title: Interaction of heart rate and hypothermia on global myocardial contraction of the isolated rabbit heart.
abstract: 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.
authors.affiliation: Centre for Experimental Surgery and Anaesthesiology, University of Leuven, Belgium.
authors.forename: M
authors.initials: M
authors.lastname: Mattheussen
authors.forename: K
authors.initials: K
authors.lastname: Mubagwa
authors.forename: H
authors.initials: H
authors.lastname: Van Aken
authors.forename: R
authors.initials: R
authors.lastname: Wusten
authors.forename: A
authors.initials: A
authors.lastname: Boutros
authors.forename: W
authors.initials: W
authors.lastname: Flameng
mesh_terms: 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
chemical_list: D000318:Adrenergic beta-Agonists; D002314:Cardioplegic Solutions; D002316:Cardiotonic Agents; C074097:Krebs-Henseleit solution; D014325:Tromethamine; D005947:Glucose; D007545:Isoproterenol; D002118:Calcium