閉塞性肺疾患における不均等換気の検討

Studies on Uneven Ventilation in Cases with Chronic Obstructive Lung Disease

　換気の不均等性の指標⊿N₂は窒素1回呼吸法（SBN₂法）より，またIDI（吸気不均等分布指数）は窒素多呼吸洗い出し法（MBN₂法）より算出されるが，この両値が乖離する症例に屡々遭遇する^1）。

　本論文では不均等換気が著明に出現する閉塞性肺疾患，特に気管支喘息と慢性肺気腫の⊿N₂とIDIを対比し，それぞれの特徴を検討した。また気管支喘息の非発作時に比して発作時には⊿N₂及びIDIの上昇傾向が認められるが，ここではIDI上昇の機序を解明するために，単位肺容量あたりの分時換気量（V/V）の関数として肺容量（V）の連続正規分布を仮定し，simulationからIDI上昇を惹起する条件を検索した。さらに放射性同位元索xenon-133の洗い出し曲線より肺の関心領域のV/Vを算出しsimulation法による推論の妥当性を検討した。

　Pulmonary function tests were examined in 15 cases with chronic pulmonary emphysema and in 47 cases with bronchial asthma.

　Increases in RV, RV/TLC ratio, IDI, ⊿N₂, Zrs and decreses in VC, %VC, FFV_1･0, FFV_1･0% were observed during acute asthmatic attacks. The reduction in VC, %VC, FEV_1･0, FEV_1･0% in emphysema was more than in bronchial asthma.

　The percentage changes in FEV_1･0 and in IDI due to acute asthmatic attacks were well correlated. RV/TLC ratio and ⊿N₂ were well correlated in bronchial asthma.

　In order to clarify the mechanism of increases in IDI during acute asthmatic attacks the method of computation was used for recovering the nitrogen washout from the assumption of continuous normal distributions of volume (V) as a function of V/V ratio. As a result of analysis, IDI was increased when volume ratio of fast and slow compartment became to be one or when the difference between V/V of fast and slow compartment became larger. Regional ventilation study using radioactive xenon demonstrated that such an assumption was valid in bronchial asthma.