Hypertension Journal

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A Chapter from History
  JOHTN
HISTORICAL VIGNETTES
A Chapter from History
Rajeev Agarwala
Consultant
Department of Cardiology, Jaswant Rai Speciality HospitalMeerut, Uttar Pradesh, India
Corresponding Author: Rajeev Agarwala, ConsultantDepartment of Cardiology, Jaswant Rai Speciality HospitalMeerut, Uttar Pradesh, India
Phone: +919837034842
e-mail: rajeev_jrsh@yahoo.co.in
 
ABSTRACT
Measuring blood pressure is standard clinical procedureperformed on every adult patient. But, one hardly remembersthe person who first conceptualized blood circulationtheory or the one who measured blood pressurequantitatively. It is rightly quoted by Johannes Muller that"the discovery of the blood pressure was more importantthan the discovery of the blood." Through his profoundexperiments, William Harvey was the first person tocorrectly describe blood's circulation in the body. Heshowed that arteries and veins form a complete circuit.The circuit starts at the heart and leads back to the heart.The heart's regular contractions drive the flow of bloodaround the whole body. Harvey made his discoveriesby ignoring medical textbooks and preferring his ownobservations and the deductions he made during dissectionsof animals. Harvey published his masterpiece in1628 - referred to as De Moto Cordis - the Motion of theHeart. This revolutionary concept of blood circulationencouraged physicians and physiologists for developingtechniques of blood pressure measurement. It tookalmost 100 years to discover blood pressure measurementtechnique by Reverend Stephen Hales in 1733.
How to cite this article: Agarwala R. A Chapter from History.Hypertens J 2017;3(1):42-43.
Source of support: Nil
Conflict of interest: None
 
 

INTRODUCTION

Measuring blood pressure is standard clinical procedureperformed on every adult patient. But, one hardly remembersthe person who first conceptualized blood circulationtheory or the one who measured blood pressurequantitatively. It is rightly quoted by Johannes Muller that"the discovery of the blood pressure was more importantthan the discovery of the blood." Through his profoundexperiments, William Harvey was the first person tocorrectly describe blood's circulation in the body. Heshowed that arteries and veins form a complete circuit.The circuit starts at the heart and leads back to the heart.The heart's regular contractions drive the flow of bloodaround the whole body. Harvey made his discoveriesby ignoring medical textbooks and preferring his ownobservations and the deductions he made during dissectionsof animals. Harvey published his masterpiece in1628 - referred to as De Moto Cordis - the Motion of theHeart. This revolutionary concept of blood circulationencouraged physicians and physiologists for developingtechniques of blood pressure measurement. It tookalmost 100 years to discover blood pressure measurementtechnique by Reverend Stephen Hales in 1733.

Stephen Hales, an English clergyman, had creativeand inquisitive mind that led to crucial findings inscience. His interest in scientific experiments first cameto public notice when he read a paper to the Royal Societyconcerning the effects of the sun's rays on the rising sapin trees. He measured "the force of the sap" or root pressure.This was a new technique of measurement in plantphysiology and this research was published in "VegetableStaticks." Further, he worked on animal physiology and became the first person who measured blood pressurequantitatively. The classic experiment (Fig. 1) by whichblood pressure was first measured was published in hismanuscript Haemastaticks.1

 
In his publication, he wrote: "In December, I causeda mare to be tied down alive on her back. A fistulawas placed on her withers...having laid open the leftcrural (femoral) artery about three inches from her belly,I inserted into it a brass pipe whose bore was one sixthof an inch in diameter, and to that, by means of anotherbrass pipe which was fitly adapted to it, I fixed a glasstube, of nearly the same diameter, which was nine feetin length: Then untying the ligature of the artery, theblood rose in the tube 8 feet 3 inches perpendicularabove the level of the left ventricle of the heart; ... whenit was at its full height, it would rise and fall at and aftereach pulse 2, 3 or 4 inches; ... then I took away the glasstube, and let the blood from the artery mount up in openair, when the greatest height of its jet was not above2 feet. I measured the blood as it ran out of the artery,and after each quart was run out, I refixed the glasstube to the artery to see how much force the blood wasabated; this I repeated to the 8th quart, and then its forcebeing much abated, I applied the glass tube after eachpint had flowed out."1,2

Three horses were used in this manner, all of themkilled as considered unfit for service. Certainly, it is difficultto believe that he would obtain ethical approvalfor such experiments today. From one of the horses, hemeasured the blood lost by bleeding and after adding the probable amount in the large veins, he estimated the totalas five wine gallons. He recognized it as low, remarkingthat: "There is doubtless considerably more, but it is noteasy to determine how much." The jugular pressure inone of the horses he found to be 12 inches when quiet,but this rose to 52 inches when the animal struggled.

A Chapter from History
Fig. 1: Artist's impression of Stephen Hale's experiment in whichblood pressure was first measured in a horse (Reproduced fromMedical Times 1944 by kind permission)
 
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A Chapter from History

Hales went on to measure blood pressure in a numberof animals and estimated that the blood pressure inhumans would be approximately 7.5 feet, which if convertedinto millimeters of mercury corresponds to asystolic pressure of 176 mm Hg.

Hale's another distinguished finding in animal physiologywas calculation of cardiac output. For calculation ofcardiac output, he filled the left ventricle of a dead horseheart with warm beeswax, which was then cooled andsolidified. Heart muscle was then cut away and volumeof ventricle was measured (160 mL). Cardiac output wasfound to be 61 per minute as the heart rate was 36 beatsper minute. He also introduced the concept of peripheralresistance, vascular diameter estimation, and resistanceacross the vascular tree. Owing to his remarkable contributionin modern cardiovascular physiology, he wasconsidered as the "Father of Hemodynamics."

Extensive research was done later, to measure bloodpressure accurately. Until 1855, arterial puncture was aprerequisite for measurement of blood pressure withthe available apparatus. Samuel Siegfried Karl Rittervon Basch and Potain made substantial contribution forthe development of instruments for noninvasive measurementof blood pressure. Though the introductionof sphygmomanometer in clinical practice was encouragedby several physicians, the British Medical Journal held the view that by using the sphygmomanometer"we pauperize our senses and weaken clinical acuity."It was Scipione Riva-Rocci, an Italian physician, whodesigned the modern sphygmomanometer for noninvasivemeasurement of blood pressure.3 He proposed useof brachial artery (rather than radial artery) to measureblood pressure as it offers larger arterial size and a moredirect continuity with aortic blood pressure. Moreover,he devised pneumatic cuff which allowed exertion ofan even circumferential pressure around the artery andthereby avoided overestimation of blood pressure due tothe eccentric compression of the more peripheral arteries.Apart from these distinguished features, the instrumentwas simple to use and so small that it was possible tomeasure blood pressure at the bedside. The contributionmade by Riva-Rocci did not go unnoticed as the Americanneurosurgeon Harvey Cushing used the instrument inhis surgical intervention and made it successful worldwide.The sphygmomanometer which was designed byhim required few marginal modifications. His discoveryof white-coat effect and blood pressure variability is validtill today despite the implication of more sophisticatedmethods of measuring blood pressure.

 
REFERENCES
  1. Karamanou M, Papaioannou TG, Tsoucalas G, Tousoulis D,Stefanadis C, Androutsos G. Blood pressure measurement:lessons learned from our ancestors. Curr Pharm Des2015;21(6):700-704.
  2. Burget GE. Stephen hales (1677-1761). Ann Med Hist 1925;2:109-116.
  3. Mancia G. Scipione Riva-Rocci. Clin Cardiol 1997 May;20(5):503-504.

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