Ventilation-Perfusion Matching

In a lung unit with ventilation-perfusion (V/Q) mismatch, which of the following best describes the pathophysiological consequence when V/Q ratio is less than 0.1?

A 62-year-old man with chronic obstructive pulmonary disease (COPD) undergoes arterial blood gas analysis. His PaO₂ is 55 mmHg (normal ~95 mmHg) despite supplemental oxygen at FiO₂ 0.40. All of the following mechanisms could explain his hypoxemia EXCEPT:

Two patients undergo pulmonary function testing and blood gas analysis. Patient A has a V/Q ratio of 0 in 30% of lung units (true shunt), with PaO₂ 65 mmHg on room air and 68 mmHg on 100% O₂. Patient B has a V/Q ratio of 3.0 in 30% of lung units (dead space), with PaO₂ 62 mmHg on room air and 95 mmHg on 100% O₂. Which finding best distinguishes a true shunt from dead space ventilation?

Which regional lung zone normally exhibits the lowest ventilation-perfusion ratio under quiet breathing in the upright position?

A 58-year-old man with COPD presents with dyspnea and hypoxemia (SpO₂ 88% on room air). Arterial blood gas shows PaO₂ 55 mmHg, PaCO₂ 52 mmHg, pH 7.32. Clinical examination reveals decreased breath sounds bilaterally with prolonged expiration. Which investigation is most appropriate to quantify the degree of ventilation-perfusion mismatch and guide oxygen therapy?