ACCURACY AND RELIABILITY OF COMMERCIAL LU NG-FUNCTION DIAGNOSTIC SYSTEMS AND RESPIRATORY MONITORS IN NEWBORN-INFANTS

Reliability and accuracy of the measured ventilatory and lung mechanic al parameters of different diagnostic systems (SensorMedics 2600, Med- Science RDS 4500) and respiratory monitoring systems (BICORE CP-100, m onitor of Babylog 8000) were investigated using a mechanical lung mode l. The accuracy of pressure and volume signals was measured statically over 6h. The errors of estimated lung mechanic parameters (compliance C, resistance R, time constant T = R.C) were determined for the model parameters Ci = 3.9; 6.4; 10.0; 13.0 ml/kPa and Ri = 4.0; 10.0 kPa/l/ s without and with endotracheal tubes (12 Ch, 16 Ch). Altogether 27 pa rameter combinations were used. The lung mechanic parameters were meas ured by single occlusion tests. The Babylog 8000 permits only the meas urement of the endinspiratory quasistatic compliance C = V(T)/(P(max) - PEEP). The investigations have shown that - excepted the CP-100 (vol ume measuring error > 14%) - the accuracy of static measurements was s ufficient and in conformity with the allowed tolerances. No significan t changes were found over 6h. The mean errors of measured lung mechani c parameters differed extremely in relationship to the time constant o f the model. They are for T < 80ms/T greater-than-or-equal-to 80 ms 7. 4%/-3.5% (SM 2600), -8.4%/-5.8% (CP-100) and -22.0%/-17.3% (Babylog 80 00) for compliance, 4.6%/-3.8% (SM 2600) and 189.0%/43.4% (CP-100) for resistance. No reliable measurements of lung mechanics were possible with the RDS 4500 due to software problems. We found, the smaller the time constant the higher the measuring errors of lung mechanic paramet ers. There are big differences between the investigated devices. Up to now for exact measurements expensive diagnostic systems can not be re placed by respiratory monitors.