Age-related diminution of the cardiovascular autonomic responses: diagnostic problems in the elderly

Summary. To study the usefulness of standard cardiovascular autonomic reflex tests in the elderly, 224 healthy controls and 49 aged diabetic patients were examined. Based on the data obtained from healthy controls, age-related reference values for several autonomic indices were calculated and their usefulness was tested with aged diabetic patients. It was found (1) that in elderly subjects (aged 50 years) the indices based on heart rate differences are more suitable for the assessment the autonomic parasympathetic control than indices based on R/R interval ratios, (2) that the tests (and indices) of choice in the elderly subjects are the Valsalva manoeuvre (Valsalva difference and tachycardia difference) and the active orthostatic test (Max-Rest difference, immediate and later change in systolic blood pressure), (3) that the usefulness of the deep breathing test is limited in the elderly, (4) that such commonly used indices as the Valsalva ratio and the Max/Min ratio in orthostatic test are not useful in the elderly, and (5) that the isometric handgrip test is of little use in the assessment of the autonomic function in the elderly. In conclusion, standard cardiovascular autonomic reflex tests can be used in the assessment of autonomic function to some extent also in the elderly subjects. However, one must bear in mind the limitations in their applicability in that age group.,     

Changes in autonomic cardiovascular control in mid-pregnancy

Summary. Spectral analysis of heart rate variability was used to study autonomic nervous control in mid-pregnancy. Fifty women (age 22–36 years) with singleton pregnancies (mean duration of gestation 27.7 weeks) and 39 non-pregnant female controls (age 21–39 years) were studied using controlled breathing and orthostatic tests. During spontaneous breathing the overall heart rate variability was lower in pregnant subjects indicating a decreased parasympathetic tone at rest. The decreased parasympathetic tone probably counts for the increased heart rate in pregnancy. The parasympathetic efferent capacity of autonomic cardiac control was found to be similar in pregnant and non-pregnant subjects, as no difference was seen during controlled breathing in periodic heart rate variability between the groups. Standing up caused a similar change in low frequency and mid-frequency bands in both groups, but high frequency heart rate variability increased in pregnant subjects and decreased in the controls indicating an increased sympathetic tone at rest in mid-pregnancy.     

Diabetic cardiovascular autonomic neuropathy: clinical implications

Diabetic cardiovascular autonomic neuropathy (DCAN), the impairment of the autonomic balance of the cardiovascular system in the setting of diabetes mellitus (DM), is frequently observed in both Type 1 and 2 DM, has detrimental effects on the quality of life and portends increased mortality. Clinical manifestations include: resting heart rate disorders, exercise intolerance, intraoperative cardiovascular lability, orthostatic alterations in heart rate and blood pressure, QT-interval prolongation, abnormal diurnal and nocturnal blood pressure variation, silent myocardial ischemia and diabetic cardiomyopathy. Clinical tests for autonomic nervous system evaluation, heart rate variability analysis, autonomic innervation imaging techniques, microneurography and baroreflex analysis are the main diagnostic tools for DCAN detection. Aldose reductase inhibitors and antioxidants may be helpful in DCAN therapy, but a regular, more generalized and multifactorial approach should be adopted with inclusion of lifestyle modifications, strict glycemic control and treatment of concomitant traditional cardiovascular risk factors, in order to achieve the best therapeutic results. In the present review, the authors provide aspects of DCAN pathophysiology, clinical presentation, diagnosis and an algorithm regarding the evaluation and management of DCAN in DM patients.     

Diagnosis of diabetic autonomic neuropathy: a multivariate approach

AIM/HYPOTHESIS: In the diagnosis of diabetic autonomic neuropathy (DAN) various autonomic tests are used. We took a novel statistical approach to find a combination of autonomic tests that best separates normal controls from patients with DAN. METHODS: Twenty-four patients with Type-1 diabetes mellitus considered as having mild to moderate DAN as well as 10 normal, nondiabetic control subjects were analysed, searching for a test or a combination of tests that would optimally discriminate Type-1 diabetes mellitus from controls. Variations of heart rate during deep breathing (deltaR6) and during a Valsalva manoeuvre (VR), the number of reactive sweat glands on the foot (testing sympathetic sudomotor function), and the response of human pancreatic polypeptide to hypoglycaemia [ln(deltahPP+1)] were evaluated. RESULTS: Respective values for respective sensitivity and specificity values were: deltaR6, 96 and 70%; VR, 96 and 60%; sweat gland function, 71 and 90%; and ln(deltahPP+1), 71 and 90%. In a multivariate analysis approach a single discriminant function separating patients with Type-1 diabetes mellitus from nondiabetic controls was generated [Logit P=288.5-[14.7 deltaR6]-[26.6 ln(deltahPP+1)]]. This function allowed complete separation of patients with Type-1 diabetes mellitus from normal controls. CONCLUSION/INTERPRETATION: We conclude that the combined determination of deltaR6 and of ln (deltahPP+1) optimally separates subjects with parasympathetic impairment from normal subjects. In addition, this combination of tests may serve as a sensitive method for the assessment of DAN.     

Heart rate recovery: autonomic determinants,methods of assessment and association with mortality and cardiovascular diseases

Cardiovascular disease (CVD) is the primary cause of mortality worldwide. Cardiac autonomic dysfunction seems to be related to the genesis of several CVDs and is also linked to the increased risk of mortality in CVD patients. The quantification of heart rate decrement after exercise – known as heart rate recovery (HRR) – is a simple tool for assessing cardiac autonomic activity in healthy and CVD patients. Furthermore, since The Cleveland Clinic studies, HRR has also been used as a powerful index for predicting mortality. For these reasons, in recent years, the scientific community has been interested in proposing methods and protocols to investigate HRR and understand its underlying mechanisms. The aim of this review is to discuss current knowledge about HRR, including its potential primary and secondary physiological determinants, as well as its role in predicting mortality. Published data show that HRR can be modelled by an exponential curve, with a fast and a slow decay component. HRR may be influenced by population and exercise characteristics. The fast component mainly seems to be dictated by the cardiac parasympathetic reactivation, probably promoted by the deactivation of central command and mechanoreflex inputs immediately after exercise cessation. On the other hand, the slow phase of HRR may be determined by cardiac sympathetic withdrawal, possibly via the deactivation of metaboreflex and thermoregulatory mechanisms. All these pathways seem to be impaired in CVD, helping to explain the slower HRR in such patients and the increased rate of mortality in individuals who present a slower HRR.     

Ventricular repolarization and heart rate responses during cardiovascular autonomic function testing in LQT1 subtype of long QT syndrome

Background: In the most prevalent LQT1 form of inherited long QT syndrome symptoms often occur during abrupt physical or emotional stress. Sympathetic stimulation aggravates repolarization abnormalities in experimental LQT1 models. We hypothesized that autonomic function tests might reveal the abnormal repolarization in asymptomatic LQT1 patients.
Methods: We measured heart rates (HRs) and QT intervals in nine asymptomatic carriers of a C-terminal KCNQ1 mutation and 8 unaffected healthy subjects using an approach of global QT values derived from 28 simultaneous electrocardiographic leads on beat-to-beat base during Valsalva maneuver, mental stress, sustained handgrip, and light supine exercise.
Results: LQT1 patients exhibited impaired shortening of both QTpeak and QTend intervals during autonomic interventions but exaggerated lengthening of the intervals—a QT overshoot—during the recovery phases. The number of tests with a QT overshoot was 2.4 ± 1.7 in LQT1 patients and 0.8 ± 0.7 in unaffected subjects (P = 0.02). Valsalva strain prolonged T wave peak to T wave end interval (TPE) in LQT1 but not in unaffected patients. LQT1 patients showed diminished HR acceleration in response to adrenergic challenge whereas HR responses to vagal stimuli were similar in both groups.
Conclusions: Standard cardiovascular autonomic provocations induce a QT interval overshoot during recovery in asymptomatic KCNQ1 mutation carriers. Valsalva maneuver causes an exaggerated fluctuation of QT and TPE intervals partly explaining the occurrence of cardiac events during abrupt bursts of autonomic activity in LQT1 patients.     

Does plasma L-arginine level play a role in regulation of blood pressure during exercise and autonomic nervous function?

Little is known of L -arginine's role in autonomic nervous regulation and physiological responses to dynamic exercise. We assessed heart rate and blood pressure during a maximal bicycle ergometer test and heart rate variability at rest in 15 healthy male volunteers, age 22–38 years. Venous blood samples for plasma L -arginine measurements were taken when subjects were sitting at rest before and at the end of exercise. The autonomic nervous function was assessed with time and frequency domain analysis of heart rate variability. Plasma L -arginine level decreased during maximal exercise from 71·4 μmol l^?1 to 51·0 μmol l^?1 (P < 0·0001) for all subjects studied. The systolic blood pressure during the maximal exercise test was inversely correlated with plasma L -arginine level at rest (r = ?0·70, P < 0·01). Normalized low frequency band of power spectral analysis of heart rate variability correlated with L -arginine level at rest (r = 0·66, P < 0·01). In conclusion, plasma L -arginine level decreased in physical exercise, and plasma L -arginine level at rest was positively associated with the sympathetic component of power spectral analysis of heart rate variability at rest, and inversely with systolic blood pressure during physical exercise.     

Attenuated Valsalva heart rate response in subjects with smoking history: possible role of autonomic dysfunction

Summary. The effects of smoking habits on aotnomic cardiovascular heart rate reflexes were studied in 143 healthy subjects by using the Valsalva manoeuvre and deep breathing tests. Smoking seemed to cause attenuation of the Valsalva heart rate response. This attenuation was present also after adjustment for possible confounding factors including alcohol consumption. Our findings show that in subjects with smoking history there may occur dysfunction in some part of the autonomic reflex arch mediating the Valsalva heart rate response.     

康复运动对冠心病患者心脏自主神经功能的影响

摘要 目的：探讨有氧运动对冠心病患者心脏自主神经功能的影响。 方法：18例女性冠心病患者（实验组）,14例女性非冠心病患者（对照组）为本研究的受试者,在康复程序前、后,对她们进行了运动前（安静时）和运动后的心率变异性（HRV）指标的测定,其中包括极低频功率（VLF）、低频功率（LF）、高频功率（HF）、总功率（TP）和低高频比值（LF/HF）。 结果：①与对照组相比,实验组康复程序前安静时VLF、LF、HF和TP均显著降低,而LF/HF显著增高（P＜0.01）,运动后也有相似的趋势。②与康复程序前相比,12周心脏康复程序后,实验组安静时VLF、LF、HF和TP均有显著增高,LF/HF有所降低（P＜0.01和P＜0.05）;运动后HF显著增高,LF/HF显著降低（P＜0.05）。③与安静时相比,康复程序前实验组递增负荷运动后心率变异性指标均无显著性改变;康复程序后实验组递增负荷运动后VLF、LF、TP和LF/HF均有显著降低（P＜0.01和P＜0.05）;对照组递增负荷运动后VLF、LF、HF和TP均有显著降低（P＜0.01和P＜0.05）,LF/HF有显著增高（P＜0.01）。 结论：12周运动心脏康复程序不仅可以提高冠心病患者安静时自主神经的调节功能,而且对改善一次急性运动后自主神经的均衡性也有积极作用。     

老年高血压及合并2型糖尿病对心脏自主神经功能及左室结构、功能的影响

目的探讨老年高血压及合并2型糖尿病对心脏自主神经功能及左室结构、功能的影响。方法回顾性分析140例老年高血压门诊患者临床资料,根据其合并2型糖尿病情况分为糖尿病组(38例)和对照组(102例),均予以彩色多普勒超声心动图检查。对比2组受试者入组时血浆神经肽Y(NPY)、神经降压素(NT)等自主神经功能指标、舒张末期左心室内径(LVEDd)、收缩末期左心室内径(LVESd)、室间隔厚度(IVST)、左心室后壁厚度(LVPWT)等左室结构指标、心室射血分数(LVEF)、左心室短轴缩短率(FS)等左室收缩功能指标及二尖瓣口舒张早期/晚期血流充盈速度(E/A)等左室舒张功能指标检查结果差异。结果糖尿病组受试者入组时血浆NPY水平、LVEDd、LVESd、IVST、LVPWT及二尖瓣口舒张晚期血流充盈速度(A)水平均显著高于对照组(P0.05或P0.01);血浆NT水平、LVEF、FS及部分左室舒张功能指标包括E、E/A检查结果则显著低于对照组(P0.05或P0.01)。结论老年高血压患者合并2型糖尿病会对其心脏自主神经功能、左室结构及左室功能造成较大的影响,需引起临床重视。     

Autonomic cardiovascular regulation in patients with obstructive sleep apnoea: a study based on spectral analysis of heart rate variability

The aim of this study was to assess the function of the autonomic nervous system in patients with obstructive sleep apnoea syndrome (OSAS). The study was designed as a cross‐sectional case–control study. Fifty‐one patients were included, and the findings were compared with those in 66 controls. Spectral analysis of heart rate variability (HRV) during supine rest, during controlled breathing and after tilting was performed in each patient and control case. The patients performed overnight sleep recordings the night before the HRV recordings. Individuals with an apnoea–hypopnoea index (AHI) above 20 were regarded as OSAS patients and those with AHI lower than 20 as snorers. Differences in HRV and blood pressure between patients and controls were analysed by multiple linear regression with age, body mass index and sex as independent variables. During free and controlled breathing there was a significant decrease in indices reflecting vagal modulation, indicating parasympathetic dysfunction in OSAS patients compared with controls. The mid‐frequency component was also significantly reduced in OSAS patients after tilting but not in the lying position. This may be related to the parasympathetic dysfunction, but could also indicate a decreased sympathetic reserve capacity. We found no significant relation between AHI and indices of vagal modulation in the patient group. Our findings show an autonomic dysfunction in patients with OSAS. The dysfunction involves the parasympathetic system, and may be related to the increased cardiovascular mortality and malignant arrhythmia described in OSAS.     

The influence of resistance exercise with emphasis on specific contractions (concentric vs. eccentric) on muscle strength and post-exercise autonomic modulation: a randomized clinical trial

Background

Compared to eccentric contractions, concentric contractions result in higher cardiovascular stress. However, we do not know how these two types of contractions influence cardiac autonomic modulation during the post-exercise recovery period.

Objective

to compare the effect of resistance training that is performed with concentric vs. eccentric emphasis on muscle strength and on post-exercise recovery which was assessed by examining heart rate variability (HRV), for the knee extensor muscle group in young healthy adults.

Methods

For this study, 105 men between 18 and 30 years of age were randomized into 4 groups: concentric control (CONCC), eccentric control (ECCC), concentric training (CONCT) and eccentric training (ECCT). The CONCC and ECCC groups underwent one session of resistance exercise (RE) using the knee extensor muscle group (3 sets of 1 repetition at 100% of the maximal repetition [1MR]) and the CONCT and ECCT groups performed 10 training sessions. The HRV was analyzed at baseline and across four recovery periods (T1, T2, T3 and T4).

Results

The ECCT group exhibited increased muscle strength at the end of the study. Regarding cardiac autonomic modulation, the CONCC and ECCC groups exhibited increases in overall variability (SDNN and SD2) at T1 compared to baseline, and the ECCT group demonstrated increases in variables reflecting vagal modulation and the recovery process (RMSSD, SD1 and HF [ms²]) at T1, T2 and T4 compared to baseline.

Conclusions

Resistance training with emphasis on eccentric contractions promoted strength gain and an increase in cardiac vagal modulation during recovery compared to baseline.