History of continuous noninvasive arterial pressure

The article reviews the evolution of continuous noninvasive arterial pressure measurement (CNAP). The historical gap between ease of use, but intermittent upper arm instruments and bulky, but continuous “pulse writers” (sphygmographs) is discussed starting with the first efforts to measure pulse, published by Jules Harrison in 1835. Such sphygmographs led a shadowy existence in the past, while Riva Rocci's upper arm blood pressure measurement started its triumphant success over 100 years ago. In recent times, CNAP measurement introduced by Jan Penáz in 1973 enabled the first recording of noninvasive beat-to-beat blood pressure resulting in marketed products such as the Finapres™ device and its successors. Recently, a novel method for CNAP monitoring has been designed for patient monitoring in perioperative, critical and emergency care, where blood pressure needs to be measured repeatedly or even continuously to facilitate the best care for patients.

Early sphygmographs Prior to quantitative measurement, which was applied in medicine in the 19th century, diagnostic possibilities of hemodynamic activities had been limited to qualitative sensing of pulse through palpation. In some cultures, sensitive palpation is still a main part of medicine like pulse diagnosis in Traditional Chinese medicine (TCM) or the identification of the ayurvedic doshas. The introduction of the stethoscope and the methods of auscultation by René-Théophile-Hyacinthe Laennec in 1816 changed the medical behavior consistently and forced the need of quantitative hemodynamic measurements. The first instrument which could measure the force of pulse with a mercury filled glass tube was developed by Jules Harrison in 1835. Jean Léonard Marie Poiseuille invented the first mercury “Hemodynameter”, a forerunner of the sphygmomanometer in 1821. The first sphygmograph (pulse writer) for the continuous graphical registration of pulse dates back to Karl von Vierordt in 1854. More popular, however, was the improved sphygmograph from the French physiologist and pioneer in cinematography Étienne-Jules Marey (1863). In his famous book “La méthode graphique“ (1878) and his studies with the photographic gun, Marey's work was related to cardiovascular movements of heart and vessels.

Besides Marey's sphygmograph, a device developed by the Austrian Samuel von Basch attracted attention and was introduced in Europe in 1880 . A fluid filled bladder placed on the wrist was able to detect pulse; the pressure, which was necessary for the disappearance of the pulses, was measured with a mercury manometer. This allowed the first measurement of systolic blood pressure. Several other sphygmographs were developed in the late 19th century, especially in Great Britain, France and Germany. These instruments were portable, reasonably accurate and widely available, so physicians even used them at the bedside.

Simple and accurate sphygmomanometers displace sphygmographs In 1896, the Italian Scipione Riva-Rocci introduced the first mercury-sphygmomanometer placed on the upper arm. It enabled the measurement of absolute systolic blood pressure. Since the finding of the characteristic sounds by the Russian Nikolai Sergejev Korotkoff in 1905, the upper arm method also allows the registration of absolute diastolic blood pressure. One year after Riva-Rocci's findings, Leonard Erskine Hill and Harold Barnard reported blood pressure monitoring during anesthesia for the first time. Their almost concurrently invented devices consisted of a narrow armlet to occlude the brachial artery, a small bicycle-type metal pump and a metal manometer graduated in mmHg. It seems surprising that the first report of blood pressure monitoring during anesthesia did not mention the use of sphygmographs, which had already been in common use at this time . One reason might be that the former practice totally relied on the observation of breathing as the sole method of monitoring; even the palpation of pulse during ether or chloroform administration was not recognized as a good practice. Another reason may be found directly in the title of the report: “A simple and accurate form of sphygmometer or arterial pressure gauge contrived for clinical use” – implying that for clinical use the device must be simple and accurate.

Early vascular unloading technique While the sphygmomanometer had started its triumphant advance, only a few pulse registration devices were invented in the 20th century. Plain plethysmographic devices like pulse oximeters are, of course, the exception, but they cannot be used for blood pressure measurement. If at all, they can measure blood volume changes. These volume changes cannot easily be transformed into pressure, because the elastic components of the arterial wall are not linear and the smooth muscles also consist of non-elastic parts.. The goal is to unload the arterial wall in order to linearize this phenomenon with a counter pressure as high as the pressure inside the artery. Blood volume is kept constant by applying this corresponding pressure from the outside. The continuously changing outside pressure that is needed to keep the arterial blood volume constant directly corresponds to the arterial pressure. It is an instantaneous, continuous measure for arterial blood pressure, which is the basic principle of the so-called “vascular unloading technique”. In 1942, the German physiologist Richard Wagner introduced a mechanical system for the identification of blood pressure at the arteria radialis using a mechanical version of the vascular unloading technique, where a counter pressure unloads the arterial wall.

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