<unk>  is due to increased distribution of blood to the pulmonary circulation when a person lies flat or closer to a horizontal position. Lying flat decreases the inhibitory effect that the gravity usually has on the blood that is coming back to the heart from the lower extremities of the body. This increases the right sided venous return. In a normal person, this redistribution of blood has little effect on respiratory function as the left ventricle has the adequate capacity to suddenly increase its stroke volume (as a result of the Frank-Starling mechanism). In a person with heart failure, the left ventricle has an inadequate capacity to respond to increased arrival of blood from the pulmonary circulation. This leads to the pooling up of blood in the pulmonary circulation. The increased intra-parenchymal pulmonary intravascular pressure can also result in hydrostatic pressure related fluid transudation into the alveoli, thus causing pulmonary edema and further worsening shortness of breath. Thus, shortness of breath is commonly experienced after a reasonably short time lying near to flat for a person with left ventricular failure. This is different from the dyspnea experienced by someone with lung parenchymal pathology (both restrictive and obstructive) when lying down, which is sudden and instead related to an acute change in diaphragmatic/accessory respiratory muscle mechanical advantage lost when moving the body into a more horizontal position.
Orthopnea
Hyperpnea
Myxedema
Apnea
Cornea
Chest pain
Anuria
Dysuria