Elevated diaphragmatic blood flow during submaximal exercise in rats with chronic heart failure.

The exercise blood flow response of muscles involved in respiration was determined in rats with a myocardial infarction (MI), which was produced by tying the left main coronary artery, and in rats that underwent sham operations (Sham). Arterial blood gases, acid-base parameters, and blood flow (ml/100 g of tissue) to the diaphragm, intercostals, and transverse abdominis muscles were measured during steady-state treadmill exercise (20% grade, 28 m/min). The responses of MI rats that were classified as having a small (MIS < 25%, n = 7), medium (25% < or = MIM < or = 35%, n = 8), and large (MIL > 35%, n = 7) infarct were compared with those of Sham (n = 12) rats using analysis of variance techniques. Results demonstrated that arterial PO2 and PCO2 were similar for all groups during exercise (PaO2 = 110-112 mmHg; PaCO2 = 28-29 mmHg) even though the MIM and MIL groups had developed a significant amount of pulmonary congestion, and the MIL group demonstrated indicators of severe left ventricular dysfunction. Blood flow to the diaphragm during exercise was significantly greater for the MIL group of rats, although blood flow to the intercostals and transverse abdominis muscles was similar across the different groups. Results from this study support the contention that MI rats (including rats with decompensated heart failure) will achieve the same effective alveolar ventilation during exercise as that found for Sham rats and in the process maintain arterial O2 saturation.(ABSTRACT TRUNCATED AT 250 WORDS)