Wednesday, December 11 (2019); Respiratory system
A well-matched V/Q ratio is 1.0, i.e. the lung unit receives as much ventilation as blood flow, and this should establish ideal conditions for good gas exchange. Wherever the V/Q ratio is low, there is an excess of blood flow as compared to ventilation, and therefore the effluent blood will be relatively hypoxic. Wherever there is an excess of ventilation, the global CO2 clearance will be poor in spite of vigorous airflow because the amount of blood delivered to these units is insufficient. These conditions are relatively absent in the healthy organism, but they can arise in disease states such as COPD, asthma, pulmonary oedema, and under the effects of positive pressure ventiltion.