Relationship between spectral components of cardiovascular variabilities and direct measures of muscle sympathetic nerve activity in humans

BACKGROUND: Spectral analysis of RR interval and systolic arterial pressure variabilities may provide indirect markers of the balance between sympathetic and vagal cardiovascular control. METHODS AND RESULTS: We examined the relationship between power spectral measurements of variabilities in RR interval, systolic arterial pressure, and muscle sympathetic nerve activity (MSNA) obtained by microneurography over a range of blood pressures. In eight healthy human volunteers, MSNA, RR interval, intra-arterial pressure, and respiration were measured during blood pressure reductions induced by nitroprusside and during blood pressure increases induced by phenylephrine. Both low-frequency (LF; 0.10 +/- 0.01 Hz) and high-frequency (HF; 0.23 +/- 0.01 Hz) components were detected in MSNA variability. Increasing levels of MSNA were associated with a shift of the spectral power toward its LF component. Decreasing levels of MSNA were associated with a shift of MSNA spectral power toward the HF component. Over the range of pressure changes, the LF component of MSNA variability was positively and tightly correlated with LF components of RR interval (in normalized units; P < 10(-6)) and of systolic arterial pressure variability (both in millimeters of mercury squared and normalized units; P < 5 x 10(-5) and P < 5 x 10(-6), respectively). The HF component of MSNA variability was positively and tightly correlated with the HF component (in normalized units) of RR-interval variability (P < 3 x 10(-4)) and of systolic arterial pressure variability (P < .01). CONCLUSIONS: During sympathetic activation in normal humans, there is a predominance in the LF oscillation of blood pressure, RR interval, and sympathetic nerve activity. During sympathetic inhibition, the HF component of cardiovascular variability predominates. This relationship is best seen when power spectral components are normalized for total power. Synchronous changes in the LF and HF rhythms of both RR interval and MSNA during different levels of sympathetic drive are suggestive of common central mechanisms governing both parasympathetic and sympathetic cardiovascular modulation.     

Effects of passive tilt and submaximal exercise on spectral heart rate variability in ventricular fibrillation patients without significant structural heart disease

It has been shown that tilt and exercise elicit significant changes in autonomic activity in normal subjects and that submaximal exercise causes a greater reduction in heart rate variability (HRV) in animals susceptible to ventricular fibrillation (VF). Whether there is an abnormal HRV response to tilt and exercise in patients at risk of sudden cardiac death (SCD) remains unknown. Short-term HRV before and during passive tilt and exercise was studied in 12 survivors of out-of-hospital cardiac arrest with documented VF and compared with 12 age- and sex-matched normal controls. No patient had significant structural heart disease or left ventricular dysfunction. HRV was computed as total-frequency (TF, 0.01 to 1.00 Hz), low-frequency (LF, 0.04 to 0.15 Hz) and high-frequency (HF, 0.15 to 0.40 Hz) components. There was no significant difference between normal controls and SCD survivors in HRV before or during tilt or submaximal exercise testing. The HF component was significantly decreased during tilt compared with that in the supine position in both normal controls (5.85 +/- 0.61 vs 5.08 +/- 0.95 In(msec2), p = 0.005) and patients (5.58 +/- 1.49 versus 4.74 +/- 1.18 In(msec2), p = 0.003). There was again no significant change in the TF or LF components during tilt in either patients or controls. All frequency components were significantly decreased during submaximal exercise testing in both patients and controls. However, there was no significant difference in any of these tilt- and exercise-induced changes in HRV between normal controls and SCD survivors.(ABSTRACT TRUNCATED AT 250 WORDS)     

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.     

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.     

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.     

Heart rate and blood pressure variability in obese normotensive subjects

OBJECTIVE: To assess autonomic modulation of cardiovascular activity in massively obese subjects. DESIGN: Cross-sectional clinical study. SUBJECTS: 43 age-matched normotensive subjects: 15 moderately obese (body mass index (BMI) < 40); 14 massively obese (BMI > 40) and 14 nonobese controls (BMI < 26). MEASUREMENTS: Using power spectral analysis, heart rate and arterial pressure variability were determined at rest and after sympathetic stress (tilt). Two spectral components were analysed: a low-frequency (LF) component at around 0.1 Hz, predominantly reflecting sympathetic modulation and a high-frequency (HF) component at around 0.26 Hz, reflecting parasympathetic modulation. RESULTS: Spectral data for heart rate showed that the massively obese subjects had lower LF [mean +/- s.e.m.] normalized units (NUs) at rest (35.1 +/- 0.9) and after tilt (56.1 +/- 2.1), than the moderately obese subjects (LF NUs at rest 53.9 +/- 4.2, P < 0.001; LF NUs tilt: 66.8 +/- 5.6, P < 0.001) and nonobese control subjects (LF NUs at rest, 56.6 +/- 3.0, P < 0.001); (LF NUs tilt: 81.7 +/- 1.7, P < 0.001). Data for systolic arterial pressure variability measured at rest exhibited the inverse pattern, the massively obese group having higher mean LF values (LF mm Hg2 rest: 15.0 +/- 1.4; LF mm Hg2 tilt: 15.7 +/- 1.5) than the moderately obese group (LF mm Hg2 rest 3.2 +/- 0.7, P < 0.001; LF mm Hg2 tilt: 7.2 +/- 2.0, P < 0.001) and than the nonobese control subjects (LF mm Hg2 rest 3.5 +/- 0.5, LF mm Hg2 tilt 8.5 +/- 0.8, P < 0.001). Regression detected a significant association between BMI and LF of systolic pressure (beta = 0.364; P = 0.0007), In LF of heart rate (beta = -5.555; P = 0.00001) and very low frequency (VLF) of diastolic pressure (beta = -3.305; P = 0.0020). CONCLUSION: Obesity seems to increase sympathetic modulation of arterial pressure, but diminishes modulation of heart rate. Because our obese subjects had high plasma noradrenaline levels, their low LF power of heart rate could reflect diminished adrenoceptor responsiveness.     

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.     

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.     

Alteration of cardiovascular vagosympathetic control evaluated by spectral analysis of variations of heart rate and blood pressure in obesity

Several studies suggest alterations of parasympathetic and sympathetic control in obesity. We have already shown that more than 40% of non diabetic obese subjects have alterations of parasympathetic control of heart rate (HR) variations. The present study aimed to investigate parasympathetic and sympathetic cardiovascular control by using spectral analysis. Sixty-two non diabetic obese subjects were compared to 38 sex-matched healthy controls. Spectral analysis was performed by Anapres system and identified two particular peaks: the one of high frequency (0.20-0.25 Hz) for heart rate variations during controlled breathing which depends on parasympathetic activity, the other of low frequency (around 0.10 Hz) for systolic BP variations in the standing position which mainly depend on sympathetic activity. In control subjects the amplitude of the high frequency peak (r = -0.556, p < 0.0001) but not the amplitude of the low frequency peak correlated negatively with age. In the obese subjects both the high and low frequency peaks correlated negatively with age (r = -0.249; p = 0.05 and r = -0.289, p = 0.036 respectively) and did not correlate with body mass index. The high frequency peak was significantly lower than in controls (4.80 +/- 3.37 (SD) vs 8.38 +/- 4.14; p < 0.0001). In the 25 obese subjects over 40 years the low frequency peak was also significantly lower than in controls (10.00 +/- 3.10 vs 11.95 +/- 4.25; p < 0.05). This study suggests that 1) age must be taken into account when interpreting the cardiovascular parameters under vagosympathetic control; 2) in non diabetic obese subjects vagal activity is decreased and in those over 40 years sympathetic activity is also decreased.     

Time and frequency domain analyses of heart rate variability during orthostatic stress in patients with neurally mediated syncope

The role of autonomic balance during upright tilt in patients with neurally mediated syncope is unclear. To assess the characteristics of autonomic tone during orthostatic stress, 15 patients (mean age 32 years) with recurrent episodes of syncope (> or = 2) and a positive response to a 30-minute 60 degrees upright tilt were compared with the following control groups: (1) 15 patients (mean age 33.5 years) with > or = 2 episodes of recurrent syncope and a negative tilt response, and (2) 15 age- and sex-matched healthy volunteers (mean age 34 years) with no previous history of presyncope or syncope. Time domain measurements assessed were mean RR interval, standard deviation of normal RR intervals, and percentage of normal consecutive RR intervals differing by > 50 ms. Frequency domain measurements of the low-frequency (LF) and high-frequency (HF) bands were obtained, and the LF/HF ratio was also calculated. All variables were calculated in the supine position and during the first 5 minutes of upright tilt. No significant difference was observed in the time and frequency domain variables in the supine position between control groups with a negative head-up tilt response and the group with a positive response. The percentage of normal consecutive RR intervals differing by > 50 ms during the first 5 minutes of head-up tilt was significantly higher in the group with positive tilt tests than in the controls (25 +/- 12% vs 7 +/- 4%, p < 0.001).(ABSTRACT TRUNCATED AT 250 WORDS)     

Relationship between repeated measures of hemodynamics, muscle sympathetic nerve activity, and their spectral oscillations

BACKGROUND: We determined the intraclass correlation coefficients (ICC) of repeated measures of the mean levels and variability of RR and muscle sympathetic nerve activity (MSNA) in 7 normal subjects. We examined whether spontaneous fluctuations in RR and MSNA over repeated measurements were mirrored by changes in spectral components of RR and MSNA. METHODS AND RESULTS: Twenty-minute recordings of respiration, RR, blood pressure (BP), and MSNA were performed at day 1, 1 week, 1 month, and 3 months and divided into two 10-minute periods for the analysis of short-term reliability. Comparison between these recordings also determined the long-term reliability. Linear regressions examined the relationship between changes in these measurements and changes in spectral components of RR and MSNA. All analyses were carried out blinded to subject and session. Short-term ICC of RR, BP, MSNA and of the variabilities of RR and MSNA (in % of total power) ranged between .98 and .70 and indicated a good short-term reliability. The long-term reliability of RR variability was comparable to MSNA variability (range of ICC, .34 to .52). Spontaneous decreases in RR during the repeated recordings were accompanied by increases in sympathetic drive, as evidenced by increases in the ratio of low-frequency to high-frequency variability (LF/HF ratio) of RR interval (r=-.43, P<.01) and by increases in MSNA (r= -.36, P=.01). The changes in the LF/HF ratio of RR were mirrored by parallel changes in the LF/HF ratio of MSNA (r=+.30, P<.05). Spontaneous decreases in BP were accompanied by increases in the LF/HF ratio of MSNA (r=-.52; P=.0001). CONCLUSIONS: Heart rate, MSNA, and their variability are stable in the short-term, but less so over the long term. Spontaneous changes in repeated measurements of RR interval and blood pressure over the long term are accompanied by parallel changes in the normalized spectral components of RR and MSNA variability. Thus even over an extended period, there is a synchrony between changes in absolute cardiovascular measures and changes in their spectral components.     

Endometrial connexin expression in the mare and pig: evidence for the suppression of cell-cell communication in uterine luminal epithelium

AIMS: To study the dose-response effects of intravenous terbutaline on the cardiovascular and respiratory autonomic nervous regulation. METHODS: The study followed a randomized, placebo-controlled crossover design in six healthy adult volunteers. The terbutaline dose ranged from 10 to 30 microg min(-1) We continuously measured electrocardiogram, finger systolic arterial pressure (SAP) and flow-volume spirometry in supine and upright positions at baseline and during 3 h drug infusion. The periodic variability components of R-R intervals (time between successive heart beats) and SAP in relation to respiration were assessed using spectral analysis techniques. The regularity of the time series was assessed by approximate entropy (ApEn) and the convolutedness by fractal dimension (FD). RESULTS: Terbutaline dose-dependently decreased total variability of R-R intervals, low frequency (LF) variability of R-R intervals (10 s waves), high frequency (HF) variability of R-R intervals (respiratory variability), total variability of SAP, HF variability of SAP, baroreflex sensitivity, plasma potassium concentration, approximate entropy of R-R interval and of SAP as well as fractal dimension of R-R interval. Terbutaline dose-dependently increased heart rate, LF/HF ratios of R-R intervals and of SAP, LF variability of SAP, minute ventilation and plasma terbutaline concentration. CONCLUSIONS: Terbutaline infusion decreases parasympathetic cardiovascular reactivity, baroreflex sensitivity, dimensionality of heart rate and plasma potassium concentration; it increases sympathetic dominance in cardiovascular autonomic balance, minute ventilation, and the regularity of heart rate and blood pressure time series.     

Psychosocial and ethical issues in surgical approaches to end-stage lung disease

This study aimed to determine whether alterations in cardiovascular dynamics before syncope are related to changes in spontaneous respiration. Fifty-two healthy subjects underwent continuous heart rate (HR), arterial blood pressure (BP), and respiratory measurements during 10-min periods of spontaneous and paced breathing (0.25 Hz) in the supine and 60 degrees head-up tilt positions. Data were evaluated by power spectrum and transfer function analyses. During tilt, 27 subjects developed syncope or presyncope and 25 remained asymptomatic. Subjects with tilt-induced syncope had significantly greater increases in low-frequency (0.04-0. 15 Hz) systolic BP, diastolic BP, and HR power during tilt than the asymptomatic subjects (P 相似文献   

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.     

Twenty-four hour time and frequency domain variability of systolic blood pressure and heart rate in an experimental model of arterial hypertension plus obesity]

Modifications of heart rate (HR) and systolic blood pressure (SBP) variabilities (V) have been reported in the human syndrome arterial hypertension plus insulin-resistance. The aim of this study was to characterize the 24 h SBPV and HRV in both time and frequency domains during weight increase in dogs fed ad libitum with a high fat diet. Implantable transmitter units for measurement of blood pressure and heart rate were surgically implanted in five beagle male dogs. BP and HR were continuously recorded using telemetric measurements during 24 hours, before and after 6 and 9 weeks of hypercaloric diet in quiet animals submitted to a 12h light-dark cycle. To study nychtemeral cycle of SBP and HR, two periods were chosen: day (from 6.00 h to 19.00 h) and night (from 23.00 h to 6.00 h). Spontaneous baroreflex efficiency was measured using the sequence method. Spectral variability of HR and SBP was analyzed using a fast Fourier transformation on 512 consecutive values and normalized units of low (LF: 50-150 mHz, reflecting sympathetic activity) and high (HF: respiratory rate +/- 50 mHz, reflecting parasympathetic activity) frequency bands were calculated. The energy of total spectrum (from 0.004 to 1 Hz) was also studied. Body weight (12.4 +/- 0.9 vs 14.9 +/- 0.9 kg, p < 0.05). SBP (132 +/- 1 vs 147 +/- 1 mmHg, p < 0.05) significantly increased after 9 weeks of hypercaloric diet. A nycthemeral HR rhythm was present at baseline (day: 79 +/- 1 vs night: 71 +/- 1 bpm) but not after 9 weeks (day: 91 +/- 4 bpm ; night: 86 +/- 2 bpm). Concomitantly, the efficiency of spontaneous baroreflex decreased at 6 weeks (36 +/- 1 vs 42 +/- 2 mmHg/ms, p < 0.05). A significant decrease in HF energy of HRV was found after 6 but not after 9 weeks. LF energy of SBPV was increased at 6 but not at 9 weeks (table). [table: see text] In conclusion, this study shows that an hyperlipidic and hypercaloric diet induces transient variations in autonomic nervous system activity which could be the physiopathological link between obesity, insulin-resistance and arterial hypertension.     

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.     

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)     

Parasympathetic activity is a major modulator of the circadian variability of heart rate in healthy subjects and in patients with coronary artery disease or diabetes mellitus

Autonomic heart rate control was assessed by power spectral analysis of heart rate variability in 24-hour ambulatory electrocardiographic recordings from 23 healthy subjects, 14 patients with coronary artery disease without cardiac dysfunction, and 14 patients with diabetes mellitus. The log value of the ratio of the low-frequency component (LF = 0.04 to 0.15 Hz) to the high-frequency component (HF = 0.15 to 0.5 Hz) and logHF were employed as indexes of sympathetic and parasympathetic activity, respectively. Diurnal and nocturnal logLF, logHF, and log(LF/HF) values were calculated for heart rates of 60, 70, and 80 beats/min. Intergroup differences among these three variables were not significant at any heart rate. Although a heart rate-related decrease in logHF was generally observed, the relationship between log(LF/HF) and heart rate was not consistent. The correlation between diurnal and nocturnal logHF values was significant at all three heart rates (r = 0.63, 0.87, and 0.59), whereas the diurnal log(LF/HF) was correlated with the nocturnal value only at 70 beats/min (r = 0.77). These results suggest that the heart rate during normal daily activities is a reliable indicator of parasympathetic tone, if not sympathetic tone, in healthy subjects and patients with coronary artery disease or diabetes mellitus.     

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.     

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.