Does the brachial artery Doppler flow velocity waveform reflect changes in downstream impedance?

Abstract

Brachial artery Doppler flow velocity waveforms were recorded from 10 nonpregnant women and 19 women with uncomplicated pregnancies. The pregnant group showed higher peak systolic frequencies (3.24 compared with 2.26, p = 0.01), higher maximum end-diastolic frequencies (0.62 compared with 0.25, p = 0.01), and lower pulsatility indices (2.57 compared with 3.95, p = 0.06) when compared with the nonpregnant group. These Doppler changes could reflect the increase in maternal cardiac output and decline in systemic vascular resistance that occur in normal pregnancy. The effect on brachial artery Doppler of acutely increasing downstream impedance by hand immersion in ice-cold water was studied in nine women with uncomplicated pregnancies at 32 to 38 weeks' gestation. Immersion for 15 seconds was associated with a significant reduction in peak systolic frequencies (from 3.06 to 1.97, p less than or equal to 0.005) and maximum end-diastolic frequencies (from 0.82 to 0.03, p less than or equal to 0.005) and a significant increase in the pulsatility index (from 1.87 to 5.62, p less than or equal to 0.005). These changes persisted for the duration of immersion (60 seconds). After immersion, the brachial artery flow velocity waveform returned to its preimmersion pattern by 60 seconds. We conclude that in normal pregnancy, the maternal brachial artery Doppler flow velocity waveform reflects acute and chronic changes in downstream impedance.