The vascular lab uses non-invasive techniques to assess markers of endothelial and vascular health.
We routinely perform assessments of both physiological and structural markers of vascular health for our own research projects and as a service for other investigators at Duke and externally. Some of these procedures as well as data from our research are detailed below.
Some of the procedures we employ include:
Physiological markers of vascular disease are dynamic measures that can be influenced by stress or medications. Consequently they are usually measured in the mornings following an overnight fast and other preparations.
- Brachial artery flow-mediated dilation
- Pulse wave velocity (PWV) and pulse wave reflection (PWR) analysis of vascular stiffness
- Plethysmographic limb blood flow
- Carotid intimal-medial thickness (CIMT)
- Doppler ankle-brachial index (ABI)
Brachial Artery Flow-Mediated Dilation
Brachial artery flow-mediated dilation (BAFMD) is a dynamic assessment of endothelial function, measured in response to forearm reactive hyperemia. It has been associated with nitric oxide bioavailability and shown to be prognostic in coronary artery disease and peripheral arterial disease. The response of the brachial artery has been shown to be similar to that of the coronary arteries but is much easier to measure and so is often used as a surrogate measure.
Above is a typical image of the brachial artery with specialized software tracking the vessel wall over time. We have also set image acquisition to only capture diastole images.
The figures below (left) show the diameter responses over time of healthy subjects versus subjects with CVD to the hyperemic stimulus. Notice the healthy subjects dilate over 5 percent, whereas the CVD group peak at 2 percent. This is reflected (right) in the bar graph of responses from different disease states.
(H = healthy, RF = CVD risk factor subjects, DM = type 2 diabetics, PAD = peripheral arterial disease)
Cardiovascular disease (CVD) risk factors associated with abnormal BAFMD (and reduced NO bioavailability) include:
- Cigarette smoking
- Oxidative stress
- Sedentary lifestyle
Pulse wave velocity (PWV) and reflection (PWR) analysis of vascular stiffness
Pulse Wave Reflection
The blood pressure waveform is the sum of the pressure wave generated by the left ventricle and the pressure waves reflected from terminations and bifurcations in vascular beds.
Stiffer arteries (the aorta and muscular arteries) increase the speed of the traveling pressure waves, leading to earlier return to the heart of the reflected waves.
Vasodilation and vasoconstriction of the muscular arteries changes both the size and speed of the reflected waves.
An earlier return of the reflected pressure wave changes the pressure waveform by increasing the central systolic and pulse pressures. In the aorta, the reflected wave moves also more into systole.
These changes may have important clinical implications, including:
Central pulse pressure increases, increasing risk of stroke and renal failure (increasing arrows)
Left ventricle (LV) load increases, increasing LV mass, and accelerating progress towards LV hypertrophy and heart failure (increasing arrows)
Coronary artery perfusion pressure in diastole decreases, increasing risk of myocardial ischemia (decreasing arrows)
Pulse Wave Velocity
Pulse wave velocity is a direct measure of arterial stiffness and has been shown in large populations to predict coronary artery disease and stroke. Pulse waves are waves that push against the artery walls with every heartbeat as blood moves through arteries to supply body tissues. Pulse wave velocity is the speed with which one wave or pulse travels from the heart through the arteries of the body.
Typically, the faster the pulse wave travels, the stiffer the arteries, and vice-versa. For example, a pulse wave velocity of around six metres per second (m/s) is considered highly compliant (a healthy arterial system), whereas velocities in excess of 14 m/s indicate stiffer arteries (a less healthy arterial system).
Plethysmographic Limb Blood Flow (Arterial and Venous Function)
We use strain gauge plethysmography to look at whole limb arterial inflow, venous capacitance, and maximum venous outflow. This test detects possible blockages in arteries, endothelial dysfunction, and deep venous thrombosis in the legs.
Structural Markers of Vascular Disease
Carotid intimal-medial thickness
Carotid intimal-medial thickness (CIMT) levels have been shown to predict cardiovascular events such as heart attack and stroke.
We take multiple measures of the IMT in multiple sections of the carotid arteries at several different angles of interrogation. Using specialized software to measure the artery lining and data from the Atherosclerosis Risk in Communities trial (ARIC), we can estimate the rank score of individuals’ CIMT compared with data from people with of the same age, race and gender.
CIMT Prediction Trials
Atherosclerosis Risk in Communities (ARIC) study
- 7289 females, 5552 males, 45-70 years, no history of coronary artery disese, followed four to seven years
- Hazard ratio for myocardial infarction of coronary heart disease high versus low tertiles were 6.69 for females and 2.88 for males
Cardiovascular Health Study
- 5858 subjects, older than 65 years, no apparent coronary heart disease, followed for 6.2 years
- Highest quintile = 3.87RR of myocardial infarction or stroke versus lowest
- Strong predictor even after adjustment for risk factors
Doppler Ankle-Brachial Index (ABI)
This test is used to diagnose peripheral artery disease. It compares blood pressures in the feet with those in the arms to find out if there is a reduction in perfusion in the lower limbs. A normal ABI is 1.0 or greater (with a range of 0.90 to 1.30).
Katherine L Ham, MS
Mitch VanBruggen, MA
Office: The Andrew Wallace Clinic Building
3475 Erwin Road, Durham, NC, 27710