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Efficiency of cold passover and heated humidification under continuous positive airway pressure

¹ Dept of Pneumology, Allergology and Sleep Medicine, University Witten/Herdecke, and ² Medizintechnik für Arzt und Patient (MAP), Martinsried, Germany

CORRESPONDENCE: W.J. Randerath, Klinik Ambrock, Dept of Pneumology, Allergology and Sleep Medicine, Ambrocker Weg 60, 58091, Hagen, Germany. Fax: 49 2331974209. E-mail: winfried.randerath@dland.de

Keywords: apnoea, breath tests, humidity, positive pressure ventilation, respiratory system

Received: August 1, 2001
Accepted February 18, 2002

This study was supported by the MAP, Martinsried, Germany.

Cold passover and heated humidifiers are employed for the prevention of side-effects associated with continuous positive airway pressure (CPAP) treatment. However, to date, it has not been possible to separately measure the humidity of inspired and expired air. The aim of this study was to compare the relative humidity of the inspired air and the water loss during respiration between cold passover and heated humidifiers under CPAP.

Humidity and temperature were determined separately for the respiratory phases, without humidification, with cold passover and heated humidifiers in 10 healthy subjects. Humidity was measured with a capacitive hygrometer, temperature with a "Type K" thermosensor, and impedance of the total respiratory system with impulse oscillometry.

The relative humidity (rH) of the inspired air (mean±sd) increased significantly from 24.0±9.1% rH (34.8±1.0°C, no humidifier) to 34.5±10.1% rH (34.6±1.0°C) under cold humidification, and to 53.9±13.2% rH (35.0±1.1°C) under heated humidification. With heated humidification, water loss was reduced by 38% compared to cold humidification. The impedance increased from 5.7±1.8 cmH₂O·L·s^–1 (no humidifier) to 6.7±1.8 cmH₂O·L·s^–1 (heated humidifier).

The authors conclude that the use of a heated humidifier during continuous positive airway pressure appreciably increases the relative humidity of the inspired air and reduces the water loss during respiration.

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