Response-time enhancement of a clinical gas analyzer facilitates measurement of breath-by-breath gas exchange

Tidal ventilation gas-exchange models in respiratory physiology and medicin e not only require solution of mass balance equations breath-by-breath but also may require within-breath measurements, which are instantaneous functi ons of time. This demands a degree of temporal resolution and fidelity of i ntegration of gas flow and concentration signals that cannot be provided by most clinical gas analyzers because of their slow response times. We have characterized the step responses of the Datex Ultima (Datex Instrumentation , Helsinki, Finland) gas analyzer to oxygen, carbon dioxide, and nitrous ox ide in terms of a Gompertz four-parameter sigmoidal function. By inversion of this function, we were able to reduce the rise times for all these gases almost fivefold, and, by its application to real on-line respiratory gas s ignals, it is possible to achieve a performance comparable to the fastest m ass spectrometers. With the use of this technique, measurements required fo r non-steady-state and tidal gas-exchange models can be made easily and rel iably in the clinical setting.