左室最大充満速度の関連因子に関する基礎的研究

Experimental study on determinant factors of peak filling velocity in left ventricule

　近年，左室圧下降脚を指数関数で近似した圧降下時定数が拡張期指標として注目され^1）臨床応用されている^2）。しかし，収縮期心機能指標の鋭敏性においては駆出期の指標が等容収縮期の指標よりも優れていること^3）を考えると，拡張期においても等容弛緩期の圧降下速度指標よりも急速充満期の指標の方が優れている可能性がある。充満期指標としては最大充満率ないし最大充満速度があり，すでに左室造影法^4）・RI心血管造影法^5,6）・M-mode心エコー図法^7,8）等を用いて臨床応用されているものの，その基礎的研究が極めて少ないため，得られたDataの正当な評価は依然困難と言わざるを得ない。

　本研究の目的は，麻酔開胸犬を用い心外膜保存下と心外膜切開下（以下，心膜保存・心膜切開）において各種の負荷を加え，超音波パルス法^9）による左室内径の最大充満速度への影響について検討し，whole heartにおける最大充満速度の関連因子を明らかにすることである。

To assess the determinant factors of peak filling velo-city (Vf) in left ventricule (LV), three types of inter-ventions, i.e. change of preload (saline infusion or vena cava inferior (VCI) occulusion), afterload (nitro-purusside or methoxamine) and contractility (isoprote-renol or propranolol) were performed in anesthetized open chest intact or open pericardium dogs under fixed rate atrial pacing.

Velocity (Vf and peak ejection velocity (Ve)) were measured by direct differentiation of LV internal di-mension which was measured by a pair of ultrasonic crystal probes implanted into the anterior and posterior subendcardial walls. Additionally, pericardiectomy was performed in intact pericardium dogs to assess effect of pericardium on Vf.

Vf was significantly faster than Ve in both groups (p< 0.005). Vf increased after nitroprusside, isoprote-renol and saline infusion, and it decreased after metho-xamine, propranolol and VCI occlusion (p<0.05).

After interventions, percent changes in Vf were linearly related to those in Ve (Pericardium intact ; Vf=0.74*Ve+2.97 r=0.700 p<0.0005, Pericardium open ; Vf=1.08*Ve+0.20 r=0.870 p<0.0005). Vf was also closely related with other ejection factors (systolic excursion (SE), percent fractional shortening and end-systolic dimension (ESD)), but was not so closely rela-ted with relaxation factors (time-constant (T), peak negative dP/dt).

After pericardiectomy, Vf, SE, EDD and ESD in-creased significantly (p< 0.05), but other parameters remained stationary.

The close relationship between Vf and SE suggests that SE is one of determinant factors of Vf.

Change of Vf was susceptible to contractility, and depended on preload and afterload, so the elastic recoil may be associated with LV filling (Vf).

Pericardiectomy increased LV compliance (Vf) and augmented preload (EDD), improving LV pump func-tion (SE).