The time course of left ventricular (LV) circumferential stress and fiber shortening velocity (V) were determined at 20 msec intervals in 30 patients from simultaneous recordings of LV pressure (micromanometer) and LV dimensions (echography). In 12 patients with normal LV function, endocardial and midwall maximal (max) V, V at peak stress, and endocardial mean V were significantly greater than in 3 patients with myocardial disease. Peak stress was less in the normal subjects (mean=241 g/cm2, range 180 to 310 g/cm2) than in those with myocardial diseases (mean=371 g/cm2, range 280 to 513 g/cm2). V was reduced in 5 of 7 patients with chronic LV volume overload, while peak stress ranged from normal in 3 to increased in 4. Max V, mean V, and peak stress were normal in 3 patients with chronic LV pressure overload; V at peak stress was normal in 2. Good correlation was observed between angiographic determinations of mean V and endocardial max V, V at peak stress and mean V. Induced changes in preload in 5 patients (dextran infusion at constant heart rate) produced a 12.2% increase in peak stress (P<0.05), and insignificant changes in max V (3.7% increase, P=NS), in V at peak stress (5% decrease, p<0.05), in mean V (0.7% increase, P=NS). Increasing afterload with angiotensin in 7 patients (peak stress increased by 45%, P<0.01) reduced max V, V at peak stress nd mean V by 33%, 39%, and 37%, respectively. Lowering afterload in one patient (amyl nitrite) produced an increase in V. Improvement in V was observed in all instances during positive inotropic stimulation (isoproterenol in 3 normals, digoxin in 4 with myocardial disease). The response of endocardial and midwall V to loading and contractility were similar. In man, V is an index of myocardial contractility which is affected minimally by changes in preload but responds inversely to changes in afterload. Its sensitivity to acute afterload changes may, at times, limit its clinical applicability.
ASJC Scopus subject areas
- Cardiology and Cardiovascular Medicine
- Physiology (medical)