An IBM PC-based system for the assessment of cardio-respiratory function using oscillating inert gas forcing signals

Objective. An IBM PC-based real-time data acquisition, monitoring and analy sis system was developed for the assessment of cardio-respiratory function, i.e. airway dead space, alveolar volume and pulmonary blood flow, using os cillating inert inspired gas forcing signals. Methods. The forcing gas mixt ure was generated by an in-house sinusoid gas delivery unit. The system int erfaced with a mass spectrometer and an airway flow transducer, and perform ed real-time tracking of the breath-by-breath end-inspired, end-expired and mixed-expired concentrations. It calculated the cardio-respiratory paramet ers using two, i.e. continuous and tidal, in-house mathematical models of t he lungs. The system's performance was evaluated using a mechanical bench l ung, laboratory subjects and awake adults breathing spontaneously. Its pred ictive accuracy was compared with the measured volumes of the bench lung; s ingle breath CO2 test for airway dead space and N-2 washout for alveolar vo lume in laboratory subjects and awake adults; and thermal dilution techniqu e for pulmonary blood flow in laboratory subjects. Results. Close agreement s were found between the true and predicted airway dead space, i.e. mean di fferences of -12.39%, 14.47% and -17.49%, respectively, and that of alveola r volume, i.e. -8.03%, -3.62% and 7.22%, respectively, in the bench lung, l aboratory subject and awake adult studies; and that of pulmonary blood flow (-23.81%) in the laboratory subjects using the continuous lung model. Even closer agreements were observed for airway dead space (-5.8%) and alveolar volume (-4.01%) of the bench lung and for pulmonary blood flow (-8.47%) in the laboratory subjects using the tidal lung model. Conclusions. A system was developed to deliver, monitor and analyse on-line, and in real-time, ou tput data from the sinusoid forcing technique. The technique was administer ed using the system in various subjects, and produced favourable prediction s.