The Validity And Reproducibility Of A 5-minute Endurance Test Of The Diaphragm Muscle

Abstract

Diaphragmatic function could be important in treating respiratory failure. Electrical stimulation and accelerometer-based mechanomyography have been used to identify the endurance index of various muscles, but not of the diaphragm. PURPOSE: Measure the validity and reproducibility of an endurance test of the diaphragm muscle using electrical stimulation of the phrenic nerve. METHODS: Ten healthy subjects (21.3±1.1 yrs) were tested in the supine position on two separate occasions within one week. Custom-made stimulation electrodes were placed on the left (n=12) or right (n=2) phrenic nerve, which lies underneath the sternocleidomastoid muscle. The stimulation intensity to induce a vigorous contraction was determined. An accelerometer was placed on the abdomen. The endurance test consisted of 5 minutes of electrical stimulation on 5 Hz, with a sampling rate of 400 Hz. The average acceleration per minute was recorded. The endurance index, which equals the ending value/peak value*100, was then calculated. A series of practice tests were performed before data collection. RESULTS: The test was successfully completed 27/30 times. The time to find the phrenic nerve was 43.9±50.4 s for trial 1 and 25.9±26.3 s for trial 2. The average endurance index for trial 1 and 2 were 70.5±11.2% and 70.4±12.4%, respectively (between days, p=0.54, CV=7.71%). CONCLUSIONS: The time to find the phrenic nerve decreased with practice. The endurance test was reproducible and did not have an order effect. With additional training and testing, the diaphragm endurance test may be practical in clinical populations.