Non-invasive Assessment of Microvascular and Endothelial Function

The overall goal of these procedures is to non-invasively, visualize the microcirculation using capillary and assess endothelial function with plethysmography using capillary. This is accomplished by first inducing postocclusive reactive hyperemia on the subject's arm. Next images are taken to identify all functionally perfused capillaries.

Then using plethysmography, a strain gauge is wrapped around the subject's forearm and plethysmography measurements of forearm blood flow are recorded. Ultimately, results can be obtained non-invasively that show capillary density through direct visualization by capillary and endothelial function through post react hyperemia strain gauge plethysmography. The main advantage of this technique over existing methods like video cap and invasive plethysmography, is that it is less expensive and non-invasive.

Assisting me in demonstrating the procedure will be nausea. Fache, my research coordinator from my laboratory Nail fold capillaries in the dorsal skin of the third finger are visualized using a stereo microscope that uses 250 watt halogen fiber optic lamp illumination, a 3.2 x objective and is linked to a four megapixel spot. Insight monochrome digital camera and a laptop computer with a spot imaging software to carry out the capillary technique following a minimum 10 hour overnight fast, and 20 minutes of seated rest seat the subject in a temperature controlled room and have them raise their left hand to heart level to limit movement.

Have the patient rest their left hand and forearm on a folded blanket at the base of the microscope, and use a second covered blanket to loosely cover the forearm and hand to detect the capillaries perfused at rest. Take a series of baseline photo micrographs over a period of three minutes. Capillary density is defined as the number of capillaries per square millimeter of nail fold skin and is computed as the mean of poor measurements obtained from the four most clearly focused images least distorted by movement.

To quantify functionally perfused capillaries, induce postocclusive reactive hyperemia by inflating an occlusion cuff on the upper left arm to 40 millimeters, mercury above systolic pressure for 10 minutes. Release arterial occlusion and immediately begin taking images for one minute to identify all functionally perfused capillaries. Following 10 minutes of rest to quantify maximum capillary density induce venous occlusion by inflating the arm cuff to 60 millimeters of mercury for 60 seconds.

After releasing the cuff, immediately begin taking images as before. Endothelial function is assessed before and after postocclusive reactive hyperemia using non-invasive plethysmography measurements of forearm blood flow according to the method of sivertson. Using an automatic blood pressure cuff placed on the opposite arm measures systolic and diastolic blood pressures and heart rate.

Next place an upper arm occlusion cuff on the subject's arm and use a sling bandage connected to an adjustable intravenous pole to comfortably suspend the arm at heart level Following 10 minutes of supine rest, have the subject in a seated position loop a mercury and rubber strain gauge, stretched to 10%beyond its resting length around the subject's forearm, five centimeters below the antecubital fossa. Connect the strain gauge to a plasm graft that's connected to a doppler recorder to occlude blood flow to the hand. Place a pediatric cuff around the subject's wrist and inflate to 200 millimeters of mercury.

Then inflate the upper arm cuff on the opposite arm to 50 millimeters of mercury. Deflate it for one and a half seconds, and then rapidly reinflate and then deflate it to induce postocclusive hyperemia induced maximal vasodilation or FBF max. Immediately use the strain gauge to take four consecutive measurements in 30 seconds of forearm blood flow.

To compute the ratio FBF max over FBF base as an estimate of vasodilation. Divide the mean of the four fbf max values by the mean of the four FB F base values. Calculate forearm vascular resistance at maximal vasodilation or FVR max as the mean arterial pressure or map divided by FBF max.

A comparison of the appearance of the microvasculature between normotensive and hypertensive individuals is shown here. The left panel shows the typical network of straight capillaries in well-organized rows in a normal oten individual. In contrast, the right panel reveals a more disarranged pattern of shrunken coiled capillaries.

Lower capillary density following reactive hyperemia indicates impaired functional capillary recruitment and therefore functional rarefaction. After watching this video, you should have a good understanding of how to visualize the microcirculation and assess endothelial function non-invasively.