[2] 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.
When a person is recumbent, or is lying down, blood is redistributed from the lower extremities and abdominal cavity (splanchnic circulation) to the lungs.
[5] 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.
[5] The perception of dyspnea is theorized to be a complicated connection between peripheral receptors, neural pathways, and the central nervous system.
[5] Respiratory muscles and vagal afferent neural pathways relay information from the chest wall/airways to the central nervous system, facilitating the presentation of dyspnea.
[6] For example, for people who enter the emergency room with shortness of breath, a diagnosis is achieved through a physical examination, electrocardiography, chest radiograph, and if necessary, a serum BNP level.
[3] More serious forms of dyspnea can be identified through accompanying findings, such as low blood pressure, decreased respiratory rate, altered mental status, hypoxia, cyanosis, stridor, or unstable arrhythmias.
[9] Dyspnea is a subjective symptom, meaning it can only be expressed by the person experiencing it, and it is imperative in diagnosis to distinguish it from other breathing problems.
[11] The shortness of breath sensation felt from PND can typically be relieved by maintaining an upright position while sleeping.
[12] According to the study, researchers were able to conclude that ~70% of people with heart failure had breathing disorders while they slept, while half of that ~70% also experienced central sleep apnea with Cheyne Stokes respiration (CSA-CSR).
[12] Atrial fibrillation, the male gender, an age greater than 60, and awake PaCO2 being less than or equal to 38 mm Hg were all risk factors associated with CSA-CSR.