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Dyspnea is defined as an abnormally uncomfortable awareness of breathing, it is one of the principal symptoms of cardiac and pulmonary disease and ranges from an increased awareness of breathing to intense respiratory distress. Dyspnea occurs after strenuous exertion in normal, healthy, well-conditioned subjects and after only moderate exertion in those who are healthy but unaccustomed to exercise (dyspnea of deconditioning). It should therefore be regarded as abnormal only when it occurs at rest or at a level of physical activity not expected to cause this symptom.

Dyspnea is associated with a wide variety of diseases of the heart and lungs, chest wall, and respiratory muscles as well as with anxiety. Among patients with cardiac dyspnea, this symptom is most commonly associated with and caused by pulmonary congestion, as occurs in cases of left ventricular failure or mitral stenosis. The interstitial and alveolar edema stiffens the lungs and stimulates respiration by activating "J" receptors in the lung. Less frequently, cardiac dyspnea occurs secondary to a reduced cardiac output, without pulmonary engorgement, as in cases of tetralogy of Fallot. Both Borg and Noble and the American Thoracic Society have developed scales that are useful in quantitating the severity of dyspnea.

The sudden development of dyspnea suggests
 1. pulmonary embolism
 2. pneumothorax
 3. acute pulmonary edema
 4. pneumonia, or airway obstruction.

In contrast, in most forms of chronic heart failure, dyspnea progresses slowly over weeks or months. Such a protracted course may also occur in patients with a variety of unrelated conditions, including obesity, pregnancy, and bilateral pleural effusion.
Inspiratory dyspnea suggests obstruction of the upper airways
Expiratory dyspnea characterizes obstruction of the lower airways.

Exertional dyspnea suggests the presence of organic diseases, such as left ventricular failure or chronic obstructive lung disease whereas dyspnea developing at rest may occur in patients with pneumothorax, pulmonary embolism, pulmonary edema, or anxiety neurosis.

Dyspnea that occurs only at rest and is absent on exertion is almost always functional. A functional origin is also suggested when dyspnea, or simply a heightened awareness of breathing, is accompanied by brief stabbing pain in the region of the cardiac apex or by prolonged (more than 2 hours) dull chest pain. It is often associated with difficulty in getting enough air into the lungs, claustrophobia, and sighing respirations that are relieved by exertion, by taking a few deep breaths, or by sedation. Dyspnea in patients with panic attacks is usually accompanied by hyperventilation. A history of relief of dyspnea by bronchodilators suggests asthma as the cause, whereas relief of dyspnea by rest and diuretics suggests left ventricular failure. Dyspnea accompanied by wheezing may be secondary to left ventricular failure (cardiac asthma) or primary bronchial constriction (bronchial asthma).

In patients with chronic heart failure, dyspnea is a clinical expression of pulmonary venous and capillary hypertension. It occurs either during exertion or in resting patients in the recumbent position, in whom it is relieved promptly by sitting upright or standing (orthopnea). Patients with left ventricular failure soon learn to sleep on two or more pillows to avoid this symptom. In patients with heart failure, dyspnea is often accompanied by edema of the lower extremities, upper abdominal pain (due to congestive hepatomegaly), and nocturia.


Disorders Causing Dyspnea and Limiting Exercise Performance, Pathophysiology, and Discriminating Measurements
Disorders Pathophysiology Measurements that Deviate from Normal

Air flow limitation Mechanical limitation to ventilation, mismatching of VA/, hypoxic stimulation to breathing VE max/MVV, expiratory flow pattern, VD, VT; VO2 max, VE/VO2 , VE response to hyperoxia, (A - a) PO2
Restrictive Mismatching VA/, hypoxic stimulation to breathing
Chest wall Mechanical limitation to ventilation VE max/MVV, PACO2 , VO2 max
Pulmonary circulation Rise in physiological dead space as fraction of VT, exercise hypoxemia VD/VT, work-rate-related hypoxemia, VO2 max, VE/VO2 , (a - ET)PCO2 , O2 -pulse

Coronary Coronary insufficiency ECG, VO2 max, anaerobic threshold VO2 , VE/VO2 , O2 -pulse, BP (systolic, diastolic, pulse)
Valvular Cardiac output limitation (decreased effective stroke volume)
Myocardial Cardiac output limitation (decreased ejection fraction and stroke volume)
Anemia Reduced O2 -carrying capacity O2 -pulse, anaerobic threshold VO2 , VO2 max, VE/VO2
Peripheral circulation Inadequate O2 flow to metabolically active muscle Anaerobic threshold VO2 , VO2 max
Obesity Increased work to move body; if severe, respiratory restriction and pulmonary insufficiency VO2 -work-rate relationship, PAO2 , PACO2 , VO2 max
Psychogenic Hyperventilation with precisely regular respiratory rate Breathing pattern, PCO2
Malingering Hyperventilation and hypoventilation with irregular respiratory rate Breathing pattern, PCO2
Deconditioning Inactivity or prolonged bed rest; loss of capability for effective redistribution of systemic blood flow O2 -pulse, anaerobic threshold VO2 , VO2 max
VA = alveolar ventilation; = pulmonary blood flow; VE = minute ventilation; MVV = maximum voluntary ventilation; VD/VT = physiological dead space/tidal volume ratio; O2 = oxygen; VO2 = O2 consumption; (A - a)PO2 = alveolar-arterial PO2 difference; (a - ET)PCO2 = arterial-end tidal PCO2 difference.
Modified from Wasserman D: Dyspnea on exertion: Is it the heart or the lungs? JAMA 248:2042, 1982, Copyright 1982, the American Medical Association.

American Thoracic Society Scale of Dyspnea
Descriptions Grade Degree
Not troubled by shortness of breath when hurrying on the level or walking up a slight hill 0 None
Trouble by shortness of breath when hurrying on the level or walking up a slight hill 1 Mild
Walks more slowly than people of the same age on the level because of breathlessness or has to stop for breath when walking at own pace on the level 2 Moderate
Stops for breath after walking about 100 yards or after a few minutes on the level 3 Severe
Too breathless to leave the house; breathless on dressing or undressing 4 Very severe
From Fishman AP: Approach to the patient with respiratory symptoms. In Fishman's Pulmonary Diseases and Disorders. 3rd ed. New York, McGraw-Hill, 1998, pp 361393.

Paroxysmal nocturnal dyspnea is caused by interstitial pulmonary edema and sometimes intraalveolar edema, most commonly as a consequence of left ventricular failure. This condition, usually beginning 2 to 4 hours after the onset of sleep and often accompanied by cough, wheezing, and sweating, may be quite frightening. Paroxysmal nocturnal dyspnea is often ameliorated by the patient's sitting on the side of the bed or getting out of bed; relief is not instantaneous but usually requires 15 to 30 minutes. Although paroxysmal nocturnal dyspnea secondary to left ventricular failure is usually accompanied by coughing, a careful history often discloses that the dyspnea precedes the cough, not vice versa. Nocturnal dyspnea associated with pulmonary disease is usually relieved after the patient rids himself or herself of secretions rather than specifically by sitting up.

Patients with pulmonary embolism usually experience sudden dyspnea that may be associated with apprehension, palpitation, hemoptysis, or pleuritic chest pain. The development or intensification of dyspnea, sometimes associated with a feeling of faintness, may be the only symptom of the patient with pulmonary emboli. Pneumothorax and mediastinal emphysema also cause acute dyspnea, accompanied by sharp chest pain. Dyspnea is a common "anginal equivalent", that is, a symptom secondary to myocardial ischemia that occurs in place of typical anginal discomfort. This form of dyspnea may or may not be associated with a sensation of tightness in the chest, is present on exertion or emotional stress, is relieved by rest (more often in the sitting than in the recumbent position), is similar to angina in duration (i.e., 2 to 10 minutes), and is usually responsive to or prevented by nitroglycerin.


Algorithm for the evaluation of the patient with dyspnea. The pace and completeness with which one approaches this framework depend on the intensity and acuity of the patient's symptoms. In the patient with severe, acute dyspnea, for example, an arterial blood gas measurement may be one of the first laboratory evaluations, whereas it might not be obtained until much later in the work-up in a patient with chronic breathlessness of unclear cause. A therapeutic trial of a medication, for example, a bronchodilator, may be instituted at any point if one is fairly confident of the diagnosis based on the data available at that time. DVT = deep venous thrombosis; CHF = congestive heart failure; DLCO = diffusing capacity of the lung for carbon monoxide. (From Schwartzstein RM, Feller-Kopman, D.: Approach to the patient with dyspnea. In Braunwald E, Goldman L [eds]: Primary Cardiology. 2nd ed. Philadelphia, WB Saunders, 2003, pp 101116.)


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