Data collection and analysis from a respiratory inductance plethysmograph.

A respiratory inductance plethysmograph, Respitrace, was used to assess the respiratory effects of narcotic analgesia for the first 24 hours after surgery. Data were collected on-line from the plethysmograph with an Apple][+ microcomputer and stored on disc for later analysis of respiratory rates and tidal volumes, and also periods of central or obstructive apnoea using the difference in phase angle between the abdominal and respiratory components. This involved the measurement of, on average, more than 20,000 breaths per patient and techniques of data compression were required to store this amount of information on a single floppy disc. Frequent nursing interventions reduced the accuracy of tidal volume and phase angle measurements, but respiratory rates were obtained accurately breath by breath.