Brownout (medical)

Brownout (medical)

A brownout, or grey-out, is a transient loss of vision characterised by a perceived dimming of light accompanied by a brown hue and a loss of peripheral vision.Fact|date=February 2007 It is a precursor to fainting or a blackout and is caused by hypoxia, a loss of blood pressure or restriction of blood flow to the brain. It is commonly experienced when suddenly standing up (see orthostatic hypotension), especially if sick, hungover, or suffering from low blood pressure or shock. Usually recovery is rapid and a brownout can be readily reversed by lying down.

A brownout may be brought on intentionally or unintentionally through hyperventilation (See fainting game under "self-induced hypocapnia, and "shallow water blackout."

A brownout, or grey-out, may also be experienced by aircraft pilots pulling high positive "g"-forces as when pulling up into a loop or a tight turn forcing blood to the lower extremities of the body and lowering blood pressure in the brain. This is the reverse of a redout, or a reddening of the vision, which is the result of negative G forces caused by performing an outside loop, that is by pushing the nose of the aircraft down. Redouts are potentially dangerous and can cause retinal damage and hemorrhagic stroke. Pilots of high performance aircraft can increase their resistance to brownout by using a G-suit, which controls the pooling of blood in the lower limbs but there is no suit yet capable of controlling a redout. In both cases symptoms may be remedied immediately by easing pressure on the joystick. Continued, or heavy G force will rapidly progress to g-LOC (G force induced Loss of Consciousness).

Another common occurrence of brownouts are in roller coaster riders. Many roller coasters put riders through high positive G forces, particularly in vertical loops and helices.Fact|date=February 2007 Roller coasters rarely have high enough negative G forces to induce redouts, as most low-G elements are designed to simulate weightlessness.

Also, grey-out may occur after donating blood, resulting in a loss of blood pressure and insufficient blood reaching the brain. However, the onset of such grey-outs is usually gradual and preventable by lying down so that the cardiovascular system does not need to work against gravity to reach the brain.Fact|date=April 2007


Wikimedia Foundation. 2010.

Игры ⚽ Нужна курсовая?

Look at other dictionaries:

  • Brownout — may refer to:* Brownout (medical) a dimming of the vision caused by loss of blood pressure or hypoxia (sometimes referred to as a grey out). * Brownout (electricity) drop in voltage in an electrical power supply, so named because it typically… …   Wikipedia

  • Brownout (aviation) — In aviation, a brownout (or brown out ) is an in flight visibility restriction due to dust or sand in the air.cite book publisher = National Transportation Safety Board title = Special Investigation Report on Emergency Medical Services Operations …   Wikipedia

  • Гипервентиляция — (от др. греч. ὑπέρ  над, сверху + лат. ventilatio  проветривание)  интенсивное дыхание, которое превышает потребности организма в кислороде. Различают гипервентиляцию как симптом заболевания и гипервентиляцию в дайвинге… …   Википедия

  • Потеря сознания на малой глубине — Постановочная фотография показывает, как выглядит жертва потерявшая сознание под водой, оставшись незамеченной. У этого термина существуют и другие значения, см. Потеря. Потеря сознания на малой глубине возникает в …   Википедия

  • Power outage — A power outage (also known as power cut , power failure , power loss , or blackout ) is the loss of the electricity supply to an area.The reasons for a power failure can for instance be a defect in a power station, damage to a power line or other …   Wikipedia

  • List of Coalition aircraft losses in Afghanistan — The following is a list of Coalition aircraft losses in Afghanistan. It covers both helicopters and fixed wing aircraft. 2008 *July 2: A US UH 60 Black Hawk helicopter was shot down by RPG and small arms fire south of the Afghan capital in Logar… …   Wikipedia

  • List of aviation accidents and incidents during the Iraq War — This list of aviation accidents and incidents during the Iraq War includes accidents and incidents with Coalition and civilian aircraft during the Iraq War. At least 116 helicopters and 20 fixed wing aircraft have been lost in Iraq since the 2003 …   Wikipedia

  • Uninterruptible power supply — A small free standing UPS …   Wikipedia

  • Cesar Lacbu Nucum — Kuya Cesar Born Cesar L. Nucum, Sr. May 15, 1938(1938 05 15) Candaba, Pampanga Died May 17, 2007(2007 05 17) (aged 69) Quezon City, Philippines Nationality …   Wikipedia

  • Smart grid — Public infrastructure …   Wikipedia

Share the article and excerpts

Direct link
Do a right-click on the link above
and select “Copy Link”