Breathing including abdominal movement could affect the blood velocity (BV) measurement in the visceral arteries. The present study investigated the effect of breathing frequency on the renal artery (RA) and superior mesenteric artery (SMA) BV measurements. We measured mean arterial pressure (MAP), heart rate (HR) and BV in the RA and SMA using the Doppler technique at different respiratory frequencies. Nine subjects performed breath-holding (<40 s), and spontaneous and controlled breathings at a constant rate of 12, 15 and 20 breaths min -1. The breathing frequency did not significantly affect the BV in either artery. The BVs at these frequencies were not significantly different from those during spontaneous breathing and breath-holding. There were no significant differences in MAP and HR among trials. This result suggests that the effect of breathing frequency adopted in this study could be neglected in the RA and SMA measurements.
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