Effects of the anticholinesterase edrophonium on spectral analysis of heart rate and blood pressure variability in humans

Sick Sinus Syndrome Observed in a Patient with Cholinesterase Deficiency

A 58-year-old woman complained of general fatigue and was diagnosed with sick sinus syndrome (SSS) by ambulatory electrocardiogram, which demonstrated sinus arrest at midnight and paroxysmal atrial fibrillation (AF) at nighttime. Since her plasma cholinesterase (ChE) activity had been persistently zero, she was diagnosed with ChE deficiency. She refused permanent pacemaker implantation, and treatment with positive chronotropic drugs is ongoing. A novel association of ChE deficiency with SSS is theoretically possible rather than coincident, considering that ChE plays a key role in cholinergic influences on the sinus node leading to sinus bradyarrhythmia and on the atria, causing vagally mediated AF.

Fixation stability of the upward gaze in patients with myasthenia gravis: an eye-tracker study

Objective

To quantify fixation stability of the upward gaze in patients with myasthenia gravis (MG) using an eye tracker.

Methods and analysis

In this study, 21 normal subjects, 5 patients with MG with diplopia, 5 patients with MG without diplopia and 6 patients with superior oblique (SO) palsy were included. Subjects fixated on a target in the upward direction for 1 min. The horizontal (X) and vertical (Y) eye positions were recorded using an eye tracker. Fixation stability was first quantified using the bivariate contour ellipse areas (BCEA) of fixation points as an index of whole stability. Then, the SDs of the X and Y eye positions (SDX and SDY, respectively) were quantified as indices of directional stability, with the data divided into three 20 s fractions to detect temporal fixation fluctuation.

Results

BCEAs were larger in patients with MG (both with and without diplopia) than normal subjects and patients with SO palsy, without significant differences among the three 20 s fractions. Compared with normal subjects, SDXs were larger only in patients with MG with diplopia; SDYs were larger in both patients with MG with and without diplopia. In addition, SDYs in patients with MG with diplopia were larger than those in patients with MG without diplopia and patients with SO palsy. Furthermore, a significant difference among the three 20 s fractions was detected for SDYs in patients with MG with diplopia.

Conclusion

Patients with MG, especially those with diplopia, exhibit fixation instability in the upward gaze. Non-invasive quantification of fixation stability with an eye tracker is useful for precisely identifying MG-specific fatigue characteristics.

Trial registration number

UMIN000023468; pre-results.

Changes in Heart Rate Variability in patients under local anesthesia

Spectral analysis of Heart Rate Variability (HRV) is widely used for the assessment of cardiovascular autonomic control. Several studies have shown the effect of anesthetic agents on HRV parameters. In this study a systematic approach of HRV analysis has been employed. The effect caused by the ectopic beats on the spectral measurements has been investigated and results are presented. A detrending method using Wavelet Packets has been developed which was able to remove slow varying trend from HRV signals without causing significant changes in the low frequency (LF) and high frequency (HF) component of the HRV signal. Using this methodology electrocardiogram (ECG) signals from 14 patients undergoing local anesthesia (brachial plexus block) were analyzed with parametric Autoregressive (AR) method. The results showed that the LF/HF ratio values calculated from the HRV signal decreases within an hour of the application of the brachial plexus block compared to the values at the start of the procedure. This change was noticed in approximately 80% of the patients.

Heart rate and blood pressure variability as markers of sensory blockade with labour epidural analgesia

PURPOSE

To evaluate the correlation between the progression of somatosensory blockade and changes in autonomic outflow following the onset of labour epidural analgesia.

METHODS

Twelve labouring parturients consented to participate in the study. Baseline electrocardiogram, blood pressure (BP) and respiratory rate were recorded for ten minutes. The epidural consisted of 0.125% bupivacaine with 50 microg of fentanyl (total volume 20 mL). Measurements were repeated for ten minutes after initiation of the block. The level of sensory block was measured bilaterally with loss of sensation to ice at two-minute intervals. Wavelet transform was used to obtain heart rate (HR) and BP variability every two minutes following the loading dose of epidural medication. High frequency power of HR variability was used to assess changes in parasympathetic activity. The total power of BP variability was used to assess changes in sympathetic activity. A nonparametric repeated measures ANOVA was used for the variability data, and a Spearman rank correlation test was used to evaluate the relationship between the sensory block and HR and BP variability.

RESULTS

The sensory block progressed to T9 at ten minutes post-epidural and was the mirror image of the decrease in total power of BP variability. High frequency power of HR variability increased to a plateau at six minutes post-epidural. A significant correlation was found between the increase in sensory block and the observed decrease in BP variability (r = -1.000, P = 0.0028).

CONCLUSION

In this study of labouring parturients, BP variability correlated with the progression of both sympathetic and somatosensory block following epidural anesthesia, while HR variability was shown to be a surrogate marker of increased parasympathetic activity.