各種疾患における心臓の機械力学的性質の変化とくに : 圧負荷,および,容量負荷への反応様式について
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The purpose of this paper is to present the mechanical behavior of the human heart in normal subjects and patients that may be known from the tension-velocity-length relationships of the heart muscle when the left ventricular cavity is considered to be a complete elastic sphere with uniform thickness. Methods and materials The intraventricular tension (T.) of the left ventricle was calculated from a formula P・R/2 where P was supposed to be the intraventricular pressure and actually obtained from the brachial arterial blood pressure by Korotkoff's method. R was the radius of the contracting sphere as proposed by Rodbard. In this study R was calculated from the stroke volume (SV), i.e., 47πR^3/3, that was obtained by our modified Wezler-Boger's method. The mean velocity of myocardial shortening (V.) was calculated from 2πR/ ejection period. The tension gradient was obtained from tension (T.)/isometric contraction period. The isometric contraction and ejection periods were determined by Blumberger's method. The mean myocardial tension (Tm.) was obtained by using the mean brachial arterial blood pressure (Pm=Pd+0.43×Δp) while the diastolic myocardial tension (Td.) was calculated by the diastolic brachial arterial blood pressure. The mean tension gradient (Tm.G.) and the diastolic tension gradient (Td.G.) were also obtained in this way. A total of 337 subjects studied in this paper comprised 122 normal subjects, 83 hypertensive patients without cardiac dilatation or failure, 10 hypertensive patients with cardiac decompensation, 35 patients with hyperthyroidism without cardiac dilatation or failure, 10 patients with thyrotoxic heart disease with cardiac decompensation, 37 patients with anemia without cardiac dilation or failure, 8 patients with aortic insufficiency of which severity was of the first grade in the A.M.A. classification, 14 patients with mitral stenosis with the severity of the first or second grade, and 18 patients with mitral stenosis with the severity of the second or third grade in the A.M.A. classification. Results 1. Normal subjects 122 normal subjects were grouped to the following three groups by age; the juvenile group (13 to 29 years of age, 40 subjects), the middle-aged group (30 to 59 years, 59 subjects) and the senile group (60 to 75 years, 33 subjects). It was demonstrated that Tm., Td., V., Tm.G. and Td.G. were changed only slightly among the three groups and they could serve sufficiently as the control for further investigations. 2. Arterial hypertension The observation on 83 hypertensive patients revealed that the tension and the tension gradient were increased about 40 and 30% respectively while the increase in the mean velocity of shortening remained only 4%. In view of the vascular dynamics classified by Wezler-Boger, the patients were subgrouped to 16 cases of the M type (Minutenvolumentypus), 21 cases of the W+E' type (Widerstands- und Elastizitatstypus), 10 cases of the W type (Widerstandstypus), 11 cases of the E' type (Elastizitatstypus) and 25 cases of the N type (Normaltypus). The increase in Tm., V. and Tm.G. were 48, 17 and 50% respectively in the M type. Tm. and Tm.G. were increased as much as 27 and 17% respectively, however, V. was decreased by 9% in the W+E' type. Tm. and Tm.G. were increased 42 and 15% whereas V. was decreased 2% in the W type. In the E' type, the increase in Tm., V. and Tm.G. were 52, 9 and 43% respectively. In the N type, the increase in Tm., V. and Tm.G. were 43, 5 and 34% respectively. The large myocardial tension may develop most quickly and the mean velocity of shortening may be fastest in the M type hypertension. On the contrary, the myocardial tension and the myocardial tension gradient may be larger than those in normal health though the mean velocity of shortening may be decreased below the normal and may be slowest in the W+E' type and W type hypertension. In the E' type hypertension with the sclerotic "Windkessel", the myocardial tension and the myocardial tension gradient may be increased. The mean velocity of shortening, however, may not be so much increased as in the M type. 3. Anemia and hyperthyroidism The increase in Tm., V. and Tm.G. were 9, 17 and 28% respectively in 37 cases of anemia. The increase in Tm., V. and Tm.G. were 16, 23 and 58% in 35 cases of hyperthyroidism. 4. The mechanical behavior of the left heart under chronic pressure or volume overload The results suggest that the mechanical behavior of the left heart under chronic pressure overload may be characterized by a change in pattern of Tm., Tm.G. and V. in the following order: "Tm.>Tm.G.>normal values>V." On the other hand, the characteristic pattern of the behavior of the left heart under chronic volume overload may be "Tm.G.^>V.> Tm.>normal values". 5. Valvular heart diseases In 8 patients with aortic insufficiency, Tm., V. and Tm.G. were increased as much as 23, 8 and 44% respectively. In mild mitral stenosis (14 cases), the change in Tm., V. and Tm.G. were -4, 0 and -1% respectively. In severe mitral stenosis (18 cases), the change in Tm., V. and Tm.G. were -7, +2 and -17% respectively. The results suggest that the mechanical behavior of the left heart may not differ markedly from the normal heart in slight to mild mitral stenosis. When mitral stenosis is advanced, a volume load in a negative sense (negative volume load) to the left heart may affect the mechanical behavior of the left ventricle. 6. Heart failure. It was noted that immediately after the recovery from heart failure, Tm., V. and Tm.G. were markedly increased in most cases of hypertensive cardiac disease (W+E' type) and they even became larger than the averages of the W+E' type hypertension. The results may support the concept that at a certain stage of impending hypertensive heart failure, the behavior pattern of the left heart may be changed and the left heart may challenge the overload with its maximal abilities till exhaustion. In thyrotoxic heart disease, however, the behavior pattern of the left heart may not be changed until the heart fails.
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