Effect of diabetes mellitus on heart rate variability in patients with congestive heart failure

This study sought to determine if the severity of autonomic perturbations in patients with heart failure are affected by the presence of diabetes. Decreased HRV is frequent in diabetic patients free of clinically apparent heart disease and has been invoked as a risk factor for sudden cardiac death. However, reduced HRV is also commonly present in patients with left ventricular dysfunction. The effect of diabetes on autonomic dysfunction in this setting is not known. Holter ECGs from 69 diabetic patients and 85 nondiabetic control subjects with heart failure were analyzed. The severity of autonomic dysfunction was assessed using 24-hour time- and frequency-domain HRV analysis. Prognostically important time- and frequency-domain HRV measures (SDNN, SDANN5, total power, and ultra-low frequency power) were not different between the two groups. Time- and frequency-domain parameters modulated by parasympathetic tone (pNN50, RMSSD, and HF power) were depressed to a similar degree in the diabetic and the nondiabetic groups. The low frequency power was significantly lower in diabetic patients (5.8 +/- 0.7 vs 5.3 +/- 1.0, P = 0.02). The ratio of low to high frequency power was substantially lower in the diabetic group (2.2 +/- 0.2 vs 1.4 +/- 0.2, P < 0.0001). These differences were more apparent in insulin-treated diabetics. In the presence of heart failure, HRV parameters that are most predictive of adverse outcome are similar in diabetic and nondiabetic patients. Furthermore, during increased sympathetic stimulation in the setting of heart failure, diabetes does not worsen parasympathetic withdrawal but may mitigate sympathetic activation.     

Correlation Between Time-Domain Measures of Heart Rate Variability and Scatterplots in Postinfarction Patients

Heart rate variability (HRV) is usually measured in time or frequency domains. Beat-to-beat variability, which cannot be assessed by frequency-domain analysis, and can only be assessed globally by time-domain analysis, provides information concerning the nonlinear behavior of heart rate. This beat-to-beat variability can be displayed on Scatterplots, where each RR interval is plotted against the preceding RR interval. However, the relationship between Scatterplots and other measures of HRV is unknown. We studied the correlations between time-domain measures and scatterplot length, width, and area in 50 postinfarction patients. Scatterplot length and width were measured after printing. Scatterplot area was calculated from length and width, assimilating the plot to an ellipse. Long-term variability indexes (SDNN and SDANN) were strongly correlated with scatterplot length (r > 0.9, P < 0.0001), and short-term variability parameters (pNN₅₀ and variability index) with scatterplot width (r > 0.9; P < 0.0001). Scatterplots are, therefore, a simple way of providing information concerning long- and short-term HRV. Furthermore, measurement of scatterplot width at different given RR intervals could be an approach to the evaluation of short-term HRV for different heart rates. This could provide a simple way of assessing cardiac parasympathetic modulation at different heart rates.     

原发性高血压患者醛固酮/肾素比值与心率变异性和QT间期的关系研究

目的探讨高血压患者醛固酮/肾素比值(ARR)与心率变异性(HRV)及QT间期的相关性。方法选取研究对象179例,根据ARR中位数分为ARR低值组和ARR高值组,比较2组24 h动态心电图(Holter)、24 h动态血压(ABPM)、常规心电图、血清钾、血清钠等,比较2组的HRV、QT间期等指标以及相关性。结果 2组Holter中的SDNN、SDNN Index、SDANN Index、RMSSD以及QTc、血钾、血钠有显著差异(P0.05)。校正相关因素后,ARR与SDNN、SDNN Index、SDANN Index、RMSSD、血钾呈负相关(r=-0.444、-0.677、-0.381、-0.623、-0.432,P0.05),与QTc、血钠呈正相关(r=0.391、0.379,P0.05)。多因素Logistic回归分析显示,SDNN、SDNN Index、SDANN Index均是ARR的独立相关因素(P0.05)。结论原发性高血压患者中醛固酮高与心率变异性减少密切相关。     

慢性心力衰竭患者T辅助淋巴细胞与心脏自主神经功能的相关性研究

目的 探讨慢性心力衰竭(CHF)患者T辅助淋巴细胞(Th)和心率变异性(HRV)的相关性.方法 选择CHF患者96例及健康体检者30名为研究对象,以γ-干扰素(IFN-γ)和白细胞介素-10(IL-10)分别代表Th1和Th2细胞,采用流式细胞仪测定所有入选者外周血淋巴细胞内细胞因子IFN-γ和IL-10的阳性率,用24 h动态心电图(Holter)分析HRV特征.结果 CHF患者淋巴细胞IL-10阳性率明显低于健康对照组[(16.4±5.8)%、(26.8±3.7)%,t=9.243,P＜0.001],淋巴细胞IFN-γ阳性率明显高于健康对照组[(18.4±7.3)%、(7.3±4.6)%t=7.917,P＜0.001];HRV各指标均明显低于健康对照组,24 h正常心动周期的标准差(SDNN)为(9 8.6±21.3)、(145.1±42.6)ms,24 h内5 min节段平均心动周期的均值标准差(SDANN)为(83.9±22.4)、(136.5±39.6)ms,标准差平均值指数(SDNNI)为(40.6±14.5)、(55.8±17.9)ms,相邻正常心动周期差值均方根(RMSSD)为(20.7±12.9)、(29.1±12.6)ms,相邻两正常心动周期差值＞50 ms的个数所占的百分比(PNN50)为(5.6±3.7)%、(11.8±4.4)%(t值分别为7.904、9.645、4.733、3.132、7.654,P均＜0.05),CHF患者IL-10阳性率与SDNN、SDANN、SDNNI、RMSSD、PNN50呈显著正相关(r值分别为0.49、0.57、0.58、0.47、0.52,P均＜0.01),IFN-γ阳性率及IFN-γ/IL-10比值与SDNN、SDANN、SDNNI、RMSSD、PNN50均呈显著负相关(r值分别为-0.49、-0.54、-0.57、-0.52、-0.53,-0.52、-0.64、-0.57、-0.58、-0.67,P均＜0.01).结论 CHF患者自主神经系统参与Th1/Th2平衡调节,交感神经系统促进Th1效应,副交感神经系统促进Th2效应.     

心力衰竭患者的心率变异分析研究

目的探讨慢性心力衰竭(CHF)患者心率变异性(HRV)的变化,研究了HRV各指标与心功能程度(NYHA分级)、原发病、心衰类型的关系。方法选取CHF患者76例与正常对照组24例进行回顾性分析。结果正常对照组比较,CHF试验组SDNN,SDANN降低,差异有统计学意义。结论CHF患者HRV部分指标变化可作为判定CHF严重程度的参考指标。各项HRV指标变化大小可能与CHF患者的原发病无关,但部分似与心衰类型有关。     

慢性充血性心力衰竭患者的心率变异性分析

目的：评价心率变异性在慢性充血性心力衰竭患者中的变化。方法：用24h动态心电图研究慢性充血性心力衰竭患者与对照组的心率变异性及比较其他心脏结构及功能参数。结果：慢性充血性心力衰竭组的SDNN，SDANN，LF，HF，LF／HF均较对照组显著降低（P＜0．05），且随心衰严重程度增加，心率变异性呈递减，并与LVEF，LVEDD及LVSF改变相关（P＜0．05或P＜0．01）。结论：心率变异性可作为了解心衰程度、指导治疗和判定预后的参考指标之一。     

Long‐term stability of heart rate variability in chronic stable angina pectoris,and the impact of an acute myocardial infarction

Background: Heart rate variability (HRV) reflects the balance between cardiac parasympathetic and sympathetic autonomic influences. Reduced HRV has adverse prognostic implications. The time course for changes in HRV over prolonged periods of time and the influence of an acute coronary event on HRV are not well established. Methods: Heart rate variability was assessed in patients with chronic stable angina pectoris, who were followed for 3 years within the Angina Prognosis Study in Stockholm. Patients who suffered an acute myocardial infarction after the study were re‐examined after this event. We assessed HRV by the simple geometric method differential index, and traditional time‐ and frequency‐domain measurements of HRV. Results: The differential index was essentially unchanged during the study (i.e. the ratio month 36/month 1 was 1·00 ± 0·06, n = 261). Also most other time and frequency indices of HRV (SDNN, r‐MSSD, SDNNIDX, total power, and VLF, LF, HF respectively; n = 63) remained largely unchanged; pNN50 and LF/HF were, however, less reproducible. In 21 patients with a subsequent acute myocardial infarction, SDNN, SDNNIDX, total power, LF and LF/HF were reduced following the event, whereas differential index, pNN50 and HF remained unchanged. Conclusions: Differential index and other indices of HRV are stable and reproducible in patients with chronic stable angina pectoris. High‐frequency HRV (reflecting cardiac parasympathetic activity) and the differential index changed little following an acute coronary event, and may be suitable for predictions of the future risk of sudden death even in the presence of a recent acute coronary event.     

Heart rate variability and diastolic heart failure

Diastolic heart failure accounts for up to 40% of patients with congestive heart failure (CHF), and is associated with a better prognosis as compared to patients with systolic dysfunction. Nevertheless, patients with diastolic dysfunction have a significantly higher mortality as compared to the normal population. Reduced heart rate variability (HRV), a marker of autonomic dysfunction, is associated with increased mortality in patients with systolic heart failure. We therefore sought to determine to what extent HRV is altered in a population of patients with diastolic heart failure. Twenty-four hour ambulatory (Holter) recordings were performed in 19 consecutive patients with diastolic heart failure, in 9 patients with systolic heart failure, as well as in 9 healthy volunteers (normal controls). Time and frequency domain HRV variables were obtained for all three groups of patients. Both Time and Frequency domain variables were found to be reduced in both heart failure groups compared to normal controls. When compared with each other, patients with diastolic function had relatively higher values of HRV variables, compared to those with systolic dysfunction (SDNN, Total power, ULF power, all P 相似文献   

冠心病患者心率变异性与冠状动脉病变的关系

摘要： 目的 通过对比研究冠心病患者心率变异性（HRV）和冠状动脉病变程度，探讨两者间是否存在联系，为诊断冠心病提供更多途径。 方法 随机选取冠心病患者120例作为实验组，分别为SAP、 UAP、STEMI和NSTEMI，每组平均30例。选取健康体检者31例作为正常对照组。所有入选对象于入院后24小时内行24小时动态心电图（DCG）检查，冠心病患者均接受选择性冠状动脉造影检查。采用SPSS 13.0统计软件进行统计学分析。结果 随冠状动脉病变程度加重，反映交感神经系统功能的心率变异性指标SDNN 、SDANN、SDNN Index等显著降低(P＜0.05)，而反映副交感神经系统功能的心率变异性指标rMSSD、pNN50则无显著变化。 结论 HRV可作为一个无创伤性指标间接反映冠状动脉病变程度，为冠心病临床诊断提供依据。     

Heart Rate Variability in Patients with Familial Amyloid Polyneuropathy

The purpose of this study was to evaluate heart rate variability (HRV) in patients with familial amyloid polyneuropathy (FAP) using the time- and frequency-domain analysis. The study population consisted of 19 patients with FAP, and 19 age and sex matched normal volunteers. The 24-hour Holter recordings of all subjects in sinus rhythm and off medication were analyzed. Five time-domain indices of HRV were computed. The frequency component of HRV was calculated by fast Fourier transform analysis of the RR intervals. The power spectrum of the low frequency (LF) between 0.04–0.15 Hz and high frequency (HF) between 0.15–0.40 Hz and the LF/HF ratio was calculated. Global measures of HRV including the standard deviation of the mean of RR intervals (SDNN) and the standard deviation of 5-minute mean RR intervals (SDANN) were decreased in patients with FAP. Specific vagal influences on HRV including the proportion of RR intervals more than 50 milliseconds different (pNN50) and the HF power on spectral analysis were less in patients with FAP. LF power and LF/HF ratio were more decreased in patients with FAP at the advanced stage than at the early stage. In conclusion, HRV was significantly decreased in patients with FAP at the early stage, and sympathetic activity was more decreased in patients at the advanced stage. These findings suggest that the decrease of the HRV is an indicator of this disease and the power spectral analysis of the HRV is beneficial in assessing the severity of the autonomic dysfunction.     

β受体阻滞剂对老年慢性心衰患者HRV与Tei指数的影响

目的通过观察心率变异性(HRV)指标与Tei指数,探讨β受体阻滞剂对心功能Ⅱ、Ⅲ级心衰患者HRV与心功能的影响。方法选择心功能Ⅱ、Ⅲ级心衰患者68例,分为β受体阻滞剂组(40例)和常规治疗组(28例),β受体阻滞剂组患者在常规治疗的基础上加用小剂量的β受体阻滞剂治疗,治疗前及治疗6月后分别检测HRV各项指标及Tei指数。结果两组的SDNN、SDANN、rMSSD、pNN50指标和Tei指数治疗后与治疗前比较,差异均有统计学意义(t分别=3.38、5.30、2.22、3.68、7.60;2.11、1.89、2.33、1.73、1.72,P均<0.05),β受体阻滞剂组与常规治疗组治疗后比较,差异亦均有统计学意义(t分别=1.75、1.83、1.87、5.06、4.59,P均<0.05)。β受体阻滞剂组LF/HF和MHR治疗后较治疗前明显下降,差异均有统计学意义(t分别=2.76、3.40,P均<0.05),与常规组治疗后比较,差异均有统计学意义(t分别=1.75、2.18,P均<0.05),而常规组治疗前后比较,差异均无统计学意义(t分别=0.04、0.16,P均>0.05)。结论随着心功能的改善,β受体阻滞剂可减慢老年慢性心衰患者平均心率,改善老年慢性心衰患者自主神经功能和心功能。     

Evolution of Cardiac Autonomic Nervous Activity Indices in Patients Presenting with Transient Left Ventricular Apical Ballooning

Backround: Transient left ventricular (LV) apical ballooning (AB) is characterized by a rapidly reversible, acute LV systolic dysfunction, triggered by physical or emotional stress. Despite observations strongly suggesting catecholamine-mediated myocardial stunning due to enhanced sympathetic activity, the early time course of heart rate variability (HRV) has not been described.
Methods: We prospectively enrolled 39 consecutive patients (median age = 68 years, range 35–85 years, 38 women) with LV AB. Indices of HRV were extracted from 24-hour ambulatory electrocardiograms on the day of hospital admission, on days 2 and 3, and 3 months after the hospitalization.
Results: Within 48 hours after hospital admission, the indices of HRV were markedly depressed (standard deviation of normal-to-normal [NN] intervals [SDNN] 89.6 ± 19.9 ms; mean standard deviation of NN intervals for 5-minute segments [SDNNi] 37.8 ± 6.2 ms; root mean square of consecutive difference of normal-to-normal intervals [rMSSD] 23.0 ± 9 ms; standard deviation of the averages of NN intervals for all 5-minute segments [SDANN] 70.1 ± 18.0 ms; geometric triangular index [TI] 23.7 ± 5.9 ms), recovered in the subacute phase and had normalized at 3 months follow-up (SDNN 124.7 ± 24 ms; SDNNi 47.1 ± 5.7 ms; rMSSD 31.1 ± 10.5 ms; SDANN 118.5 ± 27 ms; TI 31.2 ± 8 ms; all P < 0.05). Mean RR-interval increased from 845 ± 121 ms on day 1, to 929 ± 84 ms at 3 months (P = 0.06).
Conclusions: A marked depression of cardiac parasympathetic activity was observed in the acute phase of LV AB, followed by recovery of autonomic modulation between the subacute and the chronic phases. The rapid return of parasympathetic function may partially explain the favorable outcomes of patients presenting with LV AB.     

Heart rate variability and 24-hour minimum heart rate

Heart rate variability (HRV) indices based on 24-hr electrocardiograph recordings have been used in clinical research studies to assess the aggregate activity of the autonomic nervous system. Although 24-hr HRV is generally considered noninvasive, use in research protocols typically involves considerable data collection and processing expenses and substantial participant burden. The purposes of this research methods evaluation were to describe the relationships between 24-hr minimum heart rate (HR) and several 24-hr time domain HRV indices (Ln SDNN, Ln SDANN, Ln SDNNIDX, Ln RMSSD, and Logit50) across several research data sets (normal women, normal men, children enrolled in a study of recurrent abdominal pain, women with irritable bowel syndrome, sudden cardiac arrest survivors, and heart failure patients) and to explore the possibility that 24-hr minimum HR might serve as a simpler alternative or adjunct to HRV measures in some situations. The correlations of global HRV measures (e.g., Ln SDNN, Ln SDANN) with 24-hr minimum HR were consistently larger (typical r approximately -.80) than with average HR (typical r approximately -.50). In repeated measurements, change in minimum HR was also correlated with change in general HRV (typical r approximately -.60). However, modest differentiation of minimum HR and HRV measures was noted in patients taking certain classes of cardiac medications (e.g., anti-arrhythmics, beta blockers). Twenty-four-hour minimum HR is correlated with general time domain HRV measures and might be useful as a simpler proxy, surrogate, or auxiliary variable in some clinical research applications, especially those in which participants are not receiving cardiac medications.     

Consistency of multicenter measurements of heart rate variability in survivors of acute myocardial infarction

Heart rate variability (HRV) analysis from 24-hour ambulatory ECG has been widely used in risk stratification of patients after myocardial infarction (MI). The accuracy of HRV assessment is known to potentially vary when different commercial systems are used. However, the consistency of HRV measurements has never been fully investigated. Twenty-six post-MI patients (mean age 59 +/- 8 years, 22 men) were studied, of whom 13 succumbed to sudden cardiac death (SCD) within 1 year and 13 remained alive for at least 3 years (MI survivors). Each patient had a 24-hour Holter ECG recorded before hospital discharge. HRV analysis was performed four times from the same recordings using three different Holter tape analysis systems (Marquette, Reynolds, and CardioData) by four independent operators (CardioData system was used twice, once in the United Kingdom and once in the United States). Mean normal-to-normal RR intervals (mNN) and 3 HRV parameters (SDNN, RMSSD, and HRV triangular index [HRVi]) were derived from each recording. The consistency of mNN and HRV measurements was evaluated by coefficient of variance (CV) and by the Bland-Altman method. The results demonstrated that (1) all indices measured by different systems were statistically similar (P = NS) except the measurement of RMSSD (P = 0.01), (2) the measurements of mNN were highly reproducible with a maximum mean difference of 1.8 +/- 13.8 ms and maximum limits of agreement from -14.6 to +15.6 ms. The maximum mean differences were--1.8 +/- 1.4 unit and 4.4 +/- 9.6 ms for HRVi and SDNN, respectively, and RMSSD was less reproducible with a maximum mean difference of--11.1 +/- 11.5 ms, and limits of agreement from -16.2 to +9.6 ms; and (3) the consistency of mNN (CV 0.9% +/- 0.9%) was significantly higher than that of HRVi, SDNN, and RMSSD (P < 0.0001). The consistency of HRVi was similar to that of SDNN (4.8% +/- 2.1% vs 5.7% +/- 4.8%, P = 0.4), and the consistency of RMSSD (26.6% +/- 13.3%) was significantly lower than that of the other measurements (P < 0.00001). In conclusion, the measurements of mNN by different analytical systems are the most consistent among the parameters studied. The global 24-hour measurements of HRV (SDNN and HRVi) are highly reproducible, whereas the measurement of short-term HRV components (RMSSD) is significantly less reproducible.     

Variable Effects of Physical Training of Heart Rate Variability, Heart Rate Recovery, and Heart Rate Turbulence in Chronic Heart Failure

Background: Heart rate variability (HRV), heart rate turbulence (HRT), and heart rate recovery (HRR), indices that reflect autonomic nervous system (ANS) activity, are outcome predictors in patients with chronic heart failure (CHF). It is not clear, however, whether they reflect the same components of ANS activity. No study has examined the effects of physical training (PT) training on HRV, HRT, and HRR in CHF.
Study Objective: To examine the responses of HRV, HRT, and HRR to a PT program in patients presenting with CHF.
Methods: In 41 patients (mean age = 58.7 ± 10.2 years) in New York Heart Association CHF functional classes II or III, and with a left ventricular ejection fraction <40%, HRV, HRT, and HRR were measured before and after 8 weeks of PT.
Results: The training was clinically effective in all patients. Before versus after PT, standard deviation of all normal RR intervals increased from 107 ± 30 to 114 ± 32 ms (P = 0.047), high frequency increased from 210 ± 227 to 414 ± 586 ms²/Hz (P = 0.02), and the low/high frequency ratio decreased from 1.8 ± 1.55 to 1.1 ± 1.2 (P = 0.002). HRT and HRR did not change significantly after PT.
Conclusions: In patients with CHF, the positive effects of PT were limited to HRV indices, which reflect parasympathetic activity, without significantly changing HRR and HRT. These observations indicate that different mechanisms modulate HRV, HRR, and HRT, which provide complementary information regarding ANS activity. The 8-week PT program failed to completely normalize ANS function.     

美托洛尔对冠心病心绞痛患者心率变异性的影响

目的 分析美托洛尔对冠心病心绞痛患者心率变异性的影响.方法 回顾性选取2020年1月至2021年1月本院收治的98例冠心病心绞痛患者作为研究对象,依据治疗方法将其分为常规治疗组和美托洛尔组,各49例.常规治疗组依据患者的实际病情给予个体化心内科西药治疗,美托洛尔组在常规治疗组基础上给予美托洛尔治疗.比较两组的心绞痛发作...     

Impact of chronic DDD pacing on time-domain indexes of heart rate variability in patients with hypertrophic obstructive cardiomyopathy

The aim of this study was to examine whether DDD pacing affects time-domain indexes of heart rate variability (HRV) in patients with hypertrophic obstructive cardiomyopathy (HOCM). We studied 11 patients (7 men, age 52 +/- 8 years) with HOCM refractory to drugs. In all patients a DDD pacemaker was implanted and the atrioventricular delay was programmed to ensure a full ventricular activation sequence. Time-domain indexes of HRV (mean NN, SDANN, SDNN, SD, rMSSD, pNN50) were determined from 24-hour Holter recordings 3 days before and 1 year after pacemaker implantation. The pacemaker was turned off during the second recordings. The same indexes were determined in ten healthy controls at the same time points. The controls showed no significant differences in any of the measured parameters between the two time points. The HOCM patients showed an increase in SD (from 27 +/- 13 to 41 +/- 13 ms, P < 0.001), rMSSD (from 18 +/- 5 to 32 +/- 8 ms, P < 0.001), and pNN50 (from 1.03 +/- 1.06 to 8.52 +/- 4.84%, P < 0.0001). As a result, the values of these three parameters, which were lower in the HOCM patients than in the controls before pacing, were restored to normal levels by the end of the study. In conclusion, our findings indicate that long-term pacing in HOCM patients restores the sympathovagal balance in the heart by increasing vagal activity.     

阿托伐他汀对原发性高血压合并高脂血症患者的心率变异性的影响

目的探讨原发性高血压合并高脂血症患者的心率变异性（HRV）特点及阿托伐他汀对其影响。方法 50例原发性高血压合并高脂血症患者,口服阿托伐他汀（10 mg/d）8周,观察治疗前后HRV变化并与正常对照组（40例）比较。结果原发性高血压合并高脂血症患者的HRV时域参数（SDNN、SDANN、SDNN Index）治疗前明显低于正常组,给予阿托伐他汀8周干预治疗后HRV指标明显上升。低频功率与高频功率比值（LF/HF）显著降低（P〈0.01）。结论原发性高血压合并高脂血症患者自主神经活动明显受损,其迷走神经张力降低,交感神经张力相对增高,发生心源性猝死的危险性明显增加。阿托伐他汀能有效地提高心脏迷走神经张力,降低交感神经张力,有可能减少心律失常性死亡。     

Posttransplant improvement in heart rate variability correlates with improved quality of life

A prospective evaluation of 37 kidney and 20 kidney-pancreas transplant recipients was conducted to assess the relationship between pre- to posttransplant changes in heart rate variability (HRV) and quality of life (QoL). Assessments of 24-hour interbeat variability (pNN50 and rMSSD, SDNN, SDANN) and power spectral analysis of total, low (sympathetic), and high (parasympathetic) frequency components of HRV were performed. The Sickness Impact Profile was used to assess three dimensions of QoL (physical, psychosocial, and total functioning) prior to and at 6 months following transplantation. Changes in vagally mediated time domain measures of HRV were related to changes in physical and total functioning. Stronger correlations occurred between biobehavioral measures in kidney-pancreas recipients, with the strongest relationships occurring between changes in HRV frequency domain measures and changes in physical functioning. Findings indicate that changes in HRV and QoL are related, suggesting that interventions that enhance transplant recipients' HRV may also enhance their QoL.     

Assessment of autonomic nervous system functions in patients with vitamin B12 deficiency by power spectral analysis of heart rate variability

The purpose of this study was to test the autonomic nervous system function of patients with vitamin B12 deficiency (megaloblastic anemia) by measuring heart rate variability (HRV). The study population consisted of 17 vitamin B12 deficient patients and 15 age- and sex-matched normal volunteers. HRV was measured by power spectral analysis from which power of the low frequency (LF) peak (0.04-0.15 Hz), normalized units of the LF peak (LFNU), power of the high frequency (HF) peak (0.15-0.4 Hz), normalized units of the HF (HFNU), and ratio of power of LF to power of HF (LF:HF) were calculated. Vitamin B12 deficient patients had lower LF, LFNU, HF, HFNU, and LF:HF ratio than normal volunteers (P < 0.05). Decreases in sympathetic indices (LF and LFNU) were greater than those measured in parasympathetic indices (HF and HFNU). All HRV parameters correlated positively with the level of vitamin B12 (P < 0.001) and negatively with the duration of disease (P < 0.001). After vitamin B12 replacement the HRV parameters of patients and controls became comparable (P > 0.05). Our data suggest that autonomic sympathetic and parasympathetic nervous activities are decreased in patients with vitamin B12 deficiency, an abnormality that can be corrected by vitamin B12 replacement therapy.