Direct Intra-arterial Recording
The first method established for measuring blood pressure, intra-arterial recording, was discovered in 1733 when Hales inserted a thin glass tube into a horse’s artery during a surgical procedure. The level of the blood rose and fell within the glass tube because of changes in arterial pressure associated with heart action. Experimentation with this method permitted Hales to directly observe changes in blood pressure by measuring the level of the blood in the glass tube.
With continued experimentation, blood pressure gauges of this type became standardized so measures of blood pressure could be compared across time and situations as well as across species.
Despite its impracticality due to problems associated with blood loss and potential infection, direct intra-arterial measures of blood pressure are still considered the ‘gold standard’ of measurement (Littler and Komsuoglu, 1989). Not only are these measures made directly from catheters positioned in the circulatory system, but they also permit continuous measures of blood pressure on a beat-by-beat basis. Thus, momentary fluctuations in blood pressure in response to various environmental stimuli can easily be detected. But despite the accuracy of intra-arterial methods, their impracticality for clinic use led to the reliance on pulse palpation (sensing variations in the pulse by touch) as a gross estimate of arterial pressure obtained during clinic visits in the 1800s.