Hypoxic Pulmonary Vasoconstriction
Encyclopedia
Hypoxic pulmonary vasoconstriction is a paradoxical, physiological
phenomenon in which pulmonary arteries constrict in the presence of hypoxia
(low oxygen levels) without hypercapnia
(high carbon dioxide levels), redirecting blood flow
to alveoli
with a higher oxygen content.
The process might at first seem illogical, as low oxygen levels should theoretically lead to increased blood flow to the lungs to receive increased gaseous exchange. However, it is explained by the fact that constriction leads to redistribution of bloodflow to better-ventilated areas of the lung, which increases the total area involved in gaseous exchange.
Several factors inhibit this process including increased cardiac output, hypocapnia
, hypothermia
, acidosis
/alkalosis
, increased pulmonary vascular resistance, inhaled anesthetics, calcium channel blockers, PEEP, HFV, isoproterenol
, nitrous oxide
, and vasodilators.
(HAPE). For this reason, most climbers carry supplemental oxygen to prevent hypoxia, edema, and HAPE. The standard drug treatment of dexamethasone
does not alter the hypoxia or the consequent vasoconstriction, but stimulates fluid reabsorption in the lungs to reverse the edema.
Physiology
Physiology is the science of the function of living systems. This includes how organisms, organ systems, organs, cells, and bio-molecules carry out the chemical or physical functions that exist in a living system. The highest honor awarded in physiology is the Nobel Prize in Physiology or...
phenomenon in which pulmonary arteries constrict in the presence of hypoxia
Hypoxia (medical)
Hypoxia, or hypoxiation, is a pathological condition in which the body as a whole or a region of the body is deprived of adequate oxygen supply. Variations in arterial oxygen concentrations can be part of the normal physiology, for example, during strenuous physical exercise...
(low oxygen levels) without hypercapnia
Hypercapnia
Hypercapnia or hypercapnea , also known as hypercarbia, is a condition where there is too much carbon dioxide in the blood...
(high carbon dioxide levels), redirecting blood flow
Blood flow
Blood flow is the continuous running of blood in the cardiovascular system.The human body is made up of several processes all carrying out various functions. We have the gastrointestinal system which aids the digestion and the absorption of food...
to alveoli
Pulmonary alveolus
An alveolus is an anatomical structure that has the form of a hollow cavity. Found in the lung parenchyma, the pulmonary alveoli are the dead ends of the respiratory tree, which outcrop from either alveolar sacs or alveolar ducts, which are both sites of gas exchange with the blood as well...
with a higher oxygen content.
The process might at first seem illogical, as low oxygen levels should theoretically lead to increased blood flow to the lungs to receive increased gaseous exchange. However, it is explained by the fact that constriction leads to redistribution of bloodflow to better-ventilated areas of the lung, which increases the total area involved in gaseous exchange.
Several factors inhibit this process including increased cardiac output, hypocapnia
Hypocapnia
Hypocapnia or hypocapnea also known as hypocarbia, sometimes incorrectly called acapnia, is a state of reduced carbon dioxide in the blood. Hypocapnia usually results from deep or rapid breathing, known as hyperventilation....
, hypothermia
Hypothermia
Hypothermia is a condition in which core temperature drops below the required temperature for normal metabolism and body functions which is defined as . Body temperature is usually maintained near a constant level of through biologic homeostasis or thermoregulation...
, acidosis
Acidosis
Acidosis is an increased acidity in the blood and other body tissue . If not further qualified, it usually refers to acidity of the blood plasma....
/alkalosis
Alkalosis
Alkalosis refers to a condition reducing hydrogen ion concentration of arterial blood plasma . Generally, alkalosis is said to occur when pH of the blood exceeds 7.45. The opposite condition is acidosis .-Causes:...
, increased pulmonary vascular resistance, inhaled anesthetics, calcium channel blockers, PEEP, HFV, isoproterenol
Isoproterenol
Isoprenaline or isoproterenol is a medication used for the treatment of bradycardia , heart block, and rarely for asthma...
, nitrous oxide
Nitrous oxide
Nitrous oxide, commonly known as laughing gas or sweet air, is a chemical compound with the formula . It is an oxide of nitrogen. At room temperature, it is a colorless non-flammable gas, with a slightly sweet odor and taste. It is used in surgery and dentistry for its anesthetic and analgesic...
, and vasodilators.
High altitude pulmonary edema
Climbing tall mountains can induce full lung hypoxia due to decreased atmospheric pressure. This hypoxia causes hypoxic vasoconstriction that ultimately leads to high altitude pulmonary edemaHigh Altitude Pulmonary Edema
High altitude pulmonary edema is a life-threatening form of non-cardiogenic pulmonary edema that occurs in otherwise healthy mountaineers at altitudes typically above ....
(HAPE). For this reason, most climbers carry supplemental oxygen to prevent hypoxia, edema, and HAPE. The standard drug treatment of dexamethasone
Dexamethasone
Dexamethasone is a potent synthetic member of the glucocorticoid class of steroid drugs. It acts as an anti-inflammatory and immunosuppressant...
does not alter the hypoxia or the consequent vasoconstriction, but stimulates fluid reabsorption in the lungs to reverse the edema.