An electrocardiogram (ECG) is a device that measures a heartbeat by recording electrical signals made by the heart's beating. ECG machines are very common pieces of medical equipment in use in hospitals the world over. ECG machines owe a lot to the research of many scientists who conducted experiments concerning electricity in animals, which led to the development of the first ECG machine.
The first recording of an electrocardiograph is often debated, yet is usually credited to Alexander Muirhead, who attached wires to a patient at St. Bartholomew's Hospital in London. Some sources claim that he simply used a Siphon Recorder of William Thompson (Lord Kelvin), while others claim that he used a Lippmann capillary electrometer to measure the current. In a biography written after his death, his wife claims that he refrained from publishing his findings on medical equipment so as not to mislead fellow scientists.
Other attempts with such medical equipment were reported, however, the machine that is considered the first ECG machine is the String Galvanometer, which was invented by Willem Einthoven shortly after the start of the 20th century. Einthoven received the Nobel Prize in 1924 for his work inventing the first ECG machine. These ECG machines were large, weighing almost 600 pounds and required a patient to immerse his hands and feet in buckets of salt water, which amplified the current. The electric signal was conducted by silver plated quartz filaments which moved according to the smallest current and its movements were recorded on a photographic plate. Even though earlier electrocardiographs have been reported, the fact is that none of them were accurate enough to be used to perform medical diagnostics.
Even though these were among the first ECG machines to ever be used, the data measured had a level of accuracy that almost rivals modern day medical equipment. The String Galvanometer was first purchased by the University of Edinburgh in 1908, after which many other clinics began to use them for diagnosing heart disease and other internal problems. This medical device was used widely until 1928, when a modification of an existing table cardiograph produced a portable device (at 50 pounds, powered by a 5V battery) which was developed by what is now the Philips Company. Even though huge advances have been made in this field, modern ECG machines still follow the same principles laid out by Einthoven.