Thomas Young (1773–1829) and the first description of the volume-rate regulation of cardiac output

Abstract

Thomas Young (1773–1829) is considered one of the greatest minds and polymaths of all time. His colossal academic impact led to major contributions in the fields of medicine (ophthalmology), physics (wave theory of light), anthropology (coining the term “Indo-European”) and ancient history (contribution to deciphering Egyptian hieroglyphs) [1]. As a trained physician, Young's work in the field of medicine is considered to encompass his seminal work on vision and optical accommodation with some work on the understanding of infectious diseases and the introduction of a simple rule to calculate child medication doses. Posthumously, his work on fluid statistics and hydraulics led to the application of the Young–Laplace equations in the understanding of cardiovascular hemodynamics and pulmonary airway physiology [2]. His work on Young's modulus and elasticity led to the description of the water hammer pulse pressure rise and the prediction of the relationship between arterial stiffness and pulse wave velocity [3–5]. He also recognized cardiac output as the predominant driver of the systemic circulation (as opposed to the older contradicting theory of arterial wall musculature in generating blood flow) [3,6]. Young however also developed fundamental concepts in cardiac output regulation that have not been acknowledged in the international literature for over 200 years. Our modern appreciation of cardiac output (Fig. 1) is derived fromWilliamHarvey's initial description of the cardiac circulation, and the studies of Reverend StephenHales (identifying blood pressure), Albrecht von Haller (describing vascular resistance), Daniel Bernoulli (calculating the work of the heart) and subsequently Ernst Starling's identification of the myocardial contractile apparatus for cardiac output regulation. The eventual calculation of cardiac output came via the Fick principle (Adolf Eugen Fick in 1870) and through dilution methods applying the Stewart (1897) and Hamilton (1932) equations [7,8]. In his 1808 Croonian lecture delivered to the Royal Society entitled “On the Functions of the Heart and Arteries” [3], Young identified “the quantity of blood transmitted [by the heart]... remain[s] the same as in perfect health ... the pulse, if more frequent, must be weaker, and if slower, it must be stronger”. From this statement there is evidence that Young had an appreciation for stroke volume [SV] (“quantity of blood transmitted” by the heart). He then recognized that in health, changes in the pulse [heart rate—HR] result in reciprocal changes in SV (“if more frequent, must be weaker, and if slower, it must be stronger”). From this we can identify that Young was developing the earliest concepts of the regulation of cardiac output whichwere the product of heart rate and stroke volume; a concept readily understood today as CO=HR×SV. In summary, I describe Thomas Young's first description of cardiac output regulation. To the best of my knowledge this has not been formally identified in the international literature since his 1808 original Crooninan lecture. It reveals Thomas Young's detailed appreciation of cardiovascular regulation that likely benefited from his authoritative background in physics (natural philosophy) and the general study of biological systems. His concepts pre-dated the Frank–Starling law by over a century and represent the broad genius of this polymath that contributed to our understanding of modern cardiac physiology.