The external work-pressure time integral relationships and the afterload dependence of Frank-Starling mechanism.

摘要: The mechanisms underlying the Frank-Starling Law of heart are elusive and prevalent notion suggests that it is afterload independent. However, isolated fiber studies reveal determines cardiac function through cross-bridge dependent mechanisms. study explores roles afterload, in situ. LV was exposed by left-thoracotomy adult sheep (72.6+/-8.2 kg, n=8). Pressure transducers were inserted into aorta, a flowmeter placed around aortic root, volume assessed sonocrystals. Occluders aorta inferior vena cava enabled control preload. Different afterloads imposed partial occlusions. Transient occlusions (IVCOs) preformed whenever steady. A highly linear relationship found between external work (EW) pressure time integral (PTI) (R(2)=0.98+/-0.01) during each transient IVCO (n=48). slope EW-PTI (WPTiR) preload independent since, for any given EW PTI lay on straight line. Interestingly, WPTiR dependant: 33.3+/-4.1 mJ/mmHg.s at baselines decreased 1.0+/-0.50 with every 1 mmHg.min/L increase peripheral resistance. unique obtained both occlusion release phases IVCO, while two distinct EW-preload or PTI-preload relationships observed. novel ties Frank (pressure development) Starling (EW production) phenomena together. dependence highlights adaptive to changes afterload.