Impacts of body positions on the geniohyoid muscle contraction and swallowing difficulty in healthy adults

Abstract

Background: Body positions affect swallowing and gastroesophageal reflux. Swallowing impairment is one of the main causes of aspiration pneumonia. To prevent pneumonia, evaluation of body positions on gastroesophageal reflux recommended 30 degrees or higher semi-recumbent positions. The geniohypoid muscle and tongue play central roles in swallowing. However, the effects of body positions on contracting rates in the geniohyoid muscle and tongue pressure are unclear. Moreover, correlations between geniohyoid muscle contracting rates and subjective swallowing difficulties are unclear.

Aims: This study aimed to identify the proper body positions on contracting rates in the geniohyoid muscle, tongue pressure, and subjective swallowing difficulties.

Materials & methods: Twenty healthy adults swallowed 15- or 50 ml of water at 90 degrees sitting, 60- and 30 degrees semi-recumbent, and 0 degrees supine positions. We scored the subjective swallowing difficulties and measured the tongue pressure and the number of swallows. An ultrasound evaluated the geniohyoid muscle size and contracting rates.

Results: At sitting and 60 degrees semi-recumbent positions, the geniohyoid muscle showed greter contracting rates than at 30 degrees semi-recumbent and supine postions (P < 0.05), which resulted in easier swalloiwng. Greater tongue pressure was weakly correlated with fewer swallows (r = -0.339, P = 0.002), whereas the body positions did not affect.

Conclusion: Considering swallowing and gastroesophageal reflux together, a trunk angle of 60 degrees or more might be beneficial for reducing the risk of aspiration.

Keywords: aspiration; aspiration pneumonia; body position; swallowing muscle.

Figure 1

The body positions during the measurement. (a) We set 4 angles as the body positions. From left to right, 90 degrees at the sitting, 60 and 30 degrees at two semi‐recumbent positions, and 0 degrees at the supine position. (b) A wheelchair with adjustable backrest angles was applied. Participants sat in a wheelchair with their heads positioned midline and stabilized by a headset. The neck position was fixed at a slight chin‐down position. The lower limbs were bent at the knees, and the feet were on a stand.

Figure 2

The ultrasound analysis of the geniohyoid muscle. (a) We assessed the distance between the mandible and the hyoid bone. We marked a position one‐third from the mandible as the measurement point. (b) We located a probe at the point in the coronal plane. (c) The white dotted line is the geniohyoid muscle. We positioned the probe at the marked point, traced the edge of the geniohyoid muscle, and measured the cross‐sectional area. (d) We measured the width and thickness of the geniohyoid muscle, as shown in (d). The horizontal arrow shows width, and the vertical arrow shows thickness. To avoid readers' confusion, we divided images for measurement, one for the area (c) and another for length (d).

Figure 3

The shape and contracting rate of the geniohyoid muscle at four positions. (a) Width (left panel) and thickness (right panel) of the geniohyoid muscle at four body positions in females. (b) Width (left panel) and thickness (right panel) of the geniohyoid muscle at four body positions in males. (c) Width to thickness ratio of the geniohyoid muscle at four body positions. (d) The contracting rate of the geniohyoid muscle at four body positions. Values are mean ± standard error. *p < .05 versus 0 degrees at the supine position. ^# p < .05 versus 30 degrees at the semi‐recumbent position.

Figure 4

Tongue pressure, number of swallows, and subjective scoring of swallowing difficulties at four body positions. (a) Maximum tongue pressure at four body positions in females (left panel) and in males (right panel). Males showed greater tongue pressures at the sitting and 30 degrees semi‐recumbent positions than females (p < .05). (b) A number of swallows at four body positions. (c) Scoring of swallowing difficulties at four body positions. Values are mean ± standard error. *p < .05 versus 0 degrees at the supine position. ^# p < .05 versus 30 degrees at the semi‐recumbent position.

Figure 5

Relationships between measured indices. (a) Relationship between maximum tongue pressure and the number of swallows. (b) Relationship between subjective scoring of swallowing difficulties and shapes of the geniohyoid muscle. (c) Relationship between subjective scoring of swallowing difficulties and the geniohyoid muscle contracting rates.