<prompt> True about primary pulmonary hypoventilation is:Does not respond to chemical stimuliHypocapnoea and normal PaO2Common in childrenRespiratory alkalosis is diagnostic  <response>: Answer is A Does not respond to chemical stimuli: Ventilatory responses to chemical stimuli are reduced or absent- Harrison 16111570 Primary pulmonary hypoventilation Characterized by: Impaired chemoreception resulting in decreased ventilatory drive. Chronic hypercapnia and hypoxemia in the absence of identifiable neuromuscular disease or mechanical ventilatory impairment. Presentation : Occurs in all age groups but majority of cases have been repoed in males aged 20-50 years. Early: lethargy, fagtigue, daytime somnolence, disturbed sleep and morning headache. Late: Cyanosis polycythemia, pulmonary hypeension, congestive hea failure. Note : Dyspnea is uncommon despite severe aerial blood gas derangements because of impaired chemotherapy. Diagnosis : The key diagnostic feature is respiratory acidosis in the absence of respiratory muscle weaknesses or impaired ventilatory mechanics. 