While in college, I drove a 1970 pea-green Datsun, which I fondly called, 'The Green Ghost.' That car, a rolling death trap, almost made a ghost out of me. The tires were bald, the radiator had a hole in it and gas fumes leaked into the passenger compartment. The stick shift occasionally slipped out of gear and the car sometimes threw an epileptic fit without warning---once resulting in a dizzying 360 degree spin through a busy intersection.
I suppose I could have taken better care of my car had I not been so completely ignorant of basic automotive mechanics. Despite my carelessness, The Ghost rallied on for some time, right up until the bitter end. In retrospect, with a bit more time spent learning about cars, I might have avoided the catastrophic breakdowns that eventually doomed the car to the scrap heap.
Now, more than two decades later, whenever I think of the human heart, I think of my old car. What's the connection? Keep reading.
What a marvelous piece of evolutionary engineering the heart is. Designed to pump 1.3 gallons of blood per minute at cruising speed, the heart can move four times that amount at full throttle. And at less than a pound and little bigger than a closed fist, it can push 1.5 million gallons of high-octane plasma through 50,000 miles of vessels each and every year. More exquisite than the finest Swiss watch and with a lifetime warranty of 100 years or more, not even Rolls Royce can give you a better return on your investment.
So why don't we take better care of it?
Despite our need to boldly go "where no man has gone before," whether it's the top of Mount Everest or the desolate plains of Mars, for many people, the real undiscovered country is the human body. In truth, most of us are only marginally more knowledgeable about the inner workings of our own body than were our ancestors of a century ago. That ignorance has turned out to be the death of far too many of us.
It may be too late for the mishandled automobiles of reckless youth, but there's still time to learn about your heart.
Under the Hood and Behind the Sternum
The basic mechanics of the heart are, elegantly simple, yet complex. The heart is essentially a blood pump for the cardiovascular system. Divided into left and right halves, it is designed to cycle blood through the body---somewhat like the way motor oil is cycled through your car's moving parts. The heart is dual-pump organ divided into four chambers and lies along the midline of the body between the lungs in an area called the mediastinum (media-stein-um). The two upper chambers are called the atria and are known as the left and right atrium. The two lower chambers are the ventricles and are designated as the left and right ventricles. Think of the atria as primer pumps and the more muscular ventricles as the power pumps that do most of the 'heavy lifting' of pumping blood. Although these two sides work in concert, the left side and particularly the left ventricle actually pumps with greater force than the right side.
The outer wall of the heart is made up of three layers of tissue called the epicardium, myocardium and endocardium. Of these three layers, the myocardium, made up of tough muscle tissue, is the thickest and lies sandwiched between the other two. The myocardium is responsible for the heart's ability to contract and uses adenosine triphosphate (ATP), as its energy source. The heart is enclosed within a double-walled protective sac called the pericardium, which inhibits excess distension of the heart while also helping to anchor it in place.
Blood enters the heart via the right atrium from the coronary veins, which return blood from the heart wall, and through the vena cava (vee-na-kay-va). The vena cava is a large vessel that runs the length of the torso. It is one of the major veins that carries blood from the tissues of the body to the heart. It branches in the upper chest (where it is called the superior vena cava) into the subclavian veins, just above the heart. From here, it turns into a network of veins that branch out to the arms and hands. The vena cava descends below the heart (the inferior vena cava) where it branches again at about the waist (the common iliac) and proceeds along the legs as the femoral veins and a network of smaller vessels.
Think of the blood returning to the heart via these veins as 'used' blood. Like a used car, this blood has been through the system and has acquired some mileage. It is also deoxygenated (lacks oxygen) and carries some waste material. The blood fills the right atrium until the pressure in this chamber becomes greater than the pressure in the right ventricle, which lies directly below. The ventricle dilates (expands), which creates a low-pressure vacuum. An ingeniously designed 'door', the tricuspid valve, which separates the right atrium from the ventricle, opens up and allows blood to flow down into the ventricle. About two-thirds of the blood flow is gravity-fed. The rest comes as the atrium contracts (squeezes). The pressure-sensitive triscuspid valve works like the anti-backup tire spikes found in some parking garages. It allows blood to flow in only one direction, preventing back-flow.
Now the ventricle contracts, pushing the blood up through the pulmonary trunk, a large artery that feeds blood out to the lungs. The returning blood is like a pre-owned car that's been meticulously detailed. It comes back cleaned up and oxygenated. This blood enters the heart through the left atrium via the pulmonary veins. A similar sequence of events occurs on the left side of the heart as it did on the right. In fact, this blood cycling on the left and right sides of the heart occur simultaneously. The blood from the left atrium then flows into the left ventricle via the bicuspid valve, which functions similarly to the tricuspid valve on the right.
As pressure builds in the left ventricle, the blood is pushed up into the aorta, a large artery that serves as the main trunk of the systemic arterial system. The aorta arches above the heart where branches supply blood to the head and neck. It then heads south down toward the waist where it branches at about the same place as the inferior vena cava. In fact, the arteries and veins are like two highway systems that essentially go to the same places. The aorta feeds blood via the arterial network out to the body's tissues. Your blood pressure measurement reflects the aortic pressure curve (the range from high to low pressure that occurs in the aorta).
Like your car, your heart has an electrical system, which triggers the rhythmic contractions and dilations required for proper blood flow. This process of electrical signaling, contraction, dilation and blood flow is collectively referred to as the cardiac cycle. The total amount of blood the heart pumps per minute is called the cardiac output while the dynamic range of output (the difference between output at rest and output at maximum exercise levels) is called the cardiac reserve.
This process of cycling blood throughout the body will continue for every second of every minute of every day for the rest of your life. Over a journey of 65 years or more, your heart can pump 95 million gallons of blood over more than 3 million miles of vascular highway! That's not all. Even with 70 percent of the heart's blood flow effectively impeded, the cardiac equivalent of driving with a nearly dry oil well, the heart can keep rolling along with minimal problems. Once you cross that 70 percent barrier however, things can go from bad to worse, fast. In fact, the heart's strength, it's delicate engineering, is also its weakness. Electrical signals can be blocked or timing can fall off (bundle branch blocks), arteries can get gummed up (angina pectoris), valves can stick (valve stenosis) or leak (mummers) and pumping efficiency can decline. Is it any wonder, then, that our heart gives out when we skimp on the day-to-day maintenance? Just imagine what it would mean if you only had one car and it had to last for your entire life.
Unlike many older cars, our hearts don't come with a user's manual, but don't worry. You don't need to be a brain surgeon to understand the basics of how it works. That's the first step in learning how to provide the proper maintenance to keep it running. Now that you know a little more about what goes on 'under the hood,' perhaps you can see how important it is to take care of your heart. Most of us only get one. A proper diet along with exercise and a reduction in stress goes a long way toward keeping your heart tuned up and ready for your own journey through life.
