Assessing Endothelial Vasodilator Function with the Endo-PAT 2000

Introduction

The overall goal of the following experiment is to assess the ability of the endothelium to induce relaxation of the vessel wall by assessing the change in digital pulse volume amplitude after reactive hyperemia. The digital pulse volume signal is measured by the EndoPat device and reflects Peripheral Arterial Tone (PAT). The endoPAt probe is placed on the patient’s finger to record PAT signals. In the same arm the blood pressure cuff is inflated to suprasystolic pressure for 5 minutes then rapidly deflated which induces reactive hyperemia reflecting increased blood flow to the hand. The pulse wave amplitude is recorded before and after the period of reactive hyperemia. These values are compared and a Reactive Hyperemia Index(the RHI) is calculated. The increase in RHI indirectly reflects the ability of the endothelium to induce a flow-mediated vasodilation.

Protocol

1. Patient Preparation

• 1.1Prior to beginning the study, the patient needs to fast for at least 4 hours, and also abstain from caffeine, tobacco, vitamins or any medications that might affect vascular tone during the study for at least 8 hours. The patient should wear loose-fitting clothes and be free of jewelry on the upper extremities.
• 1.2With respect to location, the study should be conducted in a quiet, dimly lit, temperature-controlled exam room.
• 1.3Apply a blood pressure cuff to each arm and allow the arm to be supported at the patient’s side.
• 1.4To allow the patient to reach cardiovascular steady state, they should be relaxed and comfortable in the supine position for at least 15 minutes.
• 1.5Measure the blood pressure in the arm that is not occluded during the Endo-PAT study. It is important to know the blood pressure so that the cuff on the other arm can be inflated to a suprasystolic pressure during the arterial occlusion phase of the study.

Preparing the Endo-PAT System

• 1.6To prepare the Endo-PAT system for acquiring data, Open the Endo-PAT 2000 software and click on the icon labeled patient information in order to create a new patient file.
• 1.7Complete the patient information dialog box by including the patient ID, age, gender, height, weight, and blood pressure. Entering the patients name is optional. If needed, there is an area to text comments.
• 1.8Next, select 2 new PAT probes and connect them to the pneumo-electrical tubing by inserting the connector tab into the probe until it clicks.
• 1.9Finally, insert the probes into the sockets of the arm-supports and press the deflate button on the top of the Endo-PAT 2000 device. The system is now ready for experimentation.

Conducting the Endo-PAT Study

• 1.10Ensuring that it is free from cuts and injury, select a finger, preferably the index finger, which should be free of cuts and injury, for to placement of the Endo-PAT probe. Make sure that the fingernail is appropriately trimmed.
• 1.11Prior to beginning the experiment, ensure that the study finger into the probe it is all the way to the back of the probe. The patient should indicate that they can feel the back of the probe with the tip of their finger. After about 5 seconds, push the “Inflate” button on the top of the Endo-PAT 2000 device.
• 1.12Next attach a foam anchor ring at the base of the middle finger to its very end and make sure that the foam ring and the PAT probe do not touch. Otherwise, the ring may mechanically interfere with the probe.
• 1.13Create a 7–10cm loop with the pneumo-electrical tubing. This loop should extend from the PAT probe and return to the foam ring on the adjacent finger and the rest of the tubing pointing out from the middle finger. Then, anchor the tubing to the foam ring with the attached clip and gently tape the tubing to the tip of the finger.
• 1.14Position the patient’s arms so that the forearms are supported on the arm supports and the fingers can dangle freely. Make sure the probes are not in contact with any objects, including the arm support, foam ring, tubing, the mattress or another finger.
• 1.15Click the standby icon on the Endo-PAT’s computer screen and adjust the time base to 1 minute. Next, adjust the signal gain on the screen to maximize signal clarity and inspect the PAT signals from the two probes. Confirm that there are no signal artifacts. If any artifact is present, verify that the probes are not touching anything and that the patient is not moving their fingers.
• 1.16To begin the trial, click the “Go” icon on the Endo-Pat’s computer screen. Start the stopwatch, by clicking the “Start/Stop Timer” icon. This will initiate a five-minute count down for the baseline-recording period. After five minutes, stop the stopwatch by clicking same timer icon as you did in starting this timer.
• 1.17Talent to patient Synced Audio: Talent tells the patient that they are going to inflate the cuff for the occlusion phase and that they should stay relaxed. Reminds them not to move the fingers.
• 1.18After 5 minutes of baseline recording, quickly inflate the cuff pressure to 60mmHg above the patient’s systolic pressure or 200mmHg, whichever is higher. Next, change time base on the screen of 30sec and the gain of the occluded side to 10,000 and verify that blood flow to the hand has stopped in this arm by checking for an absence of a PAT signal.
• 1.19Confirm the occlusion by increasing the gain at the occluded side to 500. The gain from the other arm should not need to be changed. This modification checks for signals at a periodicity that matches the signal from the control arm - a pattern indicative of incomplete occlusion. If this is the case, then inflate the cuff further until no signals can be seen or up to a maximum cuff inflation of 300mmHg.
• 1.20Using the stopwatch function of the software, initiate a five-minute count down for the arterial occlusion-recording period. Toward the end of five minutes, remind the patient that they should not move their fingers and the cuff will release shortly. After exactly five minutes, deflate the cuff as quickly as possible and click the timer icon to stop the timer.
• 1.21Click the Start/Stop Timer icon again to initiate a five-minute post occlusion recording period. Stop the timer after five minutes and click the Test Sto icon to complete the study.
• 1.22At the end of the study, remove the probes, tape, and foam rings from the patient’s fingers. Disconnect the PAT probes from the pneumo-electrical tubing and discard these probes.
• 1.23To review the data, load the study file to the screen using the load icon. To run the automatic analysis, click the “magician stick” icon. The occlusion period will be marked in blue and the test result will be displayed, including the Reactive Hyperemia Index (RHI) and Heart Rate (HR), in the right hand column of the screen.
• 1.24To review additional data, including study parameters, calculated variables, patient information, and measures of signal quality, click the “Open Results of Last Calculation” icon. This will open a spread sheet with study parameters and results for all analyses performed to date, with the last line in the table containing data from the most recent analysis.

Assessment of Endothelial Vasodilator Function

• 4.1Figure 1 shows a representative recording of an individual with normal endothelial vasodilator function, which is characterized by an increase in the signal amplitude after cuff release relative to baseline.
• 4.2Figure 2 shows a recording that is characteristic of an individual with endothelial vasodilator dysfunction. Specifically, the increase in the pulse amplitude with reactive hyperemia is less than normal.

Figure 1.

Figure 2.

Conclusion

Once mastered, this technique can be correctly performed in 30 minutes. While performing this procedure, it’s important to remember to have the subject relaxed, with their fingers motionless during the recording.

The EndoPAT is a rapid and operator-independent technique to assess the effects of cardiovascular risk factors on endothelial vasodilator function and to determine the effects of drug therapy and lifestyle changes.

After watching this video, you should have a good understanding of how to assess endothelial vasodilator function using the EndoPAT.

Key Points.

• 0.1The main advantage of this technique over existing methods, such as duplex ultrasound to assess flow-mediated vasodilation, is that this technology is less operator dependent, can be more rapidly performed and requires less expensive technology.
• 0.2EndoPAT methodology can be used to determine how nutrition, environment, genetics, lifestyle, and drugs effect endothelial function.
• 0.3This technique may provide useful information in a diverse array of vascular diseases, where endothelial dysfunction may be the first observable manifestation of disease.
• 0.4These vascular disorders include atherosclerosis, metabolic disorders, vasculitides and renal disease.
• 0.5Numerous studies have shown that endothelial vasodilator dysfunction is an independent marker of increased risk for cardiovascular morbidity and mortality. Evidence of endothelial dysfunction may provide a rationale for intensification of medical therapy.
• 0.6Generally, individuals new to this method will be able to quickly incorporate the technology into their clinical or research work, as the EndoPAT is user friendly and not operator dependent.