#ALVEOLAR DEAD SPACE PLUS#

The surface area available for gas exchange is therefore reduced. The associated destruction of alveolar septa results in enlarged air spaces. Pulmonary artery obstruction by an embolus (arising from thrombus, gas, fat or amniotic fluid) results in the downstream alveoli being ventilated but not perfused, thus increasing VDAlv. No gas exchange is possible in these spaces.

Anatomical dead space is that portion of the airways (such as the mouth and trachea to the bronchioles) which conducts gas to the alveoli. Anatomic and alveolar dead space together are referred to as physiological dead space, which is the true value of V d as represented in the equations.

#ALVEOLAR DEAD SPACE PLUS#

In addition, the increase in intrathoracic pressure reduces venous return to the right ventricle, which in turn reduces pulmonary artery pressure. The total dead space (also known as physiological dead space) is the sum of the anatomical dead space plus the alveolar dead space. Increased alveolar dead space explains how these diseases lead to decreased gas exchange with an unchanged V e. In the lung apices, the increase in alveolar pressure causes compression of the pulmonary capillaries, reducing alveolar perfusion. Positive end-expiratory pressure and positive pressure ventilation both increase alveolar pressure. Like upright posture, this leads to insufficient perfusion of the lung apices, a high VМ‡/ QМ‡ ratio and thus an increase in VDAlv. Low pulmonary artery pressure for example, as a result of reduced right ventricular output. The apical alveoli are well ventilated but not adequately perfused, which increases VDAlv. Owing to the effect of gravity, blood only just perfuses the lung apices (i.e. However, VDAlv may increase as a result of: In normal lungs, VDAlv is negligible as alveolar ventilation and perfusion are well matched. Dead Space measurement Mid inspiration-Deep breath of Oxygen Exhales Nitrogen content of expired air is continuously measured Initial gas exhaled (phase I) is the gas that fills the dead space and consequently contains no N2. 48) and VDAnat is measured using FowlerвЂ™s method. VDPhys is measured using the Bohr equation (see p. As VDPhys=VDAnat+VDAlv, the alveolar dead space can be calculated if VDPhys and VDAnat are known.

How is alveolar dead space measured and what factors affect it?ДЄlveolar dead space cannot be measured directly. The next step was to calculate the late dead-space fraction (folate) which represents the dead-space fraction of the gas at the end of a hypothetical expiration with a volume equal to 15 percent of predicted TLC.

Alveolar dead space