In 1929, Edgar V. Allen described a noninvasive evaluation of the patency of the arterial supply to the hand of patients with thromboangitis obliterans (Am J Med Sci 1929;178:237). In the early 1950s, Allen's test was modified (Wright I. Vascular diseases in clinical practice. Chicago: Year Book Medical Publishers, 1952) for use as a test of collateral circulation prior to arterial cannulation. This test involves the examiner occluding the patient's ulnar and radial arteries while the patient makes a fist, causing the hand to blanch. The patient is then asked to extend the fingers. After the hand is open, the examiner releases the ulnar artery while continuing to maintain pressure on the radial artery. Adequate collateral circulation is felt to be indicated by return of normal color to the hand. The patient is instructed not to hyperextend the fingers when opening the hand. Hyperextension may cause a decrease in perfusion to the arch, possibly resulting in a false interpretation of the Allen test (Anesthesiology 1972;37:356). The modified Allen's test can be performed quickly and easily, but it is susceptible to error. (With Allen's original test, both hands were tested simultaneously. The patient clenched both fists tightly for 1 minute while the examiner compressed one artery of each hand. This method helps diagnose complete occlusion, just as Allen intended. The test was later modified, however, to evaluate the adequacy of collateral circulation. To perform the modified Allen's test, the examiner compresses both arteries while the patient's fists are clenched. The patient then opens the hand, and the adequacy of circulation is evaluated when the examiner releases one of the arteries.) This study was designed to combine the modified Allen's test with the sensitivity of oximetry and plethysmography to provide a quantifiable and reproducible evaluation of the palmar collateral circulation with or without the subject's cooperation. Superficial palmar arches of 90 normal volunteers (aged 22-45 years) were evaluated with the modified Allen's test. These results were compared with the flow patterns demonstrated by plethysmography and pulse oximetry. All of the modified Allen's tests were normal, with the palmar blush occurring in an average of 2.3 seconds (range, 2-5 s). Results were recorded independently by two observers, with agreement in all cases. Four of the 90 (4.4%) palmar arches were found to have abnormal circulatory patterns. Plethysmography clearly demonstrated the dominant arterial supply to the hand and, in appropriate cases, indicated the existence of an incomplete arch. The four abnormal circulatory patterns (two incomplete palmar arches and two other aberrant arterial communications) were clearly shown by plethysmography. Pulse oximetry was found to be too sensitive. Significant changes in flow did not result in a decrease in saturation. Only the incomplete superficial palmar arches resulted in a change in saturation. The two abnormal arterial communications were not detected by pulse oximetry. Pulse oximetry also could not show dominant flow patterns. Our findings indicate that plethysmography can be used to demonstrate palmar collateral circulation, but that pulse oximetry cannot.
