apex vs base of lung dead space and ahunt

At the arteriolar end, the vessels expand, but further down the vessel, Pv falls below PA and the vessel is squeezed. Zone 2: Towards the center of the lung, Pa exceeds the PA, while venous pressure is still less that PA. This results in crushing of the alveolar capillaries resulting in minimal flow. Zone 1: At the apex of the lungs, alveolar pressure PA is greater than either Pa or Pv, the pressures inside the pulmonary arterioles and venules, respectively. Regional distribution of perfusion - As we showed in the lecture on perfusion, the lung can be divided into three zones. They receive more gas with each inspiration. Basal alveoli are less distended and more compliant. Therefore they are difficult to distend further during inspiration. This distends the apical alveoli and decreases their compliance.

At the apex, intrapleural vacuum pressure is greater (more negative) because of the tendency of the lungs to 'settle' on the diaphragm and pull away from the apical chest wall. Regional distribution of ventilation - In an upright human, ventilation increases from the apex to the base of the lungs. Both of these parameters increase from the apex to the base of the lungs but not at equal rates.

b) non-ideal lung: In reality, the lungs have regional distributions of both ventilation and perfusion. This ratio allows for optimal gas exchange between lung and pulmonary capillaries. If we use the minute ventilation ( ~ 5-6 liters/min) for V instead of alveolar ventilation, then the value of V/Q for the lung as a whole comes out a little greater than 1. At rest the normal alveolar ventilation, VA, is ~ 4.2 liters/min and pulmonary blood flow, Q, is ~ 5 liters/min. A) In an ideal lung, the ventilation/perfusion (V/Q) of every alveolus is the same.

Apex vs base of lung dead space and ahunt