CHAPTER 7

The Chest and Lungs

The function of the lungs is to exchange gases between the blood and the atmosphere. As our bodies break down the food we eat into energy that can be used by the cells, oxygen is used and carbon dioxide is created by the tissues. These two gases must be exchanged every minute in order for us to stay alive. The brain controls the rate and depth of our breathing in such a way as to maintain adequate gaseous exchange. The brain's drive to breathe is controlled by the level of carbon dioxide in the blood. As this level increases (such as during exercise), we breathe faster in order to exchange more carbon dioxide from our lungs into the atmosphere. If we did not breathe faster, the carbon dioxide dissolved in our blood would cause the blood to become more acidic and our bodies do not function well with more than the normal amount of acid.

As we exercise, we also require more oxygen. However, the increased rate or depth of breathing needed to eliminate the excess carbon dioxide is usually more than enough to supply the extra oxygen needed. Only in certain abnormal circumstances is the rate and depth of breathing controlled by the level of oxygen in the blood.

If we were unable to eliminate enough carbon dioxide from our lungs over a period of several hours or days, our kidneys would begin to compensate. They would sense that the acid in the blood was building up and would hold on to more base (or alkaline) than usual in order to keep the level of acid in the blood at the normal level. So the lungs control the exchange of oxygen and the lungs and kidneys together control the exchange of carbon dioxide, and hence acid.

The mechanism of gas exchange: The lungs are enclosed in the chest wall. In order for air to enter them, the pressure inside the lungs must be less than the atmospheric pressure outside the lungs since gas flows from high pressure to low pressure just as water flows downhill. When we breathe, our chest wall expands and our diaphragm moves down, creating negative pressure in the lungs which then sucks air into them. When we exhale, our chest wall relaxes and the air flows out as the pressure in the lungs exceeds the atmospheric pressure outside (positive pressure).

The purpose of examining the chest and lungs is for the doctor to see if adequate gas exchange is occurring. As with the examination of the other organ systems, the doctor has four methods at her or his disposal: to look, listen, feel and tap.

1. Looking (Inspection): When examining the patient, the physician's first question should be: is this person exchanging enough oxygen and carbon dioxide? The second question should be: is this person having to work very hard to exchange the proper amount of gases?
   
   A person who is sitting comfortably in the office is most likely exchanging enough of these gases. On the other hand, the person who is short of breath, breathing very fast and sweating profusely is probably not exchanging enough gases.
   
   The amount of gas exchanged by the lungs is equal to the rate of breathing times the amount (or volume) of each breath. To assess how much gas exchange is occurring, the doctor must look at both the rate and the depth of breathing. Adults breathe anywhere between 12 and 20 times per minute, and children breathe much faster. When problems occur and the body needs to exchange more gases, the breathing rate may go up, the depth of breathing may increase, or both. At other times, problems such as injury may cause breathing to be painful. In these circumstances, a person may begin to take more shallow breaths (in order to have less pain), and have to breathe faster in order to compensate and exchange an adequate amount of gases.
   
   The work of breathing must also be tested. For example, when a person is unable to exchange adequate gases or becomes exhausted when trying to do so, respiratory failure is occurring and this constitutes an emergency. Treatment could be as simple as oxygen therapy or as complicated as placing them on a machine to breathe for them until they have improved.
   
   By looking at the patient, the doctor can get information which is valuable in deciding what the problem is and how to treat it. When a person has great difficulty breathing, they begin to use additional muscles to help them expand their chest wall. Muscles in the neck, which are not usually used to breathe, are asked by the brain to join in the fight to get more air. As the body exerts great force to generate large negative pressure in the lungs (to suck more air in), some parts of the chest wall collapse as they are sucked in by this large pressure. For example, a person with great difficulty breathing may have retractions (or indented areas) in between the ribs, or above the collar bone. Their stomach may move inward with breathing instead of outward as usual. In babies, the nostrils may flare out while breathing -- all these are signs to the observant doctor that difficulty in breathing is occurring and that treatment is needed.
   
   In addition, the doctor should always observe the movement of the chest wall to see if the movement is symmetrical (the same on both sides). As the lungs expand, both sides of the chest wall should move together. If not, this could be a clue to what the problem is.
   
   The doctor should also look for any deformities of the chest wall which may have been present since birth or may be due to injury or growth of tumors.

2. Listening (Auscultation): In the examination of the chest, the stethoscope is particularly important because the sounds that can be heard are often a clue to what is going on inside.
   
   Several sounds may be heard when listening to the chest, some of which are mentioned on the next page. Bronchial and vesicular breath sounds are the names given to two types of normal lung sounds. In both, the sound heard is due to air moving freely through the airways in the lungs. The pitch and quality of these sounds are different, but they are both normal and heard in most patients.
   
   An additional method of assessing breath sounds is to note whether they are normal or decreased in volume or amount. A decrease in the amount of normal breath sounds could mean that very little air is actually entering or leaving the lungs and that the person is in respiratory failure, even if other abnormal breath sounds are not present.
   
   Some types of abnormal breath sounds:
   Rales are sounds best described as crackles since they sound somewhat like the crackling of Rice Crispies in a bowl. Rales are heard when small portions of the airways which have collapsed during expiration are suddenly opened by the force of incoming air. Rales are almost always abnormal and can be due to such problems as pneumonia or fluid overload.
   
   Rhonchi are coarse sounds heard on expiration. They are due to the presence of fluid in some of the airways. As the air is forced out past the fluid, the fluid gurgles and rhonchi are heard.
   
   Wheezes are high pitched whistling sounds usually heard on expiration. They indicate that the airways are narrowed, and as air is forced through them, a whistling sound is created. Wheezing can be heard in asthma, chronic obstructive pulmonary disease and in some allergic reactions, and is an indication that additional work of breathing is being expended to rid the lungs of air.
   
   Rubs are heard when the two covering surfaces of the lung are inflamed and rub against one another. Usually these surfaces are smooth and have a lubricating fluid in-between them. However, in some infections which affect the lining of the lungs, this smoothness disappears and a rub is heard.
   
   Stridor is a high pitched sound that comes from the throat when air is being drawn into the lungs while the vocal chords are not fully open. This sound may be heard when the tissues of the throat are abnormally swollen. This sound may indicate respiratory failure.
   
   Egophony is a term describing the change in sound that may occur when lung tissue is no longer filled with air but becomes fluid filled. A patient may be asked to say "cc" while the doctor listens. If the area of the lung being examined is fluid-filled because of disease, then the "cc" sound will change to sound like "aa".

3. Feeling (Palpation): Looking and feeling go hand in hand, and many of the same abnormalities which were seen can also be felt. Doctors typically feel the movement of the chest wall during breathing to make sure that both sides are moving equally well. If one side moves less than the other it could mean that the diaphragm (muscle of breathing) is paralyzed. A doctor typically places her or his hands on a patient's back at symmetrical positions on either side and feels as the patient breathes. In addition, a doctor may press on a certain area of the chest wall to see if it is tender or if there is any evidence of injury or broken ribs. A broken rib is often tender at the site of the break. This is however difficult to distinguish from other causes of tenderness over a small area. In order to confirm that a broken rib is causing the problem, the doctor may press on the front and back of the chest wall simultaneously. Since ribs are bow-shaped, pressing from both ends (front and back of the body) will cause the broken area (if there is one) to be painful just as if it were being directly compressed. If the rib is not broken, this will not be painful at all.
   
   The sound of the voice is transmitted through the resonant air-filled lung tissue and can be felt as a vibration on the skin. Try this: place the palm of your hand on someone's bare back and ask them to say: "ninety-nine". You should feel the vibration of their voice in your hand. This is called vocal fremitus and can be either increased or decreased in certain diseases. In pneumonia, when part of the lung is filled with blood and pus instead of air, the sound is transmitted more efficiently to the skin and fremitus is increased. When fluid has filled the space between the lung and the chest wall, the sound is transmitted less efficiently and the fremitus is decreased. This occurs in such conditions as heart failure and some types of lung cancer.

4. Percussion (tapping): In examining the lungs, the doctor may tap over the chest wall in much the same way as she or he does when examining the abdomen. The sound which is heard helps to determine the state of the tissues below and can be very useful in diagnosis.
   
   If the sound over one side is like a high pitched drum (tympanitic), while the sound over the other lung is normal or hollow sounding, it might mean that one lung has collapsed inside the chest wall and has a leak. If so, this is potentially a serious and even life-threatening condition that demands immediate treatment.
   
   In the same way that fluid collections in the chest cavity (around the lungs) can be detected by feeling the absence or presence of fremitus, fluid can sometimes be detected by tapping over both sides of the chest wall. On the normal side, the sound will be hollow or resonant signifying that air-filled tissue is beneath the tapping finger. On the side with a fluid collection, the sound will be more dull at the bottom of the lung where the fluid has collected around it. You can confirm that it is fluid by having the patient lay down on her or his side. The level of fluid will move to the side which is down, and the dull sound will no longer be at the bottom of the chest wall at the back but will now be at the side of the chest wall.
   
   Fluid collections are not the only things that cause the tapped sound to be dull. Lung tissue that has collapsed and is no longer air-filled can also cause a dull sound, as can lung tissue that is infected and has become filled with blood and pus -- as commonly occurs in pneumonia.
   
   Additional lung tests, the chest x-ray: is a typical part of the medical examination for any patients with lung or heart problems. It allows the doctor to see a black and white image of the lung tissue, the heart, and the bones of the chest wall and spinal column. It is extremely useful for the evaluation of conditions such as pneumonia, heart failure, asthma, emphysema, and lung cancer. It is widely used because it is relatively inexpensive and yields such a large amount of information.
   
   The arterial blood gas is a blood test that is obtained from an artery. It tells the doctor about the composition of the blood as it comes out of the heart. It is useful in determining the oxygen content of the blood, the carbon dioxide content of the blood and the pH (or acid) content of the blood. It tells us how well the lungs are doing at exchanging gases, and if the kidneys have come into play to help the lungs. In addition, it tells the doctor what percentage of the oxygen carrying molecules in the blood are fully saturated with oxygen.
   
   Pulse oximetry is another quick and easy way of determining the percentage of the oxygen carrying molecules in the blood and if they are fully saturated with oxygen.
   
   Pulmonary function tests are performed in a laboratory and give very specific details about the function of the lungs both normally and in the diseased state. A patient is connected to a complicated breathing machine and asked to do certain respiratory maneuvers such as breathe in and out as fast and deeply as possible. A computer then analyzes the gases that go in and out of the patient's lungs, and it is able to quantify the performance of the patient in relation to normal, healthy persons.

Chapter 8