The pilot study examining the effects of swallowing position on lung volume fraction and the coordination between respiration and non-nutritive swallowing reflex.

BACKGROUND: Body position might affect the coordination between respiration and swallowing. This study was carried out to test the hypothesis that during swallowing, coordinated movements of muscle groups such as the diaphragm and rectus abdominis muscles are important to control normal swallowing apnea. OBJECTIVE: To investigate this hypothesis, respiratory parameters, swallowing apnea and muscle activity were measured in each of four body positions: sitting position with feet on the floor, 30 degrees reclining position, lateral position, and standing position. METHODS: All measurements were performed in nine healthy subjects. Nasal airflow was measured using a pneumotachometer and muscle activity was measured using an electromyograph. All lung volume fraction parameters were measured using spirometer and swallowing apnea time was calculated. RESULTS: The maximum inspiratory volume was 2.76 +/- 0.83 L in the 30 degrees reclining position, which was significantly larger than that in the other positions (p = .0001). The preliminary expiratory volume was 1.05 +/- 0.42 L in the 30 degrees reclining position, which was significantly smaller than that in the other positions (p < .0001). The swallowing apnea time during water swallowing was 1.17 +/- 0.35 sec in the lateral position and 0.87 +/- 0.28 sec in the 30 degrees reclining position, which tended to be longer than the 0.78 sec in the sitting position. CONCLUSION: We conclude that both lateral and reclining positions require a longer period of swallowing apnea compared to the sitting and standing positions. Differences in body position may significantly influence the coordination between respiration and swallowing.