The influence of lung volume on pharyngeal mechanics, collapsibility, and genioglossus muscle activation during sleep

Study Objectives: Previous studies in both awake and sleeping humans have demonstrated that lung-volume changes substantially affect upper-airway size and pharyngeal resistance and, thus, may influence pharyngeal patency. We sought to systematically investigate the isolated effects of lung-volume changes on pharyngeal collapsibility and mechanics and genioglossus muscle activation during stable non-rapid eye movement sleep. We hypothesized that lower lung volumes would lead to increased pharyngeal collapsibility, airflow resistance, and, in compensation, augmented genioglossus muscle activation. Design: Nineteen normal individuals (age, 30.4 +/- 0.5 years; body mass index,: 24.5 +/- 0.4 kg/m(2)) were studied during stable non-rapid eye movement sleep in a rigid head-out shell equipped with a variable positive/negative pressure attachment for manipulations of extrathoracic pressure and, thus, lung volume. Setting: Sleep physiology laboratory Participants: Normal healthy volunteers Interventions: N/A Measurements and Results: We measured change in end-expiratory lung volume (EELV)(magnetometers), genioglossus electromyogram (GGEMG) (intramuscular electrodes), pharyngeal pressure, and collapsibility of the pharynx in response to a brief pulse of negative pressure (-8 to -15 cm H20) under the following conditions: (1) baseline, (2) increased EELV (+1 liter), and (3) decreased EELV (46 liter). Reduced lung volumes led to increased inspiratory airflow resistance (7.54 +/- 2.80 cm H20.L-1.s-1 vs 4.53 +/- 1.05 cm H20.L-1.s-1, mean +/- SEM, P = 0.02) and increased genioglossus muscle activation (GGEMG peak 14.6% +/- 1.5% of maximum vs 8.6% +/- 1.5% of maximum, maximumP = 0.001) compared to baseline. The pharynx was also more collapsible at low lung volumes (4.3 +/- 0.5 cm H20 vs 5.4 +/- 0.6 cm H20, P = 0.04). Conclusions: We conclude that upper-airway muscles respond to changes in lung volumes but not adequately to prevent increased collapsibility. These results suggest that lung volume has an important influence on pharyngeal patency during non-rapid eye movement sleep in normal individuals.