EXERCISE RELATED CHANGES IN AORTIC FLOW MEASURED WITH SPIRAL ECHO-PLANAR MR VELOCITY MAPPING

Spiral echo-planar magnetic resonance (MR) velocity mapping was used t o measure exercise-related changes in flow in the descending thoracic aorta in 10 healthy volunteers. Flow was measured at rest and immediat ely after dynamic exercise, with a 0.5-T imager with a surface receivi ng coil and electrocardiographic triggering. Supine exercise was perfo rmed with a home-built pedaling apparatus, Spiral velocity mapping was performed in a transverse plane through the descending thoracic aorta with the subject at rest, The subject was then asked to perform maxim um exercise, stop, and hold his breath during a four-heartbeat acquisi tion time. Eight cine frames with a temporal resolution of 50 msec wer e acquired through systole, Each image was acquired in 40 msec during spiral acquisition of k-space data, starting at the center, 6 msec aft er the excitation pulse. Reproducibility of the technique was establis hed by repeating the flow measurement in four consecutive heartbeats. At rest, the heart rate (mean +/- standard deviation), mean aortic flo w, peak aortic flow, and time to peak flow were 68 beats per minute +/ - 6, 41 milliliters per beat +/- 8, 107 mL/sec +/- 20, and 175 msec +/ - 25, respectively, After exercise, the heart rate and mean and peak a ortic flow were significantly increased (P < .001), measuring 101 beat s per minute +/- 12, 57 milliliters per beat +/- 11, and 158 mL/sec +/ - 29, respectively, while the time to peak flow (115 msec +/- 32) was significantly reduced (P < .001). The four sets of values obtained for the first four consecutive heartbeats measured at rest were similar, as were those obtained for the first four heartbeats after exercise.