Name: Assessing Endothelial Vasodilator Function with the Endo-PAT 2000 (Video) | JoVE Journal
Uploaded: 2010-10-15T18:00:00.000+00:00
Duration: 7 min 46 s
Description: Learn to assess endothelial vasodilator function using the Endo-PAT 2000 device in a clinical setting. This noninvasive method evaluates cardiovascular health through reactive hyperemia index measurements.

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5 minutes

The authors would like to thank Koby Sheffy, PhD for his insightful review of this work and William Sotka for ongoing support and technical assistance.
This work was supported in part by grants from the National Institutes of Health (K12 HL087746, RC2HL103400, 1U01HL100397), and the California Tobacco Related Disease Research Program of the University of California (18XT-0098).

I.Prepare the Patient for an Endo-PAT Study
<ol>
 <li>Prior to the study, ensure the patient has fasted for at least 4 hours, and has refrained for at least 8 hours from caffeine, tobacco, vitamins or medications that might affect vascular tone. The patient may wish to use the restroom prior to the study.</li>
 <li>The Endo-PAT study should be conducted in a quiet, dimly lit, temperature-controlled exam room to reduce fluctuations in vascular tone.</li>
 <li>Cell phones or paging devices should be silenced, and restrictive clothing that could interfere with blood flow to the arms should be removed. The patient should also remove watches, rings, or other jewelry on the hands or fingers.</li>
 <li>Inspect the patient's fingers for any deformities or injuries that could affect the study. Do not place the probes on a finger that is cut or injured. Fingernails should not extend more than 5mm or 1/5 of an inch beyond the tip of the finger tissue. Trim or file fingernails if necessary to avoid damaging the internal membranes of the PAT probes and displacing the finger from the sensing region of the probe.</li>
 <li>The index finger is recommended for the study; however, if this finger is unsuitable, a different digit (except the thumb) may be used, as long as the same finger is used on both hands.</li>
 <li>The patient should be supine and comfortable for 15 minutes so as to attain a cardiovascular steady-state. Place the two arm supporters along each of the patient's sides.</li>
 <li>Measure the blood pressure using the control arm (the arm that is not occluded during the Endo-PAT study.</li>
 <li>Place a blood pressure cuff on the arm to be occluded during the Endo-PAT study. Apply the cuff snugly, but without excess pressure. Do not inflate the cuff at this time.</li>
</ol>
II.Prepare the Endo-PAT System for Study
<ol>
 <li>Launch the Endo-PAT 2000 software and click the "Patient Information" icon on the tool bar to create a new patient file.</li>
 <li>Complete the Patient Information dialog box, including patient ID, name (optional), age, gender, height, weight, systolic and diastolic blood pressures. Optional fields allow for free text comments. Select your name from the pre-defined list in the Patographer name field. If your name has not been inserted add it the list and select.</li>
 <li>Select two new PAT probes and connect to the pneumo-electrical tubing. To connect the probes, insert the connector tab into the probe slit and gently press the connector onto the probe until it clicks into place.</li>
 <li>Place the connected probes into the sockets of the arm-supports and press the "Deflate" button on the top of the Endo-PAT 2000 device.</li>
</ol>
III.Conduct an Endo-PAT Study
<ol>
 <li>Place the patient’s index fingers completely into the probes, confirm with the patient that he or she can feel the very end of the probes, and press the "Inflate" button on the top of the Endo-PAT 2000 device.</li>
 <li>Place a foam anchor ring at the base of the adjacent middle finger. Ensure that the foam ring and the PAT sensor do not touch. Otherwise the ring may mechanically interfere with the sensor.</li>
 <li>Create an approximately 7-10cm loop with the pneumo-electrical tubing. The loop should extend from the PAT sensor and return to the foam ring on the adjacent finger while the rest of the tubing that connects to the EndoPAT device is pointing out tubing to the tip of the finger. </li>
 <li>Position the patient's arms so the forearms are supported on the arm supports and the fingers dangle freely off the edge of the support. Make sure the probes are not in contact with any object, including the arm support, foam ring, tubing, the mattress or another finger.</li>
 <li>Ask the patient to refrain from moving the fingers, as this will create mechanical artifacts. It is important for the patient to be relaxed throughout the study. Explain to the patient that during the test you will inflate the arm cuff, and during that time they may feel some discomfort, numbness, or tingling.</li>
 <li>Click the "Standby" icon on the Endo-PAT's computer interface. Adjust the time base to 1 minute and adjust the signal gain on the screen to maximize signal clarity. Inspect the tracings of the PAT signals from the two probes to confirm that they are free of artifactual signals. If artifactual signals are present, veriify that the probes are not touching anything and that the patient is not moving the fingers.</li>
 <li>To begin the study, click the "Go" icon on the computer interface. 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 the "Start/Stop Timer" icon.</li>
 <li>Tell the patient that you are going to inflate the cuff for the occlusion phase and that he or she should stay relaxed and not move the fingers.</li>
 <li>Rapidly inflate the blood pressure cuff to a supra-systolic pressure of 60mmHg above the patient's systolic pressure or 200mmHg, whichever is higher and start the stopwatch again. Complete cessation of blood flow to the hand is verified by the absence of a PAT signal from the occluded arm. To confirm occlusion increase the gain on the screen of the channel of the occluded side to 20,000 while keeping the gain of the contra-lateral side constant. Decrease the time base of both channels to 30 seconds. Verify that you do not observe any signals at a periodicity that matches the signal from the control arm as this indicates an incomplete occlusion. If this is the case then further inflate the cuff until no signals are seen. The cuff may be inflated to a maximum of 300mmHg.</li>
 <li>This will initiate a five minute count down for the arterial occlusion recording period. Toward the end of the occlusion period tell the patient you are going to release the cuff and that they should continue to refrain from moving their fingers. After exactly five minutes, deflate the cuff abruptly as quickly as possible and stop the stopwatch by clicking the "Start/Stop Timer" icon.</li>
 <li>Click 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 Stop" icon to complete the study. The probes will automatically deflate.</li>
 <li>Remove the probes, tape, and foam rings from the patient's fingers and disconnect the PAT probes from the pneumo-electrical tubing. Discard the used probes.</li>
</ol>
IV.Review and Analysis
<ol>
 <li>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 highlighted 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.</li>
 <li>To 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.</li>
</ol>
V.Representative Results
A representative Endo-PAT screen of a study performed on an individual with normal endothelial vasodilator function is shown in Figure 1. A representative screen of an Endo-PAT study performed on an individual with endothelial vasodilator dysfunction is shown in Figure 2.
<img src="/files/ftp_upload/2167/2167fig1.jpg" alt="Brachial artery blood flow study; waveform graph showing control vs. experimental arm during cuff test." data-altupdatedat="1761735611000" data-alt="Figure 1"> 
 Figure 1: Normal Endothelial Vasodilator Function. Representative recording of an individual with normal endothelial vasodilator function, characterized by an increase in the signal amplitude after cuff release relative to baseline.
<img src="/files/ftp_upload/2167/2167fig2.jpg" alt="Cuff occlusion and release blood flow measurement graph; control vs. experimental arm comparison." data-altupdatedat="1761735611000" data-alt="Figure 2"> 
 Figure 2: Endothelial Vasodilator Dysfunction. Representative recording of an individual with endothelial vasodilator dysfunction.

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<li>Yamaoka-Tojo, M., Tojo, T., Kosugi, R., Hatakeyama, Y., Yoshida, Y., Machida, Y., Aoyama, N., Masuda, T., Izumi, T. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Effects+of+ezetimibe+add-on+therapy+for+high-risk+patients+with+dyslipidemia%5BTitle%5D)+AND+%22Lipids+Health+Dis%22%5BJournal%5D)">Effects of ezetimibe add-on therapy for high-risk patients with dyslipidemia.</a> Lipids Health Dis. 8 (1), 41-41 (2009).</li>
</ol>

The video development was supported by Itamar Medical Co. Dr Cooke is the inventor of patents owned by Stanford University for diagnostic and therapeutic applications of the NOS pathway from which he receives royalties.

The major cause of morbidity and mortality worldwide is atherosclerotic vascular disease, leading to stroke, myocardial infarction, heart failure, renal insufficiency, aneurysm rupture or embolism, intermittent claudication and gangrene 1,2. Endothelial dysfunction is one of the earliest events in the pathophysiological process leading to these atherosclerotic disorders 3. Furthermore endothelial dysfunction contributes to the progression of disease, by facilitating inflammation and thrombosis. 4-6. The traditional cardiovascular risk factors are associated with endothelial vasodilator dysfunction 7-11. Endothelial vasodilator dysfunction can be detected in seemingly healthy individuals that are at risk for developing cardiovascular disease 12. Furthermore, the finding of endothelial vasodilator dysfunction is predictive of major adverse cardiovascular events as well as mortality 13-16. The vasodilators released by the endothelium include vasodilator prostanoids such as prostacyclin, peptides such as adrenomedullin and atrial natriuretic peptide, and small molecules such as endothelium dependent hyperpolarizing factor, carbon monoxide and nitric oxide 17. In addition, the effect of hyperpolarizing currents generated in the endothelium can be transmitted to underlying vascular smooth muscle of smaller vessels, relaxing them 18. An indirect assessment of the generation of these endothelial vasodilator influences can be gained by studying vascular reactivity. The most prevalent method to assess endothelial regulation of vascular reactivity non-invasively has been duplex ultrasonography to detect flow-mediated vasodilation of the brachial artery 19. The tractive force of fluid flow stimulates the endothelium to release vasodilators, most prominently nitric oxide 20. This phenomenon can be observed by ultrasound in the brachial artery during increases in forearm blood flow induced by reactive hyperemia 19. This technology has been widely utilized to document the association of endothelial vasodilator dysfunction with cardiovascular risk factors; the relationship of endothelial vasodilator dysfunction to various biomarkers, such as C-reactive peptide, or asymmetric dimethylarginine (the endogenous antagonist of nitric oxide synthase); and the correction of endothelial vasodilator function with nutritional and lifestyle modifications as well as with the use of angiotensin converting enzyme inhibitors, angiotensin receptor blockers, statins, insulin sensitizing agents or aspirin 21-23. The assessment of flow-mediated vasodilation by brachial artery ultrasound requires expensive equipment, is highly operator-dependent, the response has a very small dynamic range and the signal-to-noise ratio is low. New approaches to address these problems with assessment of endothelial vasodilator function are needed 24. The Endo-PAT 2000 is a new approach to assess endothelial vasodilator function in a rapid non-invasive manner. The technique provides values for the calculation of a Reactive Hyperemia Index (RHI), which gives an indication of the endothelial vasodilator function. The RHI is the post-to-pre occlusion PAT signal ratio in the occluded arm, relative to the same ratio in the control arm, and corrected for baseline vascular tone. Studies using the EndoPAT have shown that the RHI score reflects NO-bioavailability 25. The RHI correlates with the measurement of endothelial vasodilator function in the coronary arteries 26 and with brachial FMD 27. Patients with a greater degree of cardiovascular disease exhibit a lower score 28 and values are also lower in other conditions associated with impaired endothelial function and risk of cardiovascular disease 29-33. Notably, RHI values appear to be predictive of cardiovascular outcomes 35. A low RHI (indicating endothelial dysfunction) can be reversed with treatment 36. In conclusion, we have demonstrated how to perform a reliable and reproducible test for endothelial vasodilator function with the Endo-PAT 2000. The test is noninvasive, easy to perform, and is a useful research tool. Its utility in clinical monitoring of endothelial function and in tailoring disease management is under investigation.

assessing endothelial vasodilator function with the endo-pat 2000

Assessing Endothelial Vasodilator Function with the Endo-PAT 2000

The endothelium is a delicate monolayer of cells that lines all blood vessels, and which comprises the systemic and lymphatic capillaries. By virtue of the panoply of paracrine factors that it secretes, the endothelium regulates the contractile and proliferative state of the underlying vascular smooth muscle, as well as the interaction of the vessel wall with circulating blood elements. Because of its central role in mediating vessel tone and growth, its position as gateway to circulating immune cells, and its local regulation of hemostasis and coagulation, the the properly functioning endothelium is the key to cardiovascular health. Conversely, the earliest disorder in most vascular diseases is endothelial dysfunction.
In the arterial circulation, the healthy endothelium generally exerts a vasodilator influence on the vascular smooth muscle. There are a number of methods to assess endothelial vasodilator function. The Endo-PAT 2000 is a new device that is used to assess endothelial vasodilator function in a rapid and non-invasive fashion. Unlike the commonly used technique of duplex ultra-sonography to assess flow-mediated vasodilation, it is totally non-operator-dependent, and the equipment is an order of magnitude less expensive. The device records endothelium-mediated changes in the digital pulse waveform known as the PAT ( peripheral Arterial Tone) signal, measured with a pair of novel modified plethysmographic probes situated on the finger index of each hand. Endothelium-mediated changes in the PAT signal are elicited by creating a downstream hyperemic response. Hyperemia is induced by occluding blood flow through the brachial artery for 5 minutes using an inflatable cuff on one hand. The response to reactive hyperemia is calculated automatically by the system. A PAT ratio is created using the post and pre occlusion values. These values are normalized to measurements from the contra-lateral arm, which serves as control for non-endothelial dependent systemic effects. Most notably, this normalization controls for fluctuations in sympathetic nerve outflow that may induce changes in peripheral arterial tone that are superimposed on the hyperemic response.
In this video we demonstrate how to use the Endo-PAT 2000 to perform a clinically relevant assessment of endothelial vasodilator function.

A noninvasive procedure to assess endothelial function is demonstrated using the Endo-PAT 2000.

The endothelium is a delicate monolayer of cells that lines all blood vessels, and which comprises the systemic and lymphatic capillaries. By virtue of ...

Endothelial Vasodilator function is an independent predictor of cardiovascular morbidity and mortality. The endo pat methodology is a simple way to assess the effects of drugs and nutrition on endothelial function. Today we're gonna show you how to use the end methodology in an office-based setting.Prior to beginning the study, the patient needs to fast for at least four hours and also abstain from caffeine, tobacco, vitamins, or any medications that may affect vascular tone. During the study for at least eight hours, the patient should wear loose fitting clothes and be free of jewelry on the upper extremities. With respect to location, the study should be conducted in a quiet, dimly lit temperature controlled exam room.Apply a blood pressure cuff to the arm and allow the arm to be supported at the patient's side to allow the patient to reach cardiovascular steady state. They should be relaxed and comfortable in the supine position for at least 15 minutes. Measure the blood pressure in the arm that is not occluded.During the endo pat study, move the cuff to the non-dominant arm, which will be occluded. It is important to know the blood pressure so that the cuff on the other arm can be inflated to a super systolic pressure during the arterial occlusion phase of the study. To 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, complete the patient information dialogue box by including the patient ID age, gender height, weight, and blood pressure. Entering the patient's name is optional if needed, there is an area to text comments. Next, select two new PAT probes and connect them to the Pneumo electrical tubing by inserting the connector tab into the probe until it clicks.Finally, 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, ensuring that it is free from cuts and injury. Select a finger, preferably the index finger for placement of the endo pad probe.Make sure the fingernail is appropriately trimmed prior to beginning the experiment. Ensure that the study finger is put all the way into 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 five seconds, push the inflate button on the top of the endo Pat 2000 device. Next, 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.Create a seven to 10 centimeter 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.Position 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 any other finger. The pressure cuff will be inflated for five minutes during which time you might experience a slight numbness of the hand.You can relax and please don't move your fingers. Thank you. Click the standby icon on the Endo Pats computer screen and adjust the time base to one minute.Next, adjust the signal gain on the screen to maximize signal clarity and inspect the Pats 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.To begin the trial, click the go icon on the endo Pats computer screen. Start the stopwatch by clicking the start stop timer icon. This will initiate a five minute countdown for the baseline recording period.After five minutes, stop the stopwatch by clicking the same timer icon. We are going to inflate the cuff for the ocion phase, please. You should stay relaxed and please don't move your fingers.Okay, thank you. Restart the stopwatch. Then quickly inflate the cuff pressure to 60 millimeters of mercury above the patient's systolic pressure or 200 millimeters of mercury, whichever is higher.Next, change the time base on the screen to 30 seconds and the gain of the occluded side to 10, 000 and verify that the blood flow to the hand has stopped in this arm by checking for an absence of a pat signal, confirm 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 periodo 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 300 millimeters of mercury using the stopwatch function of the software.Initiate a five minute countdown 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.Click 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 stop icon to complete the study. At the end of the study, remove the probes tape and rings from the patient's fingers.Disconnect the path probes from the Pneumo electrical tubing and discard these probes. To 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 and heart rate in the right hand column of the screen.If the boundaries of the occlusion are not marked properly, simply move the boundaries by dragging them and rerun the automatic analysis. Again, to 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 spreadsheet 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 here is 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. This recording is characteristic of an individual with endothelial vasodilator dysfunction. Specifically, the increase in the pulse amplitude with reactive hyperemia is less than normal.The endo pat is a rapid and operator independent approach to assessing the effects of cardiovascular risk factors on endothelial vasodilator function, and the beneficial effects of drug therapy. After watching this video, you should have a good understanding of how to use the endo methodology to assess endothelial vasodilator function.

assessing-endothelial-vasodilator-function-with-the-endo-pat-2000

Research

JoVE Journal

Medicine

Capillaroscopy is a non-invasive, relatively inexpensive methodology for directly visualizing the microcirculation. The forearm blood flow technique provides accepted non-invasive measures of endothelial function.

Non-invasive Assessment of Microvascular and Endothelial Function

Endothelial dysfunction is associated with numerous disease states and is predictive of adverse cardiovascular events in humans. Flow-mediated vasodilation (FMD) is a non-invasive ultrasound method of evaluating endothelial function. Methodological choices and operator experience may affect results. A systematic approach to FMD in human studies is discussed here.

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

The present article describes the methodological considerations for several non-invasive assessments of vascular function and morphology that are commonly used in medical research to assess different stages of atherosclerosis.

A Methodological Approach to Non-invasive Assessments of Vascular Function and Morphology

The flow mediated dilation (FMD) test is the most commonly utilized, non-invasive, ultrasound assessment of endothelial function in humans. Although the FMD test has been related with the prediction of future cardiovascular disease and events, it is a physiological assessment with many inherent confounding factors that need to be considered.

Ultrasound Assessment of Endothelial Function: A Technical Guideline of the Flow-mediated Dilation Test

Primary human umbilical vein endothelial cells (HUVECs) were grown to confluence within a microfluidic network device. The endothelial cell junction and F-actin distributions were illustrated and the changes in intracellular calcium concentration and nitric oxide production in response to adenosine triphosphate (ATP) were quantified in real-time at individual cell levels.

Development and Characterization of In Vitro Microvessel Network and Quantitative Measurements of Endothelial [Ca2+]i and Nitric Oxide Production

Non-invasive assessment of endothelial function in humans can be determined by the flow-mediated dilation technique. Although thousands of studies have used this technique, no study has performed this technique non-invasively in rats. The following article describes non-invasive measurement of flow-mediated dilation in the brachial and superficial femoral arteries of rats.

Ultrasound Assessment of Flow-Mediated Dilation of the Brachial and Superficial Femoral Arteries in Rats

Videomicroscopy systems are used to examine functional properties of isolated adipose tissue arterioles in response to physiological and pharmacological stimuli. This technique can be used to examine microvascular phenotypes in different adipose tissue domains in obese humans.

Assessment of Human Adipose Tissue Microvascular Function Using Videomicroscopy

This manuscript describes in vitro video microscopy protocols for evaluating vascular function in rat cerebral resistance arteries. The manuscript also describes techniques for evaluating microvessel density with fluorescently labeled lectin and tissue perfusion using Laser Doppler Flowmetry.

Evaluation of Vascular Control Mechanisms Utilizing Video Microscopy of Isolated Resistance Arteries of Rats

The present protocol describes the concepts and technical application of the tensometric myograph technique using a multi-chamber myograph system in the experimental ex vivo assessment of mouse aortic endothelial function.

Measurement of Endothelium-Dependent Vasorelaxation in the Mouse Thoracic Aorta Using Tensometric Small Volume Chamber Myography

Intradermal microdialysis is a minimally invasive technique used to investigate microvascular function in health and disease. Both dose-response and local heating protocols can be utilized for this technique to explore mechanisms of vasodilation and vasoconstriction in the cutaneous circulation.

Intradermal Microdialysis: An Approach to Investigating Novel Mechanisms of Microvascular Dysfunction in Humans

Learn to assess endothelial vasodilator function using the Endo-PAT 2000 device in a clinical setting. This noninvasive method evaluates cardiovascular health through reactive hyperemia index measurements.

Assessing Endothelial Vasodilator Function with the Endo-PAT 2000

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