Mean Consecutive Difference Research Articles

Heart rate variability in patients with major depression

We have previously reported decreased heart rate variability upon standing in panic disorder patients compared with controls. In this study, we extend our report to include patients with major depression ( n = 19). Compared to normal controls ( n = 20) and panic disorder patients ( n = 30), there was no significant difference in the immediate changes in heart rate upon standing in the depressed group. The standing heart rate variability (R-R variability) was significantly lower in panic disorder patients compared to both normal controls and depressed patients as indicated by the corrected standard deviations, the corrected mean consecutive difference, the corrected standard deviation of the mean consecutive difference of the R-R intervals, and the high frequency variability in successive R-R intervals, suggesting an increased vagal withdrawal in panic disorder patients, especially upon standing. There was no significant difference in any of the heart rate variability measures between depressed patients and normal controls.

Decreased R‐R variance in panic disorder patients

To investigate autonomic function in panic disorder patients (n = 30), we compared postural changes in heart rate and the R-R interval variance in patients and normal controls (n = 20). There was no significant difference in the immediate changes in heart rate upon standing between the groups. R-R variance was significantly decreased during resting supine condition in patients as indicated by the corrected standard deviation of the R-R intervals. The standing R-R variance was significantly lower than that of normal controls as indicated by the corrected standard deviations, the corrected mean consecutive difference and the corrected standard deviation of the mean consecutive difference of the R-R intervals, suggesting an increase in vagal withdrawal in patients, especially upon standing. If this finding is specific to panic disorder patients, it may be a useful peripheral marker for this condition.

Stimulation SFEMG in myasthenia gravis.

The diagnostic usefulness of single-fiber electromyography (SFEMG) in the diagnosis of neuromuscular transmission disorders is well established. Increased jitter is one of the earliest indications of abnormality. In patients with severe weakness, tremor, or altered consciousness, performance of the study is difficult because of the degree of cooperation needed. We studied five patients and eight normal subjects with voluntary and stimulation SFEMG techniques. Our results, in search of normal values and changes with pathology, revealed differences in the values of jitter and the percentage of abnormal fibers between both techniques. The mean consecutive difference (MCD) is smaller (on average 30% less), and the percentage of abnormal fibers is lower (on average 10% less) with the stimulation technique. These differences are largely explained by the jitter measurement of one endplate with the stimulation technique versus two endplates with the voluntary. They may also be related, however, to the difference in motor unit populations sampled with each technique.

Single-fibre electromyography with a personal computer.

A single-fibre electromyography measuring unit based upon a personal computer (Apple II) and a special triggering unit is described. Its compact size facilitates its use online, next to the patient. It is a relatively cheap system, and can be handled by one investigator and a nurse. Operation is simple, and error messages are provided. Investigation of a patient consists of measuring the time of occurrence of action potentials in up to 20 trains of complex motor unit action potentials (MUAPs). One train may consist of up to 170 MUAPs, each comprising a maximum of four single action potentials (spikes). Triggering is performed with a special unit after an initial spike, triggering at an adjustable level is only possible within an adjustable time window. This feature reduces false triggerings and allows selection of a part of a complex MUAP. Interval analysis by the computer also reduces processing of MUAPs originating from other motor units. Computed are the mean consecutive difference (MCD) values of the jitter, the variance, the percentage of blockings and the number of relevant intervals. Scatter plots can be displayed and printed of the raw data, the consecutive differences or the interpulse intervals (IPI) against the interdischarge intervals (IDI). Suspicious data may be rejected by manipulation of graphical cursors. If a MUAP consists of at least four spikes, a test can be carried out whether there is a neurogenic variability cause concomitant jitter. The system has been evaluated over the last two years in the EMG department of the Academic Hospital, Utrecht, The Netherlands.

Differentiation of spontaneous activity from normal and denervated skeletal muscle.

The discrimination of fibrillation potentials and endplate potentials based on the conventional EMG methods is difficult if there is only discrete denervation. The reliability of discrimination can be highly improved if the frequency behaviour of the potentials is taken into account. The average proportional consecutive interval difference is the best discrimination variable with 90% correct findings per analysed potential sequence. When three analyses per muscle are made, the accuracy increases to 97.2%. The second best variable is the mean consecutive difference followed by interval bandwidth, standard deviation of interval, minimum interval and finally maximum interval. The mean duration of intervals does not allow of any differentiation. The frequency analysis can be restricted to spontaneous activity sequences of ten seconds. It is immaterial which part of a prolonged sequence is analysed for ten seconds. The conventional evaluation of registered spontaneous activity either alone or with observation at the monitor under simultaneous acoustic control is inferior to the frequency analysis. The results do not allow a statement of the probability of wrong diagnosis in clinical routine work.

Calculation of the electromyographic jitter.

The electromyographic jitter is the variability at consecutive discharges in the time interval between two action potentials from two muscle fibres from the same motor unit. This paper deals with different methods of expressing the jitter. The method of choice seems to be Mean Consecutive Difference (MCD)[FORMULA: see text]where D(1), D(2) etc. are the individual time interval measurement data and n the number of discharges, preferably 50 or, if the jitter is not changing, 200. MCD can also be estimated from other measures of the jitter like Mean Range of Two (MR(2)) (giving the same estimated value as MCD), Mean Range of Five (MR(5)), Mean Range of Ten (MR(10)) and also from the Standard Deviation (SD). In a distribution without trends the following relations hold:MCD = 1·13×SDMCD = 0·49×MR(5)MCD = 0·37×MR(10)·The presence of slow variations and trends in most recordings makes SD not well suited for calculation because of the risk of getting too high estimates of the jitter.

The electromyographic jitter in normal human muscles

The jitter ( i.e., the variability in time interval at consecutive discharges between two action potentials from two muscle fibres belonging to the same motor unit) had been studied in four human muscles. The jitter, expressed as mean consecutive difference (MCD), was found to be: in m. biceps brachii: 15.7 ± 5.5 (SD) μsec; in m. extensor dig. communis: 23.4 ± 8.5 μsec; in m. frontalis: 19.1 ± 7.6 μsec; and in m. tibialis anterior: 31.5 ± 12.4 μsec. The jitter values were the same when recorded close to the end-plate zone or close to the tendon. There was no correlation between the mean inter-potential interval and the size of the jitter. At a very irregular innervation rate the jitter sometimes increased slightly, more often when recording was done close to the tendon than when close to the end-plate zone. However, the physiological unevenness of the innervation rate did not influence the jitter value. A decrease of the intramuscular temperature caused an increase of the jitter by 1–3 μsec/°C around 36°C.