Cardiac rehabilitation centers have
spread like sprouts during the last 10 years. It has become au courant to save
the heart; revascularize it; exchange it for another, or swap for a metal
act-alike. Recent evidence suggests that active people have fewer heart
problems than sedentary people, but I wouldn’t like to test that
hypothesis against populations in
nursing homes. They seem to live the longest while doing the least. It would
appear that after a certain age, activity might be counterproductive, and
cutting activity to suit the cardiac reserve might be the best game plan.
Alas, as this column has pointed out,
although a wise medical dictum is “rest the injured part” it is hard to rest
the heart. It must beat if you are to survive. Somehow, after a severe heart attack, the heart can’t
take the day off in order to heal, but continues pumping, even if
“half-heartedly”, until weeks later healing occurs and the damaged area patched
with scar tissue. The real issue is, during the damage period, how to keep the
heart beat from outrunning its oxygen supply, which will occur if the heart
requires more blood than the coronary arteries can supply.
So is the heart ever really rehabilitated?
I suspect not. Only protected. Rather it would seem that rehabilitation
benefits the heart indirectly. Exercising other muscles of the body gradually
and gently induces enzymes that make the
peripheral muscles of the body more efficient. Thus when the patient walks
there is less oxygen demand by the walking muscles. The have been conditioned
(or reconditioned), they require less oxygen than heretofore and therefore less
demand is placed on the heart. In this indirect manner rehab preserves the
heart.
Muscles themselves are quite
individual. The dark meat of fowl is conditioned for conserving oxygen and
converting it to carbon dioxide and water. The dark color is due to myoglobin,
a substance akin to hemoglobin that binds oxygen so avidly. White meat is for
anaerobic function, works with little if any oxygen. This alternate pathway for
work results in the production of lactic acid that is stored in the liver until
it can be metabolized into carbon dioxide and water. The anaerobic cycle is
sort of a safety valve in fowls. But in humans, when the heart fails to supply
adequate oxygen the production of lactic acid overwhelms the ability of the
liver to detoxify and manage it. So much lactic acid is produced that neither
the kidney or lung can compensate and put the body back in acid balance.
Lactic acidosis occurs when either the
heart can’t fulfill normal demand for oxygen delivery, or the demand of the
peripheral muscles (as in a marathon) exceeds the ability of the normal heart
to deliver enough oxygen. Conditioning of the muscles enables them to work
harder using less oxygen. Thus in heart attack patients, with diminished
cardiac reserve, increasing the efficiency of muscles calls for less heart
action, slows the rate and force of contractions. In other words, rehab “rests
the heart”. It doesn’t by itself strengthen the heart muscle, but creates
conditions in which the heart can recuperate by lessening the stress on the
heart. In the old days, after a heart attack patients were asked to lie quietly
in bed without moving for about 5 weeks in the belief that that would rest the
heart. It did in a way but when the patient got out of bed, the muscles were so
deconditioned that any movement caused increased heart rate and some shortness
of breath.
Conditioning is tricky. Runners may be
out of condition for swimming and vice versa because not all muscles are
conditioned by specific athletic agents. Rehab, on the other hand, takes all
muscles into account – or it should.
One lesson to be learned is that in the
young general good conditioning should protect the heart. However, if there is
premature coronary artery sclerosis exercise won’t protect the young, and might
be dangerous. In those cases the heart must be revascularized.
On the other hand, exercise makes
people feel better which, after all, is what life is all about. And it is much
more pleasant to walk a wooded path than a treadmill; to bicycle on lonely roads than pedal the
exercycle in the garage.