Doppler studies of foeatoplacental vessels

DOPPLER SHIFT/FREQUENCY SHIFT:-

Basic Principles of Doppler Shift:-

Sound waves sent return (reflected) at different frequencies depending on the speed of blood flow in the respective vessel. 1) In arteries blood flow velocity is much more during systole.  2) But blood flow in venous tree is more or less constant and usually reflect/depend on events in cardiac cycle (Rt. heart/Rt. Atrium).3) More speedy blood flow at the centre of artery and less speedy at the vessel wall region. Therefore different flow velocities (different frequencies are generated) are generated from arteries→computerised and plotted against time to produce a smooth wave form which is called flow velocity wave form which is also designated as FVW

How to assess placental bed resistance? Downstream Resistance?

Diastolic component of FVW is more informative about the blood flow to foetus and it reflects downstream impedance / resistance and is independent of other variables like foetal size and blood volume. Several indices are used to describe FVW e.g. S/D, RI, PI ratio.  All three indices are highly correlated.

 S/D  or  A/B ratio : Peak systolic (S)  ÷ Maximal diast flow velocity(D)

Resistance Index  (RI)        (S –D)  ÷ S

Pulsatility Index                 (S-D)    ÷ Mean Velocity.

Good Doppler Signs are a) large diast. Component in umb. Artery FVW implies low impedance i.e. good blood flow in the placenta.

SEQUENCIAL   CHANGES  IN   DOPPLER IN FGR CASES:-1) First reduction is in diast. Component in FVW in umb. Artery as reflected by rise / increasing PI of Umb artery.2) Absent or  Reversal of EDF in Umb.A. increasing PI in the U.A. is usually the first indication of a small foetus. Rise of PI in u.a.

What are the normal changes in MCA with advancing preg?

Decreasing cerebral impedance there will be more circulation in cerebrum-with rise in diast component of flow and fall of PI. (Normal).

What happens in early hypoxic changes in PI of MCA? Foetus maintains cerebral blood flow at the expense of other organs and PI falls further which means more blood to cerebrum and more diast.flow pattern. But if not corrected and with increasing resistance PI will eventually rise due to severe cerebral vasoconstriction..   PI first stage of hypoxia fall and end stage i.e. before death PI will rise. So better to have serial PI measurements than a single PI value. Do not conclude or pass an opinion about foetal condition based on single PI measurement. Insist on serial PI.

What about PSV (peak systolic velocity) of MCA as foetal condition worsens?

As foetal condition deteriorates MCA-PSV will continue to increase progressively and consistently. Therefore for day to day assessment of foetal status MCA-PSV is a better indicator that PI.

What about Venous  Flow in Ductus Venosus?.   Normally there is always a forward flow velocity during entire cardiac cycle but there is three separate FVW in Venous side(representing the cardiac events)

In case of hypoxia : Changes are :- highly pulsatile venous FVW in DV; b) increasing PSV (peak systolic flow).c) retrograde flow during atrial contractions. Normally 40% of venous blood in U. vein enters DV and rest goes to liver. Blood from DV goes to LA via F. Ovale. There are three distinct FVW patterns of waves seen in a normal DV and U. v. (which are events occurring in Cardiac cycle i.e. Ventricular systole, diastole and atrial contractions. These changes are highly correlated with foetal acidaemia.

What about Venous  Flow in Umb. Vein?

ii)     Assessment of Foetal Well-being of Foetus.

   E) Doppler studies of Foetal (cerebral a, DV, Echo, Renal,), Umbilical vessels (umb. A)

III)       IMPORTANT NOTES:

Doppler changes appear early than CTG/NST or even BPS (Modified Manning Score).

IV)       Sequential Changes in foetal/placental/ maternal blood vessels due to hypoxia and then academia =acidosis-IUD.

Shutting down blood in Aorta→ less nutrition to viscera-decreased AC→Thin limbs less peripheral fat→underwt. Foetus.

Renal blood flow less- OLIGIHYDRAMNIOS.

Brain sparing effect= blood flow in cerebral a increases-RI falls

Later due further anoxia-Cerebral oedena when eventually blood flow decreases and rise RI in MCA

Cardiac flow changes and rise of rt. atria pressure.

V)       Correlation of Umbilical artery pH (venous blood pH) with different demonstrable changes in Foetal monitoring:-Less glucose and oxygen supply due to placental resistance -=Hypoxia initiation of/formation of anaerobic Metab. In foetus→Acidaemia-→Acidotic foetus.

DOPPLER: Sequence of events in altered cardiac and foetal blood vessels dynamics.

Initial Changes: - a) COMPENSATORY MECHANISMS: - i) Foetal Echo changes ii) rise of diastolic flow in MCA .b) redistribution of flow: - Changes now occur in Umb. A e.g. PI       RI     

 Slowing of growth:-Biometry changes; Aorta(PI    ); Renal  PI(     )

Deterioration= ADEF (absent End Diast Flow) in UA.

Further Deterioration: - REDF (reversed) & later followed by DV reversal and cerebral edema and rise of PI and RI in MCA

GOOD SIGNS. In Uterine artery: - as first wave of Troph invasion is completed (first invasion is limited to spiral art supplying to endo only - intradecidual portion- only by 14 weeks0 a second wave of invasion progress to myometrial spiral a. at 14-16 wks.  High EDF,

In Umb. A: - Increase in diast. Flow EDF is raised, fall of S/D ratio; But Doppler indices must be interpreted in the light of gest age. But very high S/D ratio say above 3 may be bad sign after 30 weeks; one should pay more importance on EDF rather than S/D ratio.

IV)       Sequential Changes in foetal/placental/ maternal blood vessels due to hypoxia and then academia =acidosis-IUD.

Shutting down blood in Aorta→ less nutrition to viscera-decreased AC→Thin limbs less peripheral fat→underwt. Foetus.

Renal blood flow less- OLIGIHYDRAMNIOS.

Brain sparing effect= blood flow in cerebral a increases-RI falls

Later due further anoxia-Cerebral oedena when eventually blood flow decreases and rise RI in MCA

Cardiac flow changes and rise of rt. atria pressure.

J)       Correlation of Umbilical artery pH (venous blood pH) with different demonstrable changes in Foetal monitoring:-Less glucose and oxygen supply due to placental resistance -=Hypoxia initiation of/formation of anaerobic Metab. In foetus→Acidaemia-→Acidotic foetus.