The effect of increased genioglossus activity and end-expiratory lung volume on pharyngeal collapse

• Published in: Journal of applied physiology (1985) Vol. 109; no. 2; pp. 469 - 475
• Main Authors: Jordan, Amy S., White, David P., Owens, Robert L., Eckert, Danny J., Rahangdale, Shilpa, Yim-Yeh, Susie, Malhotra, Atul
• Format: Journal Article
• Language: English
• Published: Bethesda, MD American Physiological Society 01.08.2010
• Subjects: Adult; Airway management; Biological and medical sciences; Continuous Positive Airway Pressure; Effects; Electromyography; Exhalation; Eye movements; Female; Fundamental and applied biological sciences. Psychology; Humans; Lung - physiopathology; Lung Volume Measurements; Lungs; Magnetometry; Male; Medical instruments; Medical treatment; Middle Aged; Pharynx - physiopathology; Respiratory Muscles - physiopathology; Sleep apnea; Sleep Apnea, Obstructive - physiopathology; Sleep Apnea, Obstructive - therapy; Sleep Stages; Supine Position; Time Factors; Tongue - physiopathology; Treatment Outcome; obstructive sleep apnea; Nervous system diseases; Sleep apnea syndrome; Respiratory disease; Striated muscle; Respiratory system; pharyngeal critical closing pressure; upper airway dilator muscles; Respiratory tract; Lung volume; Critical pressure; Vertebrata; Mammalia; Expiratory collapse
• ISSN: 8750-7587; 1522-1601; 1522-1601
• DOI: 10.1152/japplphysiol.00373.2010

Increasing either genioglossus muscle activity (GG) or end-expiratory lung volume (EELV) improves airway patency but not sufficiently for adequate treatment of obstructive sleep apnea (OSA) in most patients. The mechanisms by which these variables alter airway collapsibility likely differ, with increased GG causing airway dilation, whereas increased EELV may stiffen the airway walls through caudal traction. We sought to determine whether the airway stabilizing effect of GG activation is enhanced when EELV is increased. To investigate this aim, 15 continuous positive airway pressure (CPAP)-treated OSA patients were instrumented with an epiglottic catheter, intramuscular GG-EMG electrodes, magnetometers, and a nasal mask/pneumotachograph. Subjects slept supine in a sealed, head-out plastic chamber in which the extra-thoracic pressure could be lowered (to raise EELV) while on nasal CPAP with a variable deadspace to allow CO 2 stimulation (and GG activation). The pharyngeal critical closing pressure (P CRIT ) was measured by sudden reduction of CPAP for three to five breaths each minute during non-rapid eye movement (NREM) sleep in 4 conditions: a) baseline, b) 500 ml increased EELV, c) 50% increased GG, and d) conditions b and c combined. P CRIT was found to be reduced from 2.2 ± 0.7 cmH 2 O at baseline to −1.0 ± 0.5 with increased EELV, 0.6 ± 0.7 with increased GG and −1.6 ± 0.7 when both variables were raised ( P < 0.001). The slope of the P CRIT curves remained unchanged in all conditions ( P = 0.05). However, the CPAP level at which flow limitation developed was lower in both increased EELV conditions ( P = 0.001). These findings indicate that while both increased GG and EELV improve airway collapsibility, the combination of both variables has little additional effect over increasing EELV alone.