1. DYSPNEA

2.  An unpleasant sensation of difficulty in breathing  Aware­ness that a small amount of exercise leads to a disproportionately large increase in ventilation is a common type of dyspnea, usually described as breathlessness or short­ness of breath on exertion.

3. Other sensations related to breathing include  awareness of increased muscular effort required to expand the chest during inspiration;  increased effort required to expel air from the lungs;  sensations of fatigue from the respiratory muscles;  awareness of delay in air leaving the lungs during expiration.

4.  sensation that an inspiration is urgently needed before expiration is completed,;  various sensations most often described as "tightness in the chest."  awareness of collapse or hyperinflation of lung units; obstruction of airways; and distortion or displacement of lung, mediastinum, diaphragm, or chest wall.

5. Clinical types of dyspnea  Pulmonary  Cardiac  Circulatory  Chemical  Central  Psychogenic

6. Pulmonary dyspnea Due to pulmonary function defects with a result of hypoxemia and/or hypercapnia. There are three types: 1.Inspirational dyspnea: difficult in inspiration and characterized by three depression sign  Indicates narrow or obstruction of larynx, trachea or upper bronchi.

7. 2.Expiratory dyspnea: (obstructive dyspnea) with increased ventilatory effort induces dyspnea even at rest, and breathing is labored and retarded.  presents in obstructive emphysema or asthma

8.  Mixed dyspnea: difficult in both inspiration and expiration, due to severe pulmonary diseases or chest deformities, such as severe pulmonary tuberculosis, atelectasis ( 肺 不张 ), lung infarction, pneumoconiosis, interstitial lung disease, pleural effusion,pneumothorax, and so on.

9. Cardiac dyspnea Left ventricular failure  In early stages of left heart failure, cardiac output fails to keep pace with increased metabolic need during exercise.  Respiratory drive therefore is increased largely because of tissue and cerebral acidosis, and the patient hyperventilates.

10.  Shortness of breath is often accompanied by lassitude or a feeling of smothering or sternal oppression.  Various reflex factors, including stretch receptors in the lungs, may also contribute to hyperventilation.

11.  In later stages of heart failure, the lungs are congested and edematous, the ventilatory capacity of the stiff lungs is reduced, and ventilatory effort is increased

12.  Orthopnea is the respiratory discomfort that occurs while the patient is supine, impelling him to sit up.  It is precipitated by an increase in venous return of blood to a failing left ventricle that cannot handle this increased preload.

13.  Another reason is the increased effort of breathing in the supine position.  Sometimes orthopnea occurs in other cardiovascular disorders (eg, pericardial effusion)

14.  paroxysmal nocturnal dyspnea (PND), the patient awakens gasping and must sit or stand to get his breath, which may be dramatic and terrifying.  PND may occur in mitral stenosis, aortic insufficiency, hypertension, or other conditions affecting the left ventricle

15. Except the same factors that cause orthopnea, PND is also caused by the following mechanisms:  Increased excitability of vagus, and causes vasoconstriction of coronary artery and myocardial ischemia.  Construction of smaller bronchi causes decreasing of ventilation.

16.  Cardiac asthma is a state of acute respiratory insufficiency with bronchospasm, wheezing, and hyperventilation. It may be indistinguishable from other types of asthma, but the cause is left ventricular failure

17. Circulatory dyspnea  Air hunger (acute dyspnea occurring in terminal stages of exsanguinating ( 使无 血 ) hemorrhage) is a grave sign calling for immediate transfusion.  Dyspnea also occurs with chronic anemia, coming on only during exertion, unless the anemia is extreme.

18. Chemical dyspnea  Diabetic acidosis (blood pH 7.2 to 6.95) induces a distinctive pattern of slow, deep respirations (Kussmaul breathing). However, because the breathing capacity is well preserved, the patient rarely complains of dyspnea.  In contrast, the uremic patient may complain of dyspnea because of severe panting brought about by a combination of acidosis, heart failure, pulmonary edema, and anemia.

19. Central dyspnea  Cerebral lesions (eg, hemorrhage) and head injury are often associated with intense hyperventilation that is sometimes noisy and stertorous ( 打鼾 ).  irregular periods of apnea alternate with periods in which 4 or 5 breaths of similar depth are taken (Biot's respiration).  Decreased Paco2 causes reflex CNS vasoconstriction with reduced cerebral perfusion leading to a beneficial secondary decrease in intracranial pressure.

20. Psychogenic dyspnea Hysterical types of overbreathing are common.  In one type, continuous hyperventilation leads to acute alkalosis from "blowing off" CO2 ; positive Trousseau and Chvostek signs may result from lowered serum calcium ion levels.

21.  Another type is characterized by deep, sighing respirations with the patient breathing at maximal depth until respiration is "satisfactory," when the hyperventilatory impulse subsides. This is frequently repeated.