Pulmonary volume measurements during high-frequency jet ventilation in anesthetized man

To assess the validity of indirect spirometry during conventional intermittent positive-pressure ventilation (IPPV) and high-frequency jet ventilation (HFJV), we measured changes in functional residual capacity (delta FRC) and tidal volume (VT) with two external strain gauges in eight sedated and paralyzed patients. The thoracic and abdominal gauges were calibrated simultaneously in quasi-static and dynamic conditions. The delta FRC measured during HFJV (1 to 5 Hz) and the VT measured during IPPV (0.25 Hz) were found to be equivalent by the two gauges in most patients (r = .90 and r = .99, respectively), but no correlation was found between the VT values inferred by each gauge in HFJV (r = .54). During HFJV, spectral analysis of the gauge signals showed important damping of the abdominal motion (AB) and an amplification of the thoracic displacements (RC) in four patients when measurements were taken at greater than 3 Hz. We conclude that, provided the partition of the volume between AB and RC remains constant, indirect spirometry may measure VT in IPPV and delta FRC in HFJV, but it fails to measure VT accurately during HFJV.