UltrasoUnd Physics & instrUmentation - Pegasus Lectures

4.2.5 Pressures in the Venous Side are Low .........................................................................797
4.3 The Venous System ...................................................................................................................797
4.3.1 Dichotomizing the Cardiovascular System ..................................................................797
4.3.2 Venous Pressure ...........................................................................................................797
4.3.3 Venous Capacitance and Circulatory Pressure .............................................................798
4.3.4 Hydrostatic Pressure ....................................................................................................798
4.3.5 The Calf Muscle Pump ................................................................................................799
4.3.6 Respiration Related Changes .......................................................................................800
4.3.7 Venous Resistance and Transmural Pressure ...............................................................801
4.3.8 When Things Go Wrong: Effects of Edema ..............................................................802
5. The Subcritical Diseased Cardiovascular System at Rest ...................................................................803
5.1 Asymptomatic Patients ..............................................................................................................803
5.2 Asymptomatic Patients with Exercise (Unmasking a Subcritical Stenosis)..............................805
5.3 Symptomatic Patients and Critical Stenoses .............................................................................807
6. Spectral Doppler as a Means of Assessing Hemodynamics ................................................................808
6.1 What Doppler Tells Us ..............................................................................................................808
6.2 Returning to the Hemodynamic Equations ...............................................................................809
6.3 Characteristics of the Spectrum .................................................................................................809
6.3.1 Systolic Acceleration and Pressure ..............................................................................809
6.3.1.1 Doppler Acceleration for a Healthy Large Vessel ......................................809
6.3.1.2 Doppler Risetime for a Diseased Vessel .....................................................810
6.3.2 The Spectral Window ..................................................................................................811
6.3.2.1 Presence in Healthy Vessel .........................................................................811
6.3.2.2 Absence in Diseased Vessel ........................................................................811
6.3.2.3 Absence of the Spectral Window in a Healthy Vessel ................................812
6.3.3 Systolic Acceleration and Velocity Distribution ..........................................................812
6.3.4 Flow Reversal and Phasicity ........................................................................................813
6.3.4.1 Normal Flow Reversal ................................................................................813
6.3.4.2 Abnormal Flow Reversal ............................................................................814
6.3.4.3 Arterial Signal Components .......................................................................815
6.4 Velocity Criteria .........................................................................................................................815
6.4.1 Peak Velocity ...............................................................................................................816
6.4.2 Mean Velocity ..............................................................................................................816
6.5 Doppler Indices and Ratios........................................................................................................816
6.5.1 General .........................................................................................................................816
6.5.2 Doppler Indices Defined ..............................................................................................817
6.5.3 Interpreting the Doppler indices ..................................................................................817
6.5.4 Angle independence of the Doppler indices ................................................................817
6.6 Murmurs and Bruits ...................................................................................................................818
6.6.1 Murmurs .......................................................................................................................818
6.6.2 A Doppler Bruit ...........................................................................................................818
6.6.3 Harmonic Bruit ............................................................................................................819
6.6.4 Fluttering ......................................................................................................................819
7. Flow Visualization ...............................................................................................................................820
aPPenDIX a: Vascular Principals
Introduction ................................................................................................................................................825
1. Electrical Principles .............................................................................................................................825
1.1 Ohm’s Law ................................................................................................................................825
Pegasus Lectures, Inc.
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