Diagnostic Tests and Procedures In Asthma, Bronchitis and Emphysema

WHO SHOULD HAVE A CHEST X­RAY?

Any patient who seeks medical care for acute or chronic airway disease deserves at least one diagnostic chest x­ray. If a chest x­ray has been recently taken another may not be necessary, but this should be left to the physician's discretion.

A chest x­ray can uncover many lung diseases such as cancer, pneumonia, tuberculosis, and pneumothorax. The chest x­ray is also useful in bronchitis, asthma, and emphysema to rule out a complicating lung condition. Thus, a normal chest x­ray is often reassuring and an abnormal one helpful in a diagnosis.

One final note. If you see a doctor because of an upper respiratory problem (such as a cold or sinus condition), not strictly a pulmonary condition, a chest x-ray may not be indicated.

DO THESE SIGNS AND SYMPTOMS ALWAYS MEAN LUNG DISEASE?

Definitely not. These signs and symptoms are non­specific; they may indicate lung disease, disease in other organs, or no disease. For example, shortness of breath may occur due to anemia (low blood count), heart disease, or even pregnancy, to name a few non­respiratory causes. Cough could be due to a simple cold and be of no consequence, or could be the first symptom of lung cancer. Hemoptysis, always a frightening symptom, could be from a bleeding nose or tooth; more commonly it is due to lung disease, but patients with some types of heart disease can also cough up blood. Chest pain could of course be cardiac in origin, but many times chest pain is due to indigestion or even muscle spasm of the chest cage.

Signs are also non­specific. Tachypnea and hyperpnea are present in every healthy person who exercises vigorously. When present in a resting individual they may be related to heart or lung disease, or less commonly to disease elsewhere. Finally, an abnormal chest x­ray (a spot or mass in the lung; fluid in or around the lungs) could be from a benign condition or from something serious, such as lung cancer.

Because of this non­specificity of signs and symptoms, each patient must be evaluated in view of the entire clinical picture. Given the presence of a bothersome symptom or abnormal sign, there is simply no substitute for a good clinical evaluation by an interested, competent physician.

WHAT ARE PULMONARY FUNCTION TESTS?

Pulmonary function tests are helpful in determining how well the lungs and respiratory system are working. There are two broad categories of tests: lung mechanics and gas exchange.

Lung Mechanics

Tests of lung mechanics tell how well your lungs and chest cage move air in and out – the mechanical function of the respiratory system. In these tests the technician will ask you to perform some sort of breathing maneuver, usually a forced expiration after a deep inhalation. How much air you breathe out and how fast you exhale it are measured by collecting the air in a special device called a spirometer; hence the basic test of lung mechanics is called spirometry.

Spirometry is a very simple test, in routine use for many years. It measures the vital capacity, or amount of air you can blow out after a deep inhalation. Since the patient is asked to force the air out, the test is called forced vital capacity (FVC). During an FVC maneuver, you should be able to blow most of the air out of your lungs in less than five seconds. Both the total amount of exhaled air and its rate of flow will determine if any serious mechanical impairment is present.

Before spirometry equipment became widely available, doctors often used the match test. The patient was asked to blow out a lighted match held 6 inches from the mouth. Inability to do this correlates with severe airway obstruction. The match test is no longer used since spirometry is much more accurate and reproducible.

Figure 5 shows the setting for spirometry. To perform this test, the subject breathes normally through a hose attached to the spirometer (there are many types and models of spirometer). The subject is then asked to take in a deep breath and blow all the air out, as hard and fast as possible. During exhalation the air is collected by the spirometer, displacing a movable "bell"; this displacement is recorded by a needle marker on a piece of rotating graph paper. The result is a plot of the total air displaced (the forced vital capacity) versus seconds (the length of time for total expiration).

Figure 5. To perform spirometry " the subject takes in a full, deep breath, then exhales forcefully and rapidly into the tube. The tube is connected to the spirometer, which records a tracing of the effort on a rotating drum. Representations of these "spirometric" curves are shown in Figure H-1.

A representation of the normal forced vital capacity is also shown in the first panel of Figure H-1. Point A represents the end of a regular, quiet breath. Point B represents maximum inhalation. After holding the breath for about a second, the subject exhales as forcibly and rapidly as possible (beginning at point C), until all the air is exhaled (point D).

One component of this test is called the peak flow. Just as its name implies, peak flow represents that part of the forced vital capacity where the air flows fastest out of the mouth. You can see this for yourself. Take in a deep breath and place a finger in front of your mouth. Now blow out as hard and as fast as you can. The entire amount of air you blew out is the forced vital capacity (point C to D in Figure H-1). However, note that the speed of the air flowing past your finger decreased over time, and was fastest just after you began blowing out. Theair speed at this fastest point (always within the first second after beginning) is the "peak flow." The normal peak flow varies according to age, sex, and height, but for most adults it falls somewhere between 400 and 700 liters/minute. Peak flow is reduced during asthma attacks. With the aid of easily portable apparatus designed to measure just peak flow, physicians now routinely use this test to determine both severity and degree of improvement from an asthma attack. (See case of Cheryl L. in Section B).

Gas Exchange

Tests of gas exchange tell how well your lungs and respiratory system are bringing in oxygen and getting rid of CO_2. This is best assessed by measuring the O₂ and CO₂ tension (the amount of pressure exerted by the gas; it reflects the quantity of gas in the blood) in arterial blood since this part of the circulation reflects what happens in the lungs. The basic test of gas exchange is called an arterial blood gas (ABG).

Venous blood fills the blue veins of your arm and is easily obtained by syringe and needle. Except for blood gas analysis, all routine blood tests are done on venous blood. Venous blood is not useful for an ABG since it does not tell how much oxygen is being delivered to the tissues. Arterial blood is somewhat more difficult to obtain than venous blood, since arteries cannot be seen. However, their pulse can be felt. Arterial blood is under higher pressure than venous blood, and arterial pressure pulsates or varies with each heart beat.

An ABG test will also give the amount of acidity in the blood, called the pH. Hence, an ABG is ordered when your physician is worried about the amount of oxygen, carbon dioxide, or pH in your blood. It is a routine test in patients with serious lung disease because there is no other way to obtain this information so quickly and accurately.

One can get very sophisticated in ordering various lung mechanics and gas exchange tests. However, spirometry and arterial blood gas analysis together are sufficient to diagnose and manage most respiratory diseases. At times other tests of pulmonary function will be done, especially in patients scheduled for major surgery of who have complex or unusual problems. Even those patients, however, will have as a minimum spirometry and ABG analysis.

WHAT ARE INTUBATION AND ARTIFICIAL VENTILATION?

Intubation is placing a plastic or rubber tube into a patient's trachea (windpipe) for purposes of securing an airway. The procedure is called endotracheal intubation. The tube, ranging between seven and nine millimeters in internal diameter, can be placed either through the nose or through the mouth. An endotracheal tube helps guarantee an open airway between the atmosphere and the patient's trachea.

By far the most common reason for intubation is so the patient can receive artificial ventilation. The artificial ventilator (also called respirator) is a machine attached via hoses to one end of the endotracheal tube. A circular cuff on the other end of the tube (the end within the patient's trachea) is inflated with air to seal the tube. In this way all the air pushed through the tube by the ventilator will not escape prematurely. This cuff also helps prevent patients from aspirating secretions into their lungs.

Only when the patient is unable to maintain adequate oxygenation or ventilation on his own is artificial ventilation required. The ventilator not only can provide more air, but can also distribute oxygen to the lungs much more effectively than can a face mask or nasal tubing.

WHAT IS A TRACHEOSTOMY?

Tracheostomy is a surgical procedure that places a hole into the trachea, below the Adam's apple. Through this hole is placed a breathing tube that has the same function as the endotracheal tube discussed above. Tracheostomy is usually done after prolonged endotracheal intubation when patients still require an artificial airway or artificial ventilation. The vast majority of patients who ever receive oral or nasal endotracheal intubation have the tube removed within a week or so. Beyond a week, problems of discomfort and inability to eat become major factors, so tracheostomy is usually performed. Tracheostomy allows removal of the endotracheal tube from the patient's mouth or nose and transfers the origin of the artificial airway to the neck. For awake patients this allows eating and swallowing. There is no set rule on when to perform tracheostomy after prior endotracheal intubation. There is some morbidity with tracheostomy just as there is with prolonged endotracheal intubation.

Examples of many of the procedures discussed are shown by the following case.

RWR: A Famous Patient

A 70­year­old man was brought to the emergency room at approximately 3 P.M., having sustained a gunshot wound to the left chest. Although alert, he felt weak and his blood pressure was slightly low. Examination of the chest showed evidence of bleeding in the thoracic cavity. For this reason a chest tube was inserted, through which was removed over a liter of blood. Because the bleeding did not rapidly stop, he was taken to the operating room where he was intubated and a thoracotomy was performed. This consisted of a six­inch incision between the ribs on the left side near the breast muscles. After much searching, the bullet was located and the lung was repaired, stopping the bleeding. Two chest tubes were left in place to drain air and fluid and the chest incision was closed. The patient was removed to the recovery room with the endotracheal tube still in place, and was attached to an artificial ventilator. He complained of some shortness of breath and required morphine for pain. Arterial blood gases showed a low O₂ tension and a chest X­ray showed a large amount of haziness on the left side. To help clear secretions, fiber optic bronchoscopy was attempted by passing the bronchoscope through the endotracheal tube already in place. An unexpected kink or narrowing in the endotracheal tube prevented complete passage of the bronchoscope and the procedure was abandoned. At this time nurses began aggressive suctioning of secretions from his airway, and he rapidly improved over the next several hours. By 3:30 A.M. the next morning his blood gases and chest X­ray improved to the point that the Patient could come off the ventilator.

He continued to receive chest physical therapy, suctioning, and pain medication as needed. Arterial blood gases showed steady improvement in the oxygen tension. The chest tubes were removed on the third post­operative day. On the fourth post­operative day he developed a fever; because of possible plugging of his airways – fiber optic bronchoscopy was again attempted. This time the flexible scope was successfully passed through his mouth without the endotracheal tube in place. Recovery progressed and he was discharged the 11th hospital day.

This patient experienced many of the procedures commonly performed in patients with medical and surgical chest problems: thoracotomy, bronchoscopy, arterial blood gases, chest X­rays, etc. Most of these procedures were either not available or primitive when this patient started out his career as a movie actor four decades earlier.

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