Doppler echocardiojgraphy measures blood flow velocities and direction of blood flow in the heart add great vessels. The characteristics of blood flow are evaluated using both audio information and a graphic display of the Doppler spectral analysis.
Qualitative and quantitative Doppler information may aid in the non-invasive assessment of:
A) Valvular Abndrmalities
Stenosis-as inpicated by increased blood flow velocity and turbulence beyond an obsbction.
Regurgitation-detection of high velocity turbulent retrograde flow in cardiac chambeb proximal to be regurgitant valve.
B) Congenital Catdiac Defects
Shunt Lesions4etection of flow across a septa1 defect or from a patent ductus arteriousius and quantification of the degree of shunting.
C) Cardiac
Timing-instantaneous velocity and direction of flow throughout the various positions of cardiac cycle.
Intensity-the amplitude of individual velocities within the Doppler signal at any point of time-the more intense the signal, the greater number of blood cells moving at that velocity.Fundamentals of Ecbocardiograpby
Types of Cardiac Dopler
There are two types of Doppler examination:
1) Pulse wave Doppler
2) Continuous wave Doppler
Both these modalities are necessary part of Doppler echocardiography and provide complimeatary information.
1) Pulse Wave Doppler
Pulse wave transducer has one Doppler crystal. This crystal emits a short burst of ultrasound at a certain frequency [PULSE REPETITION FREQUENCY(PRF)]. The ultrasqund is reflected from moving rbc's and is received by the same crystal
Qualitative and quantitative Doppler information may aid in the non-invasive assessment of:
A) Valvular Abndrmalities
Stenosis-as inpicated by increased blood flow velocity and turbulence beyond an obsbction.
Regurgitation-detection of high velocity turbulent retrograde flow in cardiac chambeb proximal to be regurgitant valve.
B) Congenital Catdiac Defects
Shunt Lesions4etection of flow across a septa1 defect or from a patent ductus arteriousius and quantification of the degree of shunting.
C) Cardiac
- Velocity time idtervals
- Estimates of catdiac output
- Other potential estimation of cardiac function
Principles of Doppler Echocardiography
Doppler echocardio@aphy is based on the Doppler effect, which was described by the Austrian phy$icist Christian Doppler in 1842.The Doppler effect $tates that sound frequency increases as the sound source moves towards the observer and decreased as the source moves away. In the circulatory system, the moving target is the red blood cells (rbc). When an ultrasound beam witb known frequency (Fo) is transmitted to the heart or great vessels, it is reflecteid by rbc's. The frequency of reflected ultrasound waves (Fr) increases when rbc'd are moving towards the source of ultrasound and vice versa. The change id frequency between transmitted and reflected sound is seemed the frequenc/y shiR (AF) or Doppler shiR (Fr-Fo).
Doppler echocardio@aphy is based on the Doppler effect, which was described by the Austrian phy$icist Christian Doppler in 1842.The Doppler effect $tates that sound frequency increases as the sound source moves towards the observer and decreased as the source moves away. In the circulatory system, the moving target is the red blood cells (rbc). When an ultrasound beam witb known frequency (Fo) is transmitted to the heart or great vessels, it is reflecteid by rbc's. The frequency of reflected ultrasound waves (Fr) increases when rbc'd are moving towards the source of ultrasound and vice versa. The change id frequency between transmitted and reflected sound is seemed the frequenc/y shiR (AF) or Doppler shiR (Fr-Fo).
If cos 0 is 0 degree [i.e., the ultrasound beam is parallel with the direction of blood flow), the maximal frequency shiR is measured because the cosine of 0 degree is 1. This explains the proper alignment of ultrasound beam or cursor with the flow of blobd to achieve accurate information.
Peak Flow Velocity fs derived from Doppler shift by rearranging Doppler equation:v=(c/2)
Peak Flow Velocity fs derived from Doppler shift by rearranging Doppler equation:v=(c/2)
 |
| Schematic diagram showing Doppler effect |
Various information can be obtained from spectral display of Blood flow-Velocity the speed of sampled blood cells (calculated from spectral analysis information).
Direction of flow--either towards or away from the transducer (positive or negative Doppler shifts).
Direction of flow--either towards or away from the transducer (positive or negative Doppler shifts).
Timing-instantaneous velocity and direction of flow throughout the various positions of cardiac cycle.
Intensity-the amplitude of individual velocities within the Doppler signal at any point of time-the more intense the signal, the greater number of blood cells moving at that velocity.Fundamentals of Ecbocardiograpby
Types of Cardiac Dopler
There are two types of Doppler examination:
1) Pulse wave Doppler
2) Continuous wave Doppler
Both these modalities are necessary part of Doppler echocardiography and provide complimeatary information.
1) Pulse Wave Doppler
Pulse wave transducer has one Doppler crystal. This crystal emits a short burst of ultrasound at a certain frequency [PULSE REPETITION FREQUENCY(PRF)]. The ultrasqund is reflected from moving rbc's and is received by the same crystal
 |
| Schematic diagram showing pulse wave transducer emitting bursts of waves. There is one Doppler crystal to emit and receive ultrasound waves |
The pulse wave trbnsducer will not send out a new burst of waves until it has received returning echoes from previous pulse, which must travel to and Go from the location indicdted by the sample volume. The pulse wave Doppler gives velocity of blood now at the level of sample volume placed along ultrasound beam.
Pulse repetition fitquency, as well as transducer frequency, plays a role in determining the maximum velocity that can be measured using a pulsed Doppler method. These rellationships come into play especially when attempting to record or to measure incteased velocities that might occur in the case of obstructive lesions such as vilvular stenosis. This maximal measured velocity is called NYQUIST LIMIT.
The NYQUIST LIIMIT-It is a sampling phenomenon, which limits the maximum fiequemcy shift measurement to one half of the sampling frequency (PRF).
By its nature, pulse wave Doppler is a sampling system while continuous wave Doppler is not. The nyquist limit is a theoretical maximum frequency that a sampling system can accurately measure.If the frequency shift is higher than the Nyquist frequency, aliasing occurs; i.e.,the Doppler spectrum is cut off the Nyquist frequency and the remaining frequency shift is recorded on the opposite side of baseline.
The PRF varies inversely with the depth of the sample volume the shallower the location of the sample volume, the higher the PRF and Nyquist frequency. In other words, higher velocities can be recorded without aliasing by pulse wave Doppler if the sample volume is closer to transducer.
Pulse repetition fitquency, as well as transducer frequency, plays a role in determining the maximum velocity that can be measured using a pulsed Doppler method. These rellationships come into play especially when attempting to record or to measure incteased velocities that might occur in the case of obstructive lesions such as vilvular stenosis. This maximal measured velocity is called NYQUIST LIMIT.
The NYQUIST LIIMIT-It is a sampling phenomenon, which limits the maximum fiequemcy shift measurement to one half of the sampling frequency (PRF).
By its nature, pulse wave Doppler is a sampling system while continuous wave Doppler is not. The nyquist limit is a theoretical maximum frequency that a sampling system can accurately measure.If the frequency shift is higher than the Nyquist frequency, aliasing occurs; i.e.,the Doppler spectrum is cut off the Nyquist frequency and the remaining frequency shift is recorded on the opposite side of baseline.
The PRF varies inversely with the depth of the sample volume the shallower the location of the sample volume, the higher the PRF and Nyquist frequency. In other words, higher velocities can be recorded without aliasing by pulse wave Doppler if the sample volume is closer to transducer.
 |
| Pulse wave across mitral valve in-patient of mitral stenosis showing phenomenon of aliasing |
2) Continuous Wave Doppler
In continuous wave Doppler, the transducer has two Doppler crystals, one to constantly transmit and one to continuously receive.
In continuous wave Doppler, the transducer has two Doppler crystals, one to constantly transmit and one to continuously receive.
 |
| Schematic diagram showing continuous wave transducer. It was two crystals one to constantly transmit and one to continuously receive |
As a result of this continuous mode of transmitting and receiving, motion of blood and tissue occurring all along the ultrasound beam will be received,analysed and displayed without an indication of the depth from which each velocity arose. Also, the maximal frequency shift that can be recorded by continuous wave Doppler is not limited by the PRF or the Nyquist phenomenon hence, it is used to detect and record the highest velocity available.
step-by-step procedures for performing those Doppler calculations which are in most fiequent use.
- Normal velocity ranges
- The simplified Bernoulli equation
- Mitral pressure half time
- Cardiac output
- Pulmonary artery flow time intervals
- Right ventricular and pulmonary artery systolic/diastolic pressure estimation
The Simplified Bernoulli Equation2
The simplified Bernoulli equation may be applied to peak velocity measurements to make non-invasive estimates of pressure gradients.
Where
step-by-step procedures for performing those Doppler calculations which are in most fiequent use.
- Normal velocity ranges
- The simplified Bernoulli equation
- Mitral pressure half time
- Cardiac output
- Pulmonary artery flow time intervals
- Right ventricular and pulmonary artery systolic/diastolic pressure estimation
The Simplified Bernoulli Equation2
The simplified Bernoulli equation may be applied to peak velocity measurements to make non-invasive estimates of pressure gradients.
Where
Vl = peak velocity proximal to an obstruction
V2 = peak velocity distal to the obstruction.
This equation takes into consideration the velocity of flow on both sides of an obstruction.
Example: Peak velocity measured in the ascending aorta is 3 m/sec ,peak velocity measured in the left ventricular outflow is 2/sec c .
Gradient across the aortic valve
= 4 (3(2)-2(2))
= 4 (9-4)
=20 mmHg.
If V is close to 1 d s e c , it can be neglected and then even simpler version of the Bernoulli equation may be used:
p=4(v)2
Example: Peak velocjity measured on the ascending aorta is 3 d s e c , velocity measured in the left Lentricular outflow tract is 1/sec .
Gradient across the iiortic valve
=4 (V)2
= 4(3)2
= 36mmHg
When V is both signlificant and discernible (a V, value of 1.2 d s e c would be considered significadt), the long form of the Simplified Bernoulli equation should be used.
Because gradient obtained using Doppler velocity measurements represent a maximal instantaneous gradient rather than a peak-to-peak gradient, there may be minor discrepancies between gradient values calculated by Doppler and those obtained in cardiac aatheterization lab.
Estimating The Severity of A-V Valve (mitral valve) Stenosis Using The Pressure Half-Tim@
Calculation
Step 1 - Measure peak velocity (V) in d s e c
Step 2 - Calculafie velocity at pressure half-time
Step 3 - Determime the length of time it takes for the flow velocity to drop to pressurd . half-time velocity
V2 = peak velocity distal to the obstruction.
This equation takes into consideration the velocity of flow on both sides of an obstruction.
Example: Peak velocity measured in the ascending aorta is 3 m/sec ,peak velocity measured in the left ventricular outflow is 2/sec c .
Gradient across the aortic valve
= 4 (3(2)-2(2))
= 4 (9-4)
=20 mmHg.
If V is close to 1 d s e c , it can be neglected and then even simpler version of the Bernoulli equation may be used:
p=4(v)2
Example: Peak velocjity measured on the ascending aorta is 3 d s e c , velocity measured in the left Lentricular outflow tract is 1/sec .
Gradient across the iiortic valve
=4 (V)2
= 4(3)2
= 36mmHg
When V is both signlificant and discernible (a V, value of 1.2 d s e c would be considered significadt), the long form of the Simplified Bernoulli equation should be used.
Because gradient obtained using Doppler velocity measurements represent a maximal instantaneous gradient rather than a peak-to-peak gradient, there may be minor discrepancies between gradient values calculated by Doppler and those obtained in cardiac aatheterization lab.
Estimating The Severity of A-V Valve (mitral valve) Stenosis Using The Pressure Half-Tim@
Calculation
Step 1 - Measure peak velocity (V) in d s e c
Step 2 - Calculafie velocity at pressure half-time
Step 3 - Determime the length of time it takes for the flow velocity to drop to pressurd . half-time velocity
Step 4 - A-V valve area (cm2) =(220/(T/1/2)ms)
Calculation of Cardiac Output Using Doppler Flow Velocities Measured in LVOT
Step 1 = Determine the cross-sectional area (CSA) of the aortic annulus (LVOT).
Step 2 = Determine the flow velocity integral (FVI) by planimetry of the area under aortic velocity curves and calculating an average
Step 3 = Calculate stroke volume (SV) + SV = FVI x CSA
Step 4 = Determine heart rate (HR)
Step 5 = Calculate Cardiac Output,
C O = S V x HR
Sources of Error in Doppler Cardiac Output Determinations Limitations of the Technique
Though it has bees suggested that Doppler echocardiography may be useful for non-invasive determinations of stroke volume and cardiac output, it should be recognized that th4re are limitations and sources of error in the technique.Because of these limitations, Doppler cardiac output calculations have been accepted especiall$ for detecting relative changes in flow volume.
Doppler cardiac oQtput calculations are based on a series of assumptions about the geometry of the aorta (or other site of velocity measurement with in the heart) and about the flow velocity profile in that vessel. Two primary assumptions abouti the hemodynamics of flow are:
1) Flow is occurring in a rigid, circular tube
2) There is a unidorm velocity profile across that tube
The greatest souroe of error in this technique is the measurement of the LVOT area.
Difficulties associated with accurate aortic flow are measurements and calculationsThe aorta is elastic and changes size over the course of a cardiac cycle LVOT area increases with increased flow volume
The diameter and cross sectional area may vary at different measurement sites
Any error in a diameter measurement will be magnified when it is squared for an area calculation. As the diameter of the aorta decreased a measurement error will increase the degree of error in the area calculation
If the vessel area is planimetered from a two-dimensional view, error may occur due to obliquity of the ultrasound beam
The blood flow velocity measurement is the second component of the cardiac output calculation. Since flow velocities are not uniform across the vessel, which spectral velocities should be used to represent aortic velocity: peak velocity,mean velocity, mode velocity?
The most important aspect of the velocity measurement is thorough sampling technique, taking care to orient the ultrasound beam as parallel to flow as possible (as indicated by the strength of the flow signal and the peak velocity measurement).
Calculation of Cardiac Output Using Doppler Flow Velocities Measured in LVOT
Step 1 = Determine the cross-sectional area (CSA) of the aortic annulus (LVOT).
Step 2 = Determine the flow velocity integral (FVI) by planimetry of the area under aortic velocity curves and calculating an average
Step 3 = Calculate stroke volume (SV) + SV = FVI x CSA
Step 4 = Determine heart rate (HR)
Step 5 = Calculate Cardiac Output,
C O = S V x HR
Sources of Error in Doppler Cardiac Output Determinations Limitations of the Technique
Though it has bees suggested that Doppler echocardiography may be useful for non-invasive determinations of stroke volume and cardiac output, it should be recognized that th4re are limitations and sources of error in the technique.Because of these limitations, Doppler cardiac output calculations have been accepted especiall$ for detecting relative changes in flow volume.
Doppler cardiac oQtput calculations are based on a series of assumptions about the geometry of the aorta (or other site of velocity measurement with in the heart) and about the flow velocity profile in that vessel. Two primary assumptions abouti the hemodynamics of flow are:
1) Flow is occurring in a rigid, circular tube
2) There is a unidorm velocity profile across that tube
The greatest souroe of error in this technique is the measurement of the LVOT area.
Difficulties associated with accurate aortic flow are measurements and calculationsThe aorta is elastic and changes size over the course of a cardiac cycle LVOT area increases with increased flow volume
The diameter and cross sectional area may vary at different measurement sites
Any error in a diameter measurement will be magnified when it is squared for an area calculation. As the diameter of the aorta decreased a measurement error will increase the degree of error in the area calculation
If the vessel area is planimetered from a two-dimensional view, error may occur due to obliquity of the ultrasound beam
The blood flow velocity measurement is the second component of the cardiac output calculation. Since flow velocities are not uniform across the vessel, which spectral velocities should be used to represent aortic velocity: peak velocity,mean velocity, mode velocity?
The most important aspect of the velocity measurement is thorough sampling technique, taking care to orient the ultrasound beam as parallel to flow as possible (as indicated by the strength of the flow signal and the peak velocity measurement).
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