Standard Deviation Of Normal-to-normal RR Intervals Research Articles

Cardiovascular Risk Factors Significantly Correlate With Autonomic Nervous System Activity in Children

BackgroundInformation is limited about the correlation between cardiovascular risk factors (CRFs) and autonomic nervous system (ANS) activity in children. MethodsIn all, 180 children aged 9 to 11 years were enrolled. Heart rate variability, obtained by 24-hour Holter recordings, was analyzed for ANS activity by measuring standard deviation of normal-to-normal RR intervals (SDNN), the standard deviation of the averaged normal-to-normal RR intervals, the root mean square of successive differences (RMSSD), low-frequency (LF), high-frequency (HF), and ratio of LF to HF. CRFs were defined as hypertension, dyslipidemia, obesity, and elevated fasting blood glucose. Children were subdivided into 4 levels: 0 (no CRF), 1 (1 CRF), 2 (2 CRFs), or 3 (3 or more CRFs). Altered ANS activity of each level was assessed. The correlation between CRF and ANS activity was analyzed by stepwise multiple regression. ResultsWith an increasing number of CRFs, there was a progressive elevation in blood pressure, obesity indices, most blood lipoprotein concentrations, and fasting blood glucose. Moreover, increase in the number of CRFs was associated with progressive reduction of SDNN, RMSSD, LF, and HF. Systolic blood pressure (SBP) correlated negatively with SDNN, RMSSD, LF, and HF. Obesity indices had a negative correlation with RMSSD and HF. As the number of CRFs increases, so does the extent of abnormal clustering of CRFs and changes in ANS activity. ConclusionsObesity and elevated SBP are associated with marked alterations in ANS activity, obesity with reduced vagal nerve activity, and elevated SBP with altered vagal and sympathetic nerve activity.

Paper Electrocardiograph Strips May Contain Overlooked Clinical Information in Screen-Detected Type 2 Diabetes Patients

A large number of nondigitized electrocardiograph (ECG) strips are routinely collected in larger cohort studies such as the ADDITION study (Anglo-Danish-Dutch Study of Intensive Treatment in People with Screen-Detected Diabetes in Primary Care). These ECG strips are routinely read manually but may contain overlooked information revealing cardiac autonomic dysfunction. The aim of this study was to investigate whether clinical information may be lost using manual R wave to R wave (RR) interval measurements in the calculation of heart rate variability (HRV) in patients with type 2 diabetes mellitus (T2DM). From the Danish part of the ADDITION study, we randomly selected 120 T2DM patients at baseline of the ADDITION study. Analysis of the ECG strips was performed using two different methods: (1) by experienced technicians using rulers and (2) by experienced technicians using a high-resolution computer-assisted method. Calculation of heart rate and time domain HRV [standard deviation of normal-to-normal RR intervals (SDNN) and root mean square of successive differences (RMSSD)] were performed with the same software. When comparing results from the two methods, the following values of Pearson's r are obtained: 0.98 for heart rate, 0.76 for SDNN, and 0.68 for RMSSD. These results indicate that heart rate and HRV measurements by the computer-assisted and manually based methods correlate. However, Bland-Altman plots and Pitman's test of difference in variance revealed poor agreements (p < .01) for both HRV measurements (SDNN and RMSSD); only heart rate showed substantiated agreement (p = .54) between the two methods. Low HRV was statistically significantly associated to high heart rate, systolic blood pressure, and diastolic blood pressure in these screen-detected T2DM patients. Paper ECG strips may contain overlooked clinical information on the status of autonomic function in patients with T2DM. In our study, manual measurements of RR intervals were inferior to the computer-assisted method. Based on this study, we recommend cautiousness in the clinical use and interpretation of HRV based on manual or low resolution measurements of RR intervals from ECG strips. High resolution measurements of RR intervals reveal significant associations between low HRV and high heart rate, systolic blood pressure, and diastolic blood pressure among patients with screen-detected T2DM. It is feasible to use a computer-assisted method to determine RR intervals in patients with T2DM.

Long-term effect of liver transplantation on cirrhotic autonomic cardiac dysfunction

There is little information on the long-term effect of liver transplantation (LT) on cardiac autonomic dysfunction in cirrhotic patients. We compared cardiac autonomic function before and in the long-term after LT. In a transversal study, we investigated 30 cirrhotics awaiting LT, 15 clinically stable patients 2-6 years after LT and 27 healthy controls. Seven cirrhotic patients were studied before LT, and 6, 12 and 33 months after LT, in a prospective fashion. Cardiac autonomic function was measured by heart rate variability (HRV) analysis during 24-h electrocardiogram recording. In the transversal study, patients with cirrhosis as compared to healthy controls had significantly reduced standard deviation of normal-to-normal RR intervals (SDNN) (p<0.001) and of the square root of the mean of squared differences between adjacent NN intervals (RMS-SD) (p<0.01), while the ratio between low frequency (LF) and high frequency (HF) at night was significantly (p<0.05) increased. Liver transplanted patients had significantly (p<0.001) higher SDNN values than cirrhotics, while RMS-SD and LF/HF at night did not differ. In the prospective study, SDNN progressively increased after LT and was significantly (p<0.05) higher at 12 and 33 months, compared to the pre-operative value. RMS-SD and LF/HF at night did not change after LT. In conclusion, the overall HRV decrease present in cirrhosis, measured by SDNN values, is partially corrected in the long-term after LT. However, parasympathetic impairment, measured by RMS-SD and LF/HF at night, is not affected even in the long-term after operation.

Analysis of heart rate variability as an index of noncardiac surgical stress

Measurement of heart rate variability (HRV) is useful in assessing the function of the autonomic nervous system and in staging of clinical diseases. The purpose of this study is to assess a feasibility of HRV for evaluating surgical stress during the noncardiac perioperative period. Standard deviation of normal-to-normal RR intervals (SDNN) and HRV triangular index derived from 24-h Holter ECC were measured in 24 patients undergoing digestive surgery. Holter ECG was performed at 1 day before operation, the first day (postoperative day 1: POD1), and the 7th day (POD7) after operation. Indices of HRV were compared with factors influencing surgical stress, such as duration of the operation and amount of blood loss during the operation, and postoperative complications. The SDNN and HRV triangular index decreased significantly on POD1 and recovered on POD7 (P < 0.05). Heart rate variability indices correlated significantly to duration and blood loss of operation (both P < 0.05). In 7 patients with postoperative complications, HRV indices were statistically lower than those in patients without complications on POD1 (P < 0.05). Our results indicate that HRV may provide useful information with respect to surgical stress.

Sympathetic Overactivity in Patients With Left Ventricular Aneurysm in Early Period After Anterior Myocardial Infarction: Does Sympathetic Activity Predict Aneurysm Formation?

Left ventricular aneurysm (LVA) is an important complication of acute transmural myocardial infarction (MI) that bears great clinical significance because of high mortality. Heart rate variability (HRV) analysis is extensively used to evaluate autonomic modulation of sinus node and to identify patients at risk for an increased cardiac mortality. In this study, the authors evaluated HRV in patients with LVA in the early period after acute anterior wall MI. They compared 18 patients (7 men, 11 women, with an average age of 56.1 +/-8.2 years) with LVA and 46 patients (34 men, 12 women, with an average age of 56.4 +/-5.9 years) without LVA. Mean heart rate, low frequency (LF) and low-frequency/high-frequency (LF/HF) ratio were significantly higher and standard deviation of normal-to-normal RR intervals (SDNN), root mean square of successive differences (RMSSD), number of NN intervals that differed by more than 50 ms from adjacent interval divided by the total number of all NN intervals (PNN50), and HF were lower in the patients with LVA. A SDNN <78 ms separated the patients with aneurysm from those without aneurysm with a sensitivity of 78%, specificity of 83%, positive predictive accuracy of 79%; a LF/HF ratio >2.4 with a sensitivity of 92%, specificity of 88%, and positive predictive accuracy of 92%. Single-vessel disease increased the left ventricular aneurysm formation by 5.1 fold, total left anterior descending artery (LAD) occlusion by 3.1 fold, mean heart rate >75 beats/minute by 2.3 fold, SDNN <78 ms by 7.9 fold, and LF/HF ratio >2.4 by 12.9 fold, but well-developed collaterals decreased the aneurysm formation by 4.4 fold. As a result, HRV analysis supplies parameters with high predictive value for LVA formation in the early period after acute anterior MI. The higher sympathetic activity and reduced heart rate variability may be associated with a higher incidence of complications such as ventricular arrhythmias and increased mortality in patients with LVA.

CARDIOVASCULAR AUTONOMIC REGULATION IN SUBJECTS WITH NORMAL BLOOD PRESSURE, HIGH–NORMAL BLOOD PRESSURE and RECENT‐ONSET HYPERTENSION

1. In the present study, we tested the hypothesis that heart rate variability (HRV) is reduced in recent-onset hypertension and that pressor responses to standard autonomic reflex tests are not any different in hypertensives compared with normotensives. We also hypothesized that subjects with high-normal blood pressure (BP) would be distinguishable from normotensives on the basis of short-term HRV indices. 2. Three groups of subjects, each consisting of 15 men and 10 women, were examined. The first group consisted of subjects with recent-onset hypertension who were not taking antihypertensive medication (mean (+/-SD) age 50 +/- 12 years; BP >/= 140/90 mmHg), the second group consisted of subjects with high-normal BP (mean age 46 +/- 13 years; BP 130-139/85-89 mmHg) and the third group consisted of subjects with normal BP (mean age 48 +/- 12 years; BP < 120/80 mmHg). The aim was to characterize the autonomic state in each group. 3. Blood pressure, heart rate (HR), indices of short-term HRV during supine rest and quiet standing, HR variation during timed deep breathing (HRVdb) and pressor responses to the cold pressor test and sustained isometric handgrip were compared between the groups. 4. Although the three groups were comparable (P > 0.1) in terms of mean HR and low-frequency (LF) power expressed in normalized units at rest and during quiet standing, the standard deviation of normal-to-normal RR intervals (SDNN) during supine rest, LF and high-frequency spectral powers during supine rest and HRVdb were lowest in hypertensives (P </= 0.05 for each), indicating diminished baroreflex modulation of RR intervals in hypertensives. 5. In contrast, LF power was highest in subjects with high-normal BP (P </= 0.05) during supine rest and this is possibly because of higher BP variability. 6. The results suggest that HRVdb provides a simple measure of cardiac vagal effects in hypertensives, the rate-pressure product provides a simple measure of overall HRV in hypertensives and, in clinical hypertension, the arterial baroreflex mechanism is reset to maintain a higher BP through diminished vagal modulation of HR and possibly heightened sympathetic outflow to the heart and resistance vessels.

Cardiovagal Response to Acute Mild Exercise in Young Healthy Subjects

The aim of the present study was to investigate the effect of a single bout of mild exercise on autonomic nervous system activity in healthy subjects. The study group comprised 18 healthy males, aged between 20 and 24 years, who had not been training regularly for the last 3 months. A supine recording of systolic arterial pressure (SAP) and RR interval and the administration of the phenylephrine test were performed at baseline and repeated after a 60-min recovery period following treadmill exercise training for 30 min at 65% of maximal heart rate. Mean SAP and RR interval, heart rate variability (HRV) indices (the standard deviation of normal-to-normal RR intervals (SDNN), the square root of the mean of squared differences between successive intervals and the percentage of adjacent RR intervals differing more than 50 ms), noninvasive spectral baroreflex sensitivity (Spe-BRS) and phenylephrine baroreflex sensitivity (Phe-BRS) were assessed before and after training. Mean SAP measured after exercise was lower than baseline (120+/-12 mmHg vs 128+/-12 mmHg, p = 0.05). Spe-BRS and Phe-BRS increased significantly after exercise, from 11.8+/-6.1 ms/mmHg to 16.0+/-7.8 ms/mmHg (p = 0.034), and from 16.0+/-8.8 ms/mmHg to 21.9+/-9.3 ms/mmHg (p = 0.022), respectively. A parallel increase was also observed in SDNN (from 81+/-44 ms to 96+/-53 ms, p = 0.02), but the other HRV indices showed no significant differences between pre- and post-exercise. A single session of mild exercise performed by sedentary young men leads to significant autonomic nervous system improvement, which suggests that even mild physical activity is beneficial for neural cardiac regulation and should be recommended to sedentary healthy subjects.

Reduced heart rate variability in hypertension: associations with lifestyle factors and plasma renin activity.

Limited information exists on the relations between heart rate variability, hypertension, lifestyle factors and renin-angiotensin-aldosterone system. A total of 191 newly diagnosed yet untreated hypertensive men and women, 35-54 years of age, were compared with an age- and gender-stratified random population sample of 105 normotensive men and women to find out independent determinants of heart rate variability. Heart rate variability was computed from 5-min ECG time series using the standard deviation of normal-to-normal RR intervals (SDNN), the square root of the mean of squared differences between adjacent normal RR intervals (RMSSD) and the fast Fourier transform spectral analysis. All absolute measures of heart rate variability were reduced in hypertension (P<0.001 for each, ANOVA). In multivariate regression analyses, reduced heart rate variability was independently associated with higher heart rate (P<0.001 for all absolute measures of heart rate variability), higher age (P=0.001 for SDNN, total and LF powers; P<0.001 for RMSSD and HF power) and higher mean arterial pressure (P<0.05 for total power, P<0.01 for the other absolute measures) but not with sodium and alcohol intakes, body mass index and smoking. Increased plasma renin activity (PRA) was an independent attributor of reduced HF power (P<0.05) and reduced RMSSD (P<0.01). Increased blood pressure and heart rate are associated with decreased heart rate variability without any direct effects on heart rate variability of lifestyle factors. High PRA is an independent determinant of diminished modulation of vagal activity.

Heart rate variability during head-up tilt testing in patients with suspected neurally mediated syncope.

The relation between heart rate variability (HRV) and outcome of head-up tilt testing (HUT) in patients with neurally mediated syncope (NMS) was studied in 30 patients with presumed NMS (33 +/- 13 years) and in 11 age-matched controls. After 15 minutes of baseline supine observation, patients were tilted to 60 degrees for 45 minutes or until syncope occurred. HRV parameters included RR intervals, standard deviation of normal-to-normal RR intervals (SDNN), and root mean square successive differences (RMSSD). HRV analysis was performed during 5-minute intervals in the supine position immediately after onset of HUT and before syncope or after 30-35 minutes of tilt in patients without syncope. Syncope occurred after a mean tilt duration of 32 minutes in 14 (47%) of 30 patients with presumed NMS, whereas all controls had an uneventful HUT. In the supine position, RR intervals and RMSSD were comparable among HUT-positive patients, HUT-negative patients, and controls (RR intervals: 799 +/- 92, 854 +/- 137, and 818 +/- 128 ms, P = NS; RMSSD: 43 +/- 40, 36 +/- 34, and 53 +/- 42 ms, P = NS). Baseline SDNN was also comparable in HUT-positive patients versus HUT-negative patients with presumed NMS (50 +/- 26 vs 52 +/- 20 ms, P = NS). Within 5 minutes preceding syncope or after 30-35 minutes of tilt, RR intervals and RMSSD were shorter in HUT-positive patients compared to HUT-negative patients, or to controls (RR intervals: 606 +/- 86 vs 710 +/- 117 and 739 +/- 123 ms, P < 0.05; RMSSD: 12 +/- 5 vs 23 +/- 19 and 40 +/- 32 ms, P < 0.05). Thus, HRV analysis in the baseline supine position was not a predictor of HUT outcome in patients with suspected NMS. Syncope during HUT seemed to be preceded by increased sympathetic activity manifested by an increase in heart rate and by a decreased parasympathetic tone manifested by a decrease in RMSSD measured for 5 minutes before the event, in comparison with HUT-negative patients and with controls.