Evaluation of a 5-Minute Endurance Test of Human Diaphragm Muscle

Abstract

Diaphragmatic function is important in treating respiratory failure. Muscle endurance has been measured using twitch electrical stimulation and accelerometer-based mechanomyography. The purpose of this study was to evaluate the reproducibility and the time to perform an endurance test on the diaphragm muscle using electrical stimulation of the phrenic nerve. Twenty healthy subjects (21.6±1.6yrs) were tested in the supine position on two separate occasions. Stimulation electrodes were placed on the left (n=18) or right (n=2) phrenic nerve underneath the sternocleidomastoid muscle. A tri-axial accelerometer was placed on the abdomen and 5 minutes of submaximal electrical stimulation at 5Hz was performed. The resultant vector of acceleration at peak and end acceleration was analyzed: endurance index = end/peak*100). The test was successfully completed 41/47 times. The endurance index for the two days was 73.8±9.4% and 72.6±11.1%, respectively. The time to find the phrenic nerve was 34.8±13.1s for the first 10 subjects and 13.0±2.8s for the second 10 subjects. For the second group, the mean difference in endurance between days was 0.03% with a 95% confidence interval of -1.6% to 1.5%. In conclusion, the diaphragm endurance test was reproducible with practice.