Minute ventilation (or respiratory minute volume or minute volume) is the
volume
Volume is a measure of regions in three-dimensional space. It is often quantified numerically using SI derived units (such as the cubic metre and litre) or by various imperial or US customary units (such as the gallon, quart, cubic inch) ...
of gas
inhaled (inhaled minute volume) or
exhaled (exhaled minute volume) from a person's
lung
The lungs are the primary Organ (biology), organs of the respiratory system in many animals, including humans. In mammals and most other tetrapods, two lungs are located near the Vertebral column, backbone on either side of the heart. Their ...
s 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. Although minute volume can be viewed as a unit of volume, it is usually treated in practice as a
flow rate (given that it represents a volume change over time). Typical units involved are (in metric) 0.5 L × 12 breaths/min = 6 L/min.
Several symbols can be used to represent minute volume. They include
(V̇ or V-dot) or Q (which are general symbols for flow rate), 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
Tidal is the adjectival form of tide.
Tidal may also refer to:
* ''Tidal'' (album), a 1996 album by Fiona Apple
* Tidal (king), a king involved in the Battle of the Vale of Siddim
* TidalCycles
TidalCycles (also known as Tidal) is a live coding ...
(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".
:
Physiological significance of minute volume
Blood carbon dioxide (PaCO
2) levels generally vary inversely with minute volume. For example, a person with increased minute volume (e.g. due to
hyperventilation
Hyperventilation is irregular breathing that occurs when the rate or tidal volume of breathing eliminates more carbon dioxide than the body can produce. This leads to hypocapnia, a reduced concentration of carbon dioxide dissolved in the blo ...
) 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
Hyperventilation is irregular breathing that occurs when the rate or tidal volume of breathing eliminates more carbon dioxide than the body can produce. This leads to hypocapnia, a reduced concentration of carbon dioxide dissolved in the blo ...
is the term for having a minute ventilation higher than physiologically appropriate.
Hypoventilation
Hypoventilation (also known as respiratory depression) occurs when ventilation is inadequate (''hypo'' meaning "below") to perform needed respiratory gas exchange. By definition it causes an increased concentration of carbon dioxide ( hypercap ...
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:
:
where
is alveolar ventilation, and
represents dead space ventilation.
References
External links
Overview at healthsystem.virginia.edu*
{{Respiratory physiology
Respiratory physiology