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← Section I · Physical Principles, Instrumentation, Examination Principles
I.I

Principles of Flow

8 cards

Notes

Flow patterns

  • Laminar flow - streamlines parallel to vessel wall, parabolic velocity profile (fastest at center). Produces a narrow spectral envelope with a clean window.
  • Plug (blunt) flow - flat velocity profile across the vessel, typical in the LVOT and proximal aorta. Narrow spectral envelope.
  • Turbulent flow - chaotic, non-parallel streamlines; spectral broadening on Doppler, mosaic (variance) pattern on color.

Volumetric flow / continuity

  • Volumetric flow (mL/s) = cross-sectional area × mean velocity.
  • Stroke volume through a site = CSA × VTI (velocity–time integral).
  • Continuity: at steady state, flow entering a chamber equals flow leaving. Basis for AVA calculation from LVOT: AVA = (CSA_LVOT × VTI_LVOT) / VTI_AV.

Pressure–velocity relationship (Modified Bernoulli)

ΔP≈4v2\Delta P \approx 4 v^2

  • Where v is the peak velocity across a narrowed orifice (m/s), and ΔP is the pressure gradient in mmHg.
  • Assumes proximal velocity is negligible (< 1.5 m/s). If proximal velocity is important: ΔP = 4(v₂² − v₁²).
  • Valid for discrete stenoses; not for long, tunnel-like obstructions.

Wall filters

  • Remove low-frequency wall-motion artifact from Doppler signals.
  • Higher wall filter → cleaner spectrum but may cut low velocities of interest (e.g., early diastolic filling).

Reynolds number (concept)

  • Higher Re (higher velocity, larger vessel, lower viscosity) → turbulent flow.
  • Doppler recognizes turbulence as spectral broadening / variance.

Poiseuille & viscosity (concept)

  • For laminar flow in a tube: Q ∝ ΔP · r⁴ / (η · L). The r⁴ dependence is why small changes in orifice size produce large flow changes.

Cards

  • basicI.I-001
    Describe laminar flow's velocity profile and its Doppler appearance.
    → Parabolic velocity profile (fastest at center, slowest at wall). Produces a narrow spectral envelope with a clear window.
  • basicI.I-002
    Describe plug (blunt) flow. Where in the heart is it typical?
    → Flat velocity profile — all streamlines move at nearly the same speed. Typical in the LVOT and proximal aorta. Produces a narrow spectral envelope.
  • basicI.I-003
    What does turbulent flow look like on spectral and color Doppler?
    → Spectral: broadening, fill-in of the envelope. Color: mosaic pattern with variance (green if variance is enabled).
  • clozeI.I-004
    Volumetric flow = cross-sectional area × mean velocity, and stroke volume through a site = CSA × VTI.
  • basicI.I-005
    State the modified Bernoulli equation.
    → ΔP ≈ 4v². Peak instantaneous gradient in mmHg = 4 × (peak velocity in m/s)². Valid when proximal velocity is negligible.
  • basicI.I-006
    When must the full form of the Bernoulli equation be used?
    → When the proximal velocity (v₁) is not negligible (typically > 1.5 m/s). Use ΔP = 4(v₂² − v₁²).
  • basicI.I-007
    What is the continuity equation and when do you apply it?
    → At steady state, flow into a chamber equals flow out. Applied to calculate AVA from LVOT: AVA = (CSA_LVOT × VTI_LVOT) / VTI_AV.
  • basicI.I-008
    What is the role of the wall filter in Doppler?
    → Removes low-frequency wall-motion artifact from the Doppler signal. Set too high, it can eliminate low-velocity flow signals of clinical interest.