Vale Professor Michael Francis O’Rourke

Professor Michael Francis O’Rourke

28 July 1937 – 5 February 2024

Michael Franics O’Rourke, Emeritus Professor at the Faculty of Medicine, University of New South Wales  and faculty member of the Victor Chang Cardiac Research Institute, passed away on Monday, 5 February, aged 86. He is survived by his five children and 15 grandchildren. He was an esteemed academic, a distinguished and passionate researcher with an outstanding international reputation.

Michael was born in Sydney on 28 July 1937. His memories of post-war survival and family challenges laid the basic groundwork of determination and persistence that stayed with him throughout his life. The manner in which he lost his mother at the age of twelve due to cancer made him acutely aware that she might have survived if the doctor had done things better.  This was one of the main driving forces to study medicine and formed the basis of his life-long aim to always strive to do things better to advance knowledge and improve the welfare of patients.

Following his medical degree (MBBS, 1960), he was a Resident and Registrar in Anaesthesia at St. Vincent’s Hospital, Sydney. From 1963-66 he undertook postgraduate research in the Department of Physiology at the University of Sydney where he obtained his Doctor of Medicine (MD) under the supervision of Professor Michael Taylor. It was during this critical and formative period that he was inspired by the work of Taylor in Sydney and Donald McDonald (clinician and physiologist) and John Womersley (mathematician), in Britain. Their work on the biophysical relationship of blood pressure and flow in arteries presented novel ways of interpreting the information in the arterial pulse in terms of waves traveling throughout the arterial tree and being reflected from the periphery.

Michael was captivated by the rewarding engagement in interdisciplinary science and by the novel concepts of arterial impedance and wave propagation, which were investigated in experimental animals and then applied to humans; concepts that were able to explain the influence of large arteries on blood pressure, and which formed the basis of most of his published work throughout his lifetime. He understood very early, long before there were epidemiological studies showing the cardiovascular risk carried by systolic pressure, that there was nothing “normal” about the then prevailing notion of normal systolic pressure being “100 plus your age”. It was related to arterial degeneration manifest as the loss of arterial distensibility that was shown to occur with age. This led to the conceptual differentiation of arterial degeneration in terms of “atherosclerosis”, causing lumen obstruction leading to risk of ischemic events, and “arteriosclerosis” causing increased stiffness of the artery wall, losing the capacity to absorb the pulsations of blood flow, hence increasing pulse pressure. This, of course, is the basis for isolated systolic hypertension in the elderly. 

While there are pharmacological means of mitigating the effects of atherosclerosis, active de-stiffening of arteries is still illusive, other than by the passive effect of lowering blood pressure. In his latter years, Michael championed this passive effect of arterial de-stiffening by applying an elastic wrap around the ascending aorta to relieve the wall stress, hence proposing a device-related therapy for reduction of pulse pressure. These ideas were tested experimentally in vitro and he was awarded a US patent for this technique.

Michael’s approach promoted the effects of wave reflection, such that pulse pressure could be reduced by decreasing the magnitude or delaying refection to occur during diastole, an observation that was seen with nitrates. It was this biophysical concept that enabled him to be the first to introduce the counterpulsation technique in Australia in the mid 1970’s. The intra-aortic ballon pump is still the main means of temporary heart assist, where the addition  of a “counter” pulse with balloon inflation during diastole increases coronary perfusion and deflation during systole reduces systolic pressure.

These basic and novel concepts in haemodynamics learned in his early years of research were expanded during his post-doctoral studies at Johns Hopkins University in Baltimore, USA in 1966-1968, where he first became acquainted with Wilmer Nichols, then a student of McDonald at Birmingham, Alabama. This friendship lasted a lifetime, and Nichols and O’Rourke have been the editors of five of the seven editions of the seminal textbook of haemodynamics “McDonald’s Blood Flow in Arteries”, with the last edition published in 2022, some 60 years after McDonald’s original monograph

Michael’s enthusiastic approach to use the “experiments of nature” to understand cardiovascular physiology led to experiments in diverse animals of different body size and shape to quantify the relationships of arterial pressure an flow. His publications include experiments in guinea pigs, rabbits, sheep, dogs, wombats, snakes and kangaroos. The kangaroo waveforms are used in physiology classes to illustrate how high-intensity wave reflection can result in peak pressure in the cardiac cycle to occur in diastole (as can occur in counterpulsation).

Michael’s ’s strive to understand the impact of large arteries on the development of hypertension led to population studies in China, showing the effects of age-related changes in arterial stiffness measured noninvasively by pulse wave velocity. These studies were seminal in establishing that vascular ageing is not only related to blood pressure but also to dietary factors such as salt consumption. These studies established the relevance of arterial stiffness and vascular ageing as significant factors that have been shown to be independent predictors of cardiovascular risk.

Michael’s ideas on the arterial pulse were solidly based on his early formative years in research and did not waver throughout his entire career. He was always open to novel approaches and applications of pulsatile phenomena, and was very respectful of innovations. However, he was also fiercely defensive of the role of arteries and wave propagation in hypertension. His persistent ideas grew throughout the years and have nourished many researchers on a global scale. An important conduit for Michael’s massive international legacy has been Professor Michel Safar in Paris. Michel embraced Michael’s approach on arterial hemodynamics in the early 1970s, which over the years produced many world-renowned researchers and culminated in the formation of the  “Paris Vascular School”. And in the most intimate of relationships, they both took the same ship that was passing by. Michel passed away on 28th of January, a week before Michael. They were both born in 1937, and both had the same  name.

Michael’s international legacy spans the globe. His fundamental work on pulsatile hemodynamics has been at the basis of many academic and scientific careers in North and South America, Canada, UK, the European Continent, Greece, South Africa, China, Japan, Korea and other parts of Asia. His intellectual influence also formed the basis for the formation of many professional societies such as the Artery Society, North American Artery, Latin American Artery, Pulse of Asia and the Vascular Age Network, all with wide international connections.

A salient and highly admirable feature of Michael’s attitude to scientific knowledge was the unwavering respect he had for insightful work done by others at other times. He wrote profusely on the work done at Guys Hospitals in London around the 1870s by Frederick Akbar Mahomed, a young physician of Irish and Indian descent. Mahomed used the sphygmograph, the device for registration of the atrial pulse, (making the pulse the first parameter in medicine to be ever graphically recorded), to diagnose disturbances in cardiovascular physiology, including hypertension, long before blood pressure could be measured with the Riva Rocci and Korotkoff techniques using the brachial cuff sphygmomanometer. Michael’s ideas led to the addition of the pulse to the conventional measurement of blood pressure measurement, thus combining  sphygmography with sphygmomanometry. This culminated in him being granted a US patent for the technology and in founding a company in 1994 to produce devices based on pulse wave analysis. The company’s SphygmoCor system (AtCor Medical) for measuring arterial stiffness and central aortic pressure noninvasively has been the global industry standard for many years.

In addition to the enthusiastic pursuit of novel ideas in haemodynamics, Michael was an academic and specialist physician. His affiliation with the University of New South Wales began in the 1970s, not long after he started at St Vincent’s Hospital, Sydney. He became a specialist cardiologist with special interests in hypertension, arterial haemodynamics, coronary artery disease, pre-hospital coronary care, community defibrillation, effects of aging on heart and arteries, and new methods for measuring arterial pressure. He was made Fellow of the Royal Australasian College of Physicians, the Royal College of Physicians in Ireland (Hon), the Cardiac Society of Australia and New Zealand, the European Society of Cardiology, the American Heart Association, and the American College of Cardiology. During the period 1981-89, he was Editor-in-Chief of the  Australian & New Zealand Journal of Medicine

In the early 1970s, Michael established the Coronary Care Units at St Vincent’s Hospital, an initiative that was used as a template for the rest of Australia. This enabled him to champion the use of the intra-aortic balloon pump for treatment of the failing heart. In addition to investigating digoxin toxicity, he conducted the pivotal multicentre trial of recombinant tissue plasminogen activator (rtPA) agents, the  “clot-buster” drugs, as therapy for heart attacks. He was the first to introduce defibrillators in aeroplanes and in the NSW Ambulance Service, with the first public access taken up by Qantas. He provided crucial support by being actively engaged in teaching personnel and providing regular training. Michael has also trained, supervised and mentored numerous physicians, specialist cardiologist and researchers, now with highly successful national and international careers. In 1989 he was recognized for his contribution to medical teaching and research with a Member of the Order of Australia (AM) with the citation “For Service to Medicine, particularly in the care of persons affected by coronary disease, and in the training of Paramedic staff.”

Although Michael was relatively successful in obtaining research funding early in his career, his track record does not boast many large research grants. However, he has left an unparalleled legacy of a published body of research work consisting of authoritative books, book chapters and over 500 articles, and some, at times, piercing letters to editors. He made efficacious use of some generous personal patient bequests and departmental funds that were able to provide the essential research assistant support. It was an active decision at some point in his career path not to strive for highly competitive grant funding. In his own way, he felt he could do things better this way.

Miichael’s final venture in the latter years was the application of pulsatile haemodynamic phenomena to the brain. He combined knowledge generated by many investigators specialising on cerebral perfusion and intracranial fluid pressure. He published an article on the topic that “ the brain is destroyed by the pulse” with Jonathan Stone, a colleague of his from the early years in the Department of Physiology at the University of Sydney (J Alzheimer’s Dis. 2015;44(2):355-73 ). His final publication was in the journal Artery Research with a list of authors that he felt helped him throughout this journey (The Human Systemic and Cerebral Circulations: Contrasts in Structure and Function, Michael O’Rourke [Sydney], Jonathan Stone [Sydney], Audrey Adji [Sydney], Mi Ok Kim [Sydney], Yan Li [China], Ji Guang Wang [China], Alberto Avolio [Sydney], Per Kristian Eide [ Denmark], Marek Czosnyka (Britain], Artery Research 2020; 26(4):197–211). Illustrations in his final publication in 2020 include the very same ones that appear in his first publications from his MD thesis in 1966. And in the short abstract of the article he writes that “ ..principles established for function of the human systemic circulation (pulsatile flow at input and steady flow at output in capillaries) can also apply to the brain, and … such knowledge can be applied in some clinical conditions including development of dementia in older subjects”. And the intimate interaction of the pulse and the brain was his prescient final trajectory of the journey that was abruptly truncated by acute myloid leukemia.

We write this obituary for Michael O’Rourke as two of the longest and continuous collaborators who have stood by his side through calm seas and roaring tempests, and have witnessed his influence as supervisor, life-long teacher, colleague, mentor and friend. Together with many others in Australia and in many other parts of the world, we have benefited greatly from Michael’s intrinsic passion for insightful knowledge, the openness to learn from others and the strive to always try to do things better. Our continuous connection with Michael over the last 20 years (Audrey Adji) and 50 years (Alberto Avolio) has left an indelible life impression.

Alberto Avolio, Professor Emeritus, Faculty of Medicine Health and Human Sciences, Macquarie University, Sydney, Australia

Audrey Adji,  Senior Postdoctoral Scientist, Victor Chang Cardiac Research Institute, Sydney, Australia