September 29, 2015
A landmark NIH study made headline news in September 2015. People might be able to reduce heart attacks, heart failure and stroke by almost a third and the risk of death by almost a quarter. How? Simply with vigorous management of high blood pressure – beyond the current guidelines.
The life-saving effect in the study was so dramatic that the NIH stopped the study early. They wanted to quickly spread the word to the 1 in 3 of us who already have high blood pressure. And of course to the 9300 people in the study.
How we monitor and control blood pressure matters.
ACT 1 – The Opening
Flashback to 1733. A scientific revolution was underway. Amateurs and professionals were exuberantly studying the world. The Enlightenment was in the air. A keen interest in science led a 56-year-old country parson named Stephen Hales to take a hydraulic technique for measuring pressure and use it on a living creature.
Hales inserted a small brass tube, 1/6 inch in diameter, into an artery in the thigh of a living horse. The mare was lying down on that December day. Hales then attached a 9-foot-tall, slim glass tube. A column of blood in the tube rose to 8 feet 3 inches above the level of the heart, and rose or fell with each pulse by 2, 3, or 4 inches. Hales had discovered blood pressure.
Almost a hundred years later, in the Paris of 1828, the next major advance came from a 29-year-old student, Jean Léonard Marie Poiseuille, as part of his doctoral dissertation. He replaced the 9-foot glass tube with a short tube of mercury, still connected to a tube inserted into an artery. He won the gold medal of the Royal Academy of Medicine for this advance. And ever since, blood pressure has been measured in millimeters of mercury, even though mercury is now obsolete.
A systolic blood pressure of 140 mm Hg is the force needed to raise a column of mercury by about 5 ½ inches.
More than a quarter century after that, in 1855, a professor at the University of Tübingen came up with a cool idea. Karl von Vierordt suggested a way to measure blood pressure without slicing into someone. Instead of opening a blood vessel, one could theoretically deduce the pressure by measuring the counterforce needed to stop the blood flow.
He called his device the sphygmograph (‘sphygmo’ comes from the word for pulse). He placed a pad over the subject’s wrist. He then added weights to a lever attached to the pad until the pulse beneath the pad stopped. Meanwhile, a pencil attached to the lever recorded the movements on a rotating drum.
Unfortunately, his device was cumbersome and didn’t really work. Great idea, though! And it inspired many variations on the theme over the next decades. Until…
ACT 2 – The Cuff
An Italian doctor named Scipione Riva-Rocci developed the first modern sphygmomanometer (‘manometer’ is a pressure meter). His breakthrough came in 1896. He wrapped a cuff around the upper arm, inflated the cuff with a rubber bulb, and watched a column of mercury in a glass tube. When he could no longer feel the pulse at the wrist with his finger, he had found the blood pressure.
Comparatively fast, precise, and a lot less painful.
How did the medical community respond? Some doctors saw this as a powerful new tool. But the British Medical Journal believed the tool was unnecessary and wrote that by using the sphygmomanometer “we pauperize our senses and weaken clinical acuity.” Physicians had relied on their fingers to gauge blood pressure without measuring since ancient Egypt.
Many physicians still thought that assessing the blood pressure by feeling the pulse with a finger was adequate, the way they had always done it. But the modern physician a hundred years ago was armed with a stethoscope, a thermometer, and a blood pressure cuff.
Over the twentieth century, our most pressing medical problems moved from infectious diseases to chronic illnesses related to our lifestyle. Of the core three diagnostic tools in the doctor’s bag, the blood pressure cuff became in many ways the most important.
In measuring blood pressure, using the stethoscope to listen to the pulse replaced a finger on the wrist in 1905, thanks to the innovation of a Russian surgeon named N. C. Korotkoff. This allowed physicians to detect both the peak (systolic) and trough (diastolic) pressures.
This technique became and has remained the gold standard of blood pressure measurement (outside the OR or the ICU). But it wasn’t actually measuring blood pressure, just the counter pressure needed to collapse a blood vessel. Among other problems, this varied with the stiffness of the vessel, the amount of muscle or other tissue over the vessel, placement of the stethoscope, background noise, and with user differences in the ability to hear quiet sounds.
Having an estimate of blood pressure is so important that in choosing our gold standard we willingly sacrificed some accuracy in order to improve safety, comfort, and convenience.
Since then, people have devised cuffs that inflate automatically. In many cases, microphones replaced the human ear and pressure sensors have replaced tubes of mercury – for more convenience, if not added reliability.
1979. Skip the microphones.
Put on a cuff. Inflate the cuff automatically. Measure the oscillations of pressure sensed as the cuff deflates. An algorithm turns this waveform into an estimate of the mean arterial pressure (MAP). From that you can estimate the likely systolic and diastolic pressures.
These oscillometric cuffs are very popular for their relative convenience. One study found the variance to the gold standard ranged from1 to 26 mm Hg in a series of 337 consecutive patients. Around 20% of patients had a significant difference.
But these cuffs still aren’t convenient enough. Many people who own blood pressure cuffs don’t carry them where they go and don’t even use them often at home.
ACT 3 - Blood Pressure Uncuffed
2015. A networked digital and mobile revolution is underway. A new Enlightenment.
Multidisciplinary teams from around the planet are racing to turn science fiction into reality. Inspired by the Qualcomm Tricorder XPRIZE, hundreds of teams set out to create wireless, portable devices capable of diagnosing more than a dozen important health conditions.
It’s what FIRST Robotics would call a “coopetition.” Each team is competing to further a shared goal: radically accelerating the ability for people to be able to learn about their bodies anytime, anywhere.
Seven finalists remain, including entrants from the United States, Ireland, Canada, Taiwan, and India. Each team is taking its own approach to design, but the entire kit must be portable, user-friendly, and weigh less than 5 pounds. The winner will be announced in 2016.
At least one of the teams has developed a breakthrough way to take and track blood pressure without a cuff.
Touch the small device to your forehead, and the sophisticated sensor array delivers the results to your smartphone. It records the time and location automatically, along with anything else you want to add.
The mission is to become the last generation to know so little about our health. If people know their numbers in different situations, they can take charge and move toward the blood pressure they want. No matter which team wins the prize.
The World Health Organization has called high blood pressure the leading underlying cause of death in the world – even before the landmark 2015 study. Achieving a healthy blood pressure may be the best thing you can do to extend your heart health, your brain health, your sexual health and your life.
We’ve moved from using a scalpel blade to open an artery and connect a 9-foot glass tube with a tied-down body, all the way to an elegant consumer device that fits in a jeans pocket.
The history of blood pressure measurement is catching up with our need to know - at the same time we’re learning that it’s even more important to know than we thought.
Alan Greene, MD
NIH Press Release: http://www.nih.gov/news/health/sep2015/nhlbi-11.htm
Blood-pressure in Medicine and Surgery: A Guide for Students and Practitioners by Edward Harris Goodman. Lea & Febiger. Philadelphia and New York. 1914.
Comparison of Automated Oscillometric Versus Auscultatory Blood Pressure Measurement. Landgraf J, Wishner SH, and Kloner RA. American Journal of Cardiology. Aug 2010. 106(3):386-388
A Short History of Blood Pressure Measurement. Proceedings of the Royal Society of Medicine. Nov 1977. 70(11):793-799. Royal Historical Society publication. Woodbridge, Suffolk, UK. 2014.
London Zoo and the Victorians 1828-1859. By Takashi Ito.
The Qualcomm Tricorder XPRIZE: http://www.tricorderxprize.org
Hales had been trying to estimate the force of the blood in the heart and the blood vessels for 25 years when he successfully used hydraulics in his Teddington, England experiments. He published his horse results, but achieved it in a dog first.
The discovery of blood pressure by Stephen Hales was more important that that of the circulation of blood by Harvey – The eminent physiologist Carl Ludwig.
The top celebrity in Paris of 1828 was not Poiseuille, of course, but a giraffe named Zaraf – the first giraffe in Europe since the 1400s. Every fashion from ladies’ dresses to men’s handkerchiefs was à la giraffe.
Torricelli had invented the mercury barometer to measure atmospheric pressure all the way back in 1646. 1 mm Hg was named 1 Torr in his honor. But no one used it to measure blood pressure, though, until Poiseuille in his dissertation titled Recherches sur la force du coeur aortique in 1828.