Aim: The aim of this study was to assess the noisiness levels produced by different gas source systems, breathing circuits setup, and gas flow rates during continuous positive airway pressure (CPAP) delivered through helmet.
Methods: This was a crossover design study. Ten healthy subjects received helmet CPAP at 5 cm H2O in random order with different gas flow rates (60 and 80 L/min), 3 diverse gas source systems (A: Venturi system, B: oxygen and air flowmeters, C: electronic Venturi system), and 3 different breathing circuit configurations. During every step of this study, a heat and moisture exchanger (HME) was placed on the helmet inlet gas port to measure the effects on noise production. Noise intensity level was recorded through a sound-level meter. Participants scored their noisiness perception on a visual analog scale.
Results: The noise level inside the helmet ranged between 76 ± 4 and 117 ± 1 Decibel A. The gas source and the gas flow rate always affected the noise level inside and outside the helmet (P < .001). The different "breathing circuit setup" did not change the noise levels inside the helmet (P = .244), but affected the noise level outside, especially when a Venturi system was used (P < .001). An HME filter placed at the junction between the inspiratory limb of the breathing circuit and the helmet significantly decreased the noise intensity inside the helmet (mean dBA without HME, 99.56 ± 13.30 vs 92.26 ± 10.72 with HME; P < .001) and outside (mean dBA without HME, 68.16 ± 12.05 vs 64.97 ± 12.17 with HME; P < .001). The perception of noise inside the helmet was lower when an HME filter was placed on the inspiratory inlet gas port (median, 6 [interquartile range, 4-7] vs 7 [5-8]; P < .001).
Conclusions: When helmet CPAP is delivered through gas flow rates up to 50 L/min, an HME placed on the helmet inlet gas port should be used to reduce noise inside the helmet and to improve patients' comfort.
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