Reliability of airway occlusion pressure as an index of respiratory motor output.

BACKGROUND Airway occlusion pressure 0.1 s after the start of inspiratory flow (P0.1) is used as an index of respiratory motor output; however, the reliability of P0.1 in this capacity has not been sufficiently investigated. Therefore, the aim of our study was to examine the reliability of P0.1. METHODS Eleven healthy subjects (7 men and 4 women) participated in our study. Subjects were placed in a supine position, and P0.1 was measured every 30 s for 5 min, following a 1-min period during which ventilation and breathing frequency were measured. A total of 10 P0.1 values were obtained, and the intraclass correlation coefficient (ICC) was used to analyze reliability. ICC values from ICC (1, 2) to ICC (1, 10) were calculated following a number of measurements (k), where ICC (1, k) was increased sequentially from 2 to 10. RESULTS The ICC (1, 2) through ICC (1, 10) values were found to be between 0.877 and 0.960 (95% CI 0.565-0.966 and 0.912-0.987, respectively). When the target coefficient was set at 0.9, the ICC (1, 1) from 10 measurements was calculated a minimum of 4 times. CONCLUSIONS Although a single measurement of P0.1 was somewhat reliable, the 95% CIs indicated that it is necessary to determine the average value of 3 or more measurements. The minimum of 4 repeat measurements were required to obtain valid results, indicating that the current method of determining P0.1 by averaging the values from at least 4 repeated measurements is valid.