Pulse wave velocity |
---|
Pulse wave velocity (PWV) is the velocity at which the blood pressure pulse propagates through the circulatory system, usually an artery or a combined length of arteries. PWV is used clinically as a measure of arterial stiffness and can be readily measured non-invasively in humans, with measurement of carotid to femoral PWV (cfPWV) being the recommended method. [1] [2] [3] cfPWV is highly reproducible, [4] and predicts future cardiovascular events and all-cause mortality independent of conventional cardiovascular risk factors. [5] [6] It has been recognized by the European Society of Hypertension as an indicator of target organ damage and a useful additional test in the investigation of hypertension. [7]
The theory of the velocity of the transmission of the pulse through the circulation dates back to 1808 with the work of Thomas Young. [8] The relationship between pulse wave velocity (PWV) and arterial wall stiffness can be dervied from Newton's second law of motion () applied to a small fluid element, where the force on the element equals the product of density (the mass per unit volume; ) and the acceleration. [9] The approach for calculating PWV is similar to the calculation of the speed of sound, , in a compressible fluid (e.g. air):
,
where is the bulk modulus and is the density of the fluid.
For an incompressible fluid ( blood) in a compressible (elastic) tube (e.g. an artery): [10]
,
where is volume per unit length and is pressure. This is the equation derived by Otto Frank, [11] and John Crighton Bramwell and Archibald Hill. [12]
Alternative forms of this equation are:
, or ,
where is the radius of the tube and is distensibility.
This equation:
characterises PWV in terms of the incremental elastic modulus of the vessel wall, the wall thickness, and the radius. It was derived independently by Adriaan Isebree Moens and Diederik Korteweg and is equivalent to the Frank / Bramwell Hill equation: [10]
These equations assume that:
Since the wall thickness, radius and incremental elastic modulus vary from blood vessel to blood vessel, PWV will also vary between vessels. [10] Most measurements of PWV represent an average velocity over several vessels (e.g. from the carotid to the femoral artery).
PWV intrinsically varies with blood pressure. [13] PWV increases with pressure for two reasons:
A range of invasive or non-invasive methods can be used to measure PWV. Some general approaches are:
PWV, by definition, is the distance traveled () by the pulse wave divided by the time () for the wave to travel that distance:
,
in practice this approach is complicated by the existance of reflected waves. [10] It is widely assumed that reflections are minimal during late diastole and early systole. [10] With this assumption, PWV can be measured using the `foot' of the pressure waveform as a fiducial marker from invasive or non-invasive measurements; the transit time correponds to the delay in arrival of the foot between two locations a known distance apart. Locating the foot of the pressure waveform can be problematic. [14] The advantage of the foot-to-foot PWV measurement is the simplicity of measurement, requiring only two pressure wave forms recorded with invasive catheters, or non-invasively using pulse detection devices applied to the skin at two measurement sites, and a tape measure. [15]
This is based on the method described by Bramwell & Hill [16] who proposed modifications to the Moens-Kortweg equation. Quoting directly, these modifications were:
"A small rise in pressure may be shown to cause a small increase, , in the radius of the artery, or a small increase, , in its own volume per unit length. Hence "
where represents the wall thickness (defined as above), the elastic modulus, and the vessel radius (defined as above). This permits calculation of local PWV in terms of or as detailed above, and provides an alternate method of measuring PWV, if pressure and arterial dimensions are measured, for example by ultrasound [17] [18] or MRI. [19]
The Water hammer equation expressed either in terms of pressure and flow velocity, [20] pressure and volumetric flow, or characteristic impedance [21] can be used to calculate local PWV:
,
where is velocity, is volumetric flow, is characteristic impedance and is the cross-sectional area of the vessel. This approach is only valid when wave reflections are absent or minimal, this is assumed to be the case in early systole. [22]
A related method to the pressure-flow velocity method uses vessel diameter and flow velocity to determine local PWV. [23] It is also based on the Water hammer equation:
,
and since
,
where is diameter; then:
,
or using the incremental hoop strain, ,
PWV can be expressed in terms of and
therefore plotting against gives a lnDU-loop, and the linear portion during early systole, when reflected waves are assumed to be minimal, can be used to calculate PWV.
Clinically, PWV can be measured in several ways and in different locations. The 'gold standard' for arterial stiffness assessment in clinical practice is cfPWV, [2] [3] and validation guidelines have been proposed. [24] Other measures such as brachial-ankle PWV and cardio-ankle vascular index (CAVI) are also popular. [25] For cfPWV, it is recommended that the arrival time of the pulse wave measured simultanously at both locations, and the distance travelled by the pulse wave calculated as 80% of the direct distance between the common carotid artery in the neck and the femoral artery in the groin. [2] Numerous devices exist to measure cfPWV; [26] [27] techniques include:
Newer devices that employ an arm cuff, [28] fingertip sensors [29] or special weighing scales [30] have been described, but their clinical utility remains to be fully established.
Current guidelines by the European Society of Hypertension state that a measured PWV larger than 10 m/s can be considered an independent marker of end-organ damage. [7] However, the use of a fixed PWV threshold value could be debated, as PWV is markedly dependent on blood pressure . [13]
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Pulse wave velocity |
---|
Pulse wave velocity (PWV) is the velocity at which the blood pressure pulse propagates through the circulatory system, usually an artery or a combined length of arteries. PWV is used clinically as a measure of arterial stiffness and can be readily measured non-invasively in humans, with measurement of carotid to femoral PWV (cfPWV) being the recommended method. [1] [2] [3] cfPWV is highly reproducible, [4] and predicts future cardiovascular events and all-cause mortality independent of conventional cardiovascular risk factors. [5] [6] It has been recognized by the European Society of Hypertension as an indicator of target organ damage and a useful additional test in the investigation of hypertension. [7]
The theory of the velocity of the transmission of the pulse through the circulation dates back to 1808 with the work of Thomas Young. [8] The relationship between pulse wave velocity (PWV) and arterial wall stiffness can be dervied from Newton's second law of motion () applied to a small fluid element, where the force on the element equals the product of density (the mass per unit volume; ) and the acceleration. [9] The approach for calculating PWV is similar to the calculation of the speed of sound, , in a compressible fluid (e.g. air):
,
where is the bulk modulus and is the density of the fluid.
For an incompressible fluid ( blood) in a compressible (elastic) tube (e.g. an artery): [10]
,
where is volume per unit length and is pressure. This is the equation derived by Otto Frank, [11] and John Crighton Bramwell and Archibald Hill. [12]
Alternative forms of this equation are:
, or ,
where is the radius of the tube and is distensibility.
This equation:
characterises PWV in terms of the incremental elastic modulus of the vessel wall, the wall thickness, and the radius. It was derived independently by Adriaan Isebree Moens and Diederik Korteweg and is equivalent to the Frank / Bramwell Hill equation: [10]
These equations assume that:
Since the wall thickness, radius and incremental elastic modulus vary from blood vessel to blood vessel, PWV will also vary between vessels. [10] Most measurements of PWV represent an average velocity over several vessels (e.g. from the carotid to the femoral artery).
PWV intrinsically varies with blood pressure. [13] PWV increases with pressure for two reasons:
A range of invasive or non-invasive methods can be used to measure PWV. Some general approaches are:
PWV, by definition, is the distance traveled () by the pulse wave divided by the time () for the wave to travel that distance:
,
in practice this approach is complicated by the existance of reflected waves. [10] It is widely assumed that reflections are minimal during late diastole and early systole. [10] With this assumption, PWV can be measured using the `foot' of the pressure waveform as a fiducial marker from invasive or non-invasive measurements; the transit time correponds to the delay in arrival of the foot between two locations a known distance apart. Locating the foot of the pressure waveform can be problematic. [14] The advantage of the foot-to-foot PWV measurement is the simplicity of measurement, requiring only two pressure wave forms recorded with invasive catheters, or non-invasively using pulse detection devices applied to the skin at two measurement sites, and a tape measure. [15]
This is based on the method described by Bramwell & Hill [16] who proposed modifications to the Moens-Kortweg equation. Quoting directly, these modifications were:
"A small rise in pressure may be shown to cause a small increase, , in the radius of the artery, or a small increase, , in its own volume per unit length. Hence "
where represents the wall thickness (defined as above), the elastic modulus, and the vessel radius (defined as above). This permits calculation of local PWV in terms of or as detailed above, and provides an alternate method of measuring PWV, if pressure and arterial dimensions are measured, for example by ultrasound [17] [18] or MRI. [19]
The Water hammer equation expressed either in terms of pressure and flow velocity, [20] pressure and volumetric flow, or characteristic impedance [21] can be used to calculate local PWV:
,
where is velocity, is volumetric flow, is characteristic impedance and is the cross-sectional area of the vessel. This approach is only valid when wave reflections are absent or minimal, this is assumed to be the case in early systole. [22]
A related method to the pressure-flow velocity method uses vessel diameter and flow velocity to determine local PWV. [23] It is also based on the Water hammer equation:
,
and since
,
where is diameter; then:
,
or using the incremental hoop strain, ,
PWV can be expressed in terms of and
therefore plotting against gives a lnDU-loop, and the linear portion during early systole, when reflected waves are assumed to be minimal, can be used to calculate PWV.
Clinically, PWV can be measured in several ways and in different locations. The 'gold standard' for arterial stiffness assessment in clinical practice is cfPWV, [2] [3] and validation guidelines have been proposed. [24] Other measures such as brachial-ankle PWV and cardio-ankle vascular index (CAVI) are also popular. [25] For cfPWV, it is recommended that the arrival time of the pulse wave measured simultanously at both locations, and the distance travelled by the pulse wave calculated as 80% of the direct distance between the common carotid artery in the neck and the femoral artery in the groin. [2] Numerous devices exist to measure cfPWV; [26] [27] techniques include:
Newer devices that employ an arm cuff, [28] fingertip sensors [29] or special weighing scales [30] have been described, but their clinical utility remains to be fully established.
Current guidelines by the European Society of Hypertension state that a measured PWV larger than 10 m/s can be considered an independent marker of end-organ damage. [7] However, the use of a fixed PWV threshold value could be debated, as PWV is markedly dependent on blood pressure . [13]
{{
cite journal}}
: CS1 maint: PMC format (
link)
{{
cite journal}}
: CS1 maint: PMC format (
link)
{{
cite journal}}
: CS1 maint: multiple names: authors list (
link) Cite error: The named reference "Mancia2013" was defined multiple times with different content (see the
help page).
{{
cite book}}
: CS1 maint: extra punctuation (
link) CS1 maint: multiple names: authors list (
link)
{{
cite journal}}
: CS1 maint: multiple names: authors list (
link)
{{
cite journal}}
: CS1 maint: PMC format (
link) CS1 maint: unflagged free DOI (
link)
{{
cite journal}}
: CS1 maint: PMC format (
link)
{{
cite journal}}
: CS1 maint: PMC format (
link)
{{
cite journal}}
: CS1 maint: PMC format (
link)