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من طرف محمد حبيب الأربعاء أكتوبر 28, 2009 7:42 pm

Dyspnea or dyspnoea (pronounced disp-nee-ah, IPA /dɪsp'niə/), from Latin dyspnoea, from Greek dyspnoia from dyspnoos, shortness of breath) or shortness of breath (SOB) is a debilitating symptom that is the experience of unpleasant or uncomfortable respiratory sensations.^[1] It is a common symptom of numerous medical disorders, particularly those involving the cardiovascular and respiratory systems; dyspnea on exertion is the most common presenting complaint for people with respiratory impairment.^[2]

Contents

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[edit] Classification

Lungs and breathing activity
Commonly confused terminology view • talk • edit

Dyspnea - Shortness of breath

Hyperventilation - increased breathing that causes CO₂ loss

Hyperpnea - faster and/or deeper breathing

Tachypnea - increased breathing rate

Hyperaeration/Hyperinflation - increased lung volume

Dyspnea has been more specifically defined by the American Thoracic Society as the "subjective experience of breathing discomfort that consists of qualitatively distinct sensations that vary in intensity. The experience derives from interactions among multiple physiological, psychological, social, and environmental factors, and may induce secondary physiological and behavioral responses."^[1]
Importantly, dyspnea is a symptom experienced by the individual, rather than a noticeable or measurable sign. Thus dyspnea is not the same as tachypnea (rapid breathing),^[3] although both may be present at the same time.
[edit] Clinical assessment

Dyspnea can be a worrying and disabling symptom for the patient. In order to assess the level of dyspnea, the doctor might ask the patient to rank the severity from 1 to 10. Alternatively a scale such as the MRC Breathlessness Scale might be used - it suggests five different grades of dyspnea based on the circumstances in which it arises.^[4]
GradeDegree of dyspnea

1	no dyspnea except with strenuous exercise
2	dyspnea when walking up an incline or hurrying on the level
3	walks slower than most on the level, or stops after 15 minutes of walking on the level
4	stops after a few minutes of walking on the level
5	dyspnea with minimal activity such as getting dressed, too dyspneic to leave the house

Some studies have suggested that up to 27% of people suffer dyspnea,^[2] while in dying patients 75% will experience it.^[5]
[edit] Pathophysiology

In general, dyspnea signals that there is inadequate ventilation.^[2] This happens when the body is unable to ventilate enough to sufficiently meet the body's needs. This situation may occur when there is increased ventilatory demand (e.g. during exercise) or reduced ability to ventilate enough (e.g. due to respiratory muscle weakness).^[3]
[edit] Mechanisms

Although the exact mechanisms of dyspnea are not fully understood, some general details have been found. It is currently thought that there are three main components that contribute to dyspnea: afferent signals, efferent signals, and central information processing. It is believed that the central processing in the brain compares the afferent and efferent signals, and that a "mismatch" results in the sensation of dyspnea. In other words, dyspnea may result when the need for ventilation (afferent signaling) is not being met by the physical breathing that is occurring (efferent signaling).^[5]
Afferent signals are sensory neuronal signals that ascend to the brain. Afferent neurons significant in dyspnea arise from a large number of sources including the carotid bodies, medulla, lungs, and chest wall. Chemoreceptors in the carotid bodies and medulla supply information regarding the blood gas levels of O₂, CO₂ and H⁺. In the lungs, juxtacapillary (J) receptors are sensitive to pulmonary interstitial edema, while stretch receptors signal bronchoconstriction. Muscle spindles in the chest wall signal the stretch and tension of the respiratory muscles. Thus, poor ventilation leading to hypercapnia, left heart failure leading to interstitial edema (impairing gas exchange), asthma causing bronchoconstriction (limiting airflow) and muscle fatigue leading to ineffective respiratory muscle action could all contribute to a feeling of dyspnea.^[5]
Efferent signals are the motor neuronal signals descending to the respiratory muscles. The most important respiratory muscle is the diaphragm. Other respiratory muscles include the external and internal intercostal muscles, the abdominal muscles and the accessory breathing muscles.
As the brain receives its plentiful supply of afferent information relating to ventilation, it is able to compare it to the current level of respiration as determined by the efferent signals. If the level of respiration is inappropriate for the body's status then dyspnea might occur. It is worth noting that there is a psychological component of dyspnea as well, as some people may become aware of their breathing in such circumstances but not experience the distress typical of dyspnea.^[5]
[edit] Causes

[edit] Pulmonary disorders

Obstructive lung diseases
Diseases of lung parenchyma and pleura
- Contagious
  - Anthrax through inhalation of Bacillus anthracis
  - Pneumonia
- Non-contagious
  - Fibrosing alveolitis
  - Atelectasis
  - Hypersensitivity pneumonitis
  - Interstitial lung disease
  - Lung cancer
  - Pleural effusion
  - Pneumoconiosis
  - Pneumothorax
  - Non-cardiogenic pulmonary edema or acute respiratory distress syndrome
  - Sarcoidosis
Pulmonary vascular diseases
- Acute or recurrent pulmonary emboli
- Pulmonary hypertension, primary or secondary
- Pulmonary veno-occlusive disease
- Superior vena cava syndrome

[edit] Other causes of diminished breathing

Obstruction of the airway
Immobilization of the diaphragm
- Lesion of the phrenic nerve
- Polycystic liver disease
- Tumor in the diaphragm
Restriction of the chest volume
- Ankylosing spondylitis
- Broken ribs
- Kyphosis of the spine
- Obesity
- Pregnancy
- Pectus excavatum
- Scoliosis
Disorders of the cardiovascular system
Disorders of the blood and metabolism
Disorders affecting breathing nerves and muscles
Psychological conditions
- Anxiety disorders and panic attacks
Medications
- Fentanyl
Other
- Carbon monoxide poisoning

[edit] See also

Air hunger
Apnea, absence of respiration
Tachypnea, fast respiration
Bradypnea, slow respiration
Eupnea, normal respiration
Orthopnea
Trepopnea
Paroxysmal nocturnal dyspnea

[edit] Footnotes

^ ^a ^b American Heart Society (1999). "Dyspnea mechanisms, assessment, and management: a consensus statement". Am Rev Resp Crit Care Med 159: 321–340.
^ ^a ^b ^c Murray and Nadel's Textbook of Respiratory Medicine, 4th Ed. Robert J. Mason, John F. Murray, Jay A. Nadel, 2005, Elsevier
^ ^a ^b West JB (2008). Pulmonary pathophysiology: the essentials (7 ed.). Baltimore: Lippincott Williams & Wilkins. pp. 45.
^ Stenton C (2008). "The MRC breathless scale.". Occup Med 58: 226–7. doi:10.1093/occmed/kqm162. PMID 18441368.
^ ^a ^b ^c ^d Harrison's Principles of Internal Medicine (Kasper DL, Fauci AS, Longo DL, et al (eds)) (16th ed.). New York: McGraw-Hill.

[edit] References

Lippincott Williams & Wilkins (2006). Stedman's Medical Dictionary, 28th Edition. Baltimore, Maryland: Julie K. Stegman. pp. 601. ISBN 0-7817-3390-1.
[edit] External links

Dyspnea at GPnotebook
How Heart Failure causes shortness of breath – An animated journey through Heart Failure

[hide] v• d• e

Symptoms and signs: respiratory system (R04-R07, 786)


Hemorrhage	Epistaxis · Hemoptysis

Abnormalities of breathing	Respiratory sounds: Stridor · Wheeze · Rales · Rhonchi · Hamman's sign Dyspnea · Hyperventilation/Hypoventilation · Hyperpnea/Tachypnea/Bradypnea · Orthopnea/Platypnea Biot's respiration · Cheyne-Stokes respiration · Kussmaul breathing Hiccup · Mouth breathing/Snoring

Other	Asphyxia · Cough · Pleurisy · Sputum Respiratory arrest · Hypercapnia/Hypocapnia Pectoriloquy: Whispered pectoriloquy · Egophony · Bronchophony Pleural friction rub Fremitus

Chest, general	Chest pain