01/03/2011 - Articles

How Good a Pump is Your Older Heart? - Part III

By: Ed G. Lakatta, MD

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Oxygen is needed for the body's cells to survive and function. The heart is the slave to your body's oxygen needs because it must pump your blood, which is the source.

To read this article with accompanying illustrations, as well as all the articles in the series, you can go to the mini-site: "Aging of Your Heart and Blood Vessels is Risky" by clicking here .

Introduction

Oxygen is needed for the body's cells to survive and function. The heart is the slave to your body's oxygen needs because it must pump your blood, which is the source of oxygen for these cells. You can compare your heart to the pump of a well supplying water to an acre of grapevines on an isolated vineyard. The vines need this well water to survive. When they are dormant in the winter they need some water. But, come spring, when they begin to bud and grow rapidly they need much more. During the vines' active period the pump on the well must work harder to provide this extra water. Your heart is your body's pump and during periods of "activity", meaning exercise such as running or walking up stairs, it must pump more blood, harder and faster, just like the well that supplies water to the vines when they are producing fruit and need more nourishment (energy). In pumping harder it changes the way it pumps.

Efficiency of Your Heart As A Pump The Heart Changes In Pumping During Exercise

The heart can change the way it pumps because it is made of elastic-like material. Thus, it is able to change shape and size depending on the amount of blood it contains at any given time point (and depending on the age of its owner). During each heartbeat the heart wall squeezes down (contracts) on the blood within its cavity and forces this blood into arteries for distribution to your body. Not all of the blood that is in the heart at the start of each heartbeat is forced out during that beat. In other words, the heart is not emptied completely with each beat and then completely re-filled before the next. The heart can be compared to a rubber cake decorator sleeve. You can squeeze as hard as you like, but you will still find some icing inside the rubber sleeve when you go to refill it. In a healthy resting heart, only about 60-65% of the blood that flows back into it between heartbeats is pumped out of it during the next beat. Some blood is left behind, just like the icing in the cake decorator sleeve. The amount of blood that does get pumped out with the each new beat relative to that amount present at the beginning of the heartbeat, is called your heart's ejection fraction (EF). From here on we will refer to it as EF.

It is measurement that doctors and cardiologists often look at to estimate how well your heart is behaving as a pump.

What Happens to Your EF At Rest As You Become Older?

On average, your EF, at rest, does not become reduced as you age. See Illustration: You can see from this illustration that at rest the young and old hearts have the same ejection fraction. Both the young and old eject about 67% of the blood in the cavity of the heart with each heartbeat at rest. They start each heartbeat holding approximately the same amount of blood (90 ml) and end the heartbeat with the same of amount of residual blood left in the heart cavity (30 ml).

Why can the old heart act the same as the young at rest? It can because the amount of blood returned to both the young and old heart at rest each minute is relatively low, and hearts don't have to work hard to circulate this blood. They could work harder, but don't have to, if relatively healthy, to keep the status quo at rest. But during vigorous exercise, young and old hearts behave differently.

What Happens to Your EF During Strenuous Exercise? Young and Old Hearts Behave Differently!

You could think of the movement of the blood returned to your heart by your body at rest at rest like a slow moving stream. Initially, the body's muscular actions, and other "reflex" commands via the spinal cord and lower brain function automatically increase the flow rate at which blood is returned back to your heart from your body. But, suddenly, there is a torrential downpour of rain (or huge increase in the volume of blood flowing into the heart with each beat). The stream swells and begins to moves faster and faster. And, like the stream in a downpour, this marked increase in blood suddenly returned to the heart from the body during vigorous exercise initially makes the heart stretch and increase in size (it swells). The "young" heart reacts immediately to this initial swelling by pumping faster and pumping harder in order to get more blood out with each beat. The "young" heart doesn't want to be swelled; it wants to stay the same "lazy size" or small size at the start of each heartbeat that it was at rest. But, how can it do this when it has to push that swollen stream of blood which is flowing into it? What will keep it from swelling? To keep its resting size at the beginning of each heartbeat and still pump out more blood the young heart increases its E.F. In other words, the younger heart in response to this increase in blood returned to it during vigorous exercise pumps a "king size" rather than a "regular" amount of blood from the heart cavity with each beat by squeezing down to smaller size at the end of each heartbeat, as shown in the illustration. For example, during strenuous exercise the young heart squeezes down "hard" so that all that is left after this heartbeat is a very small amount, say 10 ml.

This hard squeeze pushes more blood out than a soft squeeze (at rest) pushes out and EF increases up to 85-90%. It is this increase in EF, in addition to the increase in heart rate, which allows less time for the heart to fill between beats, during vigorous exercise. These things (the hard squeeze, the increase in EF, the increase in heartrate, and the decreased time to fill between beats) keeps the heart of a exercising younger persons small at the start of the next heartbeat, basically the same size as when it is at rest. Wholla! The young heart stays it's same "lazy" resting size as the heart beat begins, but squeezes down to a smaller size at the end of the heartbeat.

Heart Pumping Mode Changes During Exercise For The Older Person

During strenuous exercise the older heart can't squeeze down to the small size achieved by the younger heart at the end of the heartbeat. (We'll learn exactly why in a future article). Consequently, it cannot increase its EF like the younger heart, so the EF of the old heart is only a little increased over its resting EF. In the illustration you can see the old heart size at the beginning of strenuous exercise starts out larger than at rest, holding approximately 120 ml., and when it is squeezes down at the end of the heartbeat it holds about 35 ml of residual blood. Consequently, it cannot increase its EF as much the younger heart, so the EF of the old heart stays closer to its resting EF.

The additional inability of the old heart to increase its beating rate during vigorous exercise as discussed in the last article, Why Does Aging Cause Your Exercise Capacity to Deteriorate? permits a longer time for the heart to fill with blood between heartbeats. This longer filling time which permits more blood to fill the older heart between beats coupled to its inability to increase its EF causes the old heart to stretch (or dilate), and thus its size at both the start and end of the heart beat is increased during vigorous exercise over the size of the young heart during vigorous exercise.

The Old Heart Does "The Trick"!

Even though the old heart is unable to squeeze down to a small size at the end of the heartbeat, and thus unable to increase its EF like the young one, the old heart is still able to pump out a "king size" amount rather than a "regular" volume of blood with each heartbeat during vigorous exercise. This is the TRICK we told you about! The "trick" works because the older, dilated (or stretched out) heart, by having a larger amount of blood in its cavity at the start of each heartbeat (essentially like having a bigger fuel tank) is able to increase the volume of blood pumped at the same , E.F. as shown in the illustration.

However, this adaptation (or trick) used by the older heart i.e. to pump an increased amount of blood during vigorous exercise because it dilates, rather than increases its EF like the young heart, is not without a price! The older heart adapts, but pays because the pressure within the dilated heart cavity between heartbeats becomes increased during exercise compared to that in a smaller, younger heart.

Summary

In the first article of this Series, " Are You in Shape for Your Age? " you learned that there is an approximate 50% age associated decline in your body's maximum exercise ability and thus its maximum oxygen utilization, and that this can be measured by standardized exercise testing. In the second article, " Why does Aging Cause your Exercise Capacity to Deteriorate? " you learned about cardiac output, and that it is a major factor that determines your exercise capacity. You also learned how to calculate you maximum heart rate. You learned that an inability of the older heart to beat as fast as it did when it was younger is one of the problems with reduced exercise capacity at older ages. And finally, you learned that a decline in maximum exercise capacity with aging, in addition to a reduced maximum cardiac output is due to a decline in the older body's oxygen utilization (or ability to transport and use all the oxygen due to changes in vessels, or ""the transport system", and body composition, or "lean muscle mass".

Today's article taught you about EF and has shown you how "smart" the young heart is. It not only can beat a lot faster during exercise but also increases its EF and maintains its resting size at the start of the heartbeat. You learned that the old heart cannot increase its EF as well as the younger one, and dilates, and that is the "trick" or adaptation that allows the older heart to increase the volume of blood that it pumps in each beat during vigorous exercise equal to that of a younger heart, but at nearly the same EF as at rest or 71 %. (See diagram.) We will learn in the next article, "How Your Older Heart May Shorten Your Breath", that the higher operating pressure that accompanies dilatation of the older heart during exercise can cause "shortness the breath" to be experienced and how this can limit exercise ability.

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Created on: 12/13/2002
Reviewed on: 01/03/2011

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