![]() ![]() ![]() The ulnar and radial arteries are then compressed by the examiner's thumbs simultaneously. Traditionally, it is performed by first having the patient's arm flexed at the elbow with the fist clenched tightly to exsanguinate the hand. The modified Allen test differs from the original Allen test mainly by examining the radial and/or ulnar arteries in one hand and then repeating on the other side, if necessary. Persistent pallor in the palm indicates inadequate collateral blood flow to the hand. The time that it takes for the normal color to return should indicate the degree of collateral blood flow. The test is positive when there is a return of normal color to both hands during occlusion of either artery alone. The test is then repeated while occluding the ulnar arteries rather than the radial arteries. The initial pallor should be replaced with the hands' normal color as the ulnar arteries restore perfusion. The patient then opens both hands rapidly, and the examiner compares the color of the palms. Next, the patient squeezes their hands into tight fists, and the examiner occludes the radial artery simultaneously on both hands. The original Allen test is performed by asking the patient to elevate both arms above the head for thirty seconds in order to exsanguinate the hands. The deep arch of the hand is more commonly anatomically complete thus, the radial artery is more likely to provide the dominant blood supply, although the ulnar artery is sufficient to perfuse the hand in 97% of cases. The superficial arch is predominantly supplied by the ulnar artery. The deep palmar arch is classically described as arising from the radial artery, with or without contributions from the ulnar artery. These arches form the basis of collateral blood flow to the hands. The ulnar artery runs along the medial aspect of the forearm and at the wrist runs through Guyon's canal, where it splits into its deep and superficial palmar branches. Just distal to the wrist, it splits into superficial and deep palmar branches. The radial artery runs along the lateral aspect of the forearm between the brachioradialis and flexor carpi radialis muscles. The radial and ulnar arteries supply blood flow to the forearm and eventually to the hand. From there, the axillary arteries become the brachial arteries after passing the teres major muscles they then supply blood to the upper arm, continuing distally to the antecubital fossa, where they divide into the radial and ulnar arteries. The subclavian arteries then run beneath the clavicle and become the axillary arteries as they pass the lateral margins of the first ribs. Blood supply to the arms is carried by the left and right subclavian arteries, which arise from the arch of the aorta - the left directly and the right via the brachiocephalic, or innominate, artery.
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