December 1, 2006
Why must we breathe? Why is it so important? What makes us breathe so often? Why does a serious brain injury often result in death? Why does neuromuscular disease limit respiratory functional capacity? How does smoking cigarettes cause lung disease and how does it manifest itself? What is cystic fibrosis and why is it such a devastating disease? How does exposure to certain types of occupational hazards like coal dust affect lung function? Why do we die if we are exposed to too much carbon monoxide? What is the main underlying problem that causes premature babies to have so much respiratory difficulty?
Let’s take a look at how our lungs work and then let’s consider what we know about diseases and conditions that can diminish respiratory function to the point of severe disability and often death. By pointing out the specifics of what happens in each of these debilitating and deadly situations I hope to demonstrate to you, not only the incredible complexity of pulmonary function, but also the necessity for each component of the system to not only work right in order to be alive, but also to have the capacity to allow for survival. Logically then, evolutionary biologists, who claim that life came about solely by the forces of nature (natural selection acting on random variation) without the intervention of a mind at work, must present a plausible explanation for how such a system could come into being while still remaining functional every step along the way.
Every cell in the body needs oxygen to survive and to function properly. When the cells use oxygen (O2) for energy they produce a by-product called carbon dioxide (CO2). If the O2 level in the blood drops too low or the CO2 level rises too high in the blood it can result in death. So how does the body control the levels of these important gases in the blood stream?
The lungs are responsible for bringing O2 into the body and releasing CO2 into the atmosphere. The respiratory center, located in the base of the brain (brainstem), is itself able to continuously monitor the blood levels of CO2, and both CO2 and O2 by way of sensors located in the major arteries in the neck. With downward fluctuations of O2 and upward changes of CO2 levels, the respiratory center sends stronger and more frequent messages to the muscles of respiration (diaphragm and intercostal muscles) to have the lungs inhale and exhale harder and faster.
What Can Go Wrong?
Prolonged lack of O2 to any cell in the body eventually results in its death. For example, if a major artery on the surface of the heart (coronary artery) is blocked by a clot, then the muscle cells downstream are likely to die, causing what is known as a heart attack. If the circulation to a foot is compromised, then several toes may soon turn black causing what is known as gangrene. And if an artery in the brain gets blocked then the resulting death of the tissue affected causes what is called a stroke.
But prolonged lack of O2 to the cells of the respiratory center results not only in their death but also total body death because now the body can’t tell itself to breathe by sending the messages down the nerves to the muscles of respiration. Therefore it is clear that an injury to the brainstem or the cervical spinal cord potentially can block the formation or transmission of the electrical message to the muscles of respiration and cause death. Examples of this are massive stroke, head injury, use of sedative drugs, serious neck injury or an insult such as cardiac arrest which causes a prolonged lack of O2 to the respiratory center of the brain.
ME (Macroevolution) Break
A sincere review of respiratory control, by which the respiratory center is able to not only sense the levels of O2 and CO2 in the bloodstream, but also inherently know what the levels should be in order to maintain survival, and then be able to properly adjust the respiratory system by way of neuromuscular control, would show to most people of experience and intelligence that something other than mere randomness was at work here. Certainly a life form that was capable of managing this feat within itself would have had a definite advantage over others. But many questions would still remain: How did it develop such a complex and interdependent system in order for that survival in the first place? One can just consider a car with a faulty fuel, oil, or water temperature gauge allowing its owner to let it run out of gas, or let the engine seize, or overheat. In order for us to survive the O2 and CO2 levels in our bodies must be maintained within certain specific levels. All human experience tells us that the parts involved, the ones we call a sensor, a monitor, and a responsive system, which we know have the function of adjusting, or controlling some vital parameter in the body, can only have come about by an intelligent agent, a “mind at work”. To believe anything else without at least some sort of detailed explanation beyond the “it evolved over time” of macroevolution, goes against all human reason and experience.
Muscles of Respiration: Now What ?
When the diaphragm contracts it causes the ambient air to be inspired through the nose and mouth. The air is warmed and humidified as it continues to travel down ever decreasing caliber airways called the bronchi and bronchioles. This warmed and humidified air eventually reaches the organ of the lung namely, the alveoli, which are grape-like clustered sacs where O2 and CO2 exchange takes place in the circulation. The inherent elasticity of the lung tissue allows for the exhaling of the new mixture of air, now with less O2 and more CO2 than what was inspired seconds before. Then the whole process of breathing begins again with diaphragm and intercostal muscle contraction a few seconds later. See: http://health.howstuffworks.com/lung1.htm
Functional Lung Capacity: The Difference Between Eating or Being Eaten
One must keep in mind that for any one person, certain aspects of the components of the lung ultimately determine that individual’s pulmonary functional capacity. What does this mean practically? Well, if there is any problem with any of the components that are responsible for breathing, as described below, then it is likely that one will not be able to be as physically active as one would like to be. This is the difference between our hominid ancestors eating or being eaten. and therefore their ability to survive.
Such factors include:
Lung Capacity: largely related to:
Airflow Speed: largely related to:
Efficiency of Gas Exchange: largely related to:
So for example, you may have lungs that are the right size with enough airways and proper chest anatomy, but if there is a significant resistance to airflow, like is seen in allergic asthma and chronic smoking, where the mucus lining of the airway thickens and the muscles around the bronchi go into spasm, or in cystic fibrosis, where abnormally thick and viscous sputum build up in the airways, then you are going to be very short of breath when you try to be active and chances are you are not going to survive.
Alternatively, you could have wide open airways that have excellent airflow but the size and shape of your chest cavity is diminished due to a deformity of your thoracic spine, called kyphoscoliosis, (see: http://health.allrefer.com/health/scoliosis-scoliosis.html) which limits how much total air your lung can handle with each breath, and you will find that you have great difficulty exercising: and in a world of survival of the fittest, you will find that you just don’t measure up: so you get cut down.
Finally, you could have perfectly sized lungs and a chest cavity that allows for full expansion by way of an adequate number of airways with excellent speed of airflow but if your alveoli have been destroyed and there are airflow/circulation mismatches where, the air is there but no blood, or conversely, the blood is there but no air, all of which happens in people who get emphysema from smoking, then once again, you will not be able to adequately oxygenate your blood enough to maintain an activity needed for life as evolutionary biologists claim it must have come into being.
Now you may be sitting there reading this and saying to yourself “What does it matter about all of these medical conditions? Our hominid ancestors obviously didn’t smoke cigarettes and those who had asthma or kyphoscoliosis of the spine evidently would have gone the way of the dinosaur because these inherent defects in their systems would have resulted in them not being able to win the survival of the fittest as predicted by Darwin.
But in taking such a narrow view of what I have presented above you would be giving example of your inability to see the forest from the trees. For what I am trying to demonstrate here, by way of general information about how medical conditions that result in dysfunction of the pulmonary system would have impacted our hominid ancestors, is that the original setup to allow for adequate pulmonary functional capacity, and with it overall survival, must have been, in the words of Goldilocks, “just right!”
Every physician knows that you can have the biggest lungs in the world but if it takes too long to fill them up in order to get enough O2 in and CO2 out, you’re going to be short of breath and weak. And you can have the fastest filling lungs on the block, but if those lungs are too small to allow enough O2 in and CO2 out, even with such speedy airflow, then it’s game over. Pulmonary physicians are actually able to run tests and determine a person’s functional lung capacity and airflow speed. They know that if either of these results, or both of them combined, are below certain levels, that this means that that person is severely disabled and in fact may be eligible for social security benefits.
And even if enough air is going deep into the lungs to the alveoli, there has to be enough of them and they have to be in good working order for adequate O2 and CO2 exchange to take place to keep us alive. Not only do people with emphysema have problems here but also people with a condition called interstitial lung disease which causes thickening, or fibrosis, of the supporting tissue of the lung. This causes stiffness and loss of elasticity and eventually dysfunction and destruction of the alveoli. The causes of this condition are often a mystery. but the known ones are many and varied and include: inorganic dusts like asbestos, coal dust, and silica, various medications, and auto-immune disease (e.g. Lupus, Rheumatoid Arthritis).
Lung doctors are able to test the efficiency of alveolar function by measuring the diffusion capacity of carbon monoxide (CO) into the circulation. CO binds to the hemoglobin in the red blood cell 200x better than O2. That’s why if you are exposed to too much CO, like in a fire, your red cells will preferentially grab the CO rather than O2 and you end up dying of hypoxia.
A person breathes in an air mixture with a known amount of CO in it and then breathes it out again. The doctor then measures how much CO remains in the exhaled air and this lets her know how much ended up going across the alveoli into the circulation. People with low CO diffusion capacity have a defect in alveolar function and are very short of breath because even though they may have lots of air reaching their alveoli, they are not letting enough O2 go across into the body. But now let’s look at a couple of very unique aspects of lung function. Aspects which I think you will find very interesting.
1A. The Vacuum Effect: Give Me More Suction Scotty
The forces at work that allow the heart muscle to pump blood throughout the body and the respiratory muscles to bring air into the lungs, are exactly the opposite. All muscles work by contracting. The heart muscle encompasses the ventricles which become filled with blood. When the electrical message from the natural pacemaker in the heart causes the heart muscle to contract, this results in a drop in the volume of the ventricles and an increase in the pressure of the blood inside making it shoot out through the pulmonary or aortic valves on its way to the lungs, or the rest of the body. But that’s not how respiratory muscle contraction causes the inspiration of good clean fresh air.
Hold your nose and close your mouth and try to breathe and you’ll feel a tugging throughout your whole head and neck area like a big vacuum cleaner. When the main muscles of respiration contract they don’t squeeze the air into the body like the heart squeezes the blood out of it. Together, the muscles of respiration expand the volume of the chest and in doing so they reduce the air pressure in the chest cavity as compared to the air outside and this makes air rush in through the nose and mouth and down to the alveoli. So the heart pumps by generating a positive pressure force and the muscles of respiration cause the lungs to bring in air by generating a negative pressure force. But how do they do it?
1B. Show Me Your Muscles
The diaphragm is the main muscle of respiration. It is a large sheet of muscle that separates the chest and abdominal cavities from each other. The diaphragm is dome- shaped and points upward toward the chest cavity. When it contracts it actually flattens out causing the volume of the thorax to increase. Once again, in direct contrast to how heart muscle contraction causes a drop in the volume of the ventricle resulting in an increase of pressure and a release of blood, the expansion of chest volume by contraction of the diaphragm causes a drop in pressure in the lung resulting in air literally being sucked inside. The external intercostal muscles are positioned in such a way that when they contract they lift the chest wall upward further expanding the chest and further helping the lungs to bring in more air. And if you really need a whole lot of oxygen, like when you are exercising or running to catch a bus, you can use the accessory muscles of respiration which lift and further expand the chest by the muscles in the upper torso.
At rest, expiration of air out of the lungs occurs without the need of energy because of the natural elastic recoil contained within lung tissue. However if someone is exercising or running from a predator, their internal intercostal muscles and their abdominal muscles pressing up against the diaphragm can help expiration by diminishing the volume of the chest cavity faster thereby allowing the lungs to take air in again quicker.
1C. What can go wrong?
Examples of problems that can arise in the chest wall or respiratory muscles which can severely limit lung function include, as has already been mentioned, curvature of the upper spine, or kyphoscoliosis, and additionally, diaphragmatic muscle injury from surgery or neuromuscular disease such as muscular dystrophy or Lou Gehrig’s Disease. All of these will impact the ability of the chest wall to move well enough to afford adequate respiratory function and may limit one’s activity due to shortness of breath. So you can see that just having lungs contained in a chest cavity with neuromuscular control does not guarantee one having adequate lung functional capacity to allow for survival.
1D. ME Break
Of course one is left to ponder how this unique system in the body, which is able to apply a negative pressure at the precisely right moment, with precisely the right amount of power to allow for adequate air exchange, came about. The ribs and their muscles must be in perfect position, must be adequately innervated, and must work in a coordinated fashion. The diaphragm must have exactly the right shape and thickness so when it is maximally contracted it will provide enough of a negative force to cause enough air to enter into the lungs against the inherent forces of air resistance to allow for activities necessary for survival. To most people the whole system is a marvel in engineering. All human invention pales in comparison. But if this could come into being simply by the random forces of nature without any intelligence being involved then maybe we shouldn’t be so impressed with humanity. After all, if given enough time, anything can happen, so maybe even all of our inventions would have come about if we waited long enough.
2A. Alveolar Function; Without it you’re dead !!
As mentioned before, the “organ of the lung,” the place where all of the necessary action occurs, is in its estimated 500 million alveoli. This is where gas exchange: the taking onboard of O2 and the release of CO2, takes place. In order to achieve this each alveolus is supplied with upwards of 1,000 pulmonary capillaries, which are very thin blood vessels, that allow gas exchange to take place in the red blood cells. See: http://health.howstuffworks.com/lung2.htm
The alveoli are shaped almost in perfect spheres and my engineering son, Matthew, has advised me that a sphere is the shape that affords the greatest surface area for a given volume. The bigger the surface area of each alveolus, the more capillaries that are able to allow for the intake of O2 and the release of CO2, and the greater overall gas exchange efficiency. In fact it has been estimated that the total surface area of the alveoli of a typical adult human is about the size of a tennis court. Something to ponder isn’t it?
2B. The Problem with Preemies
But it doesn’t end here. For when the lungs try to open up not only do they have to have enough energy to fight against the elastic recoil that is built into the lung tissue, they also have to fight against the surface tension that exists between the incoming air and the fluid within the alveoli that surrounds the capillary. A special cell that surrounds the alveolus secretes a chemical called surfactant which is able to markedly reduce this surface tension and ease the ability of lung inflation.
Which brings me to “the problem with preemies” Premature babies who are born before 28-30 weeks of gestation usually are deficient in surfactant and have great difficulty breathing because they have to use so much energy just to try to inflate their lungs. The special cells that make surfactant don’t appear in the developing alveoli until about 20 weeks of gestation and then they are triggered hormonally to start making surfactant about 8-10 weeks later. You’ve got to wonder when and how surfactant came on the scene for human survival? Without it our hominid ancestors wouldn’t have hardly been able to take even their first breath, never mind grow to maturity and be able to reproduce.
For me, the belief and faith in macroevolution, as touted by the NeoDarwinian evolutionary biologists of our day, is very hard to swallow. Hey, come to think of it, swallowing is a very complicated neuromuscular process which can dysfunction due to a whole host of medical conditions. So let’s take a look at that next time because, after all, swallowing is the vital mechanical gateway to the digestive tract and life in the world.
See y’all next year!!
Howard Glicksman M.D. graduated from the University of Toronto in 1978. He practiced primary care medicine for almost 25 yrs in Oakville, Ontario and Spring Hill, Florida. He now practices palliative medicine for a Hospice organization in his community. He has a special interest in how the ethos of our culture has been influenced by modern science’s understanding and promotion of what it means to be a human being. Comments and questions about this column or any of the previous ones are welcome at firstname.lastname@example.org
Copyright 2006 Dr. Howard Glicksman. All rights reserved. International
File Date: 12.01.06