A Kr-81m inhalation method for detection of absence of uniform ventilation in asthma

In an attempt to compare inhalation methods in detecting abnormal patterns of ventilation, the following four techniques were applied in 12 asthmatic patients: spontaneous respiration with a Kr-81m gas-air mixture (SP technique); serial inhalation of a Kr-81m gas-air mixture from the level of residual volume to total lung capacity (VC technique); bolus inhalation of 10 ml or Kr-81m gas from the level of residual volume, followed by air, to total lung capacity (RV technique); bolus inhalation of 10 ml of Kr-81m gas from the level of functional residual capacity, followed by air, to total lung capacity (FRC technique). Before exercise, abnormalities were detected by the RV and FRC techniques, but no abnormalities were detected by SP and VC techniques. On studies done after exercise, the abnormalities were detected by all the described techniques. However, they were best demonstrated by the RV technique and shown least well by the VC method.