Autonomic modulation, spontaneous baroreflex sensitivity and fatigue in young men after COVID-19.

Impaired autonomic modulation and baroreflex sensitivity (BRS) have been reported during and after COVID-19. Both impairments are associated with negative cardiovascular outcomes. If these impairments were to exist undetected in young men after COVID-19, they could lead to negative cardiovascular outcomes. Fatigue is associated with autonomic dysfunction during and after COVID-19. It is unclear if fatigue can be used as an indicator of impaired autonomic modulation and BRS after COVID-19. This study aims to compare parasympathetic modulation, sympathetic modulation, and BRS between young men who had COVID-19 versus controls and to determine if fatigue is associated with impaired autonomic modulation and BRS. Parasympathetic modulation as the high-frequency power of R-R intervals (lnHFR-R), sympathetic modulation as the low-frequency power of systolic blood pressure variability (LFSBP), and BRS as the -index were measured by power spectral density analysis. These variables were compared between 20 young men who had COVID-19 and 24 controls. Independent t-tests and Mann-Whitney U tests indicated no significant difference between the COVID-19 and the control group in: lnHFR-R, P=0.20; LFSBP, P=0.11, and -index, P=0.20. Fatigue was not associated with impaired autonomic modulation or BRS. There is no difference in autonomic modulations or BRS between young men who had COVID-19 compared to controls. Fatigue did not seem to be associated with impaired autonomic modulation or impaired BRS in young men after COVID-19. Findings suggest that young men might not be at increased cardiovascular risk from COVID-19-related dysautonomia and impaired BRS.

Baroreceptor sensitivity after Valsalva maneuver in women with chronic obstructive pulmonary disease.

PURPOSE: Reduced baroreceptor sensitivity (BRS) results in changes in autonomic modulation. Patients with chronic obstructive pulmonary disease (COPD) may have altered BRS. Therefore, we compared BRS between COPD patients and normal controls. METHODS: We compared 14 COPD patients [mean (±SD) age, 62 ± 8 years] to 14 healthy controls [mean (±SD) age, 59 ± 6 years] for the loss of BRS. All patients received ß(2)-agonist therapy but were free from any other type of medication that would interfere with autonomic responses, all controls were free from cardiopulmonary disease, and none was taking medications. All participants were female, post-menopausal, had no known cardiac disease and were ex-smokers. Reduced baroreceptor sensitivity was determined using the slope of the magnitude of R-R widening over the increase in systolic blood pressure following Valsalva maneuver. RESULTS: The mean BRS in controls versus COPD patients showed a mean value of 6.15 ± 2.26 versus 1.91 ± 2.92 ms/mmHg (p < 0.001). CONCLUSIONS: These findings are consistent with other abnormalities of autonomic disruption as previously reported, and demonstrate a severe blunting of the baroreceptor response in individuals with COPD. The cause of this altered BRS response in COPD is not fully clear, we postulate that air trapping with persistent elevation of intrathoracic pressure may lead to a subsequent blunting of the sensitivity of the baroreceptors.

Oxygen supplementation and cardiac-autonomic modulation in COPD.

STUDY OBJECTIVES: Patients with COPD have an increased sympathetic modulation and reduced baroreflex sensitivity (BRS). Therefore, we studied the effects of breathing 31% supplemental oxygen (SuppO(2)) on autonomic modulation in a group of COPD patients. DESIGN: We measured autonomic modulation before and during the administration of SuppO(2) on 51 patients with COPD using time-frequency analysis of R-R intervals and BP before and after intervention. This was done via a counterbalanced crossover design. The BRS index was determined using the sequence method. RESULTS: Significant differences were seen in oxygen saturation levels following breathing with SuppO(2) ([mean +/- SD] 96.4+/-1.5%) when compared to those seen after breathing with compressed air (CA) (92.8+/-2.9%; p<0.0001). Significant increases were seen in the natural log-transformed high-frequency modulation (HFln) (SuppO(2), 10.8+/-1.3 natural logarithm [ln] ms(2)/Hz; CA, 10.6+/-1.3 ln ms(2)/Hz; p<0.028) and BRS (SuppO(2), 3.3+/-2.2 ms/mm Hg; CA, 2.8+/-1.8 ms/mm Hg) following the supplemental oxygen treatment (p<0.015). The low-frequency/high-frequency ratio of heart rate variability revealed significant differences between the two treatments (SuppO(2), 2.7 +/-1.2; CA, 3.1+/-1.3; p<0.008). The analysis of BP variability data revealed significant decreases in the HFln (CA, 6.9+/-1.0 mm Hg(2)/Hz; SuppO(2), 6.5+/-1.2 mm Hg(2)/Hz; p<0.0001). Hemodynamic data also revealed a decrease in mean heart rate after breathing SuppO(2) compared with that after breathing CA (CA, 87.3+/-13.3 beats/min; SuppO(2), 85.0+/-12.4 beats/min; p<0.0004). The arterial pulse pressure significantly decreased when breathing SuppO(2) compared with that when breathing CA (CA, 57.2+/-13.5 mm Hg; SuppO(2), 53.3+/-13.0 mm Hg; p<0.0023). CONCLUSION: Oxygen supplementation in COPD patients significantly and favorably alters autonomic modulation.

Appendicular skeletal muscle mass: effects of age, gender, and ethnicity.

This study tested the hypothesis that skeletal muscle mass is reduced in elderly women and men after adjustment first for stature and body weight. The hypothesis was evaluated by estimating appendicular skeletal muscle mass with dual-energy X-ray absorptiometry in a healthy adult cohort. A second purpose was to test the hypothesis that whole body 40K counting-derived total body potassium (TBK) is a reliable indirect measure of skeletal muscle mass. The independent effects on both appendicular skeletal muscle and TBK of gender (n = 148 women and 136 men) and ethnicity (n = 152 African-Americans and 132 Caucasians) were also explored. Main findings were 1) for both appendicular skeletal muscle mass (total, leg, and arm) and TBK, age was an independent determinant after adjustment first by stepwise multiple regression for stature and weight (multiple regression model r2 = approximately 0.60); absolute decrease with greater age in men was almost double that in women; significantly larger absolute amounts were observed in men and African-Americans after adjustment first for stature, weight, and age; and >80% of within-gender or -ethnic group between-individual component variation was explained by stature, weight, age, gender, and ethnicity differences; and 2) most of between-individual TBK variation could be explained by total appendicular skeletal muscle (r2 = 0.865), whereas age, gender, and ethnicity were small but significant additional covariates (total r2 = 0.903). Our study supports the hypotheses that skeletal muscle is reduced in the elderly and that TBK provides a reasonable indirect assessment of skeletal muscle mass. These findings provide a foundation for investigating skeletal muscle mass in a wide range of health-related conditions.

With environmental control, the effects of race and sex on blood pressure regulatory mechanisms appear diminished.

To assess environmental control on autonomic parameters between race and sex, we studied cross-sectionally, 119 West Point cadets of both sexes and of African-American and Caucasian descent. Specifically, heart period variability (HPV) and baroreceptor sensitivity index (BRSI) were assessed non-invasively. All participants had lived at the Academy for at least 1 year, had similar diets, ages, fitness status, access to medical care and educational backgrounds. Familial aggregation of hypertension was 46% for African-American and 30% for Caucasian, respectively. Autonomic outflow was assessed using the magnitude of the respiratory sinus arrhythmia (RSA) during sitting, standing and augmented breathing. Autocorrelations on 64 successive heart periods provided low frequency (LF) or high frequency (HF) distributions. The ratio of LF over HF was considered representative of sympathovagal balance. Baroreceptor sensitivity (BRSI) was assessed by recording cardiac deceleration in response to a Valsalva-induced increase in BP. Analysis of variance failed to reveal significant differences in any of these BP regulatory mechanisms between any of the groups. Prior investigations failed to control for the many environmental factors mentioned above and have therefore indicated significant epidemiological differences in the occurrence of hypertension between different races. Our results strongly suggest that environmental control seems to be an important modulator in the pathogenic mosaic of autonomic derangement, and should be strongly considered in future research.

Thermal, ventilatory, and gluco-regulatory responses during exercise following short-term acetylsalicylic acid ingestion.

Acetylsalicylic acid and exercise combined produce perturbations in thermal, respiratory and carbohydrate metabolism. However, the therapeutic implications of these therapies are antithrombotic and fibrinolytic respectively. In a double-blind, counterbalanced cross-over design of eight men, salicylate ingestion in combination with 60 min of moderate intensity exercise (50% VO2 max) significantly increased respiratory rate and oxygen consumption (p less than 0.05) both at rest and during the exercise protocol. The effect of acetylsalicylic acid ingestion on gluco-regulatory and counter-regulatory hormones was not significant compared to the placebo. These data suggest a safe prophylactic role for a combined short-term acetylsalicylic acid ingestion and exercise therapy in the development of coronary artery disease when exercising in a thermal neutral environment.

A program in Quickbasic for the estimation of cardiac output.

The current program in Quickbasic provides a valid and reliable computational method for the estimation of cardiac output, using the CO2 rebreathe method. In addition, this program will save time through speed of execution. Furthermore, the program can be used with IBM microcomputers as well as IBM compatible microcomputers.

New noninvasive computerized method for the area measurement of the dicrotic notch.

Measurement of the area of the dicrotic notch is an important noninvasive diagnostic procedure in cardiocirculatory evaluation. The methodology for measuring the magnitude of the dicrotic notch has varied considerably, ranging from visual inspection to the use of microcomputer technology. The current computerized method provides a quantitative exactitude when compared to polar planimetry. Coefficients of correlation (r) were 0.89 and highly significant (p less than 0.01). Furthermore, the current method circumvents densitometric placement variation between repeated measurements.

Computerized substrate utilization determinations from respiratory functions alone.

Non-invasive substrate utilization using expiratory gases is a cost effective and informative procedure in the nutritional management of the critically ill patient. In addition, the effect of feeding on the respiratory system depends on the substrates utilized and therefore provides information for an optimal regimen in nutritional support. However, metabolic systems to assess substrate utilization are often expensive. Hence, the program described here, in combination with the necessary instrumentation (ventilation meter, O2 and CO2 analyzer), will allow a rapid and quantitatively reliable assessment of substrate utilization.

Computer applications in thermoregulatory research.

Thermoregulatory information is a frequently used parameter in both physiological and psychophysiological research. Specific software programs using accepted formulae are not readily available to the scientist as is the hardware. The program described here uses the well-established physiological model by Burton, calculating mean skin temperature and mean body temperature. The primary goal of this microsoft Basic program is to aid the researcher through speed of execution and quantitative reliability. A few command alterations will allow this program to be used with most microcomputer systems currently available. The time saved using this program will greatly enhance the efficiency of the researcher's thermoregulatory data analyses.

A computerized respiratory sinus arrhythmia program for the non-invasive assessment of parasympathetic activity.

The availability of sophisticated signal analysis methods based on the use of micro-computers allows an accurate non-invasive assessment of parasympathetic activity, through the measurement of the respiratory sinus arrhythmia. The program described herein is in Quickbasic and consists of 5 programs. At termination of the computer analysis the results are printed which include the average heart rate for inspiration and expiration, the averaged standard deviation of the R-R intervals for inspiration and expiration, and the R-R interval in milliseconds averaged for all inspiratory and expiratory cycles. Significant correlations were obtained when comparing the analyses of the computerized program with a manual method.

Exercise training favourably affects autonomic and blood pressure responses during mental and physical stressors in African-American men.

Aerobic exercise is a powerful mechanism by which cardiovascular and autonomic parameters may be improved. We sought to quantify the extent of benefit that could be achieved by a short-term monitored exercise regimen on several autonomic parameters during recognized mental and physical stressors in young normotensive African-American men matched for a family history of hypertension, a group at high risk for the development of hypertension. Autonomic modulations were derived using spectral decomposition of the electrocardiogram and beat-to-beat blood pressures (BPs). Arterial compliance was obtained using contour analysis of the radial artery pulse wave. The analysis of variance revealed that compared with a matched sedentary control group, aerobic capacity of the trained group significantly increased by 16%. Autonomic modulations, arterial compliance and BP responses significantly improved during some of the stressors, whereas no such improvements were seen in the control group. Attenuated responses, mediated through a favourable shift in sympathovagal balance and enhanced arterial compliance, provide mechanistic evidence of how certain variables may be improved due to aerobic conditioning in a population at high risk for the development of hypertension.

The effects of acetylsalicylic acid upon carbohydrate metabolism during exercise.

The effects of acute acetylsalicylic acid (ASA) ingestion upon carbohydrate metabolism during a 60 min treadmill moderate intensity exercise (50% VO2max) were studied in eleven normal females. A double-blind crossover design was used to compare the experimental findings with placebo. No significant differences were noted during the exercise protocol in glucose, insulin, glucagon and free fatty acid utilization between placebo/exercise and acetylsalicylic acid/exercise treatment. A significant post-exercise hypoinsulinemic and antilipolytic effect occurred with ASA/exercise treatment (p less than 0.05). In addition, post-exercise glucagon levels remained unchanged with ASA, whereas a significant plasma glucagon increase was noted with placebo (p less than 0.05). These data suggest that a prophylactic acetylsalicylic acid/exercise regimen will not adversely affect gluco-regulatory and counter-regulatory metabolism during exercise and could therefore, be safely instituted as an adjunct preventive therapy.

Heart rate variability and aerobic fitness.

Heart rate variability, a noninvasive marker of parasympathetic activity, diminishes with aging and is augmented after exercise training. Whether habitual exercise over time can attenuate this loss is unknown. This cross-sectional investigation compared 72 male runners, aged 15 to 83 to 72 age- and weight-matched sedentary control subjects for the amplitude of their heart rate variability. Heart rate variability was assessed during rest while subjects were breathing at a rate of 6 breaths per minute and at an augmented tidal volume (tidal volume = 30% of vital capacity). Fitness levels were assessed with on-line, open-circuit spirometry while subjects were performing an incremental stress test. Overall results between the two groups showed that the physically active group had significantly higher fitness levels (p < 0.001), which were associated with significantly higher levels of heart rate variability, when compared with their sedentary counterparts (p < 0.001). These findings provide suggestive evidence for habitual aerobic exercise as a beneficial modulator of heart rate variability in an aging population.

Personality, effort perception and cardiovascular reactivity.

Ratings of perceived exertion and neuroendocrine reactivity (plasma catecholamines) were measured in type A and type B student volunteers during a metabolically equivalent physical stressor (cycle ergometry). Analysis of variance demonstrated that type A underrated the perception of exertion as compared to type B. Therefore, this neuropsychobiological interaction could partly explain the relationship between type A and the tissue pathology in the development of accentuated coronary heart disease.

Aging as a modulator of respiratory sinus arrhythmia.

Aging is associated with an accentuated shift toward sympathetic outflow. Evidence suggests that sympathetic and vagal-cardiac activity change reciprocally. If this hypothesis is correct, then aging would result in an attenuation of vagal-cardiac activity. The current cross-sectional investigation assessed the relationship between aging, vagal-cardiac activity, and arteriolar compliance (AC). Respiratory sinus arrhythmia (RSA) and finger plethysmography, noninvasive measures of vagal-cardiac activity and arteriolar compliance, respectively, were made on 70 normotensive male subjects (age range 15-81 years). Both RSA and AC decreased with age (r = .71 and .89, respectively, p < .001). Analysis of variance revealed significant differences between the six decade groups for RSA and AC (p < .05). These findings support the notion that there is an age-related loss of vagal-cardiac activity that could be partly explained by the loss of arteriolar compliance. These findings are consistent with the hypothesis that there is autonomic nervous system compensation of cardiovascular function in response to an age-related decrease in arteriolar compliance in a normotensive population.