Shortness of breath or difficulty in breathing is a subjective feeling that may or may not be associated with objectively reduced blood oxygenation.
Possible causes are mainly cardiovascular (i.e. pulmonary oedema from LVF), primary pulmonary disease and anemia.
Postural variation is common in cardiovascular dyspnoea. it is worse when supine, so that the patient breathes more easily when erect or sitting (orthopnoea). This is because intrathoracic pressure is increased when the patient is recumbent, raising pulmonary venous pressure and thus promoting the formation of alveolar oedema.
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