Parameters of Surface Electromyogram Suggest That Dry Immersion Relieves Motor Symptoms in Patients With Parkinsonism

Abstract

Dry immersion (DI) is acknowledged as a reliable space flight analog condition. At DI, subject is immersed in water being wrapped in a waterproof film to imitate microgravity (μG). Microgravity is known to decrease muscle tone due to deprivation of the sensory stimuli that activate the reflexes that keep up the muscle tone. In contrary, parkinsonian patients are characterized by elevated muscle tone, or rigidity, along with rest tremor and akinesia. We hypothesized that DI can diminish the elevated muscle tone and/or the tremor in parkinsonian patients. Fourteen patients with Parkinson's disease (PD, 10 males, 4 females, 47-73 years) and 5 patients with vascular parkinsonism (VP, 1 male, 4 females, 65-72 years) participated in the study. To evaluate the effect of DI on muscles' functioning, we compared parameters of surface electromyogram (sEMG) measured before and after a single 45-min long immersion session. The sEMG recordings were made from the biceps brachii muscle, bilaterally. Each recording was repeated with the following loading conditions: with arms hanging freely down, and with 0, 1, and 2 kg loading on each hand with elbows flexed to 90°. The sEMG parameters comprised of amplitude, median frequency, time of decay of mutual information, sample entropy, correlation dimension, recurrence rate, and determinism of sEMG. These parameters have earlier been proved to be sensitive to PD severity. We used the Wilcoxon test to decide which parameters were statistically significantly different before and after the dry immersion. Accepting the p < 0.05 significance level, amplitude, time of decay of mutual information, recurrence rate, and determinism tended to decrease, while median frequency and sample entropy of sEMG tended to increase after the DI. The most statistically significant change was for the determinism of sEMG from the left biceps with 1 kg loading, which decreased for 84% of the patients. The results suggest that DI can promptly relieve motor symptoms of parkinsonism. We conclude that DI has strong potential as a rehabilitation method for parkinsonian patients.

Keywords: auto-mutual information; determinism; dry immersion; electromyogram; microgravity; nonlinear dynamics; parkinsonism; rehabilitation.

Figure 1

The condition of dry immersion. ^© PetrSU/L. Gerasimova-Meigal.

Figure 2

Determinism of surface electromyogram for each patient before and after the dry immersion. The determinism tends to decrease after the dry immersion. Loading conditions are the following: arms down with no load (a.d.); 0, 1, and 2 kg loading on each hand with elbow being flexed to 90°.

Figure 3

The amplitude (RMS), the median frequency, and the determinism of surface electromyogram before and after the dry immersion. The amplitude and the determinism tend to decrease, while the median frequency tends to increase after the dry immersion. Each patient is denoted by a line. Each subplot corresponds to a combination of a parameter (the row) and a loading (the column). Loading conditions are the following: arms down without any load (Arms down); 0/1/2 kg loading on each hand with elbow being flexed to 90°. The muscle is the biceps of the left arm. The pre-immersion values are marked with crosses when the post-immersion counterpart is missing.

Figure 4

Example of surface electromyogram before and after the dry immersion procedure (patient No. 11 in Table 2; 1 kg loading; left arm). Only first second of the electromyograms is shown. This example demonstrates drop of amplitude, mutual information (MI) decay time, and determinism of electromyogram signal after the dry immersion. MI decay time may be linked to typical duration of turns of electromyogram, and determinism may be linked to regularity of electromyogram.