it takes for capillary beds to refill after they have been forcibly emptied by pressure. This standard physical examination test is done to evaluate a patient for a variety of vascular diseases,...

it takes for capillary beds to refill after they have been forcibly emptied by pressure. This standard physical examination test is done to evaluate a patient for a variety of vascular diseases, particularly arterial disease. A normal capillary refill time measures 1-3 seconds; a value greater than 3 seconds may signify some sort of pathology (but be aware that it may also just mean that the patient is cold). Measure the capillary refill time for each of your lab partner's digits in the procedure outlined below. When you have completed the activity, answer Check Your Understanding question 2 (p. 527). 1 Squeeze the end of the fingertip over the fingernail until the fingernail bed blanches (turns white). 2 Release the fingernail and count the number of seconds it takes for the fingernail bed to return to a pinkish color (note that this may occur immediately, in which case simply record it as I second). 3 Repeat for each fingertip of each hand, and record your results in Table 19.3. TABLE 19.3 Capillary Refill Times Digits: Right Hand Refill Time Digits: Left Hand Refill Time 1 (thumb) 1 (thumb) I brunt , over the lattd artery in your reck.) Venule Procedure 2 Measuring Capillery Refill Time Blood flows through arteries, which branch into successively smaller arteries until they branch into arterioles. Arterioles then feed capillary beds, Arteriole Interstitial Tissue Blood known collectively as the microcirculation, where gas, fluid cells capillaries nutrient, and waste exchange takes place (Fig. 19.3). Capillary beds are then drained by venules, which merge to form veins. Notice that capillary beds form interweav- ing networks. This creates a large surface area for the rapid exchange of substances that occurs across capillary walls. The amount of blood that flows to a tissue through capillary beds is called tissue perfusion. A tissue's perfusion is tightly regulated--if it's too low, the cells will get insufficient oxygen and nutrients and may die, and if it's too high, the high pressure in the capillaries can force excess water out of the blood and into the interstitial fluid. A simple way to assess tissue perfusion in the clinic is by measuring the capillary refill time, which is the time FIGURE 19.3 Structure of a capillary bed. Cardiovascular System - Part III: Cardiovascular Physiology - UNIT 19 – 511