Power spectral analysis of heart rate variation in diabetic patients with neuropathic foot ulceration

OBJECTIVE: To evaluate the relationship between diabetic autonomic neuropathy and diabetic neuropathic foot ulceration, we used power spectral analysis (PSA) of heart rate variation, which provides the accurate simultaneous quantification of parasympathetic and sympathetic activities, to assess autonomic function in diabetic patients. RESEARCH DESIGN AND METHODS: We studied 55 NIDDM patients including 10 diabetic patients without neuropathy, 23 diabetic patients with neuropathy and no history of foot ulceration, and 22 diabetic patients with neuropathic foot ulceration. We performed PSA of 100 R-R intervals at rest and analyzed the results by fast Fourier transformation. RESULTS: The low frequency (LF) power, which reflects sympathetic activity, and the high frequency (HF) power, which reflects parasympathetic (vagal) activity, were inversely correlated with the duration of diabetes and the fasting plasma glucose (FPG) levels. By multiple regression analysis, the FPG remained with significant influence on both LF and HF powers. The LF and HF powers were positively correlated with motor nerve conduction velocity (MCV) and sensory nerve conduction velocity (SCV) in the upper and lower limbs and the coefficient of variation of R-R intervals. The LF and HF powers were significantly reduced in patients with neuropathy and patients with foot ulceration compared with patients without neuropathy. Although the median MCV and SCV were similar between diabetic patients with neuropathy and patients with foot ulceration, both the LF and HF powers were significantly decreased in patients with foot ulceration compared with patients with neuropathy. There was no difference in the value of the LF:HF ratio, an index of sympathovagal balance, among three subgroups. We observed a positive correlation between LF and HF power in all subjects; however, the LF and HF powers were not correlated in the subgroups of patients with foot ulceration. CONCLUSIONS: These results showed that diabetic patients with neuropathic foot ulceration have a greater impairment in spectral indexes of autonomic activity obtained by PSA than patients with neuropathy and no history of foot ulceration, whereas no difference was present in nerve conduction velocities.     

Solitary plasmacytoma of the lung with light chain extracellular deposits: a case report and review of the literature

We studied a possible correlation between autonomic cardiac activity and the level of the red blood cell acetylcholinesterase (AChE) in patients with probable Alzheimer disease (AD). The influence of cholinesterase inhibitor treatment on this autonomic activity was evaluated. Twelve patients satisfying the NINCDS-ADRDA criteria of probable AD and 10 healthy controls were studied. Autonomic cardiac activity was evaluated by means of power spectral analysis (PSA) of heart rate variability (HRV) using an autoregressive algorithm on 250 consecutive electrocardiographic R-R intervals. All patients received oral eptastigmine, a new cholinesterase inhibitor, for 1 month. Before treatment, a simultaneous recording of the electrocardiographic and respiratory activities was performed at rest and subsequently during head-up tilt test at 700. Recording was repeated on the last day of treatment. The level of AChE activity during each recording was also evaluated. Spectrum power was calculated in three main frequency bands: high frequency (HF), 0.15-0.4 Hz; low frequency (LF), 0.04-0.15 Hz; very low frequency (VLF), <0.04 Hz. In addition, we calculated the total spectrum power (TSP) and the LF/HF ratio. The TSP and the absolute value of each spectral component were significantly lower in AD patients than in controls. In contrast with controls, AD patients did not show any significant change before treatment in either the LF and HF components or in the LF/HF ratio during the tilt test. However, the modification in the LF component, induced by tilting, showed a significant correlation with the level of AChE activity (p < 0.03). During the tilt test, the treatment caused changes in LF and HF components and in the LF/HF ratio similar to those observed in controls. These results suggest that the presence of autonomic cardiac dysfunction in AD patients might be due to a cholinergic deficit in the peripheral autonomic nervous system. Some aspects of this autonomic dysfunction can be normalized by cholinesterase inhibitor treatment.     

Protein and calorie effects on progression of induced chronic renal failure in cats

This study was designed to determine if there is a difference in autonomic regulation induced by posture change between postmenopausal and young women. To evaluate autonomic nervous system function, spectral analysis of heart rate variability (HRV) was done in postmenopausal women (n = 13, 46-59 years of age), age-matched men (n = 8, 45-55 years of age), and young women (n = 10, 20-37 years of age) for 3-min periods of controlled frequency breathing (15 breaths/min) in supine followed by sitting positions. In the supine position, the R-R interval variation in older persons decreased significantly compared with that during the follicular phase in young women. Furthermore, the high-frequency (HF) components of HRV, which reflect only parasympathetic activity, were lower in older subjects than in young women. Following a change of position from supine to sitting, the HF component did not change significantly in the postmenopausal women or the men, but the low/high frequency (LF/HF) component ratio, which reflects the balance of autonomic nerve activities, increased significantly in the men. These results suggest that cardiac parasympathetic tone may be reduced in older persons in comparison with young women. Furthermore, arterial baroreflex control of parasympathetic nerve activity caused by posture changes is impaired in the postmenopausal women and aged-matched men. The baroreflex control of the sympathetic component is maintained in the men but not in the postmenopausal women. These differences might result in part from changes in the level of female hormones.     

Analysis of heart rate variability demonstrates effects of development on vagal modulation of heart rate in healthy children

OBJECTIVES: Analysis of heart rate variability (HRV) has been found to be a useful method of assessing cardiovascular autonomic control, but normal values for standard HRV measures in children have not been established. We analyzed HRV in 60 healthy children aged 3 to 15 years to determine normal values and to assess the effects of development on cardiac autonomic control with the use of ambulatory electrocardiographic monitoring. RESULTS: The high-frequency (HF) component, an index of cardiac autonomic tone, increased significantly with age from 3 to 6 years (p < 0.01) and decreased with age from 6 to 15 years (p < 0.01), and the magnitude of HF correlated significantly with the R-R intervals. Thus the changes in cardiac autonomic tone could be described as a simple equation using age and heart rate. CONCLUSIONS: We present normal values and changes in the cardiac autonomic system during childhood after HRV analysis, which could lead to a better understanding and treatment of cardiac disease in children.     

Carcinoma of the vulva in women: clinical and morphopathological problems

1. To investigate the relationship between the autonomic drive to the heart and heart rate variability, as evaluated by power spectral analysis, we studied the effect of clonidine (300 microg), a central sympatholytic agent, on heart rate variability. 2. Six healthy subjects (mean age 31 +/- 3 years) were studied in the supine and the sitting position (15 min each) on two different occasions, respectively, before and after clonidine administration. Using an autoregressive approach, the low frequency (LF) and the high frequency (HF) components of power spectral analysis were measured, and their ratio was calculated. Blood pressure was monitored throughout the study and plasma catecholamines were measured at the end of each period. 3. Before clonidine, assumption of the sitting position induced increases in LF, LF/HF ratio, blood pressure and plasma noradrenaline. Clonidine induced remarkable reductions in the normalized values of the LF component and the LF/HF ratio in both the resting and the sitting position (supine: LF = -68%, LF/HF ratio = -80%; sitting: LF = -23%, LF/HF ratio = -55%) without affecting the central frequencies of LF and HF components. Blood pressure and plasma catecholamines also significantly decreased after clonidine. 4. These results support the hypothesis that the LF component of HRV, expressed in normalized units, is an indicator of the sympathetic control of the heart. In addition, this component seems to be largely of central origin, because it is markedly reduced by the central sympatholytic action of clonidine.     

Effects of clonidine on power spectral analysis of heart rate variability in mild essential hypertension

Patients with essential hypertension often show alterations of the autonomic nervous system. We evaluated the sympathetic and parasympathetic drive to the heart in 12 mildly hypertensive patients and 9 healthy subjects by power spectral analysis of heart rate variability. All subjects underwent measurements of RR interval, low (LF) and high frequency (HF) components of heart rate variability, LF/HF ratio and blood pressure in the resting and sitting positions, both before and after oral clonidine (300 microg), a central sympatholytic agent. In the supine position before clonidine, hypertensive patients had higher blood pressure and lower HF values than healthy subjects. Clonidine induced increases in RR interval and HF in both groups, while LF and LF/HF ratio decreased in healthy subjects, but not in hypertensive patients. On assuming the sitting position, both groups showed reductions in RR and HF and increments in LF and LF/HF. In healthy subjects, the response to the postural challenge was unaffected by clonidine. In contrast, hypertensive patients showed no changes in LF and LF/HF ratio, and a significantly lower decrease in HF. These differences were probably due to the existence of two subsets of patients, one exhibiting similar responses to clonidine as healthy subjects, and the other showing no appreciable response to the drug. These results suggest that hypertensive patients have an altered sympatho-vagal balance to the heart, which can be unmasked by clonidine. This phenomenon should be taken into account to achieve a better control of the overall cardiovascular risk of hypertensive patients.     

Treatment acute myocardial infarct in the pre-hospital phase

OBJECTIVE: To examine the circadian variation in the signal averaged electrocardiogram (saECG) and heart rate variability and investigate their relations in healthy subjects. METHODS: 24 hour ECGs were obtained with a three channel recorder using bipolar X, Y, and Z leads in 20 healthy subjects. The following variables were determined hourly: heart rate, filtered QRS (f-QRS) duration, low and high frequency components of heart rate variability (LF and HF), and the LF/HF ratio. RESULTS: Heart rate, f-QRS duration, HF, and the LF/HF ratio showed significant circadian rhythms, as determined by the single cosinor method. Heart rate and the LF/HF ratio increased during daytime, and f-QRS duration and HF increased at night. f-QRS duration was negatively correlated with heart rate (r = 0.95, p < 0.001) and the LF/HF ratio (r = 0.94, p < 0.001) and positively with HF (r = 0.93, p < 0.001). CONCLUSIONS: f-QRS duration has a significant circadian rhythm in healthy subjects and is closely related to the circadian rhythm of autonomic tone.     

Cardiac autonomic patterns preceding occasional vasovagal reactions in healthy humans

BACKGROUND: The wide range of clinical presentation of orthostatic vasovagal syncope suggests different underlying changes in the cardiac autonomic modulation. METHODS AND RESULTS: To evaluate the beat-by-beat modifications in the neural control of heart period preceding a syncopal event, we studied RR interval variability in 22 healthy subjects who experienced fainting for the first time during a 90 degrees head-up tilt and in 22 control subjects by means of time-variant power spectral analysis. Sympathetic and vagal modulations to the sinoatrial node were assessed by the normalized power of the low-frequency (LF, approximately 0.1-Hz) and high-frequency (HF, approximately 0.25-Hz) oscillatory components of RR variability. When the patients were supine, no differences were observed in the hemodynamic and spectral parameters of the 2 groups. During the tilt procedure, RR, LFNU, and HFNU (NU=normalized units) values were relatively stable in control subjects. During early tilt (T1), subjects with syncope had reduced RR intervals compared with control subjects. In 13 subjects with syncope, RR decreased while LFNU and LF/HF increased in the last minute of tilt before syncope (T2). Conversely, in the remaining 9 fainters, LFNU and LF/HF decreased from T1 to T2 and HFNU increased slightly. CONCLUSIONS: Two different patterns may be recognized in the cardiac autonomic changes preceding an occasional vasovagal event, namely, one characterized by a progressive increase of the marker of cardiac sympathetic modulation up to the onset of syncope, the other by a sympathetic inhibition with an impending vagal predominance. The recognition of different pathophysiological mechanisms in fainters may have important therapeutic implications.     

Effects of head-up tilting on vagal nerve activity in man

OBJECTIVES: To evaluate the contribution of the vagal nerve activity in the cardiovascular postural adaptation, effects of decremental head-up tilting (90 degrees, 64 degrees, 53 degrees, 44 degrees, 37 degrees, 30 degrees, 24 degrees, 17 degrees, 12 degrees, 6 degrees and 0 degree) on time- and frequency-domain heart rate variability variables were analyzed in healthy young female. BACKGROUND: During head-up tilting, a hydrostatic venous pooling in the extremities occurs owing to gravity. To pump up the blood toward the upper body, the sympathetic nerve activity has been shown to play an important role. So, to date, few studies evaluated the effects of vagal nerve activity to stabilize the cerebral blood flow during head-up tilting. METHODS: Eight young female volunteers (age, 23.3 +/- 0.8 years; mean +/- SD) were evaluated. The electrocardiogram (ECG) by bipolar chest leads was recorded continuously during procedures, and the bed was tilted at 0.1 interval of sine function of tilting angle from upright position (90 degrees) to supine position (0 degree). The time domain measurements of cycle length variability (co-efficient of variance in percent for R-R intervals [CVRR], number of differences between adjacent R-R intervals that are > 50ms [RR50]) and the frequency domain measurements of low (0.08 to 0.15Hz, LF), high (0.15 to 0.40Hz, HF) and total (0.08 to 0.40, TF) power were performed to assess the cardiac sympathetic and vagal nerve activity. RESULTS: The CVRR showed no significant change during decremental head-up tilting, whereas the RR50 and the square root of HF power, more specific indices of cardiac parasympathetic tone, showed significant negative linear correlations to the sine of the tilting angle. In markers of cardiac sympathetic tone, there were significant positive correlations between the sine of the tilting angle and the normalized LF power or the LF-to-HF power ratio (LF/HF). CONCLUSION: These findings suggest that, in healthy young female, not only cardiac sympathetic nervous system but also cardiac vagal nervous system respond linearly to the change in body axis component of gravity, and they may contribute reciprocally and coordinately to cardiovascular postural adaptation.     

Subject''s perceptions of the crew interaction dynamics under prolonged isolation

BACKGROUND: Short-term variability of RR interval and blood pressure occurs predominantly at low frequency (LF; approximately 0.1 Hz) and high frequency (approximately 0.25 Hz). The arterial baroreflex is thought to be the predominant determinant of the LF component of RR variability. Patients with severe congestive heart failure (CHF) have an attenuated or absent LF oscillation in RR variability. The left ventricular assist device (LVAD) offers a unique possibility for analysis of spectral oscillations in RR interval independent of any effects of blood pressure that influence these oscillations via the baroreflex. METHODS AND RESULTS: We performed spectral analysis of RR, blood pressure, and respiration in 2 patients with CHF before and after LVAD implantation. LF components of the RR-interval and blood pressure variability were absent in both CHF patients before LVAD implantation. After LVAD implantation, spectral analysis of the RR interval showed restoration of a clear and predominant LF oscillation in the native hearts of both patients, with no such oscillation evident in the blood pressure profile. CONCLUSIONS: During total circulatory support with the LVAD, the LF oscillation in RR interval of the native heart, absent in CHF, is restored. This LF oscillation in RR interval occurs in the absence of LF oscillations in blood pressure and thus is unlikely to be explained by baroreflex mechanisms. Hence, the absence of LF oscillation in the RR interval in CHF is functional and is reversible by LVAD circulation. The presence of a predominant LF oscillation in RR interval independent of any oscillation in blood pressure suggests that the LF oscillation is a fundamental property of central autonomic outflow.     

A 30-year-old woman with headache

Recent studies have reported a close association between chronic fatigue syndrome and neurally mediated hypotension. We hypothesized that this association may result from an abnormality in autonomic function among patients with chronic fatigue syndrome, which may be detectable using an analysis of heart rate variability. We prospectively studied 19 patients who fulfilled the Centers for Disease Control criteria for chronic fatigue syndrome and 11 controls. Each subject underwent a two-stage tilt-table test while wearing a Holter monitor. Heart rate variability was assessed in the supine baseline position and during upright tilt using frequency domain parameters. In the baseline supine position, high frequency (HF) power, low frequency (LF) power, and the ratio of low frequency power to high frequency power (LF/HF ratio) were similar. In both patient groups, upright tilt resulted in a similar decrease in HF power, increase in LF power, and increase in the LH/HF ratio. In conclusion, autonomic function, as assessed using an analysis of heart rate variability, does not differ in the baseline supine state, nor in response to upright tilt among patients with chronic fatigue syndrome and healthy controls.     

Power spectral analysis of heart rate variability during graded head-up tilting in patients with vasodepressor syncope

1. Two groups of age- and sex-matched subjects, eight healthy controls and 10 patients, suffering from recurrent vasodepressor syncope, participated in a study to examine autonomic function and sequential changes in power distribution of heart rate (HR) variability during graded head-up tilt. 2. The following autonomic function tests were performed: valsalva ratio, HR responses to deep breathing and posture, BP responses to sustained handgrip and postural change. Each subject was tilted at 15 degrees, 30 degrees, 45 degrees, 60 degrees and 80 degrees head-up, each for 15 min, or until symptoms occurred. The eight control subjects completed the tilt study without any symptoms, while all 10 patients developed presyncope and/or syncope at various tilt angles. 3. Resting blood pressure (BP) was lower in the patient group, while resting HR, autonomic function tests and resting HR variability components were similar in the two groups. 4. The control group showed a progressive increase in low frequency power component (LF) from supine to end tilt (delta LF 20.06 +/- 14.50%) and a progressive fall in high frequency (HF) component (delta HF - 24.62 +/- 10.64%). In contrast, in the patient group, LF fell during tilt in the presyncope period (delta LF - 10.57 +/- 12.93%, P < 0.01 vs control group). HF and HF:LF ratio responses did not differ significantly in the two groups. 5. At end tilt, the increase in plasma noradrenaline was significantly greater in the control group than in the patient group (delta NA 0.83 +/- 0.27 vs 0.28 +/- 0.14 pmol/mL, P < 0.01).(ABSTRACT TRUNCATED AT 250 WORDS)     

Hemorrhage exerts different effects on variabilities of heart rate and blood pressure in dogs

The aim of the present study was to evaluate the effects of hemorrhage on heart rate variability (HRV) and blood pressure variability (BPV) as indicators of autonomic nervous system (ANS) and hypovolemia. We induced hemorrhagic hypovolemia in 7 dogs by removing blood in graded stages (0%, 10%, 20%, 30%, 40% of the estimated blood volume; EBV). HR was unchanged during hemorrhage, while mean BP decreased significantly after 30% EBV hemorrhage. Low frequency component (LF: 0.04-0.15 Hz) of HRV significantly increased after 20% EBV hemorrhage but high frequency component (HF: 0.15-0.4 Hz) of HRV was not altered. LF of BPV increased significantly stepwise after 20% EBV hemorrhage and HF of BPV increased significantly after 30% EBV hemorrhage, showing that both LF and HF of BPV might indicate the degree of hypovolemia. During hemorrhage LF of HRV and BPV increased and HF of HRV was unchanged, indicating the shift of the autonomic balance toward sympathetic dominance. An excellent quantitative correlation between LF of BPV and the degree of hypovolemia was demonstrated during graded hemorrhage, while LF of HRV plateaued at its maximum value at 20% EBV hemorrhage. In conclusion, our study suggests that the spectral analysis of HRV and BPV during graded hemorrhage shows different characteristics in the quantitative evaluation of ANS and hypovolemia.     

The relief of postoperative pain by suppositories of buprenorphine or NSAID

The present paper investigates the effects of two anaesthetic drugs (pentobarbital and etomidate) on both short-term variabilities of systolic blood pressure (SBP) and heart rate (HR) using fast Fourier transformation and catecholamine plasma levels. HR and BP were continuously recorded through an arterial catheter and blood samples were taken from the jugular vein. Spectral analysis was performed first in the conscious state and six minutes after induction of anaesthesia on a series of 256 consecutive BP and HR values (delta t: 2 Hz). The area under the curve (AUC) was determined in the low-frequency component of the SBP (LF: 40-150 mHz), in the high-frequency band of HR (HF: respiratory frequency +/- 50 mHz) and in the total frequency spectra. Results were normalized by calculation of the ratio between AUC of LF and HF and the total AUC of the corresponding spectrum (TS). Etomidate (2 mg/kg i.v.) induced a significant increase in TS and LF without changing the LF/TS ratio or the HR variability when compared with the awake period. Catecholamine plasma levels did not change. In contrast, pentobarbital (30 mg/kg i.v.) decreased the values of LF, HF, LF/TS and HF/TS and catecholamine plasma levels. These results suggest that pentobarbital decreases the activity of the two components of the autonomic nervous system whereas etomidate induces only minimal changes.     

Clinical and haemodynamic correlates of heart rate variability in children with congenital heart disease

Heart rate variability (HRV) represents a noninvasive parameter for studying the autonomic control of the heart. Cardiac patients have a complex autonomic disturbance. The relation of HRV to this abnormality in children with congenital heart disease (CHD) has not yet been examined. The present study examined HRV indices from 24 h Holter recordings in 258 children with an operated or non-operated CHD, to determine their differences as an indicator of the severity of heart disease. The latter was defined clinically as New York Heart Association (NYHA) functional classes I to IV and haemodynamically by invasive parameters. Five time-domain measures (SDNN, SDNNi, SDANNi, rMSSD and pNN50) and three frequency-domain measures (LF, HF and balance LF/HF) were compared with normal ranges. HRV was reduced in children with CHD, except in patients of NYHA class I. The level of reduction depended on the NYHA functional class. None of the measures was significantly related to haemodynamic data. CONCLUSION: Heart rate variability is reduced in children with Congenital heart disease depending on the functional limitation but not on haemodynamic disturbances. Heart rate variability indices are sensitive markers of the clinical state.     

Voltage-dependent calcium channel promoter restores baroreflex sensitivity in conscious dogs with heart failure

BACKGROUND: The aim of this study was to determine the mechanism by which the calcium channel promoter BAY y 5959 affects the control of heart rate and baroreflex sensitivity in conscious dogs with pacing-induced heart failure (HF). METHODS AND RESULTS: We compared responses to BAY y 5959, which increases inotropy and decreases chronotropy, with those to norepinephrine (NE), which coincidentally exerts the same directional effects on inotropy and chronotropy, albeit through different mechanisms, in the presence and absence of ganglionic blockade both in control and in HF. Both BAY y 5959 and NE elicit direct effects on the heart and indirect effects through activation of reflexes, primarily the sinoaortic baroreceptor reflex. BAY y 5959 still reduced heart rate in dogs with arterial baroreceptor denervation, but not after ganglionic blockade. HF induced classic catecholamine desensitization to the inotropic effects of NE and blunted reflex bradycardia. In contrast, inotropic responses to BAY y 5959 were preserved in HF. Surprisingly, the autonomically mediated bradycardia induced by BAY y 5959 was also preserved in HF. Baroreflex sensitivity was assessed in control and in HF by pulse interval-systolic arterial blood pressure (PI/SAP) slopes constructed in response to pharmacological alterations in arterial pressure. HF depressed the PI/SAP slope from 11.5+/-1.3 to 4.8+/-0.9 ms/mm Hg, but during BAY y 5959 infusion in HF, the PI/SAP slope was restored to 24.1+/-5.2 ms/mm Hg. To assess central versus peripheral actions of BAY y 5959, the agent was infused with intra-carotid artery perfusion at a low dose, which acted centrally but did not have an effect peripherally. Under these conditions, it still decreased heart rate and restored baroreflex sensitivity (PI/SAP slope, 12.7+/-2.8 ms/mm Hg). CONCLUSIONS: Thus, the calcium promoter restores arterial baroreflex sensitivity in HF. Based on intra-carotid artery experiments, this occurs through a central nervous system and vagal mechanism.     

Application of USAF G-suit technology for clinical orthostatic hypotension: a case study

INTRODUCTION: The purpose of this study was to determine the effectiveness of a USAF anti-gravity suit (G-suit) on the stability of a patient with chronic orthostatic hypotension. METHODS: A 37-yr-old female with a history of insulin-dependent diabetes mellitus (IDDM) and symptomatic orthostasis was evaluated and the results were compared with those of non-diabetic controls, matched for age, height, and weight. Cardiac vagal tone was assessed by determination of standard deviation of 100 R-R intervals (R-R SD). We assessed the carotid-cardiac baroreflex response by plotting R-R intervals (ms) at each of eight neck pressure steps with their respective carotid distending pressures (mm Hg). Heart rate and blood pressure were recorded in response to the Valsalva maneuver (VM) performed at an expiratory pressure of 30 mmHg to assess integrated baroreflex responses. Blood pressures and heart rate were measured during three 5-min stand tests to assess orthostatic responses: a) without G-suit; b) with noninflated G-suit; and c) with inflated G-suit (50 mm Hg). RESULTS: The IDDM patient had minimal baseline cardiac vagal tone (R-R SD = 8.5 ms) compared with the average response of a control group of 24 subjects with orthostatic stability (R-R SD = 67.2 +/- 7.1 ms). Carotid-cardiac baroreflex response was virtually non-existent in the IDDM patient (Gain = 0.06 ms.mm Hg-1) compared to the control subjects (4.4 +/- 0.8 ms.mm Hg-1). VM responses corroborated the lack of cardiac baroreflex response in the IDDM patient, while blood pressure changes during the VM were similar to those of the controls. Upon standing, the IDDM patient demonstrated severe orthostatic hypotension (90 mm Hg SBP) and tachycardia without the G-suit. The G-suit, with and without pressure, reduced hypotension and tachycardia during standing. CONCLUSION: These results demonstrate successful application of Air Force technology as a useful alternative to pharmacologic intervention in the treatment of a patient with autonomic dysfunction leading to supine hypertension and orthostatic hypotension.     

Endurance training, overtraining and baroreflex sensitivity in female athletes

We examined heavy training-induced changes in baroreflex sensitivity, plasma volume and resting heart rate and blood pressure variability in female endurance athletes. Nine athletes (experimental training group, ETG) increased intense training (70-90% VO2max) volume by 130% and low-intensity training (< 70% Vo2max) volume by 100% during 6-9 weeks, whereas the corresponding increases in six control athletes (CG) were 5% and 10% respectively. Maximal oxygen uptake (VO2max) in the ETG and CG did not change, but in five ETG athletes VO2max decreased from 53.0 +/- 2.2 (mean +/- SEM) (CI 46.8-59.2) ml kg-1 min-1 to 50.2 +/- 2.3 (43.8-56.6) ml kg-1 min-1 (P < 0.01), indicating overtraining. Baroreflex sensitivity (BRS) measured using the phenylephrine technique and blood pressure variability (BPV) did not change, but the low-frequency power of the R-R interval variability increased in the ETG (P < 0.05). The relative change in plasma volume was 7% in the ETG and 3% in the CG. The changes in BRS did not correlate with the changes in plasma volume, heart rate variability and BPV. We conclude that heavy endurance training and overtraining did not change baroreflex sensitivity or BPV but significantly increased the low-frequency power of the R-R interval variability during supine rest in female athletes as a marker of increased cardiac sympathetic modulation.     

Impaired heart rate variability in patients with symptomatic NYHA class II-III hypertrophic cardiomyopathy

Power spectral analysis of heart rate variability was performed to assess cardiac autonomic function using Holter monitoring in 19 hospitalized patients with symptomatic NYHA class II-III hypertrophic cardiomyopathy (sHCM), 20 ambulatory patients with asymptomatic NYHA class I hypertrophic cardiomyopathy (asHCM) and 20 normal control subjects. Power spectral analysis decomposed the heart rate variability into high-frequency power (HF: 0.15-0.40 Hz) and low-frequency power (LF: 0.04-0.15 Hz). HF was corrected by mean RR intervals (CCVHF). CCVHF values and LF/HF ratios were used as indices of vagal and sympathetic modulations, respectively. The sHCM group demonstrated no significant elevation in CCVHF during the nighttime as compared to the daytime, while asHCM and control groups showed significant CCVHF elevation during the nighttime (p < 0.05-0.01). The nighttime CCVHF, therefore, was significantly lower in the sHCM group than in the control or asHCM group (sHCM, 1.08 +/- 0.36%; control, 1.60 +/- 0.57%; asHCM 1.82 +/- 0.77%; sHCM vs. control or sHCM vs. asHCM, p < 0.01). All of these three groups showed significant reduction in LF/HF ratio during the nighttime as compared to the daytime (p < 0.01). However, the reduction in the sHCM group was not as great as that in the control group and there was a significant difference between the sHCM and control group (2.01 +/- 1.58 vs. 1.08 +/- 0.65, p < 0.05). Two patients in the sHCM group, who later died suddenly, demonstrated very low CCVHF throughout a 24-hour period (0.2-0.8%). Both vagal and sympathetic impairment with a predominance of vagal abnormalities is suggested in patients with symptomatic NYHA class II or III hypertrophic cardiomyopathy.