Doppler Pressure Evaluation of Infrainguinal Occlusive Disease Phillip J. Bendick The measurement of lower extremity systolic pressure is by far the most widely used parameter for evaluating peripheral arterial disease. It is an easy measurement to perform with minimal testing equipment, it is a reliable and reproducible indicator of hemodynamically significant obstructive disease, and, unlike waveform analysis, it provides objective quantitative data. From Hales’s successful but very invasive measurement of mean arterial pressure in 1733, the noninvasive measurement technique has evolved with the development of the air-filled occluding cuff by Riva-Rocci in 1896, Korotkoff’s description of the auscultatory method in 1905, the data of Winsor showing the utility of pressure measurements in detecting arterial disease in 1950, and the study by Satomura in 1959 of ultrasound Doppler detection of blood flow patterns. Physiology of Arterial Obstruction The principle of continuity dictates that in a closed fluid system (such as a segment of the superficial femoral artery with no branches) when the tube narrows the flow speed must increase, converting pressure (potential) energy into velocity (kinetic) energy. For minimal narrowing, all of this kinetic energy is recovered downstream when the flow speed decreases, with no loss distally in overall blood pressure. As the narrowing reaches hemodynamic significance, viscous and flow turbulence effects prevent complete energy recovery, and there is a measurable pressure drop. The higher the volume flow, the less narrowing is required for a hemodynamically significant lesion, which is why systolic pressure is profoundly affected by stenoses with little impact on diastolic pressures. The degree of narrowing that achieves hemodynamic significance is termed a critical stenosis. This varies for different blood vessels and flow conditions. At rest in the lower extremities it typically requires at least the equivalent of a 60% diameter reduction (approximate 84% cross-sectional area reduction) to reach a critical stenosis. However, during periods of increased flow, such as during exercise, a much lower degree of stenosis results in a pressure reduction. With a fivefold increase in volume flow through the superficial femoral artery induced by exercise, the equivalent of a 40% diameter reduction (approximate 60% area reduction) can achieve hemodynamic significance. The physiologic response to a significant arterial obstruction is a reduction in distal peripheral resistance through arteriolar dilation. The relationship governing flow is pressure equals volume flow times peripheral resistance; if pressure and resistance decrease by the same relative amount, volume flow in the affected limb can remain constant. When peripheral resistance can no longer adapt enough to a pressure drop caused by arterial stenosis, ischemia results, with its associated symptoms. Technique To noninvasively measure systolic blood pressure in the lower extremities, a blood pressure cuff is placed over the limb segment of interest and inflated to a pressure 30 to 40 mm Hg above the systolic pressure, then slowly deflated (2–4 mm Hg/sec) while monitoring blood flow at a site distal to the cuff. Typically a continuous wave Doppler flowmeter is used for this purpose, monitoring one of the lower leg tibioperoneal arteries at the level of the ankle. The cuff pressure noted when the return of arterial flow is detected is taken to be the systolic pressure at the site of the occluding cuff. Ideally the inflatable cuff bladder is appropriately sized to the limb segment being measured. Current American Heart Association guidelines call for the bladder width to be 20% greater than the limb’s diameter (40% of the circumference) with the bladder length approximately two times its width. If the cuff is too narrow, pressure within the bladder will not be effectively transmitted to the tissue and the resulting systolic pressure measurement will be artifactually elevated. Ankle Pressure Measurement The most basic lower extremity systolic pressure measurement is that of the ankle pressure, which is then used to calculate the ankle-to-brachial index (ABI). The patient should be in the supine position for this measurement and should have rested for at least 15 minutes to avoid any elevation in lower extremity flows secondary to ambulation. With the pressure cuff placed at the ankle, just above the medial malleolus, the distal posterior tibial and anterior tibial/dorsalis pedis arteries are monitored to determine the ankle pressure. In some noninvasive laboratories a distal branch of the peroneal artery may be monitored as well. Typically a continuous-wave Doppler flowmeter with a probe frequency of 8 to 10 MHz is used for this. The highest of the ankle pressures on each side is divided by the higher of the right or left brachial (upper arm) systolic pressure to calculate the ABI. When the patient is supine and there is no significant obstructive disease, the ankle and the brachial pressures should be equal, with the ABI equal to 1.00. Because of measurement variability, a lower limit of 0.95 is often taken to be normal. If there is a hemodynamically significant lesion anywhere in any of the lower extremity arterial segments (aortoiliac inflow, femoropopliteal outflow, or lower leg runoff), the resting ABI is less than 0.95. The more severe the disease and the patient’s symptoms, the more the ABI is lowered. Typically an ABI of 0.70 to 0.95 correlates with a single-segment stenosis and mild claudication (Rutherford category 1 to 2); an ABI of 0.50 to 0.70 correlates with a single-segment total occlusion and more severe claudication (Rutherford category 2 to 3). Generally in patients with claudication, an aortoiliac or superficial femoral artery lesion also causes the ABI to be toward the low end of the range compared to a popliteal or below-knee lesion. An ABI less than 0.50 typically corresponds to multisegment disease, and an ABI less than 0.30 is often associated with ischemic pain at rest and/or tissue loss. When serial ABI measurements are taken over time to evaluate for any disease progression or improvement after surgery, a change of greater than ±0.15 falls outside the confidence limits for interobserver and intraobserver assessments as well as nonpathologic biologic variability and is considered a significant change. Only gold members can continue reading. 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Doppler Pressure Evaluation of Infrainguinal Occlusive Disease Phillip J. Bendick The measurement of lower extremity systolic pressure is by far the most widely used parameter for evaluating peripheral arterial disease. It is an easy measurement to perform with minimal testing equipment, it is a reliable and reproducible indicator of hemodynamically significant obstructive disease, and, unlike waveform analysis, it provides objective quantitative data. From Hales’s successful but very invasive measurement of mean arterial pressure in 1733, the noninvasive measurement technique has evolved with the development of the air-filled occluding cuff by Riva-Rocci in 1896, Korotkoff’s description of the auscultatory method in 1905, the data of Winsor showing the utility of pressure measurements in detecting arterial disease in 1950, and the study by Satomura in 1959 of ultrasound Doppler detection of blood flow patterns. Physiology of Arterial Obstruction The principle of continuity dictates that in a closed fluid system (such as a segment of the superficial femoral artery with no branches) when the tube narrows the flow speed must increase, converting pressure (potential) energy into velocity (kinetic) energy. For minimal narrowing, all of this kinetic energy is recovered downstream when the flow speed decreases, with no loss distally in overall blood pressure. As the narrowing reaches hemodynamic significance, viscous and flow turbulence effects prevent complete energy recovery, and there is a measurable pressure drop. The higher the volume flow, the less narrowing is required for a hemodynamically significant lesion, which is why systolic pressure is profoundly affected by stenoses with little impact on diastolic pressures. The degree of narrowing that achieves hemodynamic significance is termed a critical stenosis. This varies for different blood vessels and flow conditions. At rest in the lower extremities it typically requires at least the equivalent of a 60% diameter reduction (approximate 84% cross-sectional area reduction) to reach a critical stenosis. However, during periods of increased flow, such as during exercise, a much lower degree of stenosis results in a pressure reduction. With a fivefold increase in volume flow through the superficial femoral artery induced by exercise, the equivalent of a 40% diameter reduction (approximate 60% area reduction) can achieve hemodynamic significance. The physiologic response to a significant arterial obstruction is a reduction in distal peripheral resistance through arteriolar dilation. The relationship governing flow is pressure equals volume flow times peripheral resistance; if pressure and resistance decrease by the same relative amount, volume flow in the affected limb can remain constant. When peripheral resistance can no longer adapt enough to a pressure drop caused by arterial stenosis, ischemia results, with its associated symptoms. Technique To noninvasively measure systolic blood pressure in the lower extremities, a blood pressure cuff is placed over the limb segment of interest and inflated to a pressure 30 to 40 mm Hg above the systolic pressure, then slowly deflated (2–4 mm Hg/sec) while monitoring blood flow at a site distal to the cuff. Typically a continuous wave Doppler flowmeter is used for this purpose, monitoring one of the lower leg tibioperoneal arteries at the level of the ankle. The cuff pressure noted when the return of arterial flow is detected is taken to be the systolic pressure at the site of the occluding cuff. Ideally the inflatable cuff bladder is appropriately sized to the limb segment being measured. Current American Heart Association guidelines call for the bladder width to be 20% greater than the limb’s diameter (40% of the circumference) with the bladder length approximately two times its width. If the cuff is too narrow, pressure within the bladder will not be effectively transmitted to the tissue and the resulting systolic pressure measurement will be artifactually elevated. Ankle Pressure Measurement The most basic lower extremity systolic pressure measurement is that of the ankle pressure, which is then used to calculate the ankle-to-brachial index (ABI). The patient should be in the supine position for this measurement and should have rested for at least 15 minutes to avoid any elevation in lower extremity flows secondary to ambulation. With the pressure cuff placed at the ankle, just above the medial malleolus, the distal posterior tibial and anterior tibial/dorsalis pedis arteries are monitored to determine the ankle pressure. In some noninvasive laboratories a distal branch of the peroneal artery may be monitored as well. Typically a continuous-wave Doppler flowmeter with a probe frequency of 8 to 10 MHz is used for this. The highest of the ankle pressures on each side is divided by the higher of the right or left brachial (upper arm) systolic pressure to calculate the ABI. When the patient is supine and there is no significant obstructive disease, the ankle and the brachial pressures should be equal, with the ABI equal to 1.00. Because of measurement variability, a lower limit of 0.95 is often taken to be normal. If there is a hemodynamically significant lesion anywhere in any of the lower extremity arterial segments (aortoiliac inflow, femoropopliteal outflow, or lower leg runoff), the resting ABI is less than 0.95. The more severe the disease and the patient’s symptoms, the more the ABI is lowered. Typically an ABI of 0.70 to 0.95 correlates with a single-segment stenosis and mild claudication (Rutherford category 1 to 2); an ABI of 0.50 to 0.70 correlates with a single-segment total occlusion and more severe claudication (Rutherford category 2 to 3). Generally in patients with claudication, an aortoiliac or superficial femoral artery lesion also causes the ABI to be toward the low end of the range compared to a popliteal or below-knee lesion. An ABI less than 0.50 typically corresponds to multisegment disease, and an ABI less than 0.30 is often associated with ischemic pain at rest and/or tissue loss. When serial ABI measurements are taken over time to evaluate for any disease progression or improvement after surgery, a change of greater than ±0.15 falls outside the confidence limits for interobserver and intraobserver assessments as well as nonpathologic biologic variability and is considered a significant change. Only gold members can continue reading. Log In or Register to continue Share this:Click to share on Twitter (Opens in new window)Click to share on Facebook (Opens in new window) Related Related posts: Technical Aspects of Percutaneous Carotid Angioplasty and Stenting for Arteriosclerotic Disease In-Situ Treatment of Aortic Graft Infection with Prosthetic Grafts and Allografts Treatment of Dyslipidemia and Hypertriglyceridemia Intraoperative Assessment of the Technical Adequacy of Carotid Endarterectomy Stay updated, free articles. Join our Telegram channel Join
