大動脈起始部における流速を応用した左室駆出期の新しい指標，流速圧比（U2/AP）の実験的検討—心血管作動薬の及ぼす影響

Study on the new index U2/AP in canine aortic root for left ventricular performance

　著者ら^1,2）はパルスドップラ超音波装置の応用を前提として，簡単容易に計測できる循環系の機能的な指標，流速圧比（U²/AP）を考案し，それを開心手術例で検討してきた。

　本指標，流速圧比（U²/AP）は左室から大動脈に拍出された血液が持つ運動エネルギーと圧力エネルギーの比を表わしている。血液にエネルギーを与えるのは左室であるから，それらの比は左室の作動状態に関する情報を含んでいる。すなわち，左室の外部仕事量を構成する単位体積（cm³）あたりの血液の持つ運動エネルギーは，ρU²/2（ρ：血液密度g/cm³，U：血流速度cm/s）で，圧力エネルギーはP （P：圧力dyn/cm²）で表わされ，る。両者の次元はともにエネルギー（g・cm²/s²）で等しく，ρU²/2Pは無次元量となる。

　The newly proposed index U²/AP for left ventricular performance which is based on kinetic and pressure energy distribution of the left ventricle during ejection period was studied in 10 dogs before and after infusion of vasoactive drugs. The index, maxU²/sAP and mU²/mAP were obtained by measuring aortic peak flow (PF), cardiac output (CO), heart rate (HR), systolic, diastolic and mean aortic pressure (sAP, dAP, mAP), systolic ejection period (SEP), positive maximum dp/dt (max dp/dt), mean and maximum aortic velocity (mU, maxU), stroke volume (SV), systemic resistance (mAP/CO), double product (sAP×HR) and tension time index (TTI) during infusion of isoproterenol (ISP), norepinephrine (NE) and propranolol (PRN).

　In ISP infusion (5μg/kg･min, maxU²/sAP was significantly increased with increase of PF, HR, max dp/dt and mU and with decrease of mAP/CO. In NE infusion (10μg/kg･min), it was decreased with increase of sAP, dAP, mAP, max dp/dt, mAP/CO, sAP×HR and TTI and with decrease of SEP. In PRN infusion (2mg/kg･min), neighter maxU²/sAP nor mU²/mAP nor other parameters significantly varied. maxU²/sAP (n=60) showed close correlation to rnU²/mAP (r=0.79, p<0.001), to SV (r=0.61, p<0.01) and to mAP/CO (r=0.60, p<0.01).

　Small U²/AP suggests that the left ventricle does not function properly in correspondence with afterload. This index can be obtained by ultrasonic devices non-invasively and will be useful for monitoring patients in ICU and CCU.