The relationship of autonomic functional disturbance and atherosclerosis in type 2 diabetes

The aim of the study was to assess the relationship between the autonomic nerve disturbance and atherosclerotic changes in patients with type 2 diabetes. Aortic distensibility and max carotid intima-media thickness (Max IMT) were evaluated using brachial ankle pulse wave velocity (PWV) and high-resolution B-mode ultrasonography, respectively, in 135 patients (69 men, 66 women, 57 +/- 16 years) with type 2 diabetes. The autonomic neuropathy was evaluated using coefficient of variation of the RR interval (CV(R-R)) of electrocardiograms recorded at rest in a supine position. There was a significant negative correlation between CV(R-R)and Max IMT (r= -0.488, p< 0001). There were also significant negative correlations between CVR-(R a)nd the left and the right PWV(r=0.518, p<0.001; r=0.551, p<0.001, respectively). Patients with normal Max IMT, but decreased CVR-R, had a high PWV compared to patients with normal Max IMT and normal CVR-(R. )Therefore, decreased CVR-(R i)n type 2 diabetic patients may reflect atherosclerotic changes. Thus, the measurement of CVR-(R i)s a simple and quantitative test for assessing atherosclerotic as well as neuropathic complications in diabetic patients.     

Decreased tolerance to orthostatic stress in diabetics

Cardiovascular responses to head up tilt (HUT) were investigated in chronic diabetics (having disease of 8 to 10 years duration) and in control subjects. The parameters recorded were heart rate (HR), blood pressure (BP), forearm blood flow (FABF) and forearm vascular resistance (FAVR). Recordings were made first in the supine position, next after HUT, and thirdly in the recovery period after return to the supine position. Normal subjects responded to HUT by a marked increase in HR (P less than 0.001), decrease in FABP (P less than 0.001) and increase in FAVR (P less than 0.001). The diastolic blood pressure (DBP) and mean blood pressure (MBP) showed appreciable increase (P less than 0.001, P less than 0.01 respectively) without significant fall in systolic blood pressure (SBP). The maximum alteration in cardiovascular responses was observed immediately after HUT (within 15 sec). The cardiovascular responses to HUT in diabetics were found to be significantly impaired compared to control subjects. The impairment of cardiovascular responses in diabetics in indicative of autonomic neuropathy which can be detected by these tests before the development of clinical signs of the neuropathy.     

Effects of the muscle pump and body posture on cardiovascular responses during recovery from cycle exercise

The purpose of the study was to characterize the effects of muscular contractions (the muscle pump) and body posture on cardiovascular responses during recovery from moderate exercise in the upright-sitting or supine positions. Heart rate (HR), stroke volume (SV), and cardiac output (CO) were measured in seven young male subjects at rest and during 10-min of cycle exercise at 60% of peak oxygen uptake This was followed by either complete rest for 5 min (inactive recovery) or cycling at for 5 min (active recovery) in the upright or supine positions. In the upright position, an initial rapid decrease in HR was followed by a gradual decrease in HR, and this response was similar when comparing inactive and active recoveries. Upright SV during inactive recovery decreased gradually to the pre-exercise resting level, whereas upright SV during active recovery remained significantly elevated. In contrast, in the supine position, the HR during active recovery decreased, but remained significantly higher than that during inactive recovery. Changes in supine SV were similar when comparing inactive and active recovery. Thus, maintenance of SV and HR resulted in significantly greater CO during active recovery than during inactive recovery, regardless of body position. HR was greater during supine active-recovery than during supine inactive-recovery, and there was no difference in SV. These data suggest that the muscle pump is less important in facilitating venous return and vagal resumption in the supine position as compared to the upright position.     

Haemodynamic and baroreflex responses to whole-body tilting in exercising men before and after 6 weeks of bedrest

We sought to determine whether the cardiovascular deconditioning that occurs in exercising men after prolonged (42 days) bedrest in the head-down tilt (HDT) position is primarily related to mechanical changes in the heart or to an impaired arterial-cardiac-chronotropic baroreflex. Seven subjects were studied before (C, control) and repeatedly after HDT with rapid tilting between the upright and supine positions during steady-state 50-W dynamic leg exercise. Ventricular interdependence was assumed to be an index of cardiac size; it was assessed on the basis of the initial dip of arterial pulse pressure (PP) induced by a sudden tilt from the upright to the supine position (down-tilt). Arterial-cardiac-chronotropic baroreflex sensitivity (ABS) was assessed as the ratio between tilt-induced heart rate transients and the preceding (and reciprocal) transient in arterial pressure. On the first day of recovery, the initial PP dip was −4 (2) mmHg (where 1 mmHg is 0.13 kPa), less than half of the control value; on subsequent recovery days, the initial PP dip was not significantly different from the control value. When tilting from the upright to the supine position, mean ABS ranged from 1.02 to 1.06 bpm/mmHg during three separate control sessions. Tilts in the opposite direction gave lower ABS values because of the more sluggish HR response and ranged from 0.43 to 0.45 bpm/mmHg in the control situations. ABS did not change after HDT. Our results indicate that impairments of the cardiovascular system after long-term bedrest are of haemodynamic rather than baroreflex origin. Accepted: 8 March 2000     

A non-invasive approach to cardiac autonomic neuropathy in patients with diabetes mellitus

The purpose of this study was to obtain information regarding the participation of the sympathetic nervous system in cardiac autonomic neuropathy in patients suffering from diabetes mellitus employing spectral analysis of heart rate variability in the supine and standing posture. Ten insulin-dependent diabetic patients (29 +/- 2 years) with a short to moderately long duration of diabetes (11 +/- 1 years) and cardiac vagal neuropathy based on measurements of respiratory sinus arrhythmia were compared to 10 healthy volunteers (27 +/- 1 years) before and after the administration of atropine and atropine plus propranolol. In diabetic patients the reactivity in total power (delta TP) from supine to upright position was significantly lower compared to control subjects before and after atropine. There was no significant difference in delta TP between diabetics and controls after atropine plus propranolol. The magnitude of TP increase is essentially due to the increase of blood pressure related heart rate fluctuations (delta MF) from lying to standing and dependent on beta-adrenergical efferent activity to the heart. In diabetic patients as well as in normal subjects under the influence of atropine plus propranolol the delta MF power was significantly lower compared to the unmedicated control and atropine group. There was no significant difference between diabetics and controls after combined autonomic blockade. It was concluded that delta MF heart rate spectral power could serve as an indirect, non-invasive, quantitative and sensitive marker of early cardiac sympathetic damage.     

Temperamental activation and inhibition associated with autonomic function in preadolescents. The TRAILS study

We investigated the temperamental traits high-intensity pleasure (temperamental activation) and shyness (temperamental inhibition) in relation to autonomic function as measured by heart rate (HR), respiratory sinus arrhythmia (RSA), and baroreflex sensitivity (BRS) in 938 10-13-year-old preadolescents from a population cohort. Temperament was evaluated by parent reports on the Revised Early Adolescent Temperament Questionnaire. Autonomic measurements were obtained in supine and standing position. High-intensity pleasure was negatively associated with supine HR and positively with supine RSA and BRS in both genders. Shyness was positively related to supine BRS in girls only. Orthostatic-based autonomic reactivity (difference) scores adjusted for supine values were unrelated to temperamental measures. It appeared that higher scores on temperamental activation and inhibition are associated with higher cardiac vagal activity (RSA) and/or flexible regulation of autonomic balance (BRS), implicating healthy physiological functioning. Moreover, results suggest a physiological basis promoting the tendency towards engagement in high-intensity activities.     

Reliability of orthostatic responses in healthy men aged between 65 and 75 years

The purpose of this study was to investigate the short-, medium- and long-term reproducibility of cardiovascular responses during 90 degrees head-up tilt (HUT) in healthy older men. Twenty-eight healthy male subjects aged 69 (95% confidence intervals, 68-70) years participated in the study. Eight subjects underwent duplicate 90 degrees HUT tests on consecutive days, while 20 subjects underwent four 90 degrees HUT tests performed at baseline, and after 1 week, 1 month and 1 year. Following a 20-min supine resting period, each subject was rapidly tilted to the upright vertical position (90 degrees HUT) and remained in that position for 15 min. Beat-by-beat recordings of mean (MAP), systolic (SBP) and diastolic (DBP) pressures were made via Finapres, while heart rate (HR) was monitored continuously from an electrocardiogram. No significant test-retest differences (P > 0.05) were observed for the changes in HR, MAP, SBP or DBP during 90 degrees HUT. These measurements demonstrated high reproducibility (intraclass correlation coefficient, r = 0.91-0.99, P < 0.05). The supine resting and tilted HR, MAP, SBP and DBP over the 1-week, 1-month and 1-year period were not significantly different (P > 0.05) from baseline, and demonstrated high reproducibility (intraclass correlation coefficient, r = 0.82-0.98, P < 0.05). The results of this study demonstrate that in healthy older men, cardiovascular responses during orthostasis are highly reproducible, and this reproducibility is maintained over a 12-month period. These findings demonstrate that the 90 degrees HUT test offers a reproducible method of monitoring longitudinal orthostatic responses in healthy older men.     

高血压患者外周血管壁腔比与脉搏传导速度的探讨

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基于波形分析的多种PWV获取系统的设计

主动脉脉搏波速度（aoPWV）是心血管疾病的独立预测因子,但难以采用波形分析方法直接获取,医学界采用颈股PWV（cfPWV）、臂踝PWV（baPWV）、心股PWV（hfPWV）近似代替aoPWV。目前三种指标在国内外均有应用,但三者的差异性尚未得到深入研究。我们设计了一种无创脉搏波检测仪器,同步采集心电、心音和多路脉搏波信号,采用专用软件准确解析出上述三种PWV,为后续研究工作提供了基础实验平台。实测结果表明：采集的波形信号稳定、真实,可准确获取cfPWV、baPWV、hfPWV。     

The effect of major depression on postexercise cardiovascular recovery

Major depressive disorder (MDD) is associated with increased cardiovascular (CV) mortality. Dysfunctional autonomic control of the CV system may represent a mechanism explaining this relationship. Poor CV recovery after exercise, indicative of dysfunctional autonomic control of the CV system, predicts CV events and death. This is the first study to examine the association between MDD and postexercise CV recovery. Some 886 patients underwent exercise stress tests. Heart rate (HR), systolic blood pressure, and diastolic blood pressure were measured at rest, peak exercise, 1 min, and 5 min after exercise. Patients with MDD had slower HR recovery (p=.026) 1 min after exercise than non-MDD patients. No other effects of MDD were found. MDD is accompanied by a dysregulation in autonomic control of exercise-related CV recovery, suggesting that depressed individuals have a slow parasympathetic recovery from exercise.     

Spectral characteristics of heart rate fluctuations during parabolic flight

Parabolic flight is used to create short successive periods of changing gravity in a range between 0 and 1.8 Gz (1 Gz: 9.81 m/s²). The purpose of the present study was to evaluate whether cyclic variations in heart rate during ±20 s periods of stable gravity in parabolic flight reflect autonomic modulation of cardiac chronotropy. During the 29th and 32nd ESA parabolic flight campaign ECG and respiration were recorded in 13 healthy volunteers in both standing and supine postures. We developed and validated a spectral algorithm especially adapted to study frequency components of heart rate among ultrashort (±20 s) stable gravity periods of parabolic flight. A low frequency (LF) component, starting from the lowest measurable frequency (±0.05 Hz) up to 0.15 Hz was distinguished from a high frequency (HF) component, ranging from 0.16 Hz up to 0.4 Hz. Powers were calculated by integration between corresponding limits and represented in normalized units (nu). With our method, we were able to reproduce normal findings in the upright posture at 1 Gz, i.e., less power in the HF component compared to supine (HFnu: 0.18±0.09 vs. 0.40±0.16). These postural related differences are shown to be eliminated at 0 Gz (HFnu: 0.30±0.12 vs. 0.32±0.13) and amplified at 1.8 Gz phases (HFnu: 0.15±0.10 vs. 0.39±0.16) of parabolic flight. In the supine position no coherent differences were shown in the measured variables among different gravity phases. Our observations strongly indicate that spectral characteristics of heart rate fluctuations among stable gravity periods of parabolic flight reflect parasympathetic nervous system control of cardiac chronotropy. At 1 Gz, there is a normal upright situation with less parasympathetic modulation of heart rate compared to supine. This effect is augmented during 1.8 Gz-conditions due to a suppressed parasympathetic control of heart rate in the upright posture. Alternatively, at 0 Gz, increased parasympathetic control in standing position eliminates differences in cardiac chronotropy compared to supine.     

Parasympathetic heart rate modulation during parabolic flights

During parabolic flight short periods of microgravity and hypergravity are created. These changes influence cardiovascular function differently according to posture. During the 29th parabolic flight campaign of the European Space Agency (ESA), the electrocardiogram (ECG) was recorded continuously in seven healthy volunteers in two positions (standing and supine). Five different phases were differentiated: 1 g (1 g=9.81 m/s²) before and after each parabola, 1.8 g at the ascending leg of the parabola (hypergravity), 0 g at the apex, 1.6 g at the descending leg (hypergravity). We assessed heart rate variability (HRV) by indices of temporal analysis [mean RR interval (meanRR), the standard deviation of the intervals (SDRR), and the square root of the mean squared differences of successive intervals (rMSSD) and coefficient of variation (CV)]. In the supine position no significant differences were shown between different gravity phases for all HRV indices. In the standing position the 0 g phase showed a tendency towards higher values of meanRR compared to the control and to the other phases (p=NS). SDRR, rMSSD and CV were significantly higher compared to control (p<0.05). Significantly higher values for meanRR in the supine position at 1 g and hypergravity (p<0.05) were found when compared to standing. SDRR was significantly higher at 0 g in the standing position compared to supine [95 (44) ms vs. 50 (15) ms; p<0.05] and lower in other phases. rMSSD and CV showed the same trend (p=NS). We confirm that, during parabolic flights, position matters for cardiovascular measurements. Time domain indices of HRV during different gravity phases showed: (1) higher vagal modulation of the autonomic nervous system in microgravity, when compared with normo- or hypergravity in standing subjects; and (2) no differences in supine subjects between different g phases.     

Effect of body position on bilateral EEG alterations and their relationship with autonomic nervous modulation in normal subjects

This study investigated the effect of body position on the electroencephalogram (EEG) and autonomic nervous modulation, and the relationship between them using spectral analysis of EEG and heart rate variability (HRV). All healthy volunteers recruited had their electrocardiogram and EEG recorded for power spectral analysis. We found that when changing position from supine to upright, the EEG spectral components below the α band, such as δ and θ bands, were significantly decreased while the EEG spectral components above the α band, such as β, γ and ω bands, were significantly increased in both scalps. Correlation analysis showed that the θ rhythm of both scalps might be associated with the control of HR, the α and β rhythms of right scalp might be associated with vagal modulation, and the γ rhythm of left scalp might be associated with sympathetic modulation of the subject. Thus, some EEG components might be associated with the autonomic nervous modulation of the subject during positional change. There might be a mechanism located in the brain-stem which jointly controls both autonomic influences on heart rate and EEG activation.     

基于心电-脉搏波的心血管疾病识别研究

为实现心血管疾病的早期筛查,降低心血管疾病临床检测的成本。本研究基于上肢脉搏波传导速度（PWV）及脉搏波相关血液动力学基础理论,采集了总计51人的脉搏波与心电信号数据,提取了包括3种PWV和脉搏波特征参数总计16个特征参数,将不同的PWV与脉搏波特征组成3个样本特征数据集,分别建立了基于K近邻学习（KNN）和支持向量机（SVM）的心血管疾病识别模型。KNN模型分类准确率为66.28%,SVM模型分类准确率为84.3%,并通过对比不同PWV对模型性能的影响,确定了用于血管评估的最优脉搏波传导速度pwvm。研究表明基于SVM建立的分类模型对心血管疾病识别有一定可靠性,为低成本的心血管疾病早期筛查提供了新思路,也为穿戴式心血管系统监测提供了基础。     

Myocardial response to incremental exercise in endurance-trained athletes: influence of heart rate,contractility and the Frank-Starling effect

Recent evidence indicates that endurance-trained athletes are able to increase their stroke volume (SV) throughout incremental upright exercise, probably due to a progressively greater effect of the Frank-Starling mechanism. This is contrary to the widely held belief that SV reaches a plateau at a submaximal heart rate (irrespective of fitness level), owing to a limitation in the time for diastolic filling. The purpose of this investigation was to evaluate whether endurance-trained athletes rely on a progressively greater effect of the Frank-Starling mechanism throughout incremental exercise. A secondary purpose was to evaluate the effects of postural position on the cardiovascular responses to incremental exercise. Ten male cyclists participated in this investigation. Left ventricular function was assessed throughout incremental exercise in the supine and upright positions (counterbalanced) using radionuclide ventriculography. Stroke volume increased in a linear fashion during incremental exercise in both the upright and supine positions. The increases in cardiac output (Q) throughout incremental to maximal exercise (in both the supine and upright positions) were significantly related to changes in heart rate, myocardial contractility and the Frank-Starling mechanism. Percentage changes in end-diastolic volume and SV were significantly greater in the upright position versus the supine position, reflecting an increased reliance on the Frank-Starling effect to increase Q. We conclude from this investigation that highly trained endurance athletes are able to make progressively increasing usage of the Frank-Starling effect throughout incremental exercise. Postural position has a significant effect on the relative contribution of heart rate, myocardial contractility and the Frank-Starling mechanism to the increase in Q during exercise conditions.     

Effects of long-term exercise training on cardiac autonomic nervous activities and baroreflex sensitivity

Reductions in tonic vagal controls of the heart and depressed baroreflex sensitivity (BRS) have been associated with a postural fall in blood pressure (BP) and the incidence of cardiac events among older people. We examined the hypothesis that BP regulation during orthostatic challenge as well as heart rate variability (HRV) at rest can be better maintained in long-term exercise-trained, healthy, older men (aged 60–70 years). Subjects were classified into two groups; long-term exercise-trained (LTET, n=14) and sedentary (SED, n=10) according to their history of physical activity. Prior to the dynamic BRS assessment, supine resting autonomic cardiac modulation was assessed by means of time domain HRV [standard deviation of ECG R–R interval (RRISD) and the coefficient of variation (CV)]. The BRS was assessed during 60° head-up tilting by simultaneously measuring beat-by-beat systolic blood pressure (SBP) and ECG R–R interval changes. The BRS gain was determined by the regression slope coefficient based on the extent of the SBP fall and the corresponding ECG R–R shortening during the orthostatic challenge. The results indicated that the LTET group manifested greater ECG R–R interval fluctuations with significantly higher resting RRISD and CV, compared with the SED group [59.5 (10.4) versus 27.7 (7.8) ms, p<0.05; 5.5 (0.8) versus 2.8 (0.7)%, p<0.05], respectively. Using dynamic BRS testing during the acute orthostatic challenge, the LTET group showed a significantly higher BRS gain than the SED [6.4 (0.8) versus 3.8 (0.6) ms·mmHg⁻¹, p<0.017] group. These results indicate that CV and BRS are well maintained in healthy, LTET older individuals when compared with their sedentary peers. Our data suggest that this augmented autonomic cardiac modulation reflects better parasympathetic responsiveness in LTET individuals. Data provide further support for long-term exercise training as another possible cardioprotective factor that might decrease susceptibility to ventricular fibrillation as well as assist arterial BP at the onset of an orthostatic challenge in older men. Electronic Publication     

Influence of the Angiotensin II Type I Receptor Gene 1166A > C Polymorphism on BP and Aortic Pulse Wave Velocity Among Malays

Angiotensin II type 1 receptor ( AGT1R ) gene 1166A > C polymorphism has been shown to be associated with essential hypertension and aortic stiffness as measured by carotid femoral pulse wave velocity (PWV). This study was carried out to investigate the association of the 1166A > C polymorphism with blood pressure (BP) and PWV among Malay hypertensive and normotensive subjects.
Two hundred and one hypertensive subjects without evidence of cardiovascular (CV) complications and 201 age- and sex-matched normotensive subjects were studied in a cross-sectional design. Blood pressures (BP) and PWV were measured, and 1166A > C genotype was determined by polymerase chain reaction followed by restriction enzyme digestion.
The 1166C allele frequency was 7.96% and 7.73% among Malay hypertensive and normotensive subjects, respectively. There was no association of the 1166A > C polymorphism with BP in the hypertensive, normotensive or overall Malay populations. PWV was significantly higher among 1166C allele carriers as compared to non-carriers (10.52 ± 1.82 vs. 10.15 ± 1.80, p = 0.040) in the overall population, but not in the hypertensive and normotensive populations separately. In conclusion, the frequency of 1166C polymorphism is similar among Malay hypertensive and normotensive subjects. This polymorphism has no association with BP but may have an influence on PWV in Malays, which needs further investigation.     

Cardiac and autonomic responses to change in posture or vitamin C supplementation in sickle cell anemia subjects

Autonomic function following change in posture with or without vitamin C supplementation was studied in ten (10) sickle cell anemia (SCA) and twelve (12) non-sickle cell anemia (NSCA) subjects. Arterial blood pressure and electrocardiographic measurements were taken in the supine position on a couch 80 cm high and immediately on assumption of the upright position. Vitamin C was then administered orally (300 mg/day for 6 weeks). At the end of the period, blood pressure and ECG measurements were again made in the supine position and in response to change in posture.

Change in posture significantly decreased QRS amplitude, QRS duration, PR interval, RR interval and MABP but increased HR and rate pressure product (RPP) in both groups of subjects. The HR and RPP responses were significantly higher in NSCA than in SCA subjects (p < 0.001, respectively). Vitamin C caused greater reductions in QRS duration (p < 0.01), PR duration p < 0.001) in the NSCA subjects than in SCA subjects. It caused, however, greater reduction in RR duration (p < 0.001) and MABP in SCA subjects than in NSCA subjects. It also caused significantly greater increases in HR and RPP (p < 0.001, respectively) in the SCA subjects than in NSCA subjects. After vitamin C supplementation, change in posture decreased RR interval (p < 0.001), QT interval (p < 0.01) and MABP (p < 0.05) but increased RPP (p < 0.01) in NSCA subjects. In SCA subjects, there was a fall in RR interval (p < 0.001) and MABP (p < 0.01), but elevated RPP (p < 0.001). Changes (Δ) in MABP, HR and RPP were similar between NSCA and SCA subjects. In conclusion, these findings indicate a blunted cardiovascular autonomic response to change in posture in sickle cell anemia subjects. Chronic, oral, low-dose vitamin C supplementation equilibrates this response with those of non-sickle cell anemia subjects.     

脉搏波传导速度测量算法的研究及其进展

动脉弹性功能下降是心血管疾病的早期特征之一,而动脉脉搏波速度能够很好地反映动脉弹性,因此准确测量动脉脉搏波速度对预防和治疗心血管疾病有很大的帮助。测量脉搏波速度的方法主要有两种:基于容积脉搏波的检测方法和基于压力波的检测方法,其检测精度取决于波速参考点的提取。波速参考点的提取方法主要有切线法、最低点法、峰值法以及斜率最大值点法。本文分析了现有测量算法的优点和存在的不足之处,探讨了国内外的研究动向,提出测量算法的改进方案。     

Effects of Isometric Muscle Tension on Vasomotor Activity and Heart Rate

Twenty-four adults each performed two isometric exercises at three levels of exertion while finger pulse amplitude, skin temperature, heart rate, and respiration rate and amplitude were monitored. Due to exercise, pulse amplitude and skin temperature were significantly reduced while heart rate was significantly increased. The magnitude of cardiovascular (CV) effect varied in proportion to the magnitude of exercise. Further evidence for the close association between exercise and CV effects was implied by the rapid recovery of pulse amplitude and heart rate at the termination of exercise. This evidence in addition to a detailed analysis of respiration data led to the conclusion that CV reactions to isometric exercise were not mediated by respiratory variations. The implications of these, findings for studies of operant conditioning of CV and other autonomic responses are discussed.