• Demet S Sulemanji, Fangping Bao, Yandong Jiang, and Robert M Kacmarek.
• Department of Anesthesia, Critical Care and Pain Medicine, Harvard Medical School and Massachusetts General Hospital, Boston, Massachusetts.
• Respir Care. 2014 Oct 1;59(10):1487-93.

BackgroundUnidirectional breathing (UB), nose-in mouth-out (NMB) or vice versa, is thought to create PEEP, stabilize small airways, and increase expiratory flow and exhaled tidal volume (VT) in patients with expiratory obstructive disorders. However, the exact mechanism providing the benefits of UB remains unknown. Our hypothesis was that the benefits of UB are achieved mainly through reduction of upper airway dead space.MethodsSixteen stable COPD patients requiring oxygen use at home were enrolled in this prospective study at a tertiary health care center. A nasal mask and a mouthpiece were used, each having a removable one-way valve to direct the breathing pattern. Four experimentally defined patterns of spontaneous breathing, NMB, mouth-in nose-out (MNB), nose-in nose-out (NNB), and mouth-in mouth-out (MMB), were compared. Each breathing pattern lasted 5 min followed by a 5-min rest period. A NICO device continuously monitored respiratory parameters. The functional anatomical dead space volume (VD) and expired VT values were determined. Breathing efficiency (BE) was calculated as alveolar VT divided by expired volume.ResultsFunctional anatomical VD was higher in bidirectional breathing (BB) (overall: 207.4 ± 7.9 mL; MMB: 232.5 ± 72.7 mL; NNB: 182.2 ± 75 mL) compared to UB (overall: 178.1 ± 87.2 mL; NMB: 176.9 ± 91.3 mL; MNB: 179.3 ± 83.2 mL) (P < .001). BE achieved with UB (overall: 76.2 ± 6.5%; NMB: 76.8 ± 6.8%; MNB: 75.6 ± 6.3%) was higher than that with BB (overall: 66.2 ± 0.09%; MMB: 64.3 ± 0.10%; NNB: 68.1 ± 0.08%) (P < .001). The difference in BE between UB and BB was more pronounced with small VT values (UB: 73.8 ± 0.08; BB: 49.4 ± 0.09) than with large VT values (UB: 77.3 ± 0.06; BB: 63.0 ± 0.07) (P < .001).ConclusionsOur data suggest that a reduction in functional anatomic VD may be the underlying mechanism for the benefits associated with UB in COPD patients. (ClinicalTrials.gov registration NCT00784004.).Copyright © 2014 by Daedalus Enterprises.

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