Mechanical parameters determining pharyngeal collapsibility in patients with sleep apnea

Mechanical parameters determining pharyngeal collapsibility in patients with sleep apnea

8 Pages · 2010 · 288 KB · English

evaluate parameters of the “tube law” on pharyngeal pressure-flow relationships and collapsibility in patients with obstructive sleep apnea.

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Mechanical parameters determining pharyngeal collapsibility in patients with sleep apnea Arie Oliven, 1Eran Kaufman, 2Rotem Kaynan, 2Ron Oliven, 1Uri Steinfeld, 1Nave Tov, 1Majed Odeh, 1 Luis Gaitini, 3Alan R Schwartz, 4and Eitan Kimmel 2 Departments of 1Medicine and 3Anesthesiology, BnaiZion Medical Center, Technion, Haifa; 2Faculty of Biomedical Engineering, Technion, Haifa, Israel; and 4Johns Hopkins Sleep Disorders Center, Baltimore, Maryland Submitted 20 January 2010; accepted in ?nal form 21 June 2010 Oliven A, Kaufman E, Kaynan R, Oliven R, Steinfeld U, Tov N, Odeh M, Gaitini L, Schwartz AR, Kimmel E Mechanical param eters determining pharyngeal collapsibility in patients with sleep apnea J Appl Physiol 109: 1037?1044, 2010 First published June 24, 2010; doi:101152/japplphysiol000192010?The relative impact of mechanical factors on pharyngeal patency in patients with obstructive sleep apnea is poorly understood The present study was designed to evaluate parameters of the ?tube law? on pharyngeal pressure?ow relationships and collapsibility in patients with obstructive sleep apnea We developed a mathematical model that considered the collapsible segment of the pharynx to represent an ori?ce of varying diameter The model enabled us to assess the effects of pharyngeal compliance (C), neutral crosssectional area ( A o), external peripha ryngeal pressure (P ex), and the resistance proximal to the site of collapse on ?ow mechanics and pharyngeal collapsibility [critical pressure (P crit)] All parameters were measured in 15 patients with obstructive sleep apnea under propofol anesthesia, both at rest and during mandibular advance ment and electrical stimulation of the genioglossus The data was used both to con?rm the validity of the model and to compare expected and actual relationships between the tubelaw parameters and the pharyngeal pressure?ow relationship and collapsibility We found a close correla tion between predicted and measured P crit ( R  098), including changes observed during pharyngeal manipulations Cand A owere closely and directly interrelated ( R 093) and did not correlate with P critA signi?cant correlation was found between P exand P crit ( R  077; P 001) We conclude that the pharynx of patients with obstructive sleep apnea can be modeled as an ori?ce with varying diameter Pharyngeal compliance and A oare closely interrelated Pharyngeal collapsibility depends primarily on the surrounding pressure pharyngeal compliance OBSTRUCTIVE SLEEP APNEA IS a disorder characterized by pharyn geal collapse and occlusion during sleep The mechanisms responsible for this disturbance in pharyngeal patency include both anatomic and neuromuscular control factors Together, these factors render the pharyngeal region to a selfsupporting, softwalled collapsible tube (9, 29), with variable collapsibil ity During wakefulness, continuous re?ex activation of upper airway dilator muscles maintains adequate pharyngeal patency (20) During sleep and anesthesia, however, these protective mechanisms are deranged, increasing pharyngeal collapsibility and leading to partial or complete occlusions in susceptible subjects The mechanical model most commonly used to characterize pharyngeal collapsibility in the nonawake state is the Starling resistor, often served to describe ?ow mechanics of collapsible biological tubes (9, 26, 29) This simpli?ed model describes an ?ideal? collapsible tube that is highly compliant and considers only upstream or nasal pressure (P n) and the critical collapse pressure (P crit) at the pharynx as the variables that de?ne maximal inspiratory ?ow (V ? Imax ) during ?ow limitation, when P n P crit (9) This approach is simple and most useful to characterize pharyngeal collapsibility However, it provides no information about mechanical variables that affect and de?ne the collapsibility of the pharynx Such variables can be as sessed when the ?owlimiting site is viewed as a collapsible tube that in?uences the ?ow that varies with crosssectional area The crosssectional area can be described by a ?tube law? and depends on the transmural pressure and wall compliance Understanding the effects of mechanical and physiological factors on the pharynx requires a concept that integrates ?ow with pharyngeal tube law parameters The present study was designed to assess the effects of mechanical properties of the pharynx on air?ow Applying to the pharynx previously pub lished methods to calculate tubelaw parameters from the pressurearea relationship of collapsible tubes (28), we mea sured in anesthetized patients with obstructive sleep apnea mechanical tubelaw parameters and ?ow, and assessed the relative impact of each mechanical parameter on pharyngeal patency and, therefore, on ?ow limitation and obstruction To assess the expected effects

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