Ronald E. DeMeersman

The Effect of Aerobic Training and Cardiac Autonomic Regulation in Young Adults

OBJECTIVES We tested the effect of aerobic exercise on autonomic regulation of the heart in healthy young adults. METHODS Healthy, sedentary young adults (n = 149; age = 30.4 +/- 7.53 years) were randomized to receive 12 weeks of either aerobic conditioning or strength training. Primary outcomes were heart rate and RR interval variability (RRV) measured before and after training and after 4 weeks of sedentary deconditioning. RRV, a noninvasive index of cardiac autonomic regulation, reflects variability in the intervals between consecutive R waves of the electrocardiogram. RESULTS Aerobic conditioning but not strength training led to a significant increase in aerobic capacity (3.11 mL/kg/min), a decrease in heart rate (-3.49 beats per minute), and an increase in high-frequency RRV (0.25 natural log msec2), each of which returned to pretraining levels after deconditioning. Significant 3-way interactions, however, revealed autonomic effects only in men. CONCLUSIONS In sedentary, healthy young adults, aerobic conditioning but not strength training enhances autonomic control of the heart, but post hoc analyses suggested that gender plays a significant role in this exercise-related cardioprotection.

Association of body fat percentage and heart rate variability measures of sympathovagal balance

AIMS We tested the hypothesis that body fat percentage determines cardiac sympathovagal balance in healthy subjects. MAIN METHODS Heart rate variability (HRV) measurements were made of the standard deviation of the normal-normal RR intervals (SDNN) and the low frequency/high frequency (LF/HF) ratio, from time domain and fast Fourier transform spectral analysis of electrocardiogram RR intervals during trials of uncontrolled and controlled (paced) breathing at 0.2Hz. Body fat percentage was measured by dual energy x-ray absorptiometric (DEXA) scanning. Significance of differences between uncontrolled and controlled (paced) breathing was determined by analysis of variance and correlations between body fat percentage and HRV measurements by Pearsons coefficient at P<0.05. KEY FINDINGS Percent body fat was negatively correlated with LF/HF during the uncontrolled breathing (r=-0.56, two-tailed P<0.05, one-tailed P<0.01) but not during the paced breathing trial (r=-0.34, (P>0.1). SIGNIFICANCE We conclude that sympathetic activity produced by paced breathing at 0.2Hz can obscure the relationship between body fat percentage and sympathovagal balance and that high body fat percentage may be associated with low sympathetic modulation of the heart rate in healthy adolescent/young adult males.

Arterial Stiffness in Persons With Paraplegia

Abstract Background: Arterial stiffness recently has been identified as an independent risk factor for cardiovascular disease. An accurate andnoninvasive estimate of arterial stiffness can be made through close examination of the pulse wave contour, and is expressed as theaugmentation index (Al). lncreased stiffness is associated with increased systolic blood pressure (SBP) , pulse pressure, and reducedbaroreceptor sensitivity. The purpose of this study was to compare the common carotid Al in participants with paraplegia vsable-bodied controls as weil as compare group differences for blood pressure while supine and in response to gravitational stress. Participants: Study participants were 19 healthy individuals with paraplegia (below T6) and 9 able-bodied controls matched forage, height, and weight. Methods: An electronic tilt table was used for testing responses to gravitational stress at 4 angles (− 10°, 10°, 35°, and 75°). Alwas assessed at each angle of tilt using an externally applied high-fidelity strain-gauge transducer placed over the right commoncarotid artery. Results: Al was augmented in the group with paraplegia compared with the able-bodied group (8.0 ± 3.9 vs 6.7 ± 2.8 ,respectively; P < 0.05). Supine blood pressure and the SBP response to tilt did not differ between the groups, and there were notilt-angle effects on SBP. Conclusion: In normotensive persons with paraplegia, Al was increased significantly compared with matched able-bodied controls,which may suggest the premature development of arterial disease in this population.

Impact of aerobic training on cardiovascular reactivity to and recovery from challenge.

Objective: To test the hypothesis that aerobic, but not strength, training would lead to attenuated reactivity to and more rapid recovery from cognitive and orthostatic challenge and that deconditioning would reverse this effect. Methods: We conducted a randomized controlled trial contrasting the effects of aerobic versus strength training on heart rate, four indices of RR interval variability, and blood pressure reactivity to and recovery from psychological and orthostatic challenge in 149 healthy, young, sedentary adults. Subjects were randomized to 12-week aerobic or strength training programs and studied before and after training and again after 4 weeks of sedentary deconditioning. The data were analyzed by performing a Group (aerobic versus strength) by Session (study entry, post training, and deconditioning), by Period (baseline, speech, Stroop, math, tilt) three-way analysis of variance with prespecified contrasts of the effect of group assignment on reactivity and recovery. Results: Aerobic capacity increased in response to conditioning and decreased after deconditioning in the aerobic, but not the strength, training group. However, the two groups did not differ on heart rate, RR interval variability, or blood pressure reactivity to or recovery from laboratory challenge. Conclusions: These findings, from the largest randomized controlled trial to address this matter to date, raise doubts about attenuation of reactivity or enhancement of recovery as a putative mechanism underlying the cardioprotective effects of aerobic exercise. Trial Registration: ClinicalTrials.gov Identifier: NCT00365196. RCT = randomized controlled trial; RRV = RR interval variability; BP = blood pressure; SBP = systolic blood pressure; DBP = diastolic blood pressure; CAD = coronary artery disease; HR = heart rate; ECG = electrocardiogram; HF = high frequency; AUC = area under the curve; ln = natural log.

Sympathomimetics and excercise 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 ANOVAs 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 ones maximal aerobic capacity.

Aerobic Exercise Attenuates an Exaggerated Exercise Blood Pressure Response in Normotensive Young Adult African-American Men

An exaggerated exercise blood pressure response (EEBPR) may be associated with an increased risk of hypertension. We hypothesized that aerobic exercise training can decrease EEBPR and the risk for hypertension by decreasing arterial resistance. We studied the effects of aerobic training on the submaximal exercise blood pressure (BP) of eight normotensive young adult African-American men with an EEBPR. Subjects were trained on a stationary bicycle at an intensity of 70% peak oxygen uptake (VO 2peak ), for 30 min, three times per week, for 8 weeks. BP, heart rate, cardiac output (CO), stroke volume (SV) and total peripheral vascular resistance (TPR) were measured at rest and during submaximal exercise at a work intensity of 50% VO 2peak. Significance of the training effects were evaluated by comparing the pre- and post-training measures ( t -test, p < 0.05). A 15% post-training increase in VO 2peak (34.6 - 1.4 to 40 - 1.4 ml/kg/min) and a 9.5 ml post-training increase in mean resting stroke volume were found. A 16.2 mmHg decrement in mean systolic BP, an 11.5 mmHg decrement in mean diastolic BP, a 120 dyne/s/cm 5 decrement in TPR and a 1.2 l/min increase in CO were detected during the posttraining submaximal exercise tests. These results suggest that reductions in TPR may attenuate the EEBPR of normotensive African-American males following an 8-week training regimen of stationary bicycling at 70% VO 2peak . Aerobic exercise training may, therefore, reduce the risk of hypertension in normotensive African-American males by the mechanism of a reduction in TPR. Because of the limited number of subjects, the results of this study should be interpreted cautiously pending confirmation by a larger controlled trial.

Effects of high-carbohydrate and high-fat dietary treatments on measures of heart rate variability and sympathovagal balance.

AIMS We tested the hypothesis that respiratory quotient (RQ) determines sympathovagal balance associated with metabolism of stored and dietary energy substrates. MAIN METHODS Six 18-20 year-old African-American males were studied after two control pretreatments of fasting and post-treatments of metabolizing high-fat and high-carbohydrate beverages. RQ, heart rate (HR), energy expenditure (EE) and blood pressure (BP) were recorded at rest and repeated 1 h-3 h after ingesting isocaloric high-carbohydrate and high-fat beverages. Sympathovagal modulation of HR was quantified by the low frequency/high frequency (LF/HF) ratio from fast Fourier transform (spectral) analysis of the electrocardiogram RR intervals during paced breathing at 0.2 Hz. Significance of differences of peak post-treatment values from controls was evaluated by analysis of covariance and of correlations by linear regression at P<0.05. KEY FINDINGS The high-carbohydrate and high-fat treatments increased RQ, EE, HR and LF/HF with significant interactions between covariates. LF/HF values were not significant after eliminating covariance of RQ, EE and HR for the control vs. high-fat and for the high-fat vs. high-carbohydrate and after eliminating covariance of EE and HR for the control vs. high-carbohydrate treatments. Across the RQ values, correlations were significant for EE and LF/HF. SIGNIFICANCE These findings imply that high RQ and sympathetic modulation produced by metabolizing carbohydrate is associated with high resting energy expenditure. We conclude that respiratory quotient may be an important determinant of the LF/HF ratio in the heart rate variability spectrum, likely, by a respiratory chemosensory mechanism.

Effects of lung volume and chemoreceptor activity on blood pressure and R-R interval during the Valsalva maneuver

Study objectives The purpose of the present investigation was to examine the effect of lung volume and inspiration of 100 % oxygen on blood pressure and R-R interval responses during the Valsalva maneuver. Design and Participants Fourteen healthy subjects completed eight Valsalva maneuvers. Four of the maneuvers were completed after inspiring to total lung capacity while the remaining maneuvers were completed at end-expiratory lung volume. Two maneuvers completed at a given lung volume were performed under hyperoxic conditions while the remaining maneuvers were completed under normoxic conditions. Results Overall, a significant increase in blood pressure and decrease in R-R interval occurred throughout phases I–IV of the Valsalva maneuvers that were initiated from end-expiratory lung volume as compared to total lung capacity. These changes were accompanied by a concomitant increase in baroreflex sensitivity during phase IV. Furthermore, independent of lung volume the baroreflex response was attenuated under hyperoxic conditions. Conclusions We conclude that the lung volume that exists prior to the onset of the maneuver alters the blood pressure and R-R interval response during phases I–IV of the Valsalva maneuver. Furthermore, we suggest that these responses are mediated in part by changes in chemoreceptor activity since the baroreflex was reset and the sensitivity was reduced under hyperoxic conditions. Given these findings, we recommend that lung volume be controlled when patients are completing a Valsalva maneuver to obtain reliable and reproducible measures of blood pressure, R-R interval duration and baroreflex sensitivity.

Effects of Acute Nitric Oxide Synthase Inhibition on Lower Leg Vascular Function in Chronic Tetraplegia

Abstract Background/Objective: To improve our understanding of the lower-leg vascular responses of nitric oxide synthase inhibition in persons with tetraplegia. Participants: Six people with chronic tetraplegia and 6 age-matched controls. Methods: Lower-leg relative vascular resistance and venous volume variation were obtained by venous occlusion plethysmography and blood pressure by auscultation at baseline. Postintravenous infusion of the nitric oxide synthase inhibitor NG-nitro-L-arginine-methyl-ester (1 mg-kg-1) or placebo on separate days. Results: At baseline in the group with tetraplegia compared with controls, mean arterial pressure and relative vascular resistance of the leg were significantly lower. After nitric oxide synthase inhibition, mean arterial pressure and lower leg vascular resistance were significantly elevated in both groups. There were no group or intervention differences in venous volume variation. Conclusion: These preliminary results suggest that nitric oxide synthase inhibition with 1 mg-kg-1 NG- nitro-L-arginine-methyl-ester normalizes seated blood pressure and lower leg vascular resistance to control group baseline levels.