Paroxysmal nocturnal dyspnoea

Paroxysmal nocturnal dyspnea or paroxysmal nocturnal dyspnoea (PND) is an attack of severe shortness of breath and coughing that generally occurs at night. It usually awakens the person from sleep, and may be quite frightening. PND, as well as simple orthopnea, may be relieved by sitting upright at the side of the bed with legs dangling, as symptoms typically occur when the person is recumbent, or lying down. Since paroxysmal nocturnal dyspnea occurs mainly because of heart or lung problems, common risk factors include those that affect the function of the heart and lungs. Risk factors for cardiac diseases include high blood pressure, high cholesterol, diabetes, obesity, and a lifestyle lacking exercise and a healthy diet. Risk factors for lung diseases include tobacco use, including second hand smoke, pollution, exposure to hazardous fumes, and allergens. PND can be explained by mechanisms similar to those of orthopnea and typical dyspnea. When a person is recumbent, or is lying down, blood is redistributed from the lower extremities and abdominal cavity (splanchnic circulation) to the lungs. Failure to accommodate this redistribution results in decreased vital capacity and pulmonary compliance, further causing the shortness of breath experienced in PND. In addition to the redistribution of blood in the body, most cases of dyspnea are accompanied by an increase in the overall work of breathing, often caused by abnormal pulmonary mechanisms. The perception of dyspnea is theorized to be a complicated connection between peripheral receptors, neural pathways, and the central nervous system. Receptors in the chest wall and central airways, as well receptors in the respiratory center of the central nervous system, produce an increased requirement for ventilation which is not matched by respiratory output, resulting in the conscious recognition of dyspnea. Respiratory muscles and vagal afferent neural pathways relay information from the chest wall/airways to the central nervous system, facilitating the presentation of dyspnea.