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IMPACT OF BODY POSITION ON MEASURING DIAPHRAGMATIC ENDURANCE IN YOUNG, HEALTHY INDIVIDUALS

Abstract

Kristin M. Mendez, Alexander W. Parsons, Khase E. Willis, Kevin K. McCully, FACSM. University of Georgia, Athens, GA.

BACKGROUND: The diaphragm is the main inspiratory muscle of the body and important to overall respiratory health. Our lab developed a noninvasive and nonvolitional method to measure diaphragmatic endurance. The purpose of this study was to evaluate the potential effects of abdominal mass, manipulated by body position, on test outcomes. METHODS: Male and female participants (n=5, age: 26.2 ± 6.5) were tested on three separate days. All were of relatively healthy body mass indexes (25.07 ± 3.8). Day 1: anthropometric measurements were taken, and phrenic nerve stimulation familiarization was performed. Day 2: participants were placed in a 10-degree head up tilt. Day 3: participants were placed in a 10-degree head down tilt. Diaphragmatic endurance was measured on each day. The phrenic nerve was stimulated using point electrodes, causing hemi-diaphragmatic contractions. Electrical stimulation current was set at the highest intensity (mA) a person could tolerate. If too much concurrent brachial plexus activation was observed, the stimulation was decreased to an intensity that still produced a vigorous diaphragmatic contraction but reduced arm movement. A tri-axial accelerometer was placed on the participant’s abdomen to capture the acceleration of twitch contractions. The endurance test consisted of 5 minutes of stimulation at a frequency of 5 Hz. The Endurance Index (EI) represents the percentage of diaphragm acceleration that remained after 5 minutes. RESULTS: While not statistically significant, position differences did exist. Data reflected our hypothesis that EIs would be higher in the head up position with a mean value of 88.5% (5.3) compared to the supine and head down positions with mean values of 77.6% (8.0) and 78.6% (7.6), respectively. No main effect was found for body position with a repeated measures analysis of variance (Wilks Λ=.230, F2,3=5.021, p=.110) There was a large effect size between head up and both supine (d=1.6) and head down positions (d=1.5). A small effect size was seen between supine and head down (d=.1). CONCLUSIONS: Body position has the potential to influence diaphragm endurance index. This suggests abdominal mass may be a confounding factor when performing the endurance test. Performing the test with a 10-degree head up tilt may reduce the impact of abdominal mass in young, healthy individuals. Additional testing is needed with a larger sample size.

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