Obstructive Sleep Apnea Treated by Independently Adjusted Inspiratory and Expiratory Positive Airway Pressures via Nasal Mask: Physiologic and Clinical Implications

doi:10.1378/chest.98.2.317

Chest

Volume 98, Issue 2, August 1990, Pages 317-324

https://doi.org/10.1378/chest.98.2.317 Get rights and content

Treatment of obstructive sleep apnea with nasal continuous positive airway pressure mandates simultaneous increases of both inspiratory and expiratory positive airway pressures to eliminate apneas as well as nonapneic oxyhemoglobin desaturation events. We hypothesized that the forces acting to collapse the upper airway during inspiration and expiration are of different magnitudes and that obstructive sleep-disordered breathing events (including apneas, hypopneas and nonapneic desaturation events) could be eliminated at lower levels of EPAP than IPAP. To test these hypotheses, a device was built that allows the independent adjustment of EPAP and IPAP (nasal BiPAP). Our data support the hypotheses that expiratory phase events are important in the pathogenesis of OSA and that there are differences in the magnitudes of the forces destabilizing the upper airway during inspiration and expiration. Finally, applying these concepts, we have shown that by using a device that permits independent adjustment of EPAP and IPAP, obstructive sleep-disordered breathing can be eliminated at lower levels of expiratory airway pressure compared with conventional nasal CPAP therapy. This may reduce the adverse effects associated with nasal CPAP therapy and improve long-term therapeutic compliance.

Section snippets

METHODS

Fifteen OSA patients and one patient with the sleep hypopnea syndrome*¹ were studied during a full night diagnostic PSG, a full night PSG with the application of nasal CPAP, and a full night PSG during which a ventilatory assist device was utilized (BiPAP). Three OSA patients are not included in the data analyses either because the optimal settings of nasal CPAP and/or nasal BiPAP were attained too late during the night to allow a minimum of approximately one hour of sleep on these settings or

RESULTS

All 13 patients, nine men and four women, were obese (body mass index = 57.41 ± 17.2). For the group, the forced vital capacity (percent predicted) was 77.23 ± 16.4 percent, the FEV₁ (percent predicted) was 80.15 ± 18.1 percent and the FEV₁/FVC was 0.77 ± 0.09. Seven patients had a restrictive pattern on spirometry, defined as an FVC<80 percent of predicted, and three patients had an obstructive pattern (FEV₁/FVC<.7). AD patients were normocapnic during wakefulness (PaCO₂ = 38 ± 4.2). These

DISCUSSION

In this study, we have reinforced the concept that despite the absence of negative intrapharyngeal pressure, there is occlusion, or at least substantial narrowing of the upper airway during the expiratory phase preceeding apnea in OSA patients. Furthermore, we have shown that a critical level of EPAP is essential for uninterrupted upper airway patency during sleep in these patients. Finally, we have applied this concept, in conjunction with previous data, demonstrating the destabilizing

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Citation Excerpt :
As opposed to CPAP, which delivers a fixed pressure throughout the respiratory cycle, BPAP therapy allows the independent adjustment of the EPAP and the IPAP. In its initial description, BPAP therapy demonstrated that obstructive events could be eliminated at a lower EPAP compared with conventional CPAP pressures.24 For patients with uncomplicated OSA, BPAP is typically used in the spontaneous mode (ie, without a back up rate) with an IPAP and EPAP pressure difference of ≥4 cm H2O.

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: This study was supported in part by a grant from Respironics, Inc, Merit Review Funding, the United Parkinsons Foundation, the Competitive Medical Research Fund of Presbyterian-University Hospital, and NHLBI training grant 2T32HL07563-06A1.

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