Minute ventilation (or respiratory minute volume or minute volume) is the
volume
Volume is a measure of occupied 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). The de ...
of gas
inhaled
Inhalation (or Inspiration) happens when air or other gases enter the lungs.
Inhalation of air
Inhalation of air, as part of the cycle of breathing, is a vital process for all human life. The process is autonomic (though there are exceptions ...
(inhaled minute volume) or
exhaled (exhaled minute volume) from a person's
lung
The lungs are the primary organs of the respiratory system in humans and most other animals, including some snails and a small number of fish. In mammals and most other vertebrates, two lungs are located near the backbone on either side of t ...
s per minute. It is an important parameter in
respiratory medicine
Pulmonology (, , from Latin ''pulmō, -ōnis'' "lung" and the Greek suffix "study of"), pneumology (, built on Greek πνεύμων "lung") or pneumonology () is a medical specialty that deals with diseases involving the respiratory tract. 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
Flow rate may refer to:
* Flow measurement, a quantification of bulk fluid movement
* Mass flow rate, the mass of a substance which passes per unit of time
* Volumetric flow rate, the volume of fluid which passes per unit time
** Discharge (hydrol ...
(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 volume (symbol VT or TV) is the volume of air moved into or out of the lungs during a normal breath. In a healthy, young human adult, tidal volume is approximately 500 ml per inspiration or 7 ml/kg of body mass.
Mechanical vent ...
(V
T) and
respiratory rate
The respiratory rate is the rate at which breathing occurs; it is set and controlled by the respiratory center of the brain. A person's respiratory rate is usually measured in breaths per minute.
Measurement
The respiratory rate in humans is mea ...
(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 blood. ...
) 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
liter
The litre (international spelling) or liter (American English spelling) (SI symbols L and l, other symbol used: ℓ) is a metric unit of volume. It is equal to 1 cubic decimetre (dm3), 1000 cubic centimetres (cm3) or 0.001 cubic metre (m3). ...
s 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 blood. ...
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 (hypercapnia ...
describes a minute volume less than physiologically appropriate.
Relationship to other physiological rates
Minute volume comprises the sum of
alveolar ventilation
Breathing (or ventilation) is the process of moving air into and from the lungs to facilitate gas exchange with the internal environment, mostly to flush out carbon dioxide and bring in oxygen.
All aerobic creatures need oxygen for cellular ...
and
dead space ventilation
Dead space is the volume of air that is inhaled that does not take part in the gas exchange, because it either remains in the conducting airways or reaches alveoli that are not perfused or poorly perfused. It means that not all the air in each b ...
. That is:
where
is alveolar ventilation, and
represents dead space ventilation.
References
External links
Overview at healthsystem.virginia.edu*
{{Respiratory physiology
Respiratory physiology