Physical vs. technological diagnosis

In modern medicine, physicians are greatly aided in diagnosis by new machines and technology. Undoubtedly these devices provide more accurate and detailed information than the old, low-tech methods, which usually leads to better treatment for the patient. However, some vestiges of the old methods are still in use and still provide valuable information for a doctor. These methods of physical diagnosis, such as using a stethoscope and taking your pulse or blood pressure, have remained cornerstones of a clinical examination.

Ancient Egyptians, Chinese, and Greeks all recognized the value of reading the pulse to diagnosis illnesses. Many cultures identified various qualities in the feeling of the pulse and correlated those to illnesses. As early as 2600 BC the Chinese recorded observations of the effect of excess salt in the body leading to a faster pulse. However it would be many years until the the circulation of the blood and the workings of the circulatory system were understood. In 1616, William Harvey’s experiments proved that the blood flowed in a circular fashion through the body and was pumped by the heart, not the arteries themselves.

Johannes Kepler (1571-1630), famous for his study of astronomy and mathematics, was also the first person who recorded counting the pulse by the minute. Previously, analyzing the pulse rate was a strictly qualitative method. Skilled physicians may have been able to identify high blood pressure and other illnesses using this method, but it was a precise art. Using a standard unit of measurement allowed physicians to compare data and create charts for normal and abnormal readings and their meanings. By the early 170os, counting the pulse by the minute had become common. As the century progressed, more attention was paid to the quantity of pulse, not the quality.

With the increased use of pulse data, physicians began to invent devices to read and record the pulse. The first of such machines was invented in 1555 by Joseph Struthus. He pioneered the idea of representing the pulse graphically, but lacked the technology for a sophisticated device. After 1616, with new understanding about the circulatory system, the importance of stress on the heart, and a rise in quantitative readings, doctors also became interested in measuring the pressure of the blood to diagnosis disease. Physicians had discovered that one could measure the pressure inside the artery by measuring the amount of outside pressure it took to stop the flow of blood. In the late 1700s and early 1800s many cumbersome devices were made that applied measured pressure to the artery in the wrist and recoded the pulse response on a rotating cylinder covered with smoked paper.

In 1896, Italian Scipione Riva-Rocci invented a simple instrument that obstructed the artery using an inflatable arm cuff. A vertical meter filled with mercury measured the amount of pressure in the cuff. The next year, two physicians used this devise to monitor eight surgical patients while they were under anesthesia. At the turn of the century, blood pressure measurement began to reach a significant level in the United States for the first time.

The last major discovery in the measurement of blood pressure came from a young Russian doctor serving a military hospital. Using a pressure cuff, Nicolai Sergeivich Korotkoff began using a stethoscope to listen to the pulse under the cuff and noticed several distinct sounds as the pressure was released. In 1905, after further study, he was able to identify the sounds of maximal and minimal pressure of the artery. In 1927, the United States Bureau of Standards recognized this method as the most accurate for the measurement of blood pressure and it became a routine procedure in medical examination.

As a side note, the evolution of methods to measure blood pressure also illustrates medicines inter connectivity with broader science and discovery. For example, the use of pulse in diagnosis was greatly aided by standardized time. Our understanding of blood circulation was increased in 1839 when physicists determined a law for the behavior of  liquids flowing in tubes. The modern blood pressure cuff was not possible until Charles Goodyear had invented vulcanized rubber in 1839 and John Dunlap had refined it to make a pneumatic tire in 1887.

The upcoming exhibit “Tools of the Trade: Medical Instrumentation” will address the evolution of a variety of medical tools and procedures.