単一呼出曲線における"phase V"に関する研究

Further study on "phase V" in single-breath washout curve

　phase V（V相）は，Nicholら^1）により新しく導入された概念であり，彼らはAr bolusとN₂の同時洗い出し曲線を分析し，肺内におけるflow limitationの発生と関連して，phase IV（IV相）のあとにみられるAr bol—usおよびN₂のdownward deflectionに注目し，phaseVと名付けた。一方，われわれは呼気のemptying wei—ghted V_A/Qと考えられる空気呼吸時の呼気N₂曲線（Air N₂曲線）を用いて，最大呼気終末部を解析し，従来phase IVといわれていたものは，均一なunitではなく，それぞれ判然と異なったV_A/Qをもつ2つのcom—partmentが関与して，phase IVが形成されていることを見出し，発表してきた^2,3）。Air N₂曲線は，closing vol—ume現象としてのphase IVの発現に一致して，頭打ちになり，その程度に応じて，一旦下降し，その後再上昇するという特異なパターンを呈する。今回はNicholら^1）により提唱されたphase Vと，このAir N₂曲線上の再上昇波との関連を検討したので報告する。

　A downward deflection following phase IV in single-breath washout test was first termed phase V by Nicho et al., indicating the onset of whole-lung flow limitation. On the other hand, we have independently repelled to find the dramatic changes corresponding to phase IV and phase V on expiratory nitrogen curve in room air breathing "Air N₂ Curve". Special device for N₂ output of mass spectrometer (Perkin Elmer MGA1100B) was made using DC cancellation amplifier with inspired N₂concentration (F_IN2) suppressed to zero voltage and only changing fraction (F_EN2-F_IN2) of expired N₂ concentration (E_EN2) was magnified by high fidelity DC amplifier. This F_Air N₂(=F_EN2-F_IN2) versus expired volume (V_E) was designated "Air N₂ Curve" with prominent cardiogenic ripples on its ascending plateau in normal subjects. Phase V was studied in 13 healthy normal subjects using simultaneous washout N₂ and tracer boluses of He combined with Air N₂ curve at different flow rate of 0.1 L/sec to 2.0 L/sec. Alterations of terminal portion near RV of Air N₂ curve did not make any difference between expiration from TLC to RV and that from resting tidal breaths to RV without preceding inspiration to TLC. So latter procedure was utilized to analyze terminal changes of Air N₂ curve because of reasonably better reproducibility. Air N₂ curve showing gradual increase on its plateau was characterized by transient fall followedby abrupt terminal rise near RV in maximal expiration. When expiratory flow rate was increased, level of lung volume above RV indicating transient fall and terminal rise became increased accordingly. At the point where Air N₂ curve ceased to increase its N₂ concentration phase IV appeared and onset of phase V coincided with appearance of abrupt terminal rise of Air N₂ curve. Phase IV and phase V proved to be flow dependent. Mean alveolar N₂ concentration was known to be determined by V_A/Q of alveoli. Expired N₂ concentration was considered by represent integrated V_A/Q abnormality weighed by compartmental emptying pattern. It was clear from the current study on Air N₂ curve near RV that phase IV resulted from contribution of high V_A/Q compartment and that phase V to the contrary was produced by the contribution of low V_A/Q compartment.