Professor Murray Esler from the Baker Heart & Diabetes Institute discusses the Editorial - Reflections on the past four decades of mental stress research in autonomic cardiology.
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This commentary, with some observations and a description of my experience in the field of mental stress science, is my contribution to the celebration of the thirtieth anniversary of Clinical Autonomic Research, a journal that has become the benchmark publication for all those interested in the autonomic nervous system in recent years, regardless of their primary medical specialty, which in my case is the automobile.
In 1977, I returned to the Baker Medical Research Institute and the Alfred Hospital in Melbourne, Australia, after 4 years of postgraduate research and clinical training with Prof. Stevo Julius in the Hypertension Division of the University of Michigan Medical Center, where I worked as a clinical cardiologist and founded a laboratory for cardiovascular neuroscience.
I recall being struck by how the involvement of patients with myocardial infarction or ventricular arrhythmias was often precipitated by emotional turmoil in my early clinical practice in Melbourne. "I saw patients in whom armed robbery, robberies, and even an owner's racehorse winning by a "nose" had induced a heart attack. I was delighted to accept, in 1985, an invitation to participate in what I expected would be an influential national panel to discuss the relationship between mental stress and heart disease with this clinical exposure. However, I was not ready for the meeting chair's opening remark (whose name I will not say): "There is no proof that stress causes heart disease, nor will there ever be." I was saddened, but not discouraged, as this could not be true, of course. Where was his crystal ball? Even if the comment captured the pessimism that was prevalent in that era's cardiology.
Faced with this setback, by researching cardiac sympathetic responses to mental stress, I applied my newly developed noradrenaline spillover methodology to the stress-heart issue, tapping into research possibilities that are open to a cardiologist. I performed this study in a cardiac catheterization facility, using a tritiated noradrenaline infusion to measure the isotope dilution release of this catecholamine from sympathetic nerves, with sampling from the heart's coronary sinus. This was to make these measurements of noradrenaline release unique to the cardiac sympathetic nerves, all achieved during the study participants' exposure to laboratory mental stress (Fig. 1a). The applied stressor, as accepted by my institutional ethics committee, was 10 minutes of challenging mental arithmetic, only to surpass the arithmetic competence of the volunteer, and paced by a metronome. For the mathematically talented, an additional tweak was made by informing the individual that they were incorrect... when they were actually correct! In a standard experiment, we measured the secretion of adrenaline by the adrenal medulla, the release of noradrenaline from the sympathetic nerves and sympathetic nerves of the whole body, the concentrations of noradrenaline and adrenaline plasma sampled from the antecubital vein, and the firing of sympathetic outflow using microneurography in the innervation of the vasculature of the skeletal muscle in the leg.