Neuromechanical control of upper airway patency during sleep

Department of Medicine, Division of Pulmonary and Critical Care Medicine, Johns Hopkins University, Baltimore, Maryland Submitted 6 March 2006 ; accepted in final form 26 September 2006 Obstructive sleep apnea is caused by pharyngeal occlusion due to alterations in upper airway mechanical properties and/or disturbances in neuromuscular control. The objective of the study was to determine the relative contribution of mechanical loads and dynamic neuromuscular responses to pharyngeal collapse during sleep. Sixteen obstructive sleep apnea patients and sixteen normal subjects were matched on age, sex, and body mass index. Pharyngeal collapsibility, defined by the critical pressure, was measured during sleep. The critical pressure was partitioned between its passive mechanical properties (passive critical pressure) and active dynamic responses to upper airway obstruction (active critical pressure). Compared with normal subjects, sleep apnea patients demonstrated elevated mechanical loads as demonstrated by higher passive critical pressures [–0.05 (SD 2.4) vs. –4.5 cmH 2 O (SD 3.0), P = 0.0003]. Dynamic responses were depressed in sleep apnea patients, as suggested by failure to lower their active critical pressures [–1.6 (SD 3.5) vs. –11.1 cmH 2 O (SD 5.3), P < 0.0001] in response to upper airway obstruction. Moreover, elevated mechanical loads placed some normal individuals at risk for sleep apnea. In this subset, dynamic responses to upper airway obstruction compensated for mechanical loads and maintained airway patency by lowering the active critical pressure. The present study suggests that increased mechanical loads and blunted neuromuscular responses are both required for the development of obstructive sleep apnea. obstructive sleep apnea; critical pressure; mechanical properties; neuromuscular control Address for reprint requests and other correspondence: S. P. Patil, Johns Hopkins Sleep Disorders Center, Asthma and Allergy Bldg., 5501 Hopkins Bayview Circle, Rm. 4B30A, Baltimore, MD 21224 (e-mail: spatil{at}jhmi.edu )