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  1. 1. The role of doppler ultrasound in 2013 obstetrics 8th December
  2. 2. Doppler effect By Christian Doppler The apparent variation in frequency of sound waves as the source of the wave approaches or moves away relative to an observer Apparent change in sound level of a train approaches and then departs a station This apparent change in sound pitch (Doppler effect) = frequency shift, and is proportional to speed of movement
  3. 3. In clinical application US beam (with a certain frequency) insonate a certain blood vessel, the reflected frequency (= shift) is proportional to the speed of RBCs that are moving (blood flow velocity)
  4. 4. In clinical application Shift Time (cardiac cycle) Shift is highest during systole, lowest during diastole
  5. 5. Given that the velocity of flow in a particular vascular bed is inversely proportional to the downstream impedance to flow, the frequency shift therefore denies information on the downstream impedance to flow of the vascular bed under study
  6. 6. resistance or resistance Increased flow when resistance is low Decreased flow when resistance is high
  7. 7. Measure the velocity with a small of angle as possible ( depends on angle of...)
  8. 8. Fetal arterial doppler (UA) A low impedance circulation with an increased in the amount of end diastolic flow with advancing gestation ( increased tertiary stem villi) UA flow reflects the placental circulation Decreases that obliterates small muscular arteries (tertiary stem villi) = progressive decrease in end diastolic flow until absent - then reverse flow
  9. 9. Reverse flow = 70% placental arterial obliteration--> in IUGR or oligohydramnios
  10. 10. MCA Most accessible cerebral vessel to US in the fetus Carries 80% of cerebral blood flow Cerebral circulation is a high impedance Reverse of flow (against UA)
  11. 11. In the presence of fetal hypoxaemia Cerebral redistribution Brain sparing reflex Increased flow to brain, heart and adrenals Reduction in peripheral and placental circulation Fetal adaptation to O2 deprivation
  12. 12. Fetal Doppler + IUGR = confirmed by Doppler Not good for timing Presence of reversed end diastolic flow Advanced fetal compromise For delivery except for extreme prematurity Preferably by CS .... < 34w