All that follows is from the above resource.
Dyspnea, also called shortness of breath, is a patient's perceived difficulty to breathe. Sensations and intensity can vary and are subjective. It is a prevalent symptom impacting millions of people. It may be the primary manifestation of respiratory, cardiac, neuromuscular, psychogenic, or systemic illnesses, or a combination of these. Dyspnea on exertion is a similar sensation; however, this shortness of breath is present with exercise and improves with rest. This activity reviews the etiology, evaluation, and management of exertional dyspnea and highlights the role of the interprofessional team in evaluating and improving care for patients with exertional dyspnea.
Oxygen Delivery: Hb x 1.39 x SaO2 x Cardiac Output + 0.003 x Pao2
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Hb is the concentration of hemoglobin in grams per liter
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1.39- oxygen binding capacity of hemoglobin per gram
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SaO2 is hemoglobin oxygen saturation expressed as a fraction (like- 98% will be 0.98)
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Cardiac output is described as the amount of blood pumped by the heart in liter per minute
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0.003 x pao2 is the amount of dissolved oxygen in the blood in milliliters
If a body has low Hb, hemoglobinopathies, some toxicities affecting Hb (like carbon monoxide toxicity), low cardiac output (congestive heart failure [CHF], myocardial infarction [MI], arrhythmia) a person will feel dyspneic.[2]
Etiology
Dyspnea on exertion is a symptom of various diseases rather than a disease itself. As such, its etiology can be designated as arising from two primary organ systems: the respiratory system and the cardiac system. Other systemic illnesses may be culprits as well as a combination of different etiologies.
Respiratory causes may include asthma, acute exacerbation of chronic obstructive pulmonary disorder (COPD), pneumonia, pulmonary embolism, lung malignancy, pneumothorax, or aspiration.[1]
Cardiovascular causes may include congestive heart failure, pulmonary edema, acute coronary syndrome, pericardial tamponade, valvular heart defect, pulmonary hypertension, cardiac arrhythmia, or intracardiac shunting.
Other systemic illnesses, such as anemia, acute renal failure, metabolic acidosis, thyrotoxicosis, cirrhosis of the liver, anaphylaxis, sepsis, angioedema, and epiglottitis, may also cause dyspnea on exertion.
Epidemiology
The epidemiology of dyspnea on exertion is highly variable depending on etiology.[1] The most common cause of dyspnea on exertion is congestive heart failure. According to 2017 American heart association (AHA) data, heart failure affects 6.5 million Americans aged 20 years or older.[3] Similarly, about 6.3% of the US adult population has COPD.
History and Physical
The history and physical exam should ascertain whether there are any chronic underlying cardiovascular or pulmonary illnesses. Key components of history include onset, duration, aggravating factors, and alleviating factors. The presence of cough may indicate the presence of asthma, chronic obstructive pulmonary disease (COPD), or pneumonia. A severe sore throat could indicate epiglottitis. Pleuritic quality chest pain may indicate pericarditis, pulmonary embolism, pneumothorax, or pneumonia. Orthopnea, paroxysmal nocturnal dyspnea, and edema suggest a possible diagnosis of congestive heart failure. Tobacco use is a common history finding that increases the likelihood of COPD, congestive heart failure, and pulmonary embolism. If indigestion or dysphagia is present, consider gastroesophageal reflux disease or gastric secretion aspiration in the lungs. A barking quality cough, especially in children, may suggest croup. The presence of fever strongly suggests an infectious etiology.
Evaluation
Every evaluation should begin with a rapid assessment of the ABC status of the patient. Once these are determined to be stable and no life-threatening status present, a complete history, and physical exam can be collected. Vital signs should be assessed for heart rate, respiratory rate, body temperature, body mass index (BMI), and oxygen saturation. Oxygen saturation may be normal at rest, so oxygen saturation with physical exertion should be obtained. In normal physiological conditions, the pulse oximetry improves as V/Q matching improves. Fever may indicate an infectious etiology. A chest x-ray is the first diagnostic test that should be utilized in evaluating dyspnea on exertion. If abnormal, the disease process is likely cardiac or a primary pulmonary process. An echocardiogram is needed to evaluate cardiac function, pericardial space, and valvular function.
Additionally, an electrocardiogram should be obtained to evaluate for myocardial infarction or right-sided heart strain pattern. Elevated pro-brain natriuretic peptide (BNP) levels can further a congestive heart disease diagnosis. Exercise stress testing is also beneficial to determine cardiac function along with exercise oxygenation. If the chest x-ray is normal, then spirometry is needed to determine lung function. Abnormal spirometry can indicate either an obstructive pathology such as asthma, COPD, or physical airway obstruction or restrictive disease processes such as interstitial fibrosis. Spirometry can also indicate the presence of respiratory muscle weakness from muscular or neurological abnormalities.
Normal spirometry indicates a need to evaluate for hypoxia as a source of dyspnea. The restrictive pathology can be confirmed with lung volumes, which will show reduced total lung capacity (TLC). In obstructive lung disease, the TLC is increased, and the RV/TLC ratio is increased.
Diffusion capacity is reduced in disease processes that affect the alveolar membrane area and or thickness. For example, it will be reduced with interstitial lung disease (ILD), emphysema, pulmonary embolism (PE), CHF, and obesity.
Arterial blood gas testing is used for this purpose as well as to calculate the A-a gradient and assess for an acidotic state. If PaO2 is low with a normal chest x-ray, then pulmonary embolism (PE) should be considered. The pH is mostly alkalotic in the setting of PE. This is to blow carbon dioxide to relatively increase the partial pressure of oxygen.
In a pregnant female, a d-dimer with leg ultrasound and V/Q scan should be ordered first. Detection of a mismatch in two or more areas indicates pulmonary embolism. D-dimer testing has low specificity and high sensitivity. Spiral CT of the chest is an alternative to V/Q scanning. In acute settings, the CT chest with PE protocol is the gold standard.
If the dyspnea on exertion is chronic, then chronic thromboembolic pulmonary hypertension (CTEPH) should be considered, and the VQ scan is the test of choice and is considered the gold standard. The VQ scan in this setting has a "moth-eaten" appearance.
A normal scan necessitates cardiac catheterization to determine pulmonary hypertension, intracardiac shunting, or coronary artery disease. A normal cardiac catheterization diagnoses idiopathic dyspnea. If hypoxia is not present with a PaO2 greater than 70 mm Hg, correlation with oxygen saturation is needed. Abnormal oxygen saturation indicates possible carbon monoxide poisoning, methemoglobinemia, or an abnormal hemoglobin molecule.
Normal oxygen saturation requires a complete blood count (CBC) to evaluate hemoglobin content and hematocrit values. The white blood count also assesses for an immune response to possible infection. Hematocrit less than 35% is anemia.
If one cannot determine the etiology of dyspnea, then we should order a cardiopulmonary exercise test (CPET). If the CPET does not show any cardiac or pulmonary etiology, then the likely diagnosis for dyspnea on exertion is physical deconditioning.
All testing modalities should target clinical suspicion and the history and physical exam to avoid overtesting and minimize the cost to the patient.[7]
Differential Diagnosis
Acute dyspnea on exertion is most likely caused by:
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Acute myocardial ischemia
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Heart failure
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Cardiac tamponade
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Pulmonary embolism
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Chronic dyspnea is most likely caused by:
The most common diagnosis underlying dyspnea on exertion is CHF.
Complications
If left untreated, dyspnea on exertion can progress to acute respiratory failure with hypoxia or hypercapnia, further leading to life-threatening respiratory or cardiac arrest or both.
Consultations
Based on possible underlying etiology after the initial evaluation, different specialties can be consulted. As evaluation and management of dyspnea on exertion is teamwork, the following specialties need to be consulted:
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