Abstract 211

Purpose: To evaluate the accuracy of respiratory inductive plethysmography (RIP) for measurement of end-expiratory lung volume (EELV) changes at varying frequencies of high frequency oscillatory ventilation (HFOV).

Methods: A modified test lung was ventilated at a mean airway pressure of 12 cm H2O, power of 5.0, inspiratory time of 50%, flow of 15 liters/minute, and at various frequencies (7, 10, 12 and 15 Hz). A calibrated super syringe was used to increase the test lung volume in 50 cc increments. Three sets of five volume changes were performed at each of the four frequencies and compared to the recorded change in EELV. RIP records EELV in unitless numbers that we refer to as counts. These counts were calculated by determining the average EELV of five measurements within a two minute period.

Results: The known volume changes using super syringe were 50 5 cc. The mean EELV changes in counts for the different frequencies were 63.7 at 7 Hz, 52.7 at 10 Hz, 59.9 at 12 Hz, and 70.8 at 15 Hz. The average correction from RIP-derived counts to known changes in lung volume was by a factor of 0.8. At all frequencies, the correlation coefficients (below) demonstrated a linear relationship between the known volume changes and the expected changes in EELV using this correction factor. The bias was 8.1 ml (mean difference) and precision was 10.4 ml (standard deviation). The 95% limits of agreement (mean difference 1.96 × standard deviation) were between 28.6 and -12.3 ml. The mean percent difference (100 × difference between known and expected values/mean expected value) was 16.5%. (Table)

Table 1 No caption available
Full size table

Conclusion: We examined the changes in EELV of a test lung during high frequency oscillatory ventilation. We found that measured EELV change by RIP and induced changes in lung volume were significantly correlated over a range of frequencies. This suggests that RIP can be used during HFOV to quantify changes in lung volume at different frequencies.