Reflex XXXX due to regional activation of left ventricular mechanoreceptors to explain the @entity551 noted in clinical myocardial ischaemia or reperfusion.

@entity1063 @entity235 @entity13981 @entity951 @entity583 @entity551
To determine if regional increases in myocardial contractility, as may occur clinically in @entity951 , @entity583 , or coronary thrombolysis, can initiate the reflex @entity551 that sometimes accompanies these conditions, regional injections of positive inotropic agents were made into 32(3)% of the left ventricular myocardium in seven pneumonectomised @entity235 on total cardiac bypass. The coronary and systemic circulations were isolated and perfused separately. The systemic circulation was perfused at a constant rate so that changes in systemic pressure reflected changes in resistance. Regional injections of doses from 0.001 to 1.0 micrograms @entity1063 in a 0.1 ml volume appreciably increased regional contractility, detected visually and by strain gauge arches, whereas global contractility (left ventricular peak dP/dt) was increased much less. This caused a fall in the systemic pressure (resistance) of 14(2)% below the control value of 78(5)mm Hg, at the largest dose. The decreases in resistance were abolished by bilateral vagotomy, proving their reflex nature. The smaller (0.0001-0.01 micrograms) doses of @entity1063 and the smallest (0.25 micrograms) dose of @entity13981 increased regional contractility almost without increasing global contractility, indicating that the increase in regional contractility was the major cause of the reflex decrease in systemic resistance. In one animal a decrease in contractility in a control myocardial region occurred simultaneously with the experimentally produced increase in regional left ventricular contractility. This decrease may be analogous to the increase in contractility in the non-ischaemic left ventricular myocardium that occurs simultaneously with the decrease in contractility in the ischaemic region in clinical or experimental @entity583 . Left ventricular mechanoreceptors in the region with increased contractility probably initiate the reflex @entity551 that sometimes occurs in both circumstances. Thus in @entity951 or acute @entity583 the reflex @entity551 probably originates in the hyperactive non-ischaemic myocardial region, whereas in coronary arterial thrombolysis it probably originates in the newly reperfused, formerly ischaemic, region.
