Left ventricular function and haemodynamics in ponies during exercise and recovery

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Abstract
Myocardial and haemodynamic responses to strenuous treadmill exercise were monitored with chronically implanted instrumentation in seven physically untrained ponies. In two other ponies, haemodynamics were monitored using a conventional catheter technique. During exercise (mean .+-. sem heart rate = 203 .+-. 3 beats/min), left ventricular peak systolic and end-diastolic blood pressure significantly increased from 125 .+-. 2 to 208 .+-. 6 mmHg and from 29 .+-. 1 to 58 .+-. 3 mmHg, respectively (P < 0.05). Peak positive first derivative of left ventricular pressure (dP/dt) was also increased significantly, (1397 .+-. 144 to 6016 .+-. 325 mmHg/sec), as were myocardial segment velocity of shortening during systole (dL/dtsys) and stroke work (193 and 109 per cent, respectively). Paradoxically, segment systolic shortening was reduced significantly (P < 0.05) with respect to resting control values for 10 mins after cessation of exercise, with the maximal reduction of 22 per cent occurring at 2 mins post exercise. In addition, left ventricular segment stroke work decreased significantly to 67 per cent of resting control values at 2 mins post exercise. This study demonstrates that analysis of region myocardial performance in conjunction with haemodynamic data permits a detailed description of cardiac events during and immediately following exercise, facilitating definition of changes which are not readily reflected by haemodynamics. Based on these findings, the authors conclude that untrained ponies may readily complete short bouts of near-maximal exercise, yet experience significantly diminished left ventricular function in the immediate post exercise period.