Diagnosing the cause of dyspnea depends on the clinical evaluation and the results of investigative tests that will be conducted. Due to the various reasons for shortness of breath, some of the tests will not be directly related to the lungs. Not all the tests mentioned below will be conducted and the attending physician will request those tests that are needed to confirm the differential diagnosis based on the clinical evaluation.
In severe cases of labored breathing, there may be one or more signs of respiratory distress :
- flaring of the nostrils
- pursing of the lips.
- use of the accessory respiratory muscles.
- abnormal breathing sounds.
- redness of the face which progresses to a pale or blue discoloration of the face.
This should be treated as a medical emergency. Immediate testing and a quick diagnosis is necessary to treat the cause once the patient is stabilized.
A posterioanterior (PA) and lateral x-rays will be requested. Refer to Chest Pain Test for more information on common features that are noted on a chest x-ray.
A chest x-ray may help the attending doctor to diagnose the following conditions that could cause dyspnea :
- Cardiac failure.
- Chronic obstructive pulmonary disease (COPD).
- Diaphragmatic paralysis.
- Lung tumors.
- Obstructive and restrictive lung diseases.
- Pleural effusion.
- Pulmonary edema.
- Toxic airway damage from inhaling noxious fumes.
Depending on the facilities available, the findings on the chest x-ray or even a lack thereof may prompt the attending doctor to request a CT scan or MRI of the chest.
Pulmonary Function Testing (PFT)
This is also known as a lung function test (LFT) or spirometry. Pulmonary function testing involves a group of tests, of which spirometry is one of these. These tests will measure the :
- Lung volume – amount of air that the lungs can hold or take in.
- Flow rate – the rate of air flow which indicates airway narrowing or obstruction.
- Flow volume – the amount of air taken in and passed out during each breath.
- Muscle strength – air pressure during breathing which indicates the strength of the respiratory muscles.
- Diffusing capacity – efficiency of oxygen in the lungs to enter the blood stream.
- Maximal volume ventilation – tests the maximum breathing ability of the patient.
Depending on the results of many of these tests, the different causes of dyspnea may be diagnosed. Some of the conditions that may prompt a PFT include asthma, COPD, obstructive and restrictive lung diseases.
ECG and Echocardiography
An ECG monitors the electrical activity of the heart. An echocardiogram will create images of the heart movement allowing for the assessment of heart function. If there is any chest pain present along with the dyspnea, then the attending doctor may do other chest pain tests.
These tests may be requested in the following conditions that can cause dyspnea :
- Coronary artery disease.
- Heart attack (myocardial infarction).
- Heart failure.
Stress tests may be necessary to confirm certain diagnoses.
Arterial Blood Gas (ABG)
This is the analysis of the blood taken from an artery to determine the levels of oxygen and carbon dioxide in the blood. The pH (acid-base balance) of the blood will also be recorded as this changes with the presence of excessive amounts of carbon dioxide, other potentially toxic gases and metabolic disorders.
High carbon dioxide levels will lower the pH of the blood making it more acidic while low carbon dioxide levels.will make blood more alkaline. Respiratory acidosis indicates that the lungs are not able to remove carbon dioxide out of the blood at a suitable rate. Dyspnea is a common symptom of respiratory acidosis.
This test may be requested in the following conditions that can cause dyspnea :
- COPD – Emphysema and chronic bronchitis.
- Toxic airway damage from the inhalation of noxious fumes.
- Obesity-hypoventilation syndrome.
- Certain drugs – overdose and side effects.
- Neurological causes resulting in shortness of breath – head trauma, encephalitis, brainstem injury, increased intracranial pressure.
An arterial blood gas should not be confused with pulse oximetry. In this test, a sensor is placed on the finger or an ear lobe to test oxygen saturation in the blood.
Other Blood Tests
Complete Blood Count (CBC)
Also known as a full blood count (FBC), the results will help to identify an infection (pneumonia, tuberculosis) and anemia.
Refer to Chest Pain Test.
This test is useful for assessing the extent of iron-deficiency anemia. It will also assist with determining whether anemia is due to a lack of iron or due to some other cause.
Urea and Electrolytes
The results may assist with assessing certain causes of dyspnea like congestive cardiac failure, kidney failure, CNS (central nervous system) depression, lung disease and the effects of certain drugs.