EVALUATION OF NOCTURNAL BRONCHOCONSTRICTION BY ALL-NIGHT TRACHEAL SOUND MONITORING

Background - A study was undertaken to evaluate the reliability of a d igital tracheal sound analyser (ELENS-DSA) in predicting nocturnal cha nges in airways resistance in asthmatic patients. This device allows c ontinuous measurement of the proportion of the time occupied by wheezi ng (Wh%). Methods - Nocturnal polygraphic studies with simultaneous co ntinuous monitoring of tracheal sounds and airways resistance were per formed in seven patients with nocturnal asthma. In order to evaluate t he possible bias in wheezing estimation, each tracheal sound recording was passed through the automatic analyser and simultaneously monitore d with earphones by an experienced observer. Results - The device dete cted audible wheezing with an optimal sensitivity and specificity of 7 0%. Snoring was a minor cause of the relatively poor characteristics o f the system. A close correlation (p<0.001) between Wh% and airways re sistance was observed only in those patients with the highest increase in resistance; when the results of all the subjects were pooled the c orrelation observed was poor. The predictive value of Wh% in detecting changes in airways resistance during 10 minute intervals was lower th an 70%. The positive and negative predictive values of Wh% were raised to 79% and 83%, respectively, for 30 minute intervals. Conclusions - The ELENS-DSA system is a relatively crude means of detecting wheezing and assessing bronchoconstriction quantitatively. However, it is able to detect accurately nocturnal bronchoconstriction for 30 minute inte rvals. This finding, along with the fact that the monitoring is non-in vasive, suggests that it may be a promising tool, especially for patie nts during sleep.