Conversely, the alveolar ventilation at any YVE is greatest when breathing is slow and deep. Thus, the particular combination of respiratory frequency and tidal volume that is used to achieve any minute ventilation is an important determinant of both the alveolar ventilation and the dead space ventilation. Additionally, dead space ventilation can be caused by inequalities in the distribution of alveolar ventilation and perfusion. Certain lung regions have greater ventilation than perfusion. The excess of regional ventilation to blood flow can be thought of as wasted, although in most disease states, the mismatch is caused by regional deficits in perfusion rather than excessive ventilation.
T contribute significantly to dyspnea and often to respiratory failure in clinical lung disease.
3 Alveolar Ventilation Alveolar ventilation is that portion of the minute ventilation that comes into equilibrium with alveolar gas. The lungs are the only organ system normally perfused by the entire cardiac output. The pulmonary circulation serves to bring mixed venous blood into an extensive capillary network that allows ample opportunity for equilibration with alveolar gas. An important feature of the pulmonary circulation is that its perfusion occurs at a mean pressure approximately one fourth to one fifth the pressure of the systemic circulation. In the upright human, these lower pressures result in relative underperfusion of the apex of the lung and overperfusion of the base.