Respiratory volume per minute

In respiratory physiology, the respiratory volume per minute, or volume per minute, or ventilation per minute, or volume expired per minute 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 levels of carbon dioxide. It can be measured with some devices, such as a Wright respirometer, or it can be calculated from other known respiratory parameters. Note that although its name implies that it is a volume, it is in fact a flow rate (represents a change in volume over time).

Several symbols are used to represent the volume per minute. These include: ${displaystyle {dot {V}}}$VM and V_E.

Determining the volume per minute

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

Volume measurement per minute

Minute volume is the amount of gas inhaled or exhaled from a person's lungs, per minute. It can be measured by a Wright spirometer or by any other device capable of cumulative measurement of gas flow, such as mechanical ventilators.

Calculation of volume per minute

If both the tidal volume (V_T) and respiratory rate (ƒ or F_r) are known, the minute volume can be calculated by multiplying these two values. The effect of dead space on alveolar ventilation must also be taken into account, as seen below in relation to other physiological parameters.

${displaystyle {dot {V}}=V_{T}times f}$

Physiological importance of minute volume

Blood carbon dioxide levels (PaCO₂) generally vary inversely with minute volume.^{[citation needed]} For For example, a person with an increased minute volume (due to hyperventilation, for example) might demonstrate a lower level of carbon dioxide in the blood. A normal organism can alter its respiratory minute volume to maintain physiological homeostasis.

A resting minute volume in humans is approximately 5-8 liters. The volume per minute, in general, decreases in resting situations, and increases with exercise. For example, during daytime activities the volume per minute is 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 can be between 40 and 60 liters per minute.

Hyperventilation is the term that defines a minute ventilation greater than physiologically appropriate. Hypoventilation, on the other hand, describes a minute volume that is less than physiologically appropriate.

Relationship with other physiological parameters

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

${displaystyle {dot {V}}={dot {V}}_{A}+{dot {V}}}{D}}}$

where ${displaystyle {dot {V}}_{A}}$ It's alveolar vent, and ${displaystyle {dot {V}}_{D}}}$ represents the ventilation of dead space.