Ultrasound Assessment of Endothelial-Dependent Flow-Mediated Vasodilation of the Brachial Artery in Clinical Research

The overall goal of this procedure is to measure endothelium dependent, flow mediated vasodilation in the human brachial artery. This is accomplished by first preparing the subject. The second step is to measure the cross-sectional diameter of the brachial artery with B mode ultrasound.

Next, the brachial artery is occluded for five minutes. The final step is to release the cuff and measure the mean arterial velocity from doppler spectral wave forms. Ultimately, ultrasound assessment of endothelium dependent flow mediad.

Vasodilation of the brachial artery is used to show the percent increase in intimate, intimate diameter. This method can help answer key questions in the field of cardiovascular surgery, such as the effects of an intervention or risk stratification of a study population. Generally, individuals who are new to the technique will struggle at first because of the fine motor control that's necessary to find the anatomy and to optimize the ultrasound images.

A visual demonstration of this method is critical as the imaging steps after cuff release are difficult to learn. Moving the probe from a lateral to a longitudinal position while maintaining the region of interest takes practice. To begin, set up an EKG gated image capture system to record and analyze flow mediated vasodilation.

Conduct the exam in a quiet darkened room. When conducting longitudinal studies, hold repeat exams at the same time of day. When ready to begin, confirm that participants have fasted and avoided exercise for eight hours before the exam.

In addition, make sure that they have avoided caffeine or nicotine for at least four hours and avoided medications affecting vascular tone or cardiac output. For four half lives, ask the subject to supine on an exam table. Attach a three lead EKG in a standard position.

Address any orthopedic issues to ensure the subject will be comfortable and reframe from movement during the exam. Allow the subject to rest for 10 minutes before the start of the exam. After five minutes, rest, measure the subject's blood pressure by an oscillometric non-invasive blood pressure monitor.

Next, apply a five centimeter tourniquet cuff in either a proximal or distal position. Extend the subject's arm laterally and maintain it at the level of the heart. It is important to maintain the arm holding the probe in a position that resists fatigue and provide support for the wrist.

Try to minimize extension of the wrist and keep the forearm in the anatomic neutral position. Conduct a cross-sectional scan of the brachial artery beginning at the insertion of the bicep and proceeding proximally. Use color flow imaging to verify the brachial artery and to locate collateral vessels that may serve as landmarks when a suitable position is found.

Rotate the probe 90 degrees so that the proximal edge appears on the left of the ultrasound screen. A delicate touch and practice are required to maintain the correct position on the artery. Verify the orientation by pushing the tissue near the distal edge.

Mark the subject skin along the distal edge of the probe when the correct position is found. Next, align the focus setting of the probe with the deep or far wall of the brachial artery to improve lateral resolution of the image. Adjust the probe settings to a higher frequency to increase axial resolution.

Adjust the angle of the probe to optimize contrast resolution of both the near and the far walls. Small changes to the angle can result in improved contrast. Estimate the angle with a simple protractor for repeated testing.

To ensure quality measurements, ensure that the vessel is horizontal and aligned with the longitudinal axis. Make small changes in pressure to help align the artery overall. Keep pressure light to help prevent operator fatigue.

When optimized, ensure that the double lines of pinoli can be seen in both walls. Corresponding to the intimate media thickness, use gain adjustments to reduce echo in the vessel lumen. Allow at least two centimeters of intimate media thickness on both sides.

For accurate diameter measurements, record the baseline velocity using 2D Doppler mode. Place the sample gates in the middle of the lumen and maintain an intonation angle of 60 degrees. Finally, collect 60 seconds of data When ready, inflate the cuff to 50 millimeters mercury above the subject's systolic blood pressure.

Since a five centimeter tourniquet cuff will overestimate the systolic pressure, use the 2D Doppler mode to verify occlusion. Use a timer to track the duration of occlusion. Some blood pressure cuffs will slowly lose pressure over five minutes.

Periodically use 2D Doppler mode to verify complete occlusion. After four minutes and 30 seconds of occlusion, place the 2D Doppler ga slightly superficial to the longitudinal axis of the artery. Adjust the vertical scale to account for velocities two to three times higher than baseline.

Next, adjust the settings on the image capture software for three minutes and 10 seconds of recording. Begin recording 10 seconds before cuff release to capture the time of cuff release and important parameter. When measuring time to peak diameter during data analysis at the correct time, release the cuff as the artery may shift superficially after cuff release.

Make small changes to the probes position while listening for amplification of the sound to help compensate for the shift. Reposition the doppler sample gate and insulation angle. If the artery shifts after 30 seconds of velocity recording, switch the ultrasound to B mode since it is common for the probe to slide proximally during an exam.

Use vessel landmarks or the marking on the subjects skin to verify probe position. This phase of the exam is critical for obtaining accurate results. Adjust the probe position or angle to optimize the IMT on both walls as small changes can substantially improve the image.

Record the diameter for three minutes. If repeat measurements are planned, use the marking on the subject skin to record distance from the anti cubital fossa. Ask the subject to bend their arm 90 degrees and mark the crease.

Measure from this line to the line made earlier. The doppler spectral waveform shown here was obtained at baseline. The arrows indicate the extent of one cardiac cycle, which forms the basis for calculating mean arterial velocity.

Shown here is a B mode image of the baseline vessel diameter. The arrows indicate the location where the intimate intimate distance the basis for the lumen diameter was measured. This example was obtained immediately after cuff release.

In the reactive hyperemia phase. The yellow arrow indicates the moment of cuff release Wave forms obtained in the first five seconds after cuff release are used to calculate the mean velocity flow, and shear stress during reactive hyperemia. This B mode image was obtained 60 seconds after cuff release.

During the reactive hyperemia phase, like the baseline diameter, the intimate intimate distance is used to calculate reactive hyperemia diameter Once mastered, this technique can be done in 25 minutes if performed properly. Following this procedure, additional physiologic testing such as pulse wave velocity or pulse wave analysis can be performed to further quantify arterial compliance and diss extensibility. After watching this video, you should be able to perform brachi artery flow media basal dilation.

We follow current guidelines and this can be used in the upper arm and lower arm positions. The technique can also be adapted to endothelium independent basal dilation with the use of subretinal nitroglycerin.