Functional capacity in a rat model of heart failure: impact of myocardial infarction size

Abstract

Oxygen uptake (VO₂) and exercise tolerance in rats classified by myocardial infarction (MI) size are underexplored. The aim of this study was to evaluate VO₂/carbon dioxide production (VCO₂) and exercise tolerance in rats that have undergone MI. Fourteen weeks after MI or sham surgery, rats underwent an integrated approach to left ventricular function and VO₂/VCO₂, exercise tolerance and skeletal muscle weight evaluation. Based on MI size determination, rats were assigned to sham operated controls (Sham, n = 12), small myocardial infarction (SMI, n = 8), and large myocardial infarction (LMI, n = 5) groups. LMI rats showed lower systolic (ejection fraction and fractional shortening) and diastolic (E/A ratio) left ventricular function compared with SMI. VO_2max (∼24%, P < 0.05), VO_2reserve (∼30%, P < 0.05), time to exhaustion (∼36%, P < 0.05) and maximal velocity (∼30%, P < 0.05) was lower in LMI compared with sham operated controls, with no difference between SMI rats and sham operated controls. VCO_2max and respiratory exchange ratio (RER) showed no significant difference between MI rats and sham operated control rats. LMI rats demonstrated lower gastrocnemius weight (∼12%, P < 0.05) and soleus weight (∼19%, P = 0.07) compared with sham operated control rats. Significant correlations between MI size, left ventricular end-diastolic pressure, right ventricle hypertrophy, pulmonary congestion, ejection fraction, and fractional shortening with VO_2max and run distance were observed. O₂ uptake and exercise intolerance are MI size dependent.

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