Question

Ventilation-perfusion mismatch. Please explain in your own words, the importance of or relevance of the V/Q parameter. Please highlight its importance as a mathematical parameter in our mass transport models as well as its implications to clinical performance and pathologies. Max of 400 words.

Answer 1

Ventilation to the perfusion ratio (V/ Q) is the ratio of the amount of air reaching the alveoli to the amount of blood that reaches alveoli. A healthy adult can hold 200mL of oxygen in about 1 litre of blood and 1 litre of atmospheric dry air contains about 210 mL of oxygen. Thus, the ideal ventilation perfusion ratio in healthy adut is assumed to be 1.05 or approximately 1. Alteration of V/ Q is observed in certain pathological conditions, and is an indication of type 1 respiratoryfailure.

If the value of V/Q is zero (i.e. perfusion is there but zero ventilation), it is called "shunt." If theV/ Q value is approaching infinity, it is called dead space (i.e. ventilation is there but zero perfusion).

Decreased V/Q ratio: It is an indication of impaired pulmonary gas exchange that leads to low arterial partial pressure of oxygen (paO₂). Exhalation of CO2 is also impaired, but paCO₂ does not rise because due to increased respiratory rate, alveolar ventilation returns paCO₂ to within the normal range. These observations are generally found during the patholgical conditions such as chronic bronchitis, acute pulmonary edema, asthma and hepatopulmonary syndrome.

Increased V/Q ratio: This causes high arterial partial pressure of oxygen (paO₂) due to lack of re-oxygenation and low paCO₂. These findings are observed in conditions of pulmonary embolis (impaired blood circulation due to embolus), emphysema as a maladaptive ventilatory overwork of the undamaged lung parenchyma.