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


METHODS
Nineteen normal individuals (age, 30.4 +/- 0.5 years; body mass index: 24.5 +/- 0.4 kg/m2) 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.


METHODS
Sleep physiology laboratory.


METHODS
Normal healthy volunteers.


METHODS
N/A.


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 H2O) under the following conditions: (1) baseline, (2) increased EELV (+1 liter), and (3) decreased EELV (-0.6 liter). Reduced lung volumes led to increased inspiratory airflow resistance (7.54 +/- 2.80 cm H2O x L(-1) x s(-1) vs 4.53 +/- 1.05 cm H2O x L(-1) x 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, maximum P = 0.001) compared to baseline. The pharynx was also more collapsible at low lung volumes (4.3 +/- 0.5 cm H2O vs 5.4 +/- 0.6 cm H2O, 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.
Stanchina
Michael L
ML
Pulmonary/Critical Care Division, Brigham and Women's Hospital, Harvard Medical School, Boston, Mass, USA. mstanchina@lifespan.org
Malhotra
Atul
A
Fogel
Robert B
RB
Trinder
John
J
Edwards
Jill K
JK
Schory
Karen
K
White
David P
DP
D000328:Adult; D001696:Biomechanical Phenomena; D015992:Body Mass Index; D004576:Electromyography; D005152:Facial Muscles / Q000502:physiology*; D005260:Female; D006801:Humans; D008168:Lung / Q000502:physiology*; D008176:Lung Volume Measurements; D008297:Male; D010614:Pharynx / Q000502:physiology*; D012895:Sleep, REM / Q000502:physiology*