Ambulatory ventricular function monitoring for serial assessments of cardiac function during exercise

An ambulatory ventricular function monitor (VEST) facilitated measuring left ventricular (LV) function, and performing electrocardiography (ECG) in a natural environment. To assess cardiac response to a variety of exercises, LV function was serially recorded for each of 18 normal subjects using a VEST. The VEST detector was fixed over the LV region following the gated blood pool scan, and the beat-to-beat LV time-activity curve and ECG were continuously recorded. After a baseline recording was made with the subject sitting quietly, the subject performed on a bicycle exercise (n = 16), on a treadmill (n = 14), and by walking up 10-16 flights of stairs (n = 18) while wearing the VEST. The beat-to-beat radionuclide data were averaged for 15-30 seconds to calculate ejection fraction (EF), relative end-diastolic (EDV) and end-systolic (ESV) volumes, and the heart rate. Serial LV function monitoring during each exercise, particularly while walking upstairs and on a treadmill, documented rapid increases in EF during the early stages of exercise, with increases in EDV, decreases in ESV, and no change in EF in the later stages. Heart rate and systolic blood pressure increased progressively with successive stages. The pressure rate product at the peak exercise was highest during treadmill exercise (32,600) and lowest while climbing stairs (24,700). Immediately after exercise, EDV and ESV rapidly decreased and EF increased further, particularly after bicycle and treadmill exercise. These data demonstrate that the VEST can measure LV function continuously in an ambulatory environment, and that it is an effective means of evaluating normal cardiac physiology during various exercises.