Effect of breathing frequency on blood velocity in visceral arteries

Recent advances in pulsed and echo Doppler ultrasound techniques enable the blood velocity (BV) to be measured in the intra‐abdominal arteries. However, visceral arteries move rhythmically with the abdominal wall during the respiratory cycle, and hence a change in the breathing frequency – which is usually observed in response to mental or physical stress – might affect the BV in visceral arteries. In this study, we measured the BV in the renal (RA) and superior mesenteric (SMA) arteries using the Doppler technique under controlled breathing conditions. Eight subjects performed spontaneous and controlled breathings at 12, 15, and 20 breaths per minute (bpm) for 3 minutes in a random order. During each breathing condition, a Doppler‐scan probe was maintained at a constant position on the subject's anterior abdominal wall, and the Doppler beam insonation angle was kept at 60°. We averaged the 20 largest values of the beat‐by‐beat mean BV in the expiratory phase during the last 2 minutes of each breathing condition, and found that the breathing frequency did not affect the BV in either artery (0.444 ± 0.016, 0.440 ± 0.012, 0.435 ± 0.015, and 0.436 ± 0.019 m/s in RA, 0.332 ± 0.033, 0.311 ± 0.029, 0.302 ± 0.028, and 0.310 ± 0.030 m/s in SMA at spontaneous frequency (12 ± 2 bpm) and at 12, 15, and 20 bpm; mean ± SEM). These results suggest that breathing frequencies within the range adopted in this study do not affect the BV in the RA or SMA.