perfusion

Examples of perfusion in the following topics:

• External Respiration

  • While a severe ventilation–perfusion mismatch indicates severe lung disease, minor imbalances can be corrected by maintaining air flow that is proportional to capillary blood flow, which maintains the balance of ventilation and perfusion.
  • Perfusion in the capillaries adjusts to changes in PAO2.
  • In response, the arteries being supplied by the constricted airway undergo vasocontriction, reducing the flow of blood into those alveoli so that the perfusion doesn't become much greater relative to the decreased ventilation (a type of ventilation–perfusion mismatch called a shunt).
  • When airflow becomes higher relative to perfusion, PACO2 decreases, so the bronchioles will constrict in order to maintain to the balance between airflow (ventilation) and perfusion.
  • External respiration is a result of partial pressure gradients, alveolar surface area, and ventilation and perfusion matching.

• Physical Characteristics and Volume

  • In order to maintain homeostasis, blood volume and blood pressure must be high enough that blood can reach all of the body's tissues, a process called tissue perfusion.
  • Most tissues can survive without perfusion for a short amount of time, but the brain needs a continuous supply of oxygen and glucose to stay alive.
  • Many mechanisms exist to regulate blood volume and tissue perfusion, including renal water excretion in the kidney, the pumping activity of the heart, and the abilities of the arteries to constrict or dilate.
  • When blood volume becomes too low, such as from an injury, dehydration, or internal bleeding, the body will enter into a state of hypovolemic shock, in which tissue perfusion decreases too much.

• Lungs

  • Only a relatively small proportion of alveoli in the lungs are perfused with blood and actually take part in gas exchange.
  • The ratio of ventilation in the lungs and perfusion of the lungs (the air and blood supply of the alveoli respectively) is called the V/Q ratio (with Q being perfusion); it is an important indicator of efficiency in the lungs.
  • Too low perfusion (and a higher ratio) indicates alveolar dead space, while too low ventilation (and a lower ratio) indicates a shunt, which is a lack of air supply relative to perfusion.

• Sodium Balance Regulation

  • A low renal perfusion pressure stimulates the release of renin, which forms angiotensin I which is converted to angiotensin II.
  • Angiotensin II will correct the low perfusion pressure by causing constriction of blood vessels and by increasing sodium retention by a direct effect on the proximal renal tubule and by an effect operated through aldosterone.
  • The perfusion pressure to the adrenal gland has little direct effect on aldosterone secretion and the low blood pressure operates to control aldosterone via the renin angiotensin system.

• Congestive Heart Failure

  • Initially, this helps compensate for heart failure by maintaining blood pressure and perfusion, but it places further strain on the myocardium, increasing coronary perfusion requirements, which can lead to worsening of ischemic heart disease.
  • Reduced perfusion (blood flow) to the kidneys stimulates the release of renin – an enzyme that catalyzes the production of the potent vasopressor angiotensin .
  • Reduced perfusion (blood flow) to the kidneys stimulates the release of renin, an enzyme that catalyzes the production of the potent vasopressor angiotensin.

• Internal Respiration

  • The factors that influence tissue gas exchange are similar to the factors of alveolar gas exchange, and include partial pressure gradients between the blood and the tissues, the blood perfusion of those tissues, and the surface areas of those tissues.
  • Each of those factors generally increase gas exchange as those factors are increased (i.e., more oxygen diffusion in tissues with more blood perfusion).

• Homeostatic Responses to Shock

  • The prolonged vasoconstriction will also cause the vital organs to be compromised due to reduced perfusion.
  • Adenosine easily perfuses out of cellular membranes into extracellular fluid, furthering capillary vasodilation, and then is transformed into uric acid.

• Signs and Symptoms of Shock

  • Hypothermia due to decreased perfusion and evaporation of sweat, and thirst and dry mouth due to fluid depletion, may also be present.

• Compartment Syndrome

  • Elevation of the affected limb in patients with compartment syndrome is not recommended, as this leads to decreased vascular perfusion of the affected region.
  • Failure to relieve the pressure can result in necrosis of tissue in that compartment, since capillary perfusion will fall leading to increasing hypoxia of those tissues.

• Cardiopulmonary Resuscitation (CPR)

  • Administration of an electric shock to the subject's heart, termed defibrillation, is usually needed in order to restore a viable or "perfusing" heart rhythm.