Intravascular Pressures

The first measurement of the blood pressure was made by Stephen Hales (1677–1761) ( Fig. 1-3A ), the curate of Middlesex, England, who between sermons occupied himself with experiments on the mechanics of the circulation. He^[25] described one of his experiments performed (1733) on an "old mare who was to be killed, as being unfit for service":

I fixed a brass pipe to the carotid artery of a mare ... the blood rose in the tube till it reached to nine feet six inches in height. I then took away the tube from the artery and let out sixty cubic inches of blood, and then replaced the tube to see how high the blood would rise after each evacuation; this was repeated several times until the mare expired. In the three horses, death occurred when the height of the blood in the tube was about two feet.

Hales also discovered that the resistance of a vascular bed could change by mixing alcohol in the blood, which he observed could account for changes in blood pressure brought about by diverse ingested agents. In 1828, Jean L. Poiseuille ^[26] (1799–1869) repeated these experiments and devised a hemomanometer that used mercury instead of the long blood-filled tubes used by Hales. Poiseuille also showed that the blood pressure varied with respiration.

In 1854, Karl Vierrordt^[27] (1818–1884) invented a sphygmograph, acting on the principle that indirect estimation of blood pressure could be accomplished by measuring the counterpressure necessary to obliterate the arterial pulsation. Scipione Riva Rocci's (1863–1937) sphygmomanometer, described in 1896,^[28] used the same principle but used a rubber cuff that occluded a major

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Figure 1-3 Two scientists of the Enlightenment era. A, Stephen Hales (1677–1761): detail of an oil painting by T. Hudson, 1759, in the National Portrait Gallery, London. Hales was educated at Cambridge University, England and was ordained as a minister in 1703. He spent his career as minister to the parish of Teddington, England. His rudimentary studies on the gas produced by mixing Walton pyrites (i.e., ferric disulfide) and spirit of nitre (i.e., nitric acid) was the spark that prompted Priestley to pursue his studies on nitric oxide, which led to the discovery of nitrous oxide in 1773. Hales was the first to measure blood pressure and cardiac output. He also developed ventilators that brought fresh air into prisons and granaries. B, Albrecht von Haller (1708–1777): detail of an engraving by Ambroise Tardieu. Haller was born in Bern, Switzerland. He served as professor of medicine and surgery at the University of Göttingen, Germany, where he began his encyclopedic work, Physiological Elements of the Human Body, published in eight volumes between 1757 and 1766. His demonstration that "irritability" was a property of muscle and "sensitivity" was a property of nerves was derived from nearly 600 experiments on live animals. He returned to Bern in 1753, and while there he published a catalog of the scientific literature containing 52,000 references. (Portraits courtesy of the National Library of Medicine, Bethesda, MD.)

The past 50 years have seen a gradual return to direct measurements of arterial blood pressure, which are in principle much the same method used by Stephen Hales nearly 250 years ago. However, the Poiseuille method of using mercury-filled glass tubes was found to be totally inadequate for recording accurate pressures in a dynamic system. In 1876, Herbert Tomlinson^[31] introduced the principle of the strain gauge: resistance in a wire increases when it is stretched. It took 70 years after this principle was described before a strain gauge was used to measure blood pressure. In 1947, at the Mayo Clinic in Rochester, Minnesota, E. H. Lambert and E. H. Wood^[32] first reported the use of a strain gauge to measure blood pressure continuously in human subjects exposed to acceleration forces. Cannulas placed directly into vessels were first described in 1949,^[33] and since then, direct measurements of blood pressure expanded gradually into the operating room and intensive care units.

Venous pressures were of less interest to anesthesiologists until convenient methods for placing cannulas into central vascular structures were described 50 years ago by Sven Seldinger.^[34] Werner Forssman (1904–1979), a urologist, described the methods of central venous access and right heart catheterization in humans in 1929,^[35] originally experimenting on himself, and was awarded the Nobel Prize in Physiology and Medicine for his work on venous pressures in 1956. The introduction of plastic catheters^[36] gradually made it possible to measure central pressures in the clinical setting. Although arm and femoral veins were used initially, subclavian and internal jugular vein cannulation eventually replaced the peripheral sites. Pulmonary artery catheterization with a balloon-tipped, flow-directed catheter was described in 1970^[37] and has been used extensively since then by anesthesiologists to measure cardiac outputs using the Fick^[38] principle and pulmonary wedge pressures. The pulmonary artery catheter also allowed the clinician to use the well-known pressure-volume relationships of the heart described by Ernest H. Starling (1866–1927) in 1918 to maximize cardiac outputs and oxygen delivery to the tissues.

Transesophageal echocardiography (TEE) was described in 1976^[39] and used in anesthesia practice a few years later. One of the original probes used during anesthesia was fashioned from an esophageal stethoscope combined with an M-mode echocardiographic probe and was used to calculate cardiac output and ejection fraction in a 65-year-old woman undergoing mitral valve repair.^[40] An improved electronic phased-array transducer was initially applied at the University of California, San Francisco for

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