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

Schematic representation of the set-up used for the measurements. The measurement set-up comprises three modules: the impulse oscillometry for the measurement of impedance; the respiratory therapy unit; and the unit for data acquisition and processing. The subject is connected to the continuous positive airway pressure (CPAP) device and the humidifier via a nasal mask (1) and a tube system (2). The temperature of the respired air is measured within the mask (ν mask) and the hygrometer (ν hygr). Within the breathing tube there is another, small-calibre tube that transmits the pressure in the nose mask to the sensor in the CPAP device. The capacitive hygrometer for measuring the humidity in inspired and expired air (φ hygr) is located between mask and breathing tube. A valve serves to eliminate the expired carbon dioxide (3). In the impulse oscillometry unit (impulse oscillometry (IOS) device), an oscillating flow is generated and conducted, via a tube (4) and Y‐adapter (5), to the airways. The IOS device also picks up the pressure (pIOS) and flow (vIOS) signals recorded by the pneumotachograph (6) and filters out the signals produced by the oscillating flow. These signals are used to calculate the impedance. The transducer picks up all the measuring signals in the tube system and from the surroundings, and passes them, via an analogue-to-digital converter (A/D converter), to the computer (PC). pCPAP: pressure measured in the breathing tube; V′: flow measured in the breathing tube; φ amb: humidity of the ambient air; ν amb: temperature of the ambient air.