Acute

• Asthma, pneumonia, pulmonary edema, pneumothorax, pulmonary embolus, metabolic acidosis, acute respiratory distress syndrome, panic attack

Pulmonary

• Airflow obstruction (asthma, chronic obstructive pulmonary disease, upper airway obstruction), restrictive lung disease (interstitial lung disease, pleural thickening or effusion, respiratory muscle weakness, obesity), pneumonia, pneumothorax, pulmonary embolism, aspiration, acute respiratory distress syndrome

Cardiac

• Myocardial ischemia, congestive heart failure, valvular obstruction, arrhythmia, cardiac tamponade

Metabolic

• Acidosis, hypercapnia, sepsis

Hematologic

• Anemia, methemoglobinemia

Psychiatric

• Anxiety

• Orthopnea or nocturnal dyspnea
• Platypnea
• Episodic dyspnea
• Cheyne-Stokes respiration