Ventilation volume refers to the amount of air which is moved through the lungs within a set period of time, classically one minute. Ventilation volume can vary considerably, depending on what someone is doing and someone's health status. A human being at rest, for example, will have a lower ventilation volume than an athlete in peak condition sprinting for the finish line. In the case of patients on a respirator, ventilation volume is one of the things which can be controlled to keep the patient comfortable and ensure that the patient gets enough oxygen to live.
Human beings and many other organisms breathe because their cells need oxygen. Every time someone takes a breath which brings air into the lungs, a gas exchange occurs inside the lungs. Waste products like carbon dioxide are traded with the oxygen in the air, allowing these waste materials to be vented from the body when the person breathes out while the oxygen is carried to the cells in the bloodstream. Ventilation volume has a large impact on how much oxygen is available to the body.
When someone is exerting him or herself physically, more oxygen is needed by the body, which is why people breathe hard after climbing a set of stairs, and why athletes breathe hard as they are competing or working out. Conversely, a person at rest should not have a very high oxygen requirement. For those wiseGEEK readers who are curious about how hyperventilation works, hyperventilation leads to a depletion of carbon dioxide levels in the blood, which causes the pH of the blood to rise, leading to constriction of the blood vessels and subsequent lightheadedness.
It is possible to measure the ventilation volume in a human being by determining how many breaths are being taken each minute and measuring the amount of air someone is capable of breathing in and out with each breath. A medical testing technique known as spirometry can be used to determine how much air someone can breathe to make inferences about ventilation volume and to collect data about a chronic medical condition such as asthma.
In the case of someone who cannot breathe independently, the ventilation volume must be controlled by a care provider or first responder. In cardiopulmonary resuscitation, for example, ventilation volume is dependent on how many breaths are given to the patient each minute. Patients on ventilators used for artificial respiration have their ventilation volume adjusted by changing the settings on the ventilator to increase or decrease the amount of air which flows through the lungs every minute.