A recent report from the National Academy of Science documents (not for the first time!) that we humans have a unique ability to develop our heart’s capacity for stress. The investigators compare us with our relatives, the apes and chimpanzees, and say that these animals, unlike us, don’t have this resource: they are only equipped for very short periods of intense activity like fighting or climbing,
Some of this we have always been aware of. In fact, my own research on the developing heart showed that in the uterus, when the baby’s circulation operates at a low blood pressure, the heart wall is relatively thin. After birth, when the baby is delivered, the blood pressure rises normally and the heart structure changes appropriately, producing more contracting units in the heart wall and generating more energy producing units called mitochondria.
We have evolved with an ability to reshape our heart muscles not only at birth, but throughout life, so that they are optimally structured to meet the demand for the kind of stress we require of our bodies. For example, when our hearts work to pump blood against high pressure and need to generate more force, the wall of the pumping chamber thickens. Patients with chronically high blood pressure have what we call myocardial hypertrophy, which we can see on an echocardiogram. Unfortunately, the heart remodeled in this way is less well equipped for exercise. On the other hand, when we need a larger amount of blood for physical activity, the heart accommodates by increasing the beat-to-beat volume of blood to meet the muscles’ demand for an increase in oxygen. The pumping chamber needs to be thinner walled and more distensible to achieve this. Individuals who consistently engage in regular, moderately intensive exercise have a heart with less muscle, leaving a pumping chamber with an increased capacity to distend and to hold more blood per beat. (Incidentally, there are subtle but significant differences in the pattern of response to a demand for increased heart work in men and women although the basic results are similar.)
I have to confess that I am skeptical that apes and chimps don’t have the same ability as we do to modify the heart’s architecture and strength. These animals don’t do sustained moderate physical activity; only when they are fighting or climbing does their otherwise sedentary life change. In other words, stress for them is episodic and short-lived. To be sure about whether or not the hearts in other mammals have the same basic response to the type and duration of work they are asked to perform, we would have to expose them to a constant level of higher than normal blood pressure or force them to do a low level of controlled physical activity at least daily for significant periods of time to make sure they, like us, also own intelligent hearts!
Dr. Marianne Legato, Professor Emerita of Clinical Medicine at Columbia University is an internationally known academic physician, author, lecturer, and specialist in gender-specific medicine. She is founding member of the International Society for Gender Medicine and also the founder and director of The Partnership for Gender-Specific Medicine at Columbia University and its next iteration, The Foundation for Gender-Specific Medicine. These enterprises are the first collaborations between academic medicine and the private sector focused solely on gender-specific medicine: the science of how normal human biology differs between men and women and of how the diagnosis and treatment of disease differs as a function of gender and sex. Her ground breaking textbook on Gender-and Sex Specific Medicine has been published in 2017 in the 3rd edition.
She has published extensively on Gender and Sex Specific Medicine, both scientifically and for the lay public. She is also the founding editor of the journal Gender Medicine, and the Journal Gender and Genome, published for the scientific community. In 1992, Dr. Legato won the American Heart Association’s Blakeslee Award for the best book written for the lay public on cardiovascular disease. She is a practicing internist in New York City and has been listed each year in New York Magazine’s “Best Doctors” since the feature’s inception in 1993.