Reference values of total respiratory resistance, determined with the "opening" interruption technique.

In a large epidemiological survey of lung function the subjects performed maximum expiratory flow volume (MEFV) manoeuvres. They were also interviewed by trained interviewers using a standardized questionnaire. In a random subset of the subjects the resistance of the respiratory system was measured with the "opening" interruption technique, in which the mouth pressure before the end of the interruption period is divided by the flow shortly after the end of it. The subset contained men and women, and smokers as well as nonsmokers, 229 of whom were considered to be healthy because they had no history of complaints and a "normal" flow-volume curve. In this group mean inspiratory and expiratory resistances did not differ significantly (0.27 and 0.29 for men and 0.39 and 0.38 kPa.l-1.s for women). The averages of in- and expiratory resistance were 0.28 +/- 0.10 kPa.l-1.s for men and 0.39 +/- 0.11 kPa.l-1.s for women. The resistance values were slightly but significantly correlated with body height, FEV1 and MEF50, but not with smoking habits. Due to the considerable variability the method does not permit sharp discrimination between normal and abnormal subjects. However, it appears to be useful in histamine challenge testing, to detect and monitor bronchial asthma, being not subjected to the disturbing effect of forced ins- and expirations.