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.

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.

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.

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.