Testing of the resistance of peripheral blood vessels by ultrasound

The authors carried, out a test on the resistance of blood vessels to the flow of blood, (namely arteries), using an apparatus known by the name SONICAID EM 220. The SONICAID is a portable ultrasound generator and receiver weighing 3.5 kg. It consists of a transducer, and an ultra sound generator. The transducer, (which is about as large as a matchbox), receives the generated ultrasound signal, transforms it to an audible signal, and sends it to the main via a cable. The amplified signal can be monitored through a built-in speaker, or through headphones. The signal can also be recorded on tape, but th is feature was not included in the authors' unit. The SONICAID is based on the Doppler Principle; interference of reflected waves. If the generated ultrasound waves reach moving matter, (in this case a stream of blood), they are reflected back in such a way that they reach the transducer as interference waves. This signal is not unlike the sound produced by the heart during systolic contraction, or by stenotic blood vessels. The authors examined 21 ill patients with normal circulation using the SONICAID, and found it difficult to register the signals. The arteries of the forearm and lower leg could not be convincingly registered because it was difficult to determine the proper angle required to pick up the signals. In addition the area in which the signals could be picked up did not always concide with the anatomical position of the artery. These are the factors which the authors used to explain the rather inanccurate results. In 9 individuals (38%), the SONICAID indicated pathooligcal findings (false positive results). Later the authors examined 23 patients with previously confirmed vascular diseases, and obtained 15 pathological findings (65%). With 4 individuals, a false positive result was obtained, and wit the remaining 4, a false negative result, or a total of 8 false results (35%). Based on these results, the authors concluded that; the relatively large percentage of false results, the difficulty of demonstrating normal findings, and the relatively long examination time make this method of examination rather uncertain. The subjectivity of the person conducting the examination also influences the interpretation of the sounds emitted by the machine, which in turn influences the results. Objectivization, and documentation of such results is not certain. As a result, This method has no advantage over the oscillograph, and clinical examination. Such a conclusion however does not justify discontinuing the use of the more sophisticated diagnostic tools and methods used in vascular surgery.