The influence of end-expiratory lung volume on measurements of pharyngeal collapsibility

• Published in: Journal of applied physiology (1985) Vol. 108; no. 2; pp. 445 - 451
• Main Authors: Owens, Robert L, Malhotra, Atul, Eckert, Danny J, White, David P, Jordan, Amy S
• Format: Journal Article
• Language: English
• Published: United States Am Physiological Soc 01.02.2010; American Physiological Society
• Series: Pulmonary Physiology and Pathophysiology in Obesity
• Subjects: Adult; Air Pressure; Airway management; Anthropometry; Body Mass Index; Continuous Positive Airway Pressure; Female; Highlighted Topic; Humans; Lung - physiopathology; Lung Compliance - physiology; Lung Volume Measurements; Lungs; Male; Medical instruments; Middle Aged; Obesity - physiopathology; Patients; Pharynx - physiopathology; Polysomnography; Respiratory Function Tests; Respiratory Mechanics - physiology; Sleep apnea; Sleep Apnea, Obstructive - physiopathology; Sleep Apnea, Obstructive - therapy; Sleep Stages - physiology; Throat; Wakefulness - physiology
• ISSN: 8750-7587; 1522-1601; 1522-1601
• DOI: 10.1152/japplphysiol.00755.2009

Sleep Disorders Research Program, Division of Sleep Medicine, Brigham and Women's Hospital and Harvard Medical School, Boston, Massachusetts Submitted 14 July 2009 ; accepted in final form 20 November 2009 Changes in end-expiratory lung volume (EELV) affect upper airway stability. The passive pharyngeal critical pressure (Pcrit), a measure of upper airway collapsibility, is determined using airway pressure drops. The EELV change during these drops has not been quantified and may differ between obese obstructive sleep apnea (OSA) patients and controls. Continuous positive airway pressure (CPAP)-treated OSA patients and controls were instrumented with an epiglottic catheter, magnetometers (to measure change in EELV), and a nasal mask/pneumotachograph. Subjects slept supine in a head-out plastic chamber in which the extrathoracic pressure could be lowered (to raise EELV) while on nasal CPAP. The magnitude of EELV change during Pcrit measurement (sudden reductions of CPAP for 3–5 breaths each minute) was assessed at baseline and with EELV increased 500 ml. Fifteen OSA patients and 7 controls were studied. EELV change during Pcrit measurement was rapid and pressure dependent, but similar in OSA and control subjects (74 ± 36 and 59 ± 24 ml/cmH 2 O respectively, P = 0.33). Increased lung volume (mean +521 ml) decreased Pcrit by a similar amount in OSA and control subjects (–3.1 ± 1.7 vs. –3.9 ± 1.9 cmH 2 O, P = 0.31). Important lung volume changes occur during passive Pcrit measurement. However, on average, there is no difference in lung volume change for a given CPAP change between obese OSA subjects and controls. Changes in lung volume alter Pcrit substantially. This work supports a role for lung volume in the pathogenesis of OSA, and lung volume changes should be a consideration during assessment of pharyngeal mechanics. obstructive sleep apnea; obstructive sleep apnea pathogenesis; pharyngeal critical pressure; respiratory mechanics; functional residual capacity Address for reprint requests and other correspondence: R. L. Owens, Sleep Disorders Research Program, Div. of Sleep Medicine, Brigham and Women's Hospital, 221 Longwood Ave., Boston, MA 02115 (e-mail: rowens{at}partners.org ).