End systolic pressure-length relations in halothane anaesthetised dogs: effects of regional ischaemia and inotropic agents.
OBJECTIVE
The aim was to investigate the effects of regional myocardial ischaemia, calcium, and verapamil on (a) the hysteresis and (b) slope and length axis intercept of the left ventricular end systolic pressure-length relationship.


METHODS
Segment length in myocardium supplied by the left anterior descending coronary artery was measured in anaesthetised dogs using sonomicrometry. Three levels of regional myocardial ischaemia were produced by stenosis and occlusion of the left anterior descending artery (ischaemia 1, ischaemia 2, and occlusion). A snare placed around the descending thoracic aorta was used to obtain temporary aortic occlusions.


METHODS
Seven open chested mongrel dogs were used, weight 17 kg (range 16-20).


RESULTS
After abrupt release of temporary aortic occlusions, end systolic lengths were greater than before the occlusion in the normal myocardium. This hysteresis was abolished by regional myocardial ischaemia. However, hysteresis was insensitive to calcium and verapamil. The length axis intercept of the end systolic pressure-length relationship was increased during ischaemia 2, during coronary occlusion, and after administration of verapamil; its slope was increased after coronary occlusion.


CONCLUSIONS
(1) Viscoelastic properties of the myocardium make a major contribution to hysteresis of the end systolic pressure-length relationship; and (2) the length axis intercept of this relationship is not constant and its slope does not appear to be a sensitive indicator of regional myocardial contractility during regional ischaemia.
Victory
J G
JG
Nuffield Department of Anaesthetics, Radcliffe Infirmary, Oxford, United Kingdom.
Foëx
P
P
Leone
B J
BJ
D000758:Anesthesia; D000818:Animals; D002118:Calcium / Q000494:pharmacology; D003327:Coronary Disease / Q000503:physiopathology*; D004285:Dogs; D005260:Female; D006221:Halothane / Q000494:pharmacology; D008297:Male; D009200:Myocardial Contraction / Q000187:drug effects*; D013599:Systole / Q000187:drug effects; D016277:Ventricular Function, Left / Q000187:drug effects; D014700:Verapamil / Q000494:pharmacology
D014700:Verapamil; D002118:Calcium; D006221:Halothane