Reproducibility of a non-invasive real-time measure of cardiac parasympathetic activity

The role of the parasympathetic nervous system in visually induced motion sickness: systematic review and meta-analysis

The parasympathetic nervous system (PNS) has been implicated in the development of visually induced motion sickness. The objective of this study was to perform a systematic review and meta-analysis of the effect of visually induced motion sickness on validated parameters of PNS tone. Methods followed PRISMA recommendations. Controlled trials reporting validated measures of PNS tone in visually induced motion sickness in healthy adults were included. One reviewer performed the screening of articles and data extraction, and two reviewers independently performed methodological evaluation. Data were synthesised using standardised mean differences (SMDs) for all relevant outcomes using a random-effects model. Publication bias was assessed via funnel plots and Egger's test. The search strategy identified seven citations comprising 237 healthy individuals. The mean quality score was 4/10 (range 3-7). There was no difference between baseline PNS tone between individuals who developed visually induced motion sickness and those that did not. Visually induced motion sickness (VIMS)-sensitive individuals had a reduction in PNS tone, following exposure to the stimulus (mean weighted SMD = -0.45, 95% confidence interval -0.64 to -0.27, Z = -4.8, p < 0.0001). There was no evidence of heterogeneity or publication bias. These data suggest that baseline PNS parameters do not provide a useful measure of predicting the probability of developing visually induced motion sickness. However, a fall in PNS tone, as indicated by cardiac activity, is characteristic in sensitive individuals. Further work is needed to characterise these responses in clinical populations, in conjunction with improvements and standardisation in study design.

Gastric and lower esophageal sphincter pressures during nausea: a study using visual motion-induced nausea and high-resolution manometry

Nausea is the subjective unpleasant sensation that immediately precedes vomiting. Studies using barostats suggest that gastric fundus and lower esophageal sphincter (LES) relaxation precede vomiting. Unlike barostat, high-resolution manometry allows less invasive, detailed measurements of fundus pressure (FP) and axial movement of the gastroesophageal junction (GEJ). Nausea was induced in 12 healthy volunteers by a motion video and rated on a visual analog scale. FP was measured as the mean value of the five pressure channels that were clearly positioned below the LES. After intubation, a baseline (BL) recording of 15 min was obtained. This was followed by presentation of the motion video (at least 10 min, maximum 20 min) followed by 30 min recovery recording. Throughout the experiment we recorded autonomic nervous system (ANS) parameters [blood pressure, heart rate (HR), and cardiac vagal tone (CVT), which reflects efferent vagal activity]. Ten out of 12 subjects showed a drop in FP during peak nausea compared with BL (-4.0 ± 0.8 mmHg; P = 0.005), and 8/10 subjects showed a drop in LES pressure (-8.8 ± 2.5 mmHg; P = 0.04). Peak nausea preceded peak fundus and LES pressure drop. Nausea was associated with configuration changes at the GEJ such as LES shortening and esophageal lengthening. During nausea we observed a significantly increased HR and decreased CVT. In conclusion, nausea is associated with a drop in fundus and LES pressure, configuration changes at the GEJ as well as changes in the ANS activity such as an increased sympathetic tone (increased HR) and decreased parasympathetic tone (decreased CVT).

Parasympathetic alteration during sub-clinical seizures

INTRODUCTION

Autonomic instability is considered a contributing factor in sudden unexpected death in epilepsy (SUDEP). The aim of this pilot study was to measure parasympathetic activity in sub-clinical seizures to investigate autonomic instability.

MATERIALS AND METHODS

A prospective study based on Video-electroencephalography (EEG)/electrocardiography (ECG)/oxygen saturation (SAO2) recordings was selected from patients having sub-clinical seizures during stage 3 or 4 sleep. We analysed R-R intervals in the ECG from 1-min prior to the electrographic onset to the end of sub-clinical seizures. Matched non-ictal R-R baseline measurements were selected from stages 3 or 4 sleep. R-R interval data were analysed using NeuroScope software providing a cardiac index of parasympathetic activity (CIPA). BioSignal short-term heart rate variability (HRV) software was used to analyse the same R-R interval data previously analysed using NeuroScope except that sub-clinical seizure data was embedded within 5-min epochs and compared to 5-min epochs of non-ictal measurements.

RESULTS

A total of 33 sub-clinical seizures were recorded from 11 patients comprising 19 generalised sub-clinical seizures (2 patients), 9 right temporal lobe sub-clinical seizures (5 patients) and 5 left temporal lobe sub-clinical seizures (4 patients) were compared to matched non-ictal measurements. Parasympathetic activity was clearly altered during total sub-clinical seizures in terms of the CIPA (p<0.001) and 5-min HRV high frequency (HF) % (p=0.026) measures. Generalised sub-clinical seizures resulted in increased cardiac parasympathetic activity whereas temporal lobe seizures were associated with a decrease in parasympathetic activity.

CONCLUSION

This pilot study indicates that parasympathetic changes occur during sub-clinical seizures. Generalised sub-clinical seizures may be associated with more autonomic instability compared to temporal lobe sub-clinical seizures.

The value of the electrocardiogram in risk assessment in primary prevention: experience from the West of Scotland Coronary Prevention Study

Electrocardiograms (ECGs) were recorded at baseline, annually thereafter, and at run-out in the West of Scotland Coronary Prevention Study to which 6595 men aged from 45 to 65 years on entry were recruited. The baseline ECGs were analyzed with respect to (a) the primary end point of the study, namely, fatal or nonfatal myocardial infarction (MI) and (b) all-cause mortality. In addition, incident MIs were reviewed to determine those detected by ECG only. Heart rate, indexed left ventricular mass, frontal T axis, and T amplitude in lead I were all significantly predictive with respect to the primary end point in a multivariate analysis. With respect to all-cause mortality, minor ST-T changes, 10-second heart rate variability, and frontal T axis were similarly predictive. Of 355 incident MIs, 47.3% were silent or unrecognized and detected by ECG only. A simple ECG-based risk prediction equation for fatal and nonfatal MI is introduced.

Markers of autonomic tone on a standard ECG are predictive of mortality in old age

BACKGROUND

To investigate markers of autonomic tone on a standard electrocardiogram in relation to mortality in old age.

METHODS

A total of 599 inhabitants of Leiden, the Netherlands, were enrolled in a population-based follow-up study at their 85th birthday. Electrocardiograms (ECGs) were taken on entry and annually thereafter. ECGs were analysed automatically to determine four markers of autonomic tone, i.e. heart rate, the occurrence of ventricular extrasystoles and two time domain measures of heart rate variability. All participants were followed up for mortality.

RESULTS

Participants with a heart rate in the highest quartile had a 1.8-fold increased total mortality risk (95% confidence interval (CI) 1.0-3.4), but not an increased cardiovascular mortality risk. The occurrence of at least one ventricular extrasystole was related with a 2.3-fold increased total mortality risk (95% CI 1.3-3.9) and a 3.6-fold increased cardiovascular mortality (95% CI 1.6-8.2). In stratified analyses, the prognostic effect was confined to males. Both measures of heart rate variability were not related to mortality.

CONCLUSION

High heart rate and the occurrence of a ventricular extrasystole, both markers of sympathetic dominance, were predictive of mortality in old age. Two short-term measures of heart rate variability as measured on a standard 10-s ECG were not related to mortality, and hence may not reflect autonomic tone in old age.

Effect of lignocaine injection in carotid sinus on baroreceptor sensitivity during carotid endarterectomy

OBJECTIVES

This study was undertaken to test the hypothesis that there is a neural basis for baroreceptor deterioration during carotid endarterectomy (CEA), by investigating intraoperative hemodynamic changes induced by intraluminal carotid stretch stimulation, before and after application of local anesthetic to the adventitial layer of the carotid sinus region.

METHODS

This was a prospective study of 20 patients undergoing elective CEA. During CEA, before removal of the atheroma, intraluminal stretch simulation of the carotid baroreceptors (rub test) was performed before and after injection of 1% lignocaine into adventitial tissue of the artery in the region of the carotid sinus. Continuous measurements of mean arterial blood pressure (MAP), electrocardiographic r-r intervals (R-R), heart rate, cardiac vagal tone, and carotid sinus baroreflex were recorded to determine alterations in baroreceptor function.

RESULTS

Rub test before injection of lignocaine was associated with a decrease in MAP and heart rate and an increase in R-R, cardiac vagal tone, and carotid baroreflex response, indicating a functioning baroreflex. After lignocaine injection and repetition of the rub test, no significant change was seen in MAP, heart rate, R-R, cardiac vagal tone, or carotid baroreflex response, indicating a nonfunctioning baroreflex. Comparing the peak responses to the rub test stimulus before and after lignocaine injection showed significant differences for all variables (P <.05), with carotid baroreflex response and heart rate being highly significant (P <.0005).

CONCLUSIONS

The baroreflex response to intraluminal stretch stimulation of the carotid sinus area is operational in patients undergoing CEA, and this response is abolished by infiltration of local anesthetic into the periadventitial tissue around the carotid sinus.

Can cardiac vagal tone be estimated from the 10-second ECG?

BACKGROUND

Heart rate variability (HRV) recorded over 5 min or 24 h is used increasingly to measure autonomic function and as a prognostic indicator in cardiology. Measuring HRV during a standard 10-s ECG would save time and cut costs. The aim of this study, therefore, was to discover whether indices of HRV calculated over 10 s could predict cardiac vagal tone (CVT) recorded over a 5-min period by the NeuroScope, a new instrument that selectively measures vagal tone.

METHODS

A total of 50 subjects had ECGs taken at the beginning, middle and end of a 5-min measurement of CVT. Standard deviation of normal-to-normal RR interval (SDNN), root mean square of successive differences in RR intervals (rMSSD), and the average absolute difference (AAD) in RR intervals were calculated from RR intervals derived from the ECGs. Subjects were divided into a training set (n=40) and a test set (n=10).

RESULTS

Regression equations derived from the training set predicted 5-min mean CVT in the test set with r(2) of 95.8%, 92.9% and 87.9% for AAD, rMSSD and SDNN, respectively. Indices obtained from the third ECG in each set tended to give a closer relationship with CVT than those derived from the first and second ECGs: this could be because of the greater spread of the independent variables in the third set. An underlying linear physiological phenomenon could not be excluded, however, without continuing the measurements over a longer time.

CONCLUSIONS

These results demonstrate that AAD and rMSSD calculated from a 10-s ECG can accurately predict 5-min mean CVT as measured by the NeuroScope.