Abnormality on pulmonary function testing Abnormal alveolar volume 2021-02-01T13:14:58Z Only a portion of each tidal volume (Vt) reaches the alveoli and participates in gas exchange. This is referred to as the alveolar volume (Va). The remainder, the so-called dead space volume (Vd), consists of gas that fills the upper and lower airways (anatomic dead space) or reaches nonperfused or relatively poorly perfused alveoli (alveolar dead space). Alveolar volume (VA) is a volume accessible during 10-second breath-hold, measured during a single breath maneuver. VA is calculated by knowing the fractional concentration of the tracer gas (eg helium) and the volume of the gas inhaled. VA = Vi*(Fi tracer/Fa tracer). In this equation, Vi = inspired volume of tracer gas, Fi tracer= inspired fraction of tracer gas, Fa tracer = alveolar (exhaled) fraction of tracer gas.