マスフローコントローラーを用いたNOガス吸入装置の開発とその臨床応用

A New Computer Built-in NO Inhalation Device Using Mass Flow Controller, and Its Clinical Application

　肺高血圧症に対するNOガス吸入法が注目を集めている．今回，コンピューター制御による新しいNOガス吸入装置（CAT−17）を開発したので，その構造と機能および臨床応用について発表する．本装置はNO,O₂などの吸入混合気の組成のみならず，吸入気総ガス流量も任意にコントロールできる．NO₂の発生濃度は主にNO混合気のO₂濃度とNO濃度の双方に依存しており，室温20℃，空気10l（STPD）／分の流量の条件では，NO濃度60ppm以下ではNO₂の発生濃度を1ppm以下に抑えることができた．作成吸入気ガス組成は質量分析器の値と正確に一致した．肺高血圧症に対する成績では，全肺血管抵抗はNOの濃度80ppmまでは用量依存性に低下，また動脈血O₂分圧はNOの5〜10ppmという低用量で上昇の傾向がみられた．本装置は安全高精度で任意のNO混合気が作成でき，NO用量曲線の分析から肺高血圧症・その他の疾患に対して最適処方を示すことが可能となった．

A computer-controlled device (CAT-17) to create rapid mixing of NO with various O₂ concentrations has been developed in our laboratory. A one-way valve was made in an endeavor to reduce flow resistance of both inspired and expired breath. Using this device patients could inhale and exhale spontaneously under tidal ventilation through a face mask without any breathing effort. Production of NO2 at mask level in 60 ppm of NO mixture with a composition of room air was possible within 1 ppm under 10l (STPD) /min total flow at 20℃. NO inhalation showed dose-dependent reduc-tion of total pulmonary vascular resistance (TPR). Discontinuation of NO inhalation demonstrated that the NO depressed pulmonary artery pressure (PA) returned gradually to basal high level within approximately 1 minute. The effect of NO inhalation on arterial blood gases was seen in a relatively low level of NO concen-tration of around only 5 to 10 ppm. Arterial O₂ tension (PaO₂) increased with 5 to 10 ppm of NO, and a further raising of NO concentration resulted in decreased Pa₂. This indicates a new appearance of low VA/Q area.