Question

1a) If the ventilation/perfusion ( V/Q) ratio of a lung region decreases, how will the P_O2 and P_CO2 in the blood in that region change?

1b) In perfusion-limited O₂ exchange, is the P_O2 at the end of the pulmonary capillary closer to P_A,O2 or P_V,O2?

1c) Which of the following is/are higher at the base of the lung than at the apex: blood flow, V/Q, ventilation, P_O2, P_CO2?

Please explain your answers briefly and accurately.

Answer 1

1A). Po2 is decreased and Pco2 is increased. Lesser ratio of V/Q leading to reduced partial pressure of O2 (due impairment of the pulmonary air exchange) and also reduced excretion of CO2 leading to more PCO2 usually happens in athma.

1B).PAO2. Reason: Oxygen is considerably capable of diffusing into the hemoglobin but not into the tissues thereby it is described that PO2 at the end of the pulmonary capillary closer to PAO2.

The O2 is able to get into the blood, but not into the tissues, therefore it will be closer to the alveolar pressure of O2.

1c). Pulmonary capillary PCO2 & ventilation – Whilst a person is standing then the base region of the lung considerably possess the highest ventilation with more perfusion. The reason is the presence of more distended blood vessels at the base region of the lungs compared to the apex thereby it is illustrated that the blood flow per unit lung volume is considerably more at the basal region of the lung when compared to the apex. It is described that when compared to the apex of the lungs the base of lung possess more pulmonary capillary PCO2