• Define the term "ventilation-perfusion ratio"

Ventilation-perfusion (V/Q) ratio is a measure of the relationship between the amount of air entering the alveoli (V) and the amount of blood flowing through the capillaries surrounding the alveoli in the lungs (Q).

it is calculated ventilation/Perfusion

the normal value for V/Q = 0.84 as the normal ventilation = 4.2L and the CO (perfusion) is 5L and so 4.2/5 = 0.84 this is however an overall value, as the V/Q varies depending on which part of the lung it is from. differences are elaborated on below

• Describe the differences in ventilation across the lung

there are different zones throughout the lung, zones 1-4

zone 1 = apex of lung = low ventilation - low perfusion

zone 2 = apex/mid lung = low ventilation - low perfusion

zone 3 = mid/lower lung = higher ventilation - higher perfusion

zone 4 = base of lung = high ventilation - high perfusion

zone 1 - he mentions in lecture that it is always the case that alveolar pressure is higher than pulmonary pressures however in humans this is not correct he says mostly to ignore this fact

the perfusion of Zone 2 is dependant of systole/diastole of the heart, so during diastole the Pressure of Alveole are greater than the pressures of pulmonary arteries and so little/no perfusion occurs at this point however during systole the pressures of pulmonary arteries becomes greater than alveolar pressures and so perfusion occurs