Interaction of heart rate and hypothermia on global myocardial contraction of the isolated rabbit heart.
We studied the effects of mild hypothermia on cardiac contractility in isolated rabbit hearts perfused with Krebs-Henseleit solution according to the technique of Langendorff. Isovolumetric left ventricular pressure (LVP) was measured with a fluid-filled balloon. Hearts were paced after induction of atrioventricular block. At low heart rates ( < 30 bpm) mild hypothermia (cooling to 30 degrees C) induced a 32% increase in LVp (146.5 +/- 10 mm Hg at 30 degrees C vs 110.7 +/- 13 mm Hg at 37 degrees C) but this positive inotropic response was progressively lost by increasing heart rate. At pacing rates > or = 90 bpm, lower systolic LVP, higher diastolic LVP, and lower positive and negative LV dP/dt were obtained in hypothermic (93 +/- 12 mm Hg, 55 +/- 18 mm Hg, 584 +/- 137 mm Hg/s, and 323 +/- 57 mm Hg/s at 210 bpm, respectively) compared to normothermic hearts (123 +/- 4 mm Hg, 10 +/- 4 mm Hg, 1705 +/- 145.5 mm Hg/s, and 1155 +/- 78 mm Hg/s at 210 bpm, respectively.) The duration of mechanical diastole was reduced or suppressed in these hearts. Exposure to the beta-adrenoreceptor agonist, isoproterenol, improved this diastolic dysfunction during hypothermia and pacing at high rates, suggesting that the sarcoplasmic reticulum Ca2+ uptake might be involved. Our data are also consistent with an increase in myofilament Ca2+ sensitivity that is opposed by isoproterenol during hypothermia.
Mattheussen
M
M
Centre for Experimental Surgery and Anaesthesiology, University of Leuven, Belgium.
Mubagwa
K
K
Van Aken
H
H
Wusten
R
R
Boutros
A
A
Flameng
W
W
D008841:Actin Cytoskeleton / Q000187:drug effects / Q000378:metabolism; D000318:Adrenergic beta-Agonists / Q000494:pharmacology; D000818:Animals; D002118:Calcium / Q000378:metabolism; D002304:Cardiac Pacing, Artificial; D002314:Cardioplegic Solutions; D002316:Cardiotonic Agents / Q000494:pharmacology; D003971:Diastole / Q000187:drug effects; D005947:Glucose; D006339:Heart Rate; D007036:Hypothermia, Induced; D007545:Isoproterenol / Q000494:pharmacology; D009200:Myocardial Contraction / Q000187:drug effects; D011817:Rabbits; D012519:Sarcoplasmic Reticulum / Q000187:drug effects / Q000378:metabolism; D014325:Tromethamine; D016277:Ventricular Function, Left; D017725:Ventricular Pressure
D000318:Adrenergic beta-Agonists; D002314:Cardioplegic Solutions; D002316:Cardiotonic Agents; C074097:Krebs-Henseleit solution; D014325:Tromethamine; D005947:Glucose; D007545:Isoproterenol; D002118:Calcium