Am. J. Respir. Crit. Care Med., Volume 159, Number 1, January 1999, 149-157

Pharyngeal Critical Pressure in Patients with Obstructive Sleep Apnea Syndrome
Clinical Implications

EMILIA SFORZA, CHRISTOPHE PETIAU, THOMAS WEISS, ANNE THIBAULT, and JEAN KRIEGER

Sleep Disorders Unit, University Hospital, Strasbourg, France

Current evidence suggests that patients with obstructive sleep apnea (OSA) may have greater pharyngeal critical pressure (Pcrit), which reflects the increase in upper airway collapsibility. The contribution of Pcrit to the severity of OSA and to the efficacious continuous positive pressure (nCPAP_eff) therapy has never been extensively described and no data are available about the interaction of Pcrit, age, and anthropometric variables. To determine the relationship between Pcrit, severity of the disease, nCPAP_eff, and anthropometric variables we measured Pcrit in a group of 106 patients with OSA. Pharyngeal critical pressure was derived from the relationship between maximal inspiratory flow and nasal pressure, Pcrit representing the extrapolated pressure at zero flow. Upper airway resistance (Rus) was determined as the reciprocal of the slope (Pn/VI_max cm H₂O/L/s) in the regression equation. In a subgroup of 68 patients, during the diagnostic night, we measured as indices of respiratory effort, the maximal inspiratory esophageal pressure (Pes) at the end of apnea (Pes_max), the overall increase from the minimum to the maximum (Pes), and the rate of increase of Pes during apnea (RPes). As a group, the mean Pcrit was 2.09 ± 0.1 cm H₂O (range, 0 to 4.5) and the mean Rus was 11.1 ± 0.5 cm H₂O/L/s. Although men have greater Pcrit, pharyngeal collapsibility was influenced neither by neck size nor by body mass index (BMI). Although there was a significant relationship between Pcrit and apnea plus hypopnea index (AHI) (r = 0.23, p = 0.02), neck circumference was the stronger predictor of apnea frequency, with Pcrit contributing only to the 3% of the variance. In the group of patients as a whole, a model including AHI, BMI, Rus, and Pcrit explained the 36% of the variance in nCPAP_eff, with a greater contribution of AHI, Pcrit accounting for only 3% of the variation. In patients for whom the measure of respiratory effort was obtained, 42% of the variance in nCPAP_eff was explained by RPes (33%) and BMI. From these results we conclude that Pcrit alone does not yield a diagnostically accurate estimation of OSA severity and nCPAP_eff. Although individual collapsibility may predispose to pharyngeal collapse, upper airway occlusion may require the combination of several factors, including obesity, upper airway structure, and abnormalities in muscle control.

This article has been cited by other articles:

				K. Yukawa, Y. Inoue, H. Yagyu, T. Hasegawa, Y. Komada, K. Namba, N. Nagai, S. Nemoto, E. Sano, M. Shibusawa, et al. Gender Differences in the Clinical Characteristics Among Japanese Patients With Obstructive Sleep Apnea Syndrome Chest, February 1, 2009; 135(2): 337 - 343. [Abstract] [Full Text] [PDF]

				A. Oliven, E. Aspandiarov, I. Gankin, L. Gaitini, and N. Tov Collapsibility of the relaxed pharynx and risk of sleep apnoea Eur. Respir. J., November 1, 2008; 32(5): 1309 - 1315. [Abstract] [Full Text] [PDF]

				M. Younes Role of respiratory control mechanisms in the pathogenesis of obstructive sleep disorders J Appl Physiol, November 1, 2008; 105(5): 1389 - 1405. [Abstract] [Full Text] [PDF]

				D. P. White Pathogenesis of Obstructive and Central Sleep Apnea Am. J. Respir. Crit. Care Med., December 1, 2005; 172(11): 1363 - 1370. [Abstract] [Full Text] [PDF]

				A. S. Jordan, A. Wellman, J. K. Edwards, K. Schory, L. Dover, M. MacDonald, S. R. Patel, R. B. Fogel, A. Malhotra, and D. P. White Respiratory control stability and upper airway collapsibility in men and women with obstructive sleep apnea J Appl Physiol, November 1, 2005; 99(5): 2020 - 2027. [Abstract] [Full Text] [PDF]

				A. Wellman, A. S. Jordan, A. Malhotra, R. B. Fogel, E. S. Katz, K. Schory, J. K. Edwards, and D. P. White Ventilatory Control and Airway Anatomy in Obstructive Sleep Apnea Am. J. Respir. Crit. Care Med., December 1, 2004; 170(11): 1225 - 1232. [Abstract] [Full Text] [PDF]

				M. Younes Contributions of Upper Airway Mechanics and Control Mechanisms to Severity of Obstructive Apnea Am. J. Respir. Crit. Care Med., September 15, 2003; 168(6): 645 - 658. [Abstract] [Full Text] [PDF]

				K. J. Monahan, E. K. Larkin, C. L. Rosen, G. Graham, and S. Redline Utility of Noninvasive Pharyngometry in Epidemiologic Studies of Childhood Sleep-disordered Breathing Am. J. Respir. Crit. Care Med., June 1, 2002; 165(11): 1499 - 1503. [Abstract] [Full Text] [PDF]

				I. KATO, J. GROSWASSER, P. FRANCO, S. SCAILLET, I. KELMANSON, H. TOGARI, and A. KAHN Developmental Characteristics of Apnea in Infants Who Succumb to Sudden Infant Death Syndrome Am. J. Respir. Crit. Care Med., October 15, 2001; 164(8): 1464 - 1469. [Abstract] [Full Text] [PDF]

				A. Malhotra, G. Pillar, R. Fogel, J. Beauregard, J. Edwards, and D. P. White Upper-Airway Collapsibility : Measurements and Sleep Effects Chest, July 1, 2001; 120(1): 156 - 161. [Abstract] [Full Text] [PDF]

				J. P. Bacon, R. J. Farney, R. L. Jensen, J. M. Walker, and T. V. Cloward Nasal Continuous Positive Airway Pressure Devices Do Not Maintain the Set Pressure Dynamically When Tested Under Simulated Clinical Conditions Chest, November 1, 2000; 118(5): 1441 - 1449. [Abstract] [Full Text] [PDF]

				A. Boudewyns, N. Punjabi, P. H. Van de Heyning, W. A. De Backer, C. P. O'Donnell, H. Schneider, P. L. Smith, and A. R. Schwartz Abbreviated Method for Assessing Upper Airway Function in Obstructive Sleep Apnea Chest, October 1, 2000; 118(4): 1031 - 1041. [Abstract] [Full Text] [PDF]

				E. SFORZA, W. BACON, T. WEISS, A. THIBAULT, C. PETIAU, and J. KRIEGER Upper Airway Collapsibility and Cephalometric Variables in Patients with Obstructive Sleep Apnea Am. J. Respir. Crit. Care Med., February 1, 2000; 161(2): 347 - 352. [Abstract] [Full Text]