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.

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.

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.

Respiratory sinus arrhythmia alteration following training in endurance athletes.

Significant increases in maximum oxygen consumption (VO2max) were noted in nine young track athletes following an 8-week high-intensity running period (P less than 0.05). VO2max was measured, prior to and following the training program, using an on-line, open-circuit spirometry system. Parasympathetic activity was assessed using heart period variation (R-R interval in milliseconds) during carefully controlled breathing activity (R sinus arrhythmia). Following the training program, a 7.3% increase in aerobic capacity was associated with a 23.1% augmentation of efferent parasympathetic activity (P less than 0.01). These data suggest that enhanced aerobic capacity increases efferent parasympathetic tone.

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.

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.

Judo nephropathy: trauma versus non-trauma.

Nine male judo players were studied to evaluate possible renal dysfunction after repeated falls. During a 15-second period a pair of subjects took two steps and one subject performed an arm throw upon his partner. The procedure was then reversed and he was thrown by his partner. This alternating exercise was continued for a total of hundred falls per subject. This protocol was carried out twice by each subject, once on a 10-cm mat, once on a 2.5-cm mat. The compressive forces after falling on both mats were 0 joules and 5,919 joules, respectively. Experimental blood and urine samples were collected at 1, 2, 4, 9, and 24 hours post-trauma. Twenty four-hour glomerular filtration rate (GFR) was significantly inhibited during the traumatic session (2.5-cm mat). For the non-traumatic session (10-cm mat) a 24-hour GFR increase of 73.88% was noted compared to control values. Both experimental sessions demonstrated significantly increased urinary protein. Electrophoretic analysis of the urine showed a marked predominance of albumin. Hematuria present after the traumatic session grossly discolored the urine. All non-traumatic samples failed to demonstrate the presence of red blood cells in pathologic numbers. In this investigation the precipitating factor for hematuria during exercise seemed to depend largely on the severity of the mechanical trauma, and not the exercise per se.

Baroreceptor sensitivity response to phase IV of the Valsalva maneuver in spinal cord injury.

Due to the increased prevalence of ischemic heart disease and hypertension reported in individuals with chronic spinal cord injury (SCI), we investigated whether subjects with low level SCI (paraplegia), without apparent evidence of coronary artery disease, exhibit normal baroreceptor and autonomic function. Eighteen males participated in this study: seven normotensive with paraplegia, five hypertensive with paraplegia and six normotensive non-SCI controls. The Valsalva maneuver was performed by maintaining a pressure of 40 mmHg over 15 s and R-R intervals (RRI) and arterial blood pressure were measured continuously. Phase IV of the Valsalva maneuver was determined by linear regression analysis between RRI and systolic pressure, with a final slope calculated. The power spectra for RRI and blood pressure variability parameters were also analyzed, in addition to the index alpha, a frequency domain estimate of the overall gain in baroreceptor control of the RRI-arterial blood pressure. The normotensive subjects with paraplegia were found to have an impaired baroreceptor response when compared with age-matched, non-SCI controls. In addition, the levels of both the low frequency and high frequency spectral components of RRI and the index alpha were reduced in these individuals at rest. These cumulative findings strongly suggest that the integrity of the sinoaortic baroreceptors, as well as efferent parasympathetic function, may be compromised in otherwise apparently healthy individuals with chronic paraplegia.

Acetylsalicylic acid and autonomic modulation.

Loss of autonomic balance characterized by increased sympathetic activity and decreased vagal activity has been implicated as a major cardiovascular risk factor. Aspirin's cardioprotective abilities involve a multitude of physiologic processes. However, the effects of aspirin on cardiac autonomic activity are unknown. In a double-blind crossover study, 22 subjects randomly received either aspirin or placebo in the amounts of 325 mg with each meal (three times per day) over a 2.5-day period. The total amount of aspirin ingested was 2,275 mg, which resulted in plasma levels of 3.3 mg/dl. At the conclusion of each treatment, subjects were evaluated for autonomic physiology activity using standard autonomic tests. Power spectral analyses of the electrocardiograms were used to delineate autonomic function. A 2 x 4 repeated measures analysis of variance revealed significant and favorable changes in autonomic activity after the use of aspirin. Specifically, at rest high-frequency (HF) power was significantly higher (mean, 1,090 + 1,463.5 msec2) compared with the placebo (mean, 692 742 msec2) (p <0.05). Low-frequency (LF) power was significantly reduced (mean, 963 745 msec2) after aspirin compared with placebo (mean, 1,100 906 msec2). After the aspirin treatment, a significantly lower LF-to-HF power ratio (mean, 1.7 2 msec2) was noted at rest when compared with the placebo (mean, 2.5 2.7 msec2) (p <0.05). Similar significant trends were seen during the sustained isometric contraction after aspirin therapy for HF power (mean 210 2.15 msec2) compared with placebo (mean, 213 184 msec2) (p <0.05). Accordingly, the LF-to-HF power ratio was lower as well when compared to placebo treatment (mean, 2.3 3.5 msec2) (mean, 5.3 8.4 msec2) (p <0.05). No differences were found in breathing rates for hemodynamic variables between any of the protocols. The significant reduction of LF-to-HF ratio, a marker of sympathovagal balance, for both protocols appeared to be largely due to a withdrawal of LF modulation and concomitant but lesser increase in HF modulation. Favorable alterations in autonomic outflow through prostaglandin inhibition may be one of the mechanisms by which low therapeutic amounts of aspirin provide prophylactic cardioprotection.

Sympathovagal balance of the heart in subjects with spinal cord injury.

This study investigated the effect of abnormal autonomic cardiovascular function on heart rate variability (HRV) in individuals classified into four groups: complete quadriplegia, incomplete quadriplegia, low paraplegia, and non-spinal cord injury (SCI) controls. Measurements were collected at baseline and during provocative maneuvers. Spectral analysis using a fast-Fourier transform algorithm revealed two spectral components of HRV, termed low frequency (LF) and high frequency (HF); the LF-to-HF ratio (estimate of sympathovagal balance) was also calculated. Each group of subjects with quadriplegia exhibited significantly lower spectral components for both baseline and composite provocative measures compared with the non-SCI controls (P < 0.05). In addition, the group with paraplegia demonstrated significantly lower HF baseline and LF composite levels than controls (P < 0.05). No differences were observed among all groups for the LF-to-HF ratio. This consistency in the LF-to-HF ratio suggests that the two autonomic divisions that regulate the cardiovascular system maintain homeostasis even when one component is severely compromised. This is supported by the additional findings of decreased parasympathetic activity in the two groups with quadriplegia and the absence of significant differences among any of the four groups at rest in either heart rate or blood pressure.