Impact of Expiratory Port Structural Characteristics on Expiratory Pressure-Volume Area in Noninvasive Ventilation

Abstract

Background:

Patients with obstructive lung diseases are vulnerable to dynamic hyperinflation and increased work of breathing (WOB). Although ventilator circuit components influence respiratory mechanics, the impact of the expiratory port design on WOB has received limited attention. This study examined whether exhalation resistance measurements can predict expiratory pressure-volume area (PVA) in an obstructive lung disease model.

Methods:

Four expiratory ports were tested Intersurgical (IS), Philips (P), ResMed (RM), and HSINER (H). Exhalation resistance, end-expiratory pressure, and expiratory PVA were measured using a PF-301 flow analyzer. Exhalation resistance was measured using a high-flow nasal cannula at 30, 40, 50, and 60 L/min. An obstructive lung model was created using a test lung in pressure control mode (PEEP 5 cm H₂O). Statistical analyses included two-way analysis of variance (ANOVA) for exhalation resistance and one-way ANOVA with Tukey–Kramer post hoc tests for end-expiratory pressure and PVA.

Results:

The P port exhibited the lowest exhalation resistance (0.343 cm H₂O/L/s) but the highest PVA (0.013 ± 0.001 J/L) and end-expiratory pressure (0.134 ± 0.007 cm H₂O), significantly exceeding those of all other ports. The IS port demonstrated the highest exhalation resistance (0.37 cm H₂O/L/s) but intermediate PVA (0.004 ± 0.004 J/L). The H port demonstrated PVA below 0.001 J/L, and the RM port showed 0.001 ± 0.001 J/L. No significant correlation was observed between exhalation resistance and PVA (r = −0.892, R² = 0.796, P = .11).

Conclusions:

Exhalation resistance measurements did not predict respiratory mechanical burden in this obstructive lung disease model. Despite exhibiting the lowest exhalation resistance, the P port generated the highest PVA and an end-expiratory pressure elevation of 0.14 cm H₂O above set PEEP. Expiratory port characteristics beyond exhalation resistance, including structural features affecting pressure dynamics, should be evaluated to optimize circuit configuration for patients with obstructive lung disease who are vulnerable to dynamic hyperinflation.

Keywords

pressure-volume area pulmonary disease chronic obstructive respiratory mechanics noninvasive ventilation mechanical ventilation equipment design airway resistance

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