Exercise in Ponies: A Study of Myocardial Blood Flow, Coronary Vasodilator Reserve, Regional Distribution of Cardiac Output and Effects of Heart Rate on Coronary Flow

123 p.Thesis (Ph.D.)--University of Illinois at Urbana-Champaign, 1982.Transmural distribution of myocardial blood flow (MBF, 15 (mu)m diameter radionuclide labeled microspheres) was studied in 11 adult healthy ponies at rest {heart rate (HR) = 56 (+OR-) 4 beats.min('-1)}, during moderate (HR = 154 (+OR-) 3 beats.min('-1)) and severe (32 km.hr('-1), HR = 225 (+OR-) 7 beats.min('-1)) exercise performed on a treadmill. Coronary vasodilator reserve (CVR) was also examined in these animals using adenosine infusion at rest (4 (mu)M.kg('-1).min('-1)) and during severe exercise. Moderate exercise resulted in a marked increase in cardiac output, mean aortic pressure, right ventricular (RV) systolic and end-diastolic pressure (EDP), left ventricular (LV) EDP, LV max dP/dt, and a pronounced increase in trasmural MBF. Severe exercise resulted in further significant increments in all these variables. During severe exercise, endo:epi ratio for LV (0.99 (+OR-) 0.02) decreased significantly from control value (1.27 (+OR-) 0.03). With adenosine infusion during severe exercise, transmural MBF was able to further increase significantly. The data demonstrated that there remained a marked transmural CVR during severe exercise.In these same animals, blood flow (Q)(' )to the brain, kidneys, diaphragm and skeletal muscles was also examined. Cerebellar(' )Q increased significantly (32%) during severe exercise. Renal Q(' )was not changed during moderate exercise, but decreased by 81% during severe exercise. Q(' )to the diaphragm and exercising muscles increased during both levels of exercise. It was concluded that the response to severe exercise in the pony appears to be similar to that of human beings.Transmural MBF was also studied in another group of 6 ponies before and during tachycardia (HR = 150, 200 and 250 beats.min('-1)) produced by ventricular pacing. MBF increased progressively transmurally up to HR of 200 beats.min('-1). With pacing at 250 beats.min('-1), total MBF did not increase further, while LV endo: epi ratio was less than 1.00. With adenosine infusion during pacing at 250 beats.min('-1), MBF increased to the outer portions of the LV, but MBF to the inner layers of the LV decreased (LV endo:epi ratio = 0.39 (+OR-) 0.09). It was concluded that CVR in the deeper layers of the LV was exhausted during pacing at HR of 250 beats.min('-1).U of I OnlyRestricted to the U of I community idenfinitely during batch ingest of legacy ETD