Define Dead Space in Physiology

Dead space is a crucial concept in respiratory physiology, referring to the portion of inspired gas that does not participate in gas exchange between the lungs and bloodstream. In this article, we will delve into the definition, measurement, and significance of dead space.

Anatomical Dead Space

Anatomical dead space refers to the volume of the conducting airways, which is the portion of the lung's respiratory tree that contains no alveoli. This includes the trachea, bronchi, and bronchioles. Anatomical dead space is constant regardless of circulation and remains unchanged even during exercise or other physiological changes.

Physiological Dead Space

Physiological dead space, on the other hand, is the volume occupied by gas that does not participate in gas exchange in the lungs. This includes the alveolar dead space, which is the part of inspired gas that passes through the anatomical dead space to mix with gas at the alveolar level but does not engage in gas exchange.

Measurement of Dead Space

Anatomical dead space can be measured using a rapid dilution technique, where a gas (such as N2 or CO2) already present in the lungs is rapidly diluted by inspired gas (100% O2). This method is used to estimate the volume of anatomical dead space. Physiological dead space can be calculated using the Bohr equation and Bohr's method, which assumes that all expired CO2 comes from alveolar gas.

Significance of Dead Space

Dead space plays a crucial role in understanding respiratory physiology and pathophysiology. During exercise, physiological dead space is reduced due to a reduction in alveolar dead space, allowing for more efficient gas exchange between the lungs and bloodstream. In contrast, anatomical dead space remains constant, regardless of circulation.

In conclusion, dead space is a fundamental concept in respiratory physiology that refers to the portion of inspired gas that does not participate in gas exchange between the lungs and bloodstream. Anatomical dead space represents the volume of conducting airways, while physiological dead space includes alveolar dead space and is influenced by physiological changes such as exercise.

References

* Text (1990)

Define dead space in physiology