Positive Expiratory and Inspiratory Pressure During Noninvasive Ventilation Influence the Diaphragm Thickness

Background: PEEP affects the geometry and function of the diaphragm. During noninvasive ventilation (NIV), applying inspiratory positive airway pressure (IPAP) in addition to expiratory positive airway pressure (EPAP) may further affect diaphragm thickness. Therefore, this study aimed to investigate the acute effects of IPAP and EPAP on the diaphragm thickness in healthy individuals during baseline, as assessed using ultrasound (US). Methods: This physiological study was conducted using a randomized, double-blind, crossover design and included individuals aged 18–50 years. Participants with a history of smoking or other preexisting conditions were excluded. Diaphragm thickening was assessed via US during baseline under 6 conditions without positive pressure (EPAP and IPAP of 0 cm H 2 O); EPAP of 5, 10, and 15 cm H 2 O without IPAP; and IPAP of 10, 12, and 15 cm H 2 O combined with EPAP of 5 cm H 2 O. Results: Data were collected from 90 participants during baseline, with a mean age of 23.2 years and a mean body mass index of 23.9 kg/m 2 . Compared with baseline without positive pressure, EPAP levels of 10 and 15 cm H 2 O significantly increased both end-expiratory diaphragm thickness (T di,ee ) and end-inspiratory diaphragm thickness (T di,ei ) ( P < .05 for both). Similarly, an IPAP of 15 cm H 2 O combined with an EPAP of 5 cm H 2 O significantly increased T di,ei ( P < .05). Despite these effects, only IPAP at 15 cm H 2 O led to a significant increase in the diaphragm thickening fraction (TF di ) ( P < .05). Conclusions: EPAP levels of 10 cm H 2 O or higher and an IPAP level of 15 cm H 2 O during NIV significantly affect diaphragm thickness, likely because of their impact on lung volumes. Therefore, standardization of diaphragm thickness monitoring at lower EPAP and IPAP levels is recommended to minimize confounding effects between positive pressure and muscle contraction–induced thickness changes.