Blood pressure monitoring--the von Recklinghausen oscillotonometer.
Blood pressure monitoring with sphygmomanometers became common in anaesthesia in the early part of the 20th century, but it presented some challenges for the anaesthetist. Measurement by palpation was difficult as the anaesthetist often needed both hands for the administration of the anaesthetic and maintenance of the airway. Similarly, there was often insufficient access for auscultation with a stethoscope.
In 1950, C.T.Barry published a paper entitled "Oscillometry during Anaesthesia" in which he "hoped to show ... that simple oscillometers are suitable for use in the theatre, and also have advantages of their own. The oscillometric index is a useful guide, the sensitivity of these instruments allows readings to be obtained when the pressure is too low to produce audible Korotkov sounds, and the recognition of cardiac irregularities is greatly facilitated" (1).
Oscillometry had its origins in 1876 with the work of Marey who noted oscillations were produced when measuring blood pressure. His work was hampered by mercury manometers which responded slowly and dampened the oscillations. While the Americans and the English continued using mercury manometers, the French and Germans introduced and improved anaeroid manometers (2). These were based on the principle of barometers and utilised a Bourdon Tube, a hollow metal tube with a sealed distal end. This is shaped into an arc and connected to a system of levers which ultimately move a needle over a scale. Heinrich von Recklinghausen, the German physiologist, popularised the anaeroid manometer for blood pressure measurement. Heinrich was the son of Friedrich Daniel, the famous pathologist who described von Recklinghausen's neurofibromatosis. He made significant contributions to the field of blood pressure measurement and published a lengthy and comprehensive textbook on the subject in 1940 (3). In particular, he noted the need for a wider arm cuff, unlike the very narrow cuff that was first proposed by Riva-Rocci.
Oscillometry required the use of a suitable instrument to magnify the oscillations produced in the cuff by the pulsations of the artery. Many instruments were designed; all involved the use of a sensitive membrane or capsule, the movements of which were amplified. The most successful instruments were derived from the work of von Bernd who placed the capsule in an airtight box, but his instrument was too sensitive to have commercial application.
Pachon produced a simple and practical modification of von Bernd's oscillometer in an airtight box with a glass window. The box contained a very sensitive anaeroid capsule which communicated with a rubber arm cuff enclosed in canvas; the apparatus also had a pump, an escape valve and an anaeroid manometer to indicate the pressure. It was popular in Britain prior to 1950 and was still used in Europe at that time. It did have some limitations as the systolic pressure reading was very inaccurate and practitioners relied more heavily on the 'oscillometric index'. This index was devised by Pachon and consisted of a scale of graduations which allowed measurement of the swing of the needle. The significance of the index was widely debated and was thought to be governed by two factors: the pulse pressure and the tone of the peripheral arteries. In Barry's study of 204 cases, the index was seen to be a more accurate indication of problems developing during anaesthesia: "In sixteen ... cases, however, it was noted that although the systolic remained unchanged or actually rose, the oscillometric index showed a definite fall, sometimes associated with a deterioration in pulse and colour" (1).
The accuracy of oscillometers was improved by the use of a double cuff, first suggested for use in blood pressure measurement by Amblard in 1908 and popularised by Gallavardin (2). The double cuff allowed the upper cuff to be deflated while the lower cuff partially occluded the artery and thus provided further amplification of the pressure wave. Some early experiments were performed with double cuffs placing the lower cuff on the forearm, but these were never as popular as the more practical and accurate double, overlapping cuffs on the upper arm.
The more sophisticated oscillotonometer developed from these early oscillometers and is widely attributed to von Recklinghausen. The device, which was extensively used in anaesthesia, consists of two cuffs, the upper black 5 cm cuff overlapping the lower red 10 cm cuff (4). Both are connected to a single inflation bulb. The case contains a control lever, a release valve and two tambours, one connected to the atmosphere and the other to the lower sensing cuff. There is a mechanical amplification system connected to an oscillating needle and dial. Both cuffs and the airtight box are pressurised above systolic pressure and the control lever is then activated to produce a sustained leak from the upper cuff and the casing. The size of this leak is controlled by the release valve. When the needle oscillations show a definite increase, the lever is released and the needle stops at a point assumed to be the systolic pressure. Further activation of the lever allows observation of a definite decrease in the oscillations; release of the lever will again stop the needle and allow a reading of the diastolic pressure.
There were two models of the von Recklinghausen oscillotonometer, the Scala Alternans and the later Scala Alternans Altera. In the earlier model the control lever had to be pushed intermittently and did not allow for a sustained leak during deflation. Hutton and Prys-Roberts' extensive study of the Alternans oscillotonometer in clinical practice concluded that the systolic and mean arterial pressures could be ascertained with some accuracy but that the readings were influenced by both the patient and the operator. They found the oscillotonometer "useless" for the determination of diastolic pressure (5).
The von Recklinghausen oscillotonometer was manufactured in Germany but the English instruction booklet was poorly translated and extremely complicated (6). Reading it, there is no doubt that the operation of the device was open to a great deal of individual interpretation, a problem that was eventually solved by the development of the microprocessor and the creation of automatic blood pressure machines.
(1.) Barry CT. Oscillometry during anaesthesia. Anaesthesia. 1950; 5:26-35.
(2.) Naqvi NH, Blaufox MD. Blood pressure measurement. An Illustrated History. New York: The Parthenon Publishing Group; 1998.
(3.) von Recklinghausen H. Blutdruckmessung und Kreislauf in den Arterien des Menschen: Geschichte und heutige Lage der Probleme, neue Losungsversuche. Dresden; Leipzig: Steinkopff; 1940.
(4.) Corall IM, Strunin L. Assessment of the Von Recklinghausen oscillotonometer. Anaesthesia. 1975; 30:59-66.
(5.) Hutton P, Prys-Roberts C. The oscillotonometer in theory and practice. Br J Anaesth. 1982; 54:581-590.
(6.) Instructions for the use of the Oscillotonometer "Scala alternans". Geoffrey Kaye Museum of Anaesthetic History.
C. Ball, R. N. Westhorpe
Geoffrey Kaye Museum of Anaesthetic History
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|Title Annotation:||COVER NOTE|
|Author:||Ball, C.; Westhorpe, R.N.|
|Publication:||Anaesthesia and Intensive Care|
|Date:||Mar 1, 2009|
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