Contributors to beat-to-beat stroke volume variability during acute mental stress in healthy volunteers.

Acute mental stress elicits sympathetic activation, increasing heart rate and shortening the QT interval, but it is unknown whether this activation translates to stroke volume (SV) changes. Multivariate power spectral decomposition was used to assess the influence of heart rate and QT variabilities on SV variability at rest and during acute mental stress. Acute mental stress elicits mild but statistically significant increase in SV variability.

Comparison of single-lead and multi-lead ECG for QT variability assessment using autoregressive modelling.

. Beat-to-beat fluctuations in the QT interval-QT variability (QTV)-have been shown to vary amongst the different ECG leads. This study aims to compare the utility of single and multi-lead ECG to disentangle the mechanisms contributing to QTV.

Augmented Oscillations in QT Interval Duration Predict Mortality Post Myocardial Infarction Independent of Heart Rate.

Objective: This study seeks to decompose QT variability (QTV) into physiological sources and assess their role for risk stratification in patients post myocardial infarction (MI). We hypothesize that the magnitude of QTV that cannot be explained by heart rate or respiration carries important prognostic information.

Background: Elevated beat-to-beat QTV is predictive of cardiac mortality, but the underlying mechanisms, and hence its interpretation, remain opaque.

Repolarization variability independent of heart rate during sympathetic activation elicited by head-up tilt.

The fraction of repolarization variability independent of RR interval variability is of clinical interest. It has been linked to direct autonomic nervous system (ANS) regulation of the ventricles in healthy subjects and seems to reflect the instability of the ventricular repolarization process in heart disease. In this study, we sought to identify repolarization measures that best reflect the sympathetic influences on the ventricles independent of the RR interval.

Role of respiration in the cardiovascular response to orthostatic and mental stress.

The objective of this study was to determine the response of heart rate and blood pressure variability (respiratory sinus arrhythmia, baroreflex sensitivity) to orthostatic and mental stress, focusing on causality and the mediating effect of respiration. Seventy-seven healthy young volunteers (46 women, 31 men) aged 18.4 ± 2.

Altered Nocturnal Cardiovascular Control in Children With Sleep-Disordered Breathing.

Study Objectives: To assess cardiovascular control during sleep in children with sleep-disordered breathing (SDB) and the effect of adenotonsillectomy in comparison to healthy nonsnoring children.

Methods: Cardiorespiratory signals obtained from overnight polysomnographic recordings of 28 children with SDB and 34 healthy nonsnoring children were analyzed. We employed an autoregressive closed-loop model with heart period (RR) and pulse transit time (PTT) as outputs and respiration as an external input to obtain estimates of respiratory gain and baroreflex gain.

Recording duration and short-term reproducibility of heart rate and QT interval variability in patients with myocardial infarction.

Beat-to-beat variability of the QT interval (QTV) measured on surface ECG has emerged as a potential marker for ventricular repolarization instability and has been used along with heart rate variability (HRV) to predict arrhythmic risk. Since measurement modalities of QTV have not been standardized, the objective of this study was to investigate the effect of ECG recording duration on QTV as well as HRV. Using a database of 30 min ECG recorded from 500 patients with acute myocardial infraction during rest, we extracted RR and QT interval time series and estimated different HRV and QTV metrics over windows of varying length.

Relation between QT interval variability and muscle sympathetic nerve activity in normal subjects.

Beat-to-beat variability of the QT interval (QTV) is sought to provide an indirect noninvasive measure of sympathetic nerve activity, but a formal quantification of this relationship has not been provided. In this study we used power contribution analysis to study the relationship between QTV and muscle sympathetic nerve activity (MSNA). ECG and MSNA were recorded in 10 healthy subjects in the supine position and after 40° head-up tilt.