythmia, aortic value stenosis and mitral prolapse. The risk group subjects were all smokers and had a mixed distribution of hypertension, hypercholesterolemia and hyperglycemia. The commonly utilized standard traditional ultrasound pneumatic cuff examination was negative in all subjects. Anthropometric measurements and percent body fat were also obtained. Arterial diastolic antegrade flow analysis was performed with Doppler ultrasound on each subject. RESULTS: This study demonstrated that the elevated vascular risk factor group had a mean arterial distensibility measurement of 4.4 +/- 5.0%, and the control group displayed a mean measurement of 20.0 +/- 6.0%. The 50 elevated risk factor subjects showed approximately 5 times greater arterial stiffness and were identified with significance at an F test level of (p less than .001). CONCLUSION: This arterial compliance evaluation procedure is shown to be a reliable sensitive indicator of early atherosclerotic disease prior to the development of obstructive arterial lesions.

Cardiovascular effects of H2-receptor antagonists.

The type II histamine receptor antagonists, cimetidine and ranitidine, widely used in treatment of peptic ulcer disease have been reported to cause bradycardia. To evaluate the cardiovascular effects of H2 antagonists nineteen healthy volunteers were entered into a double-blind crossover comparison of cimetidine 300 mg qid, ranitidine 150 mg bid, and placebo. Subjects ingested study medicine for 7 days prior to being tested by the Bruce Exercise Test. Heart rate, blood pressure, oxygen consumption, expiratory volume, and fractional expiration of CO2 and O2 were measured at rest, exercise and recovery. A plasma sample for determination of cimetidine and ranitidine levels were obtained prior to the exercise period. Multivariate analysis and paired t test revealed no significant differences for the cardiovascular or pulmonary variables. However, in 5 subjects, the heart rate at 25% maximum VO2 was depressed 8% (P less than or equal to 0.03). This effect in a small percentage of the population suggests that further studies are needed to determine if subpopulations are affected.

Hyperlipemic response of young trained and untrained men after a high fat meal.

To test the hypothesis that endurance training is associated with a decreased lipemia after a high fat meal, 16 young men [22 to 34 years old, nine of whom were trained (T) and seven of whom were untrained (UT)] were recruited. T ran greater than 30 or biked greater than 100 miles a week, while UT had been sedentary for at least the preceding 3 months. Daily caloric intake and daily caloric expenditure during exercise were 35% and 704% greater, respectively, in T than in UT. VO2max was 31% greater, while percent body fat was 36% lower in T than in UT. Dietary composition and body height and weight were similar. After a fasting blood sample was taken, the men ate a high fat meal (approximately 56% of total calories as fat in 1100 kcal adjusted to body weight), and additional blood samples were taken hourly for 8 hours. Fasting lipids were similar. Postprandial peak triglyceride (TGmax), percent TG increase (%TGI), and total lipemic response (TLR, the area under the lipemia curve in excess of fasting TG) were 42%, 54%, and 75% greater, respectively, in UT vs. T. Stepwise regression analysis showed that the same three-variable model (training status, fasting TG, and VO2max) described the variation in TGmax (R2 = 0.97), %TGI (R2 = 0.75), and TLR (R2 = 0.92). Furthermore, this same analysis showed that after adjustment for fasting TG and VO2max, the UT group had a significantly greater postprandial lipemia whether expressed as TGmax (p less than 0.0001), %TGI (p = 0.0002), or TLR (p = 0.0002).(ABSTRACT TRUNCATED AT 250 WORDS)

Sympathomimetics and exercise enhancement: all in the mind?

During the 1972 Olympic Games, a 16 year old American athlete was compelled to return a gold medal and was disqualified from further participation. Rick Demont had used a sympathomimetic drug (ephedrine) prior to competition for treatment of his asthma as prescribed by his physician. The present research was carried out to investigate whether the administration of a sympathomimetic drug enhances maximal performance in the normal healthy individual in terms of physiological and psychological processes? Ten subjects participated in a double-blind, cross-over, counterbalanced incremental cycle ergometer test on two different occasions, once after ingesting placebo, once after ingesting ephedrine. Repeated measures ANOVA's revealed no significant differences in any of the cardiopulmonary (VE, VO2, VCO2, RQ and AT), cardiovascular (HR, BP, O2 Pulse, RPP) and psychophysiological (RPE) variables between treatments. Findings in the current investigation suggest that no advantage is obtained with the use of sympathomimetic drugs to augment one's maximal aerobic capacity.

Effect of diet upon ventilation and effort perception during a physical stressor.

The present research explored the effects of a high and low carbohydrate diet on ratings of perceived exertion (RPE) during a 10 minute bicycle ergometer test at high physical work capacity (70% of maximum aerobic capacity). Twelve female student volunteers participated and were randomly assigned the order of diet treatments in which they served as their own control and/or experimental group. Following each dietary regimen, subjects were instructed to pedal the bicycle ergometer for ten minutes at an intensity of 70% of their maximum capability. Throughout the cycling protocol, RPE scores were recorded at 2, 4, 6, 8, and 10 minutes; in addition expiratory gases were collected and analyzed by a computerized indirect calorimetry system. Results in the current investigation indicated that an increased carbohydrate intake resulted in an "ergogenic" or "work-producing" effect by attenuating the metabolic acidosis, possibly diminishing the sensations of the central cardiopulmonary effort, further attenuating the psychophysiological perceptions of effort. Conversely, ingestion of a low carbohydrate diet resulted in accentuation of the ventilatory drive eliciting higher signals of exertion during dynamic exercise.

Maximal work capacity in prepubescent obese and nonobese females.

Measurements of cardiorespiratory function during an incremental treadmill test were compared in 15 obese (OB) prepubescent girls, 7 to 12 years old, and in 15 age-matched, nonobese (NOB) controls. Open circuit calorimetry was used for data collection during the progressive work test. Maximal oxygen consumption indexed for weight was significantly lower in the obese group of girls (23.0 +/- 3.9 ml/kg/min) than in the nonobese controls (36.7 +/- 0.9 ml/kg/min). In addition, exercise tolerance was longer in the nonobese group, albeit not statistically significant. In conclusion, diminished cardiopulmonary performance and attenuated exercise tolerance in prepubescent obese females in the current investigation seemed to be influenced by excess body weight.

Adaptation to maximal effort: genetics vs. environment. A case history.

An individual's functional ability in physiological responsiveness is thought to be an interaction between his heredity and his environment. This hypothesis was tested to determine if different extragenetic influences would alter functional adaptability in a set of MZ triplets. After a 3-month aerobic physical fitness training program varying only in frequency measured values for the triplets' maximum oxygen consumption (MaxVo2) were 59.1, 44.5, and 57.8 ml/min/kg, as compared to pretreatment values of 45.2, 45.1, and 49.1 ml/min/kg respectively. These results clearly indicate intrapair differences in functional adaptability, stemming from difference in the training frequency program. The split-triplet design of this study indicates that environmental factors contribute substantially to the intrapair variance found among MZ siblings. Data extrapolation suggests that environmental stimulation of sufficient magnitude is likely to alter the functional adaptability in the individual set by his genotype.

Personality and self-motivation during biochemical fatigue.

The present study was conducted to determine whether females exhibiting the Type A behavior pattern would exert greater effort and work to higher levels of physiological fatigue in a self-motivated ergometer test. Twenty female subjects, half of them Type A and the other half Type B, were administered an incremental ergometer test to determine their peak oxygen consumption value. On the first experimental session no experimenter encouragement was given to the subjects. Consequently the test measured physical motivation levels. During a second laboratory session, each subject was continuously encouraged by the experimenter to maintain exercising until she was truly incapable of further work. The highest rate of oxygen extraction during this latter session was considered the subject's maximum oxygen consumption (i.e., VO2 max). Type A and B subjects were compared in the nonmotivated testing session (experimental session 1) to their "true" individual capacities (maximum oxygen consumption demonstrated in experimental session 2). ANOVAs indicated no significant differences in self-initiated competitive behavior during a physical stressor.