To validate the accuracy and consistency of respiratory inductive plethysmography (RIP) in measuring tidal volume after an overnight sleep, tidal volumes of 18 patients with suspected sleep disordered breathing and 8 normal volunteers were measured simultaneously with RIP (V TRIP ) and with an ultrasonic airflow meter (V TUFM ) before and after an unstrained overnight sleep on supine and lateral decubitus. The bias of the V TRIP was expressed as (V TRIP V TUFM )/ V TUFM ·100 %, limits of agreement between V TRIP and V TUFM was measured by averaged bias ±2 s . Results showed that in normal subjects, the bias of RIP before and after overnight sleep was precise and consistent in both supine (0.7 % and -1.6 %) and lateral decubitus (3.7 % and -0.56 %). In these patients, the bias of RIP before and after sleep in supine also remained small (1.9 % and 1.7 %), but it became larger in lateral decubitus (24.5 % and 20.4 %) and 11.5 % exceeded the limits of agreement observed in the evening. The patients′ body mass indices (BMI) were higher than those of normal subjects (median 34.2 vs. 27.8 kg/m 2). Pooled data showed that the bias of V TRIP in the morning on lateral decubitus but not on supine was correlated to BMI (Spearman R=0.32, n =52, P =0.02). Thus, we were led to conclude that the accuracy of V TRIP overnight was precise and consistent in normal subjects, but the deviation of V TRIP measured on lateral decubitus in patients especially in those with excessive obesity was greater, thus, the method should not be used for quantitative determination.
展开▼
