Effects of breathing on neck volume during supine position

Abstract

Objective: Fluid which accumulates in the lower extremities during the day may redistribute towards the head (rostral fluid shift) during sleep, and so may play a role in restricting the upper airway leading to sleep disordered breathing (SDB). In this pilot study, six healthy men and women were recruited to test the hypothesis that the transition to a recumbent position results in a significant increase in neck fluid volume.
Methods: Change in neck volume (NV) was measured using air plethysmography during 30 minutes of sitting (Sit) and 45 minutes following transition to a supine position (Supine). Each subject was assessed four times on separate days. Linear regression and spectral analysis were undertaken to characterize NV changes.
Results: Three men and three women (two each in their 20 s, 40 s, and 60 s) participated. BMI averaged 24.45 ± 3.9 kg/m2. Both average Sit and Supine NV shifts were significantly greater than zero, +4.33 ml/hr ± 1.63; 95% CI [1.07, 7.59]; +1.51 ml/hr ± 0.55; 95% CI [0.41, 2.61] (p < .05), respectively, however there was no significant difference between Sit and Supine. Spectral analysis of NV recordings revealed peaks at ~0.25 Hz and ~1.2 Hz, consistent with respiration and heart contraction rates, respectively. Average respiratory NV shift was 0.03 ml ± 0.01; 95\% CI [0.01-0.05] (Sitting) and 0.08 ml ± 0.02; 95% CI [0.04, 0.12] (Supine), both significantly greater than zero (p < .05), with supine fluid shifts significantly greater than during sitting (p < .01).
Conclusions: These results suggest that respiratory activity may have the dominant influence on NV when supine, potentially contributing to SDB. Further study of neck fluid shifts during respiration and its influence on sleep quality in persons with SDB is proposed.