Effect of beta blockade with and without sympathomimetic activity (ISA) on sympathovagal balance and baroreflex sensitivity

Beta blockers increase heart rate variability (HRV) and improve survival in coronary artery disease (CAD). The benefit of beta blockers with intrinsic sympathomimetic activity (ISA) in CAD still remains a matter of debate, and their effect on HRV has not yet been investigated. Therefore, we measured HRV, systolic blood pressure variability (BPV) and baroreflex sensitivity (BRS) under propranolol (PROP, without ISA, 160 mg q.d.), pindolol (PIN, with potent ISA, 15 mg q.d.) and placebo (PLA, q.d.) in 30 healthy subjects, aged 21–39 years, during controlled frequency breathing (0·30 Hz) in supine and tilt positions. PROP increased HRV in the high-frequency (0·15–0·40 Hz) band (PROP 7·4 ± 1·0; PLA 6·9 ± 1·4; PIN 6·8 ± 1·0 ln MI²; P = 0·003), decreased BPV in the low-frequency band (at 0·1 Hz, Mayer waves) (PROP 0·6 ± 0·7; PLA 1·3 ± 1·1; PIN 1·2 ± 1·2 ln mmHg²; P = 0·001) and enhanced BRS (PROP 14·6 ± 9·5; PLA 8·0 ± 6·8; PIN 8·7 ± 6·8 ms mmHg^?1; P = 0·001) in the supine position. After passive tilt, PROP decreased HRV in the low-frequency band (PROP 6·1 ± 0·9; PLA 6·5 ± 1·1; PIN 6·9 ± 0·7 ln MI²; P<0·001) and decreased Mayer waves (PROP 1·8 ± 0·8; PLA 2·4 ± 1·0; PIN 2·7 ± 0·8 ln mm Hg²; P<0·001). PIN increased the low-frequency HRV response, which is induced by passive tilt (PIN + 0·9 ± 1·0; PLA + 0·3 ± 1·3, PROP + 0·3 ± 1·0 ln MI²; P = 0·026). Our results prove that beta-adrenergic blockade with potent ISA does not increase HRV, has no beneficial effect on autonomic balance and even exaggerates sympathetic responses to passive tilt.     

Effect of posture on baroreflex sensitivity in healthy subjects

Summary. In this study we investigated whether body position has significant effects on baroreflex sensitivity in healthy subjects. Baroreflex sensitivity was calculated from pressure overshoot after the release of a Valsalva strain in the supine and sitting positions in 10 subjects. At rest, no difference was found in supine and sitting mean R-R intervals (837±82 and 858±86 ms, respectively), whereas systolic and diastolic blood pressures were lower in the supine position (111.3±24.6 vs. 141.2±12.6 mmHg, P<0.01 and 54.8±14.7 vs. 75.6±13.4 mmHg, P<0.001, respectively). Baroreflex sensitivity in the supine (9.0±4.1 ms±mmHg^-1) and sitting positions (8.8±4.9 msXmmHg^-1) did not differ significantly from each other. The correlation between supine and sitting baroreflex sensitivity was 0.96 (P<0.001) and in 9 out of 10 subjects the discrepancy between supine and sitting baroreflex sensitivity was <2.0 ms±mmHg^-1. We conclude that baroreflex sensitivity measured in the supine and sitting positions do not differ significantly from each other.     

Effects of local arteriosclerosis on carotid baroreflex sensitivity and on heart rate and arterial pressure variability in humans

The study examined whether the alterations in heart rate variability (HRV) and baroreflex sensitivity (BRS) observed in patients with coronary artery disease can also be discerned in otherwise healthy subjects with mild-to-moderate arteriosclerosis in the carotid artery bifurcation. Based on the results of carotid duplex ultrasonography, subjects were designated as either having no arteriosclerotic lesions (n = 18), unilateral (n = 19) or bilateral lesions (n = 18) in the bifurcation. Electrocardiograms were recorded and simultaneous and continuous records of arterial pressure were obtained. Resting HRV was determined by calculating the spectral power density in three frequency bands: 0-0.05 Hz [very low frequency (VLF) band], 0.05-0.15 [low frequency (LF) band] and 0.15-2 Hz (high frequency band), whereas the arterial pressure variability (APV) was determined from spectral power density of the VLF and LF bands. Carotid BRS was evaluated by measuring R-R intervals during application of pulse-synchronous graded pressures (40 to -65 mmHg) in a neck-chamber device. Analysis of variance revealed no effect of mild-to-moderate carotid arteriosclerosis on the spectral components of HRV and APV or on BRS. It thus appears that mild-to-moderate asymptomatic carotid arteriosclerosis does not affect carotid BRS, APV or HRV at rest.     

Heart rate and blood pressure variability and baroreflex sensitivity in hypercholesterolemia

Summary. To evaluate cardiovascular autonomic function in hypercholesterolaemia, we studied 16 age-matched pairs of healthy males with elevated serum cholesterol and normocholesterolaemic control subjects (altogether 37 men, aged 27–56 years). We used power spectral analysis to measure short-term heart rate and blood pressure variability, and the phenylephrine method to determine baroreceptor reflex sensitivity. The mean (SD) serum cholesterol concentration was 6.43 (1.22) among the hypercholesterolaemic subjects and 4.30 (0.44) mmol/1 among the control men (P<0.001). The respective low density lipoprotein (LDL) cholesterol concentrations were 4.44 (1.22) and 2.46 (0.38) mmol/1 (P<0.001). The total power (0.0-0.5 Hz) of heart rate and blood pressure variability did not differ between the groups, and neither did the high-frequency (0.15-0.5 Hz) and medium-frequency components (0.07-0.15 Hz). Mean (SD) baroreceptor reflex sensitivity was 18.1 (7.9) in hypercholesterolaemic and 19.4 (6.3) ms mmHg^-1 in normocholesterolaemic subjects (P=0.352). When all the subjects were analysed together, we observed a slight inverse trend between serum LDL cholesterol and baroreceptor reflex sensitivity (r= -0.235, P=0.161). In conclusion, hypercholesterolaemia does not alter autonomic neural regulation of the cardiovascular system as assessed by heart rate and blood pressure variability and baroreflex sensitivity.     

Computational and physiological background of the baroreflex sensitivity

All the commonly used definitions of baroreflex sensitivity (BRS) are based on a slope of linear relationship between systolic blood pressure and pulse interval (R–R interval). However, heart rate (HR) and R–R interval bear an inverse non‐linear relationship, which distorts determination of BRS when different HR levels are present. We analysed data of 117 healthy, normal‐weight, non‐smoking men and women aged 23–77 to show how BRS depends on the initial HR. In this data, 43% of variation in BRS is solely explained by HR. Comparisons of BRS between patients with different HR and even within the same patient with changing HR (e.g. tilt‐table test and nocturnal changes in HR) should be questioned. Consideration of the baseline HR is even more crucial, if the patients are subjected to an intervention affecting not only baroreflexes but also HR. If baseline HR is not taken into account, using the R–R interval in the estimation of BRS may lead to partially misleading values and possibly also to misinterpretation of physiological processes. We discuss alternative definitions of BRS to allow varying HRs.     

三种力量训练方案对健康青年心脏自主神经功能的影响

目的:本研究评估了不同力量训练方案对心脏自主神经功能产生的影响。方法:研究采用随机交互式的设计,20名健康男性受试者完成3次不同方案的力量训练,分别记录R-R间期:包括安静状态5min(卧位),整个力量训练期间,训练后恢复期5min(卧位),进行相应心率变异(HRV)分析,并分别进行血乳酸检测。结果:三种力量训练方案运动期及恢复期心脏的自主神经功能发生不同的调整。肌肉耐力训练方案(ME)和肌肉肥大训练方案(MH)心脏自主应答基本趋于一致,但肌肉最大力量训练方案(MM)在整个运动期间心率(HR)指标低于ME和MH(P0.05),运动中全部NN间期的标准差(SDNN)和心率变异性系数(SDNN/HR)指标略高于方案ME和MH,5min恢复期高低频比值(LF/HF)指标趋于安静状态。此外,运动后即刻MM血乳酸的浓度显著低于方案ME和MH(P0.05)。结论:方案MM在整个运动中交感活性程度相对增加,恢复期交感活性回落较快,表明不同力量训练方案对心脏自主神经功能产生影响存在差异,并可能对心脏的健康产生不同的影响。     

Effect of non-hypotensive haemorrhage on plasma catecholamine levels and cardiovascular variability in man

Background: It is well known from animal research that non‐hypotensive haemorrhage produces sympathoexcitatory responses assessable by both the rise in plasma catecholamine levels and the shift of autonomic influences on the heart to more sympathetic and less parasympathetic control. Data in humans are restricted. Methods: Heart rate variability (HRV), systolic blood pressure (FINAPRES) variability (BPV), and catecholamine plasma levels were measured before and after haemorrhage in 30 healthy blood donors and compared with those from 10 control subjects without blood loss. Spectral power of HRV and BPV in very low (0·02–0·06 Hz), low (0·07–0·14 Hz), and high (0·15–0·40 Hz) frequency bands were calculated by Fourier analysis. Catecholamine plasma levels were assayed by dual column reverse‐phased high‐performance liquid chromatography (HPLC). Results: Haemorrhage of 5·6 ± 1·2 ml kg^?1 body weight increased plasma norepinephrine levels (215 ± 92 pg ml^?1 versus 254 ± 95 pg ml^?1; P = 0·002), increased BPV in the low frequency band (Mayer waves; 1·8 ± 1·0 ln [mmHg²] versus 2·0 ± 0·9 ln [mmHg²]; P = 0·021), and decreased the vagally transmitted high frequency HRV (6·9 ± 1·1 ln [MI²] versus 6·5±1·2 ln [MI²]; P<0·0001), but did not induce significant changes in heart rate (66 ± 11 bpm versus 67 ± 11 bpm; P = 0·79) and arterial blood pressure (mean values: 84 ± 13 mmHg versus 87 ± 13 mmHg; P = 0·12). Conclusions: As suggested by plasma norepinephrine levels, systolic BPV and HRV, non‐hypotensive haemorrhage produces sympathoexcitatory responses as well as vagal withdrawal of heart rate control in humans.     

Heart rate and blood pressure variability in cardiac diseases: pharmacological implications

Summary— Even at rest, blood pressure and heart rate fluctuate continuously around their mean values. Considerable interest has recently focused on the assessment of spontaneous fluctuations in heart rate and blood pressure, ie, heart rate and blood pressure variability, using time or frequency domain indexes. Heart rate variability has been extensively studied in cardiovascular disease and has emerged as a valuable parameter for detecting abnormalities in autonomic cardiovascular control, evaluating the prognosis and assessing the impact of drug therapy on the autonomic nervous system in patients with myocardial infarction, congestive heart failure or a heart transplant. In contrast, until the recent development of noninvasive methods for continuous blood pressure recording, blood pressure variability received little attention, and this parameter remains to be evaluated in cardiovascular disease.     

Improvement in low upright baroreflex sensitivity is associated with positive clinical effect of orthostatic training

1 Aim

To assess the clinical efficacy of orthostatic training (OT) and its effect on the autonomic activity.

2 Methods

OT was performed in 38 patients (13 males, age 36.4 ± 15.2 years). Baroreflex sensitivity (BRS), heart rate variability, and quality of life (SF 36) were assessed before and after 6 months of OT. Patients with no recurrence of syncope and reduction of the presyncope number to one‐third or less were classified as responders.

3 Results

Compliance to OT was low. Only 55% (38 from 69 patients) completed the training programme; 28 patients were responders (74%) and 10 patients were nonresponders. Before OT, BRS in upright position was lower in responders than in nonresponders (sitting: 8.05 ± 3.94 ms/mm Hg vs 12.51 ± 5.3 ms/mm Hg, P = 0.04, standing: 5.08 ± 2.34 ms/mm Hg vs 7.54 ± 2.16 ms/mm Hg, P = 0.02). After OT, BRS increased in responders (sitting: 8.05 ± 3.94 ms/mm Hg to 9.31 ± 4.49 ms/mm Hg, P = 0.05; standing: 5.08 ± 2.34 ms/mm Hg to 5.96 ± 2.38 ms/mm Hg, P = 0.03). No differences in supine BRS were observed. In responders, low frequency (LF) and high frequency (HF) power in sitting and standing positions significantly increased after OT (P < 0.05). In nonresponders, there was no significant rise in BRS, LF, and HF after OT. A significant increase in quality of life was noted in responders, but not in nonresponders.

4 Conclusions

OT reduced symptoms in 74% patients who trained regularly. However, the compliance to training was low. Possible mechanism of OT is reconditioning effect on baroreceptor reactivity in upright position.     

Nitroglycerin induced syncope occurs in subjects with delayed phase shift of baroreflex action

Nitroglycerin (NTG) administration occasionally leads to syncope due to severe hypotension and bradycardia. This reaction resembles neurocardiogenic syncope but it may occur when the patient is in the supine position. To address the possible role of prevailing autonomic tone and baroreflex control in precipitation of NTG induced syncope, continuous noninvasive blood pressure and an ECG were taken shortly before NTG application in the supine position. Frequency-domain measures of heart rate variability (HRV) and noninvasive indices of baroreflex were compared between subjects who did (n = 6) and did not (n = 41) develop syncope after NTG. Both groups differed only in the phase shift (P(CR)) between oscillations of blood pressure and heart rate during controlled respiration (0.1 Hz). P(CR) was significantly delayed in subjects who developed syncope than in controls (- 99.3+/-14.1 vs -65.5+/-27.0 degrees, P = 0.002). Thus, subjects with prolonged P(CR) are prone to NTG induced syncope because of increased lagging and, consequently, less stable baroreflex control.     

Non-invasive evaluation of sympathovagal balance in athletes by time and frequency domain analyses of heart rate and blood pressure variability

SUMMARY. We examined how the time and frequency domain measures of heart rate and blood pressure variability at supine rest reflect the sympathovagal balance of 23 female and male endurance athletes. Pharmacological blocking by atropine and propranolol was used as a standard for defining autonomic control of the heart. The Rosenblueth and Simeone model for neural control of heart rate was used to calculate the sympathovagal balance index (Abai)- Atropinization significantly decreased all time and frequency domain measures of heart rate and blood pressure variability. (3-Blockade significantly decreased further the low- < 0–07 Hz) and medium-frequency power (007-0-15 Hz) variability of R-R intervals (RRI) and SD of RRI. A_bal was 0–629 ± 0019, indicating that parasympathetic activity predominated in the athletes. Basal heart rate (r= 0–519, P < 001), SD of RRI (r= -0–533, P < 0–01), root-mean-square of successive RRIs (RRI RMSSD) (r= -0–579, P < -05), RRI total (r=-0–557, P <001) and RRI high-frequency (HF) power (r= -0–582, P < 0–01) correlated significantly with A_bal and parasympathetic activity index. We concluded that the best non-invasive method of evaluating the sympathovagal balance of athletes at supine rest is to measure SD of RRI, RRI RMSSD, HF and total power of RRI variability. All heart rate variability measures were mainly parasympathetically modulated. The nature of blood pressure variability measures remained unclear and they could not be used to evaluate the sympathovagal balance among athletes.     

Spontaneous baroreflex by sequence and power spectral methods in humans,

Summary. Beat-by-beat variations in blood pressure and RR-interval are interrelated by the actions of baroreflex and non-baroreflex responses. This study had two purposes: (1) to examine the spontaneous relationships between RR-interval and systolic blood pressure to determine the relative occurrence of baroreflex and non-baroreflex responses in humans, and (2) to compare the beat-sequence method with a cross spectral estimate of the baroreflex response slope. Eight healthy men were studied during 10 h of quiet, seated rest, and six men and three women were studied during rest, rest plus fixed pace breathing, and a cold pressor test. RR-interval and continuous, non-invasive arterial blood pressure were measured with a computerized system. A baroreflex sequence was defined by a series of at least three consecutive heart beats in which systolic pressure and the following RR-interval either both increased or both decreased. A non-baroreflex relationship was defined by sequences of at least three beats by opposite directional changes of RR-interval and systolic pressure of that beat. The results showed that there were approximately 30% as many non-baroreflex compared to baroreflex slopes. Individual subject mean baroreflex and non-baroreflex slopes were highly correlated (r= 0–72, P < 0–001). Absolute slope values were not different, and they were unaffected by time, fixed pace breathing, or cold pressor test. The data showed the relatively simple beat-by-beat sequence method to yield spontaneous baroreflex response slopes that were quantitatively similar to, and highly correlated with (r= 0–85-0-94), baroreflex response slopes calculated by spectral analysis methods.     

Effects of age on the cardiac and vascular limbs of the arterial baroreflex

BACKGROUND: Healthy ageing has several effects on the autonomic control of the circulation. Several studies have shown that baroreflex-mediated vagal control of the heart deteriorates with age, but so far there is little information regarding the effect of ageing on sympathetically mediated baroreflex responses. The aim of this study was to assess the effects of ageing on baroreflex control of the heart and blood vessels. MATERIALS AND METHODS: In 40 healthy volunteers, aged 20-87 years, we applied oscillatory neck suction at 0.1 Hz to assess the sympathetic modulation of the heart and blood vessels and at 0.2 Hz to assess the effect of parasympathetic stimulation on the heart. Breathing was maintained at 0.25 Hz. Blood pressure, electrocardiographic RR intervals and respiration were recorded continuously. Spectral analysis was used to evaluate the magnitude of the low-frequency (0.03-0.14 Hz) and high-frequency (0.15-0.50 Hz) oscillations in the RR interval and blood pressure. Responses to neck suction were assessed as the change in power of the RR interval and blood pressure fluctuations at the stimulation frequency from baseline values. RESULTS: Resting low- and high-frequency powers of the RR interval decreased significantly with age (P < 0.01). However, the low-frequency power of systolic blood pressure did not correlate with age. Spontaneous baroreflex sensitivity (alpha-index) showed a significant inverse correlation with age (r = -0.46, P < 0.05). Responses of the RR interval and systolic blood pressure to 0.1 Hz neck suction stimulation were not related to age, however, the RR interval response to 0.2 Hz neck suction declined significantly with age (r = -0.61, P < 0.01). CONCLUSIONS: These results confirm an age-related decrease in cardiovagal baroreflex responses. However, sympathetically mediated baroreflex control of the blood vessels is preserved with age.     

Heart rate variability and baroreflex sensitivity in bilateral lung transplant recipients

The effects of lung afferents denervation on cardiovascular regulation can be assessed on bilateral lung transplantation patients. The high‐frequency component of heart rate variability is known to be synchronous with breathing frequency. Then, if heart beat is neurally modulated by breathing frequency, we may expect disappearance of high frequency of heart rate variability in bilateral lung transplantation patients. On 11 patients and 11 matching healthy controls, we measured R‐R interval (electrocardiography), blood pressure (Portapres^®) and breathing frequency (ultrasonic device) in supine rest, during 10‐min free breathing, 10‐min cadenced breathing (0·25 Hz) and 5‐min handgrip. We analysed heart rate variability and spontaneous variability of arterial blood pressure, by power spectral analysis, and baroreflex sensitivity, by the sequence method. Concerning heart rate variability, with respect to controls, transplant recipients had lower total power and lower low‐ and high‐frequency power. The low‐frequency/high‐frequency ratio was higher. Concerning systolic, diastolic and mean arterial pressure variability, transplant recipients had lower total power (only for cadenced breathing), low frequency and low‐frequency/high‐frequency ratio during free and cadenced breathing. Baroreflex sensitivity was decreased. Denervated lungs induced strong heart rate variability reduction. The higher low‐frequency/high‐frequency ratio suggested that the total power drop was mostly due to high frequency. These results support the hypothesis that neural modulation from lung afferents contributes to the high frequency of heart rate variability.     

Altered cardiovascular autonomic regulation after salmeterol treatment in asthmatic children

The effects of therapeutic 4 weeks' inhaled salmeterol treatment on the cardiovascular and respiratory autonomic nervous regulation was studied in 11 asthmatic children using inhaled corticosteroid medication. The study followed a randomized, double-blind, placebo-controlled cross-over design. The salmeterol dose was 50 μg twice daily. The 4-week salmeterol treatment increased baseline heart rate, low-frequency/high-frequency (LF/HF) variability ratio of R–R intervals, LF variability of systolic arterial pressure (SAP) and maximum tidal volume during the deep breathing test, as well as morning and evening peak expiratory flow (PEF) values. The 4-week salmeterol treatment decreased baseline HF variability of R–R intervals. As a response to the acute 600 μg of salbutamol, the changes in heart rate, HF variability of R–R intervals and diastolic blood pressure were significantly smaller after 4 weeks' salmeterol treatment. In conclusion, 4 weeks' therapeutic salmeterol treatment decreases basal cardiovagal reactivity, increases sympathetic dominance in the cardiovascular autonomic balance and improves pulmonary function. A tolerance develops in the cardiovascular response but not in the bronchodilatory response.     

Comparison of the effects of antenatal magnesium sulphate and ritodrine exposure on circulatory adaptation in preterm infants

We examined the effects of maternal magnesium sulphate (MgSO4) and ritodrine treatments on the autonomic cardiovascular control in preterm neonates with respiratory distress syndrome during the first 2 days of life. Serial measurements of heart rate (HR), blood pressure (BP) and respirogram were performed during the first 2 days of life in 28 preterm infants below 33 weeks of gestation with antenatal exposure to MgSO4 (n = 13) or ritodrine (n = 15), and in 12 nonexposed preterm controls. Spectral analysis was used for the quantification of HR and BP variability. Although antenatal MgSO4 exposure had no effect on HR or the systolic, diastolic or mean BP, it was associated with significant decreased beat-to-beat changes in BP. In contrast, ritodrine exposure had no consistent effects on the autonomic cardiovascular control during the first 2 days of life. Our data suggest that maternal MgSO4 treatment decreases the neonatal high frequency changes in BP. This early vascular stabilizing effect of antenatal MgSO4 exposure may contribute to a lowered risk of cerebral vascular catastrophes, in the vulnerable areas of the brain, among the preterm infants with respiratory distress syndrome.     

Autonomic cardiovascular regulation in quiescent ulcerative colitis and Crohn's disease

BACKGROUND: In inflammatory bowel diseases, changes in autonomic enteric regulation may also affect neural cardiovascular control. However, while cardiac autonomic modulation has been shown to be impaired in active ulcerative colitis, the occurrence of cardiovascular autonomic alterations, also in the quiescent phase of inflammatory bowel diseases, is still a matter of debate. The aim of our study was thus to explore the features of cardiovascular autonomic regulation in ulcerative colitis and Crohn's disease during their remission phase. MATERIALS AND METHODS: Autonomic cardiovascular control was evaluated by time- and frequency-domain indexes of spontaneous heart rate and blood pressure variability and by assessing the baroreflex heart rate control (sequence technique) in 26 patients with ulcerative colitis, in 26 patients with Crohn's disease and in 23 healthy controls. RESULTS: The groups were matched for age, gender and body mass index. They had similar blood pressure mean levels and variability. By contrast, mean heart rate, its overall variability (standard deviation), and baroreflex sensitivity were lower in ulcerative colitis patients than in controls. Moreover, all indexes related to cardiac vagal control were significantly lower in ulcerative colitis patients with respect not only to controls but also to Crohn's disease patients. CONCLUSIONS: Cardiac vagal control is impaired in quiescent ulcerative colitis only, and not in Crohn's disease, while in both bowel diseases vascular control appears preserved. Since cardiovagal modulation seems related to anti-inflammatory mechanisms, the reduced parasympathetic cardiac regulation in apparently quiescent ulcerative colitis suggests that such systemic derangement is accompanied by local subclinical inflammations, even in the absence of clinically active inflammatory processes.     

Investigation of heart rate and blood pressure variability, baroreflex sensitivity, and approximate entropy in acute brain injury patients

Purpose

The purpose of the study was to investigate longitudinally over time heart rate (HR) and blood pressure variability and baroreflex sensitivity in acute brain injury patients and relate them with the severity of neurologic dysfunction and outcome.

Methods

Data from 20 brain injured patients due to multiple causes and treated in the intensive care unit were used, with HR and blood pressure recorded from monitors and analyzed on a daily basis. We performed power spectral analysis estimating low frequencies (LF: 0.04-0.15 Hz), high frequencies (HF: 0.15-0.4 Hz), and their ratio and calculated the approximate entropy, which assesses periodicity within a signal and transfer function (TF), that estimates baroreflex sensitivity. Heart rate variance was considered as a measure of HR variability.

Results

Nonsurvivors (brain dead) had lower approximate entropy (0.65 ± 0.24 vs 0.84 ± 0.26, P < .05) and lower variance mean values (0.48 ± 0.54 vs 1.29 ± 0.42 ms²/Hz, P < .01), lower LF and HF minimum values (0.31 ± 0.88 vs 1.11 ± 0.46, P < .01; and 0.27 ± 0.42 vs 0.86 ± 0.30, P < .01, respectively), lower LF/HF (0.22 ± 0.29 vs 0.62 ± 0.28, P < .01), and lower TF mean values (0.43 ± 0.29 vs 1.11 ± 0.74, P < .05) during their whole stay in the intensive care unit in relation with survivors. The mean variance (P < .05), mean TF (P < .05), and mean LF/HF (P < .05) were significantly successful in separating survivors from nonsurvivors.

Conclusions

We conclude that in acute brain injury patients, low variability, low baroreflex sensitivity, and sustained decrease in LF/HF of HR signals are linked with a high mortality rate.     

Parasympathetic versus sympathetic control of the cardiovascular system in young patients with type 1 diabetes mellitus

Autonomic neuropathy and cardiovascular dysregulation are common complications of the diabetes mellitus (DM). The aim of the study was to test the hypothesis that cardiovascular regulation is abnormal in young patients with type 1 DM. Patients with type 1 DM (17, 10 females, 7 males) aged 12.9-31.5 years (mean+/-SEM: 22.4+/-1.0 years) were investigated. The mean duration of DM was 12.4+/-1.2 years. The control group consisted of 17 healthy probands matched for sex and age. The length of R-R intervals was measured using telemetric system (VariaCardio TF4; Sima Media) where ECG signal (sampling frequency 1000 Hz) from thoracic belt was transferred into PC for further analysis. Systolic blood pressure (SBP) was monitored beat-to-beat using volume-clamp method by Finapres 2300 (Ohmeda). Spectral power in HF band of HRV (HRV-HF) was taken as an index of parasympathetic control and spectral power in LF band of systolic BPV (BPV-LF) as an index of sympathetic control. In young patients with type 1 DM significant reduction of spectral power in HF band of the heart rate variability was found, whereas no significant difference between DM group and control group was observed in spectral power in LF band of blood pressure variability. In conclusion, we found impaired parasympathetic control of heart rate in young patients with type 1 DM. No differences in blood vessels sympathetic control were detected using spectral analysis of BPV. We suggest that abnormalities in cardiac parasympathetic regulation precede impairment of blood vessels sympathetic control in young diabetics.     

Sympathetic predominance of cardiovascular regulation during mild orthostatic stress in adolescents with chronic fatigue

Haemodynamic abnormalities have been documented in the chronic fatigue syndrome (CFS), indicating functional disturbances of the autonomic nervous system responsible for cardiovascular control. This study was designed to explore the pathophysiology in adolescent CFS-patients by analysing RR-interval (RRI) variability and diastolic blood pressure (DBP) variability during mild orthostatic stress, using an algorithm which accounts for non-stationary biosignals. A total of 27 adolescents with CFS and 33 healthy control subjects having equal age- and sex distribution underwent 15 min of 20 degrees head-up tilt (HUT). The spectral power densities of RRI and DBP were computed in the low-frequency (LF) band (0.04-0.15 Hz) and the high-frequency (HF) band (0.15-0.4 Hz) using an adaptive autoregressive algorithm to obtain a time-varying spectrum. RMSSD, a time domain index of RRI variability, was also computed. At rest, all indices of variability were similar in the two groups. During tilt, CFS patients had a larger increase in the LF/HF ratio (P相似文献