Respiratory minute volume

File:Lungvolumes Updated.png
TLC	Total lung capacity: the volume in the lungs at maximal inflation, the sum of VC and RV.
TV	Tidal volume: that volume of air moved into or out of the lungs during quiet breathing (TV indicates a subdivision of the lung; when tidal volume is precisely measured, as in gas exchange calculation, the symbol TV or VT is used.)
RV	Residual volume: the volume of air remaining in the lungs after a maximal exhalation
ERV	Expiratory reserve volume: the maximal volume of air that can be exhaled from the end-expiratory position
IRV	Inspiratory reserve volume: the maximal volume that can be inhaled from the end-inspiratory level
IC	Inspiratory capacity: the sum of IRV and TV
IVC	Inspiratory vital capacity: the maximum volume of air inhaled from the point of maximum expiration
VC	Vital capacity: the volume of air breathed out after the deepest inhalation.
VT	Tidal volume: that volume of air moved into or out of the lungs during quiet breathing (VT indicates a subdivision of the lung; when tidal volume is precisely measured, as in gas exchange calculation, the symbol TV or VT is used.)
FRC	Functional residual capacity: the volume in the lungs at the end-expiratory position
RV/TLC%	Residual volume expressed as percent of TLC
VA	Alveolar gas volume
VL	Actual volume of the lung including the volume of the conducting airway.
FVC	Forced vital capacity: the determination of the vital capacity from a maximally forced expiratory effort
FEVt	Forced expiratory volume (time): a generic term indicating the volume of air exhaled under forced conditions in the first t seconds
FEV1	Volume that has been exhaled at the end of the first second of forced expiration
FEFx	Forced expiratory flow related to some portion of the FVC curve; modifiers refer to amount of FVC already exhaled
FEFmax	The maximum instantaneous flow achieved during a FVC maneuver
FIF	Forced inspiratory flow: (Specific measurement of the forced inspiratory curve is denoted by nomenclature analogous to that for the forced expiratory curve. For example, maximum inspiratory flow is denoted FIFmax. Unless otherwise specified, volume qualifiers indicate the volume inspired from RV at the point of measurement.)
PEF	Peak expiratory flow: The highest forced expiratory flow measured with a peak flow meter
MVV	Maximal voluntary ventilation: volume of air expired in a specified period during repetitive maximal effort

Respiratory minute volume (or minute ventilation or expired minute volume) is the volume of gas inhaled (inhaled minute volume) or exhaled (exhaled minute volume) from a person's lungs per minute. It is an important parameter in respiratory medicine due to its relationship with blood carbon dioxide levels. It can be measured with devices such as a Wright respirometer, or can be calculated from other known respiratory parameters. Note that although its name implies that it is a volume, minute volume is actually a flow (it represents a volume change over time).

Several symbols can be used to represent minute volume. They include: $\dot{V}$, MV, and V_E.

Determination of minute volume

Minute volume can either be measured directly or calculated from other known parameters.

Measurement of minute volume

Minute volume is the amount of gas inhaled or exhaled from a person's lungs in one minute. It can be measured by a Wright respirometer or other device capable of cumulatively measuring gas flow, such as mechanical ventilators.

Calculation of minute volume

If both tidal volume (V_T) and respiratory rate (ƒ or RR) are known, minute volume can be calculated by multiplying the two values. One must also take care to consider the effect of dead space on alveolar ventilation, as seen below in "Relationship to other physiological rates".

$\dot{V} = V_T \times f$

Physiological significance of minute volume

Blood carbon dioxide (PaCO₂) levels generally vary inversely with minute volume. For example, a person with increased minute volume (e.g. due to hyperventilation) should demonstrate a lower blood carbon dioxide level. The healthy human body will alter minute volume in an attempt to maintain physiologic homeostasis. A normal minute volume while resting is about 5–8 liters per minute in humans. Minute volume generally decreases when at rest, and increases with exercise. For example, during light activities minute volume may be around 12 litres. Riding a bicycle increases minute ventilation by a factor of 2 to 4 depending on the level of exercise involved. Minute ventilation during moderate exercise may be between 40 and 60 litres per minute.

Hyperventilation is the term for having a minute ventilation higher than physiologically appropriate. Hypoventilation describes a minute volume less than physiologically appropriate.

Relationship to other physiological rates

Minute volume comprises the sum of alveolar ventilation and dead space ventilation. That is:

$\dot{V} = \dot{V}_A + \dot{V}_D$

where $\dot{V}_A$ is alveolar ventilation, and $\dot{V}_D$ represents dead space ventilation.

External links

• Overview at healthsystem.virginia.edu
• Overview at ccmtutorials.com
• Physiology: 4/4ch3/s4ch3_15 - Essentials of Human Physiology
• What is minute ventilation