[Studies of leakage measurements of automatic CPAP-devices]

An effective CPAP-treatment is only possible, if greater mask-and mouth leakages are prevented. In the case of greater leakages the CPAP decreases and the flow induces side effects as rhinitis and conjunctivitis. In addition to mask-and mouth leakages there exists a leakage through the exhaust valve of the mask which is necessary to avoid CO2-rebreathing. This leakage changes are dependent on the pressure. In many automatic CPAP devices the hard- and software registers the leakage in parallel with the pressure variations. However it is unclear which leakages are considered. We analysed therefore the signal of the leakage of 4 automatic CPAP-devices concerning following questions: Does the leakage measurement of the devices correspond with the pneumotachographically measured flow. How is the leakage of the mask exhaust valve taken into account.

We simulated normal breathing with a mechanical ventilator. The respective device was connected by a y-piece with a 5 mm aperture (leakage). With an external flow analyser the flow of the leakage was registered and compared with the flow measured by the automatic CPAP-device.

The flow of the devices A to C differed during 10 mbar CPAP from the value of the flow analyser by 5.0 %, 4.3 % and 11.3 %. The software of device D subtracts the leakage through the mask exhaust valve so that the indicated leakage corresponds with the mouth and mask leakage.

The leakage was sufficiently well recorded by the tested automatic devices. When evaluating the leakage signal the flow through the mask exhaust valve should be taken into account.