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Heart Beats and Lifetimes

July 24, 2005 11:07 AM

My post on Lance and his low heart beat elicited some surprise from commenters. There are disadvantages and even dangers in having a very low heart beat. I pointed out that a very low pulse makes one vulnerable to fainting because slight pressurization of the venal cavity that surrounds the heart stems the flow of blood to it and this in turn denies blood to the brain. So, if you choke or pressurize your chest, say, on a lift, you deny blood to your brain and you faint. Fainting is a protective measure for your brain. By falling prone you lower the column of blood your heart must support and save your brain which can fry in moments if denied blood and the oxygen it carries.

Though the fainting is protective, it doesn't prevent damage completely. The momentary denial of oxygen that caused you to faint does a bit of damage. Then when the blood returns it induces reperfusion ROS (reactive oxygen species) damage. At a very low pulse, the brain may live close to this denial/reperfusion injury boundary.

There surely is a healthy range of the human heart beat, though no one knows what its limits are. When my wife's heart beat got down near 32 her doctor was quite worried. An extremely low pulse can indicate congestive heart failure. On the other hand, an extremely high pulse, if continued over a period of time, can be a sign of something wrong, though the high pulse is not likely to overstress a strong heart.

What really seems to matter is the complexity of the heart rate. People talk about their pulse as though it were a clock or a metronome. This is far from true. The pulse rate or the intervals between beats are random. The statistical distribution of the intervals between beats is, you guessed it if you are a regular reader, a fractal distribution. It has a high variance and no characteristic scale or size of the interval. This has led the Ari Goldberger team at the Reyes Lab at Harvard to develop diagnostic tests of the heart based on their complexity measures.

A healthy heart has a high complexity measure, which is usually taken to be the fractal dimension. The complexity measure is (inversely) related to the exponent of the power law (here they are again, power laws are the organizational pattern of Nature). If I recall correctly, the exponent is around 1.2 to 1.5. These are, by the way, the exponents that you get in the distributions of movie revenues and extreme events in the stock market. Congestive heart failure, for example, dramatically reduces the complexity of the heart beat.

Advocates of aerobic exercise always seem to point to their low resting pulse as a benefit.

This is not a good measure. They should be pointing to the complexity of their heart rate if they want a true measure. But, mechanistic and repetitive aerobic activity actually trains some of the complexity out of the heart beat.

What might be the theory that leads people to claim that a low pulse is a good indicator of health or longevity? Well, I think a lot of it is just unthinking promotion of aerobic exercise, taken to excess.

What is the supposed mechanism by which a low pulse improves health or longevity? There really is only one theory that claims that a low heart beat rate increases longevity, and it is completely flawed. This is the theory that living things only get so many heart beats.

Calculations derived from correlations of energy intensity and mass with longevity and mass give we humans 955,787,040 heart beats in a lifetime (John Speakman, et al, "Living Fast, Dying When?" American Society for Nutritional Sciences, 2002). There are 525,600 minutes in a year. At a continuous pulse of 32 beats per minute a heart beats 16.8 million times in a year. At this annual rate, the heart could beat 56.82 years before it stops. At a more typical pulse of 70 (counting sleep and activity), the heart beats 36.79 million times per year. At this rate, we would live to be just 25.97 years old when our hearts stopped beating. A lot of us should be dead by now.

Both numbers are plainly wrong. That is because the theory is wrong. Actually, it isn't a theory, it is just a correlation of mass, energy intensity, and longevity taken over different species. The idea is based on a mechanical model of the heart. A machine does wear out faster the more intensely it works. But, why would anyone apply this model to a living organism? Because they analogize from machine to living thing. But a machine lives with entropy, it loses information to the environment as it is used and as the parts wear out the information dissipates. When the loss of information is large enough, the machine no longer functions.

Humans are far from equilibrium systems. They take in information in the form of energy and dissipate it into the environment. They eventually succumb to the second law of thermodynamics because they lose information. The information is lost when genes are damaged, when proteins take on strange shapes through glycation and other processes, when membranes lose structure and permeability so the communication between internal and external states is diminished, and when the hormone signals become garbled.

Many things contribute to this loss of information. Oxygen is one of the most potent causes of increasing entropy in the human system. Hormonal resistance is also a major cause as in the metabolic syndrome X.

Countering these forces of entropy is the major strategy underlying Evolutionary Fitness.

· Evolutionary Fitness

Comments

Posted by: Flower Online [TypeKey Profile Page] at September 12, 2006 3:45 AM

Isn't another major flaw with the heart-as-machine analogy the fact that a human body is constantly tearing itself down and (possibly) rebuilding itself based on the signals it receives? Lifestyle, diet, and mental state would seem to tell the body it's either time to decay and die or rebuild and grow.

A couple of corroborating points on the low heartbeat thing: An acquaintance - overtrained in bicycling and marathons - has a RHR of 36. He passed out during a routine blood test when a tiny bit of blood was extracted.

I know personally of two other cases where people started heavy endurance training and contracted mononucleosis when they were well into it. Neither understood how that could happen when they "were in the best shape" of their lives.

Posted by: Fugate [TypeKey Profile Page] at July 25, 2005 7:28 AM

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