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Severe drops in blood pressure can lead to fainting, with a possibility of injury. Moderate drops in blood pressure can cause confusion/inattention, delirium, and episodes of ataxia. Chronic orthostatic hypotension is associated with cerebral hypoperfusion that may accelerate the pathophysiology of dementia. [5]
In an ischaemic leg, elevation to 15 degrees or 30 degrees for 30 to 60 seconds may cause pallor. (This part of the test checks for elevation pallor.) A vascular angle of less than 20 degrees indicates severe ischaemia. [1] [2] From a sitting position, in normal circulation, the foot will quickly return to a pink colour.
Rarely, ACS can develop after a minor injury or another medical issue. [12] It can also affect the thigh, buttock, hand, abdomen, and foot. [19] [14] The most common cause of acute compartment syndrome is a fractured bone, usually the tibia. [14] [27] Leg compartment syndrome occurs in 1% to 10% of tibial fractures. [6]
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.
Orthopnea or orthopnoea [1] is shortness of breath (dyspnea) that occurs when lying flat, [2] causing the person to have to sleep propped up in bed or sitting in a chair. It is commonly seen as a late manifestation of heart failure, resulting from fluid redistribution into the central circulation, causing an increase in pulmonary capillary pressure and causing difficulty in breathing.
Acute limb ischemia may also be caused by traumatic disruption of blood flow to a limb, which may present with either hard signs or soft signs of vascular injury. [15] Hard signs include pulsatile bleeding, expanding hematomas (collections of blood), or absent distal pulses, and must be taken to surgery emergently.
Hypoxemia is caused by five categories of etiologies: hypoventilation, ventilation/perfusion mismatch, right-to-left shunt, diffusion impairment, and low PO 2. Low PO 2 and hypoventilation are associated with a normal alveolar–arterial gradient (A-a gradient) whereas the other categories are associated with an increased A-a gradient.
Chronic venous insufficiency (CVI) is a medical condition characterized by blood pooling in the veins, leading to increased pressure and strain on the vein walls. [1] The most common cause of CVI is superficial venous reflux, which often results in the formation of varicose veins, a treatable condition. [2]