Pleural pressure positive in: (A) End of inspiration, (B) End of expiration, (C) End of forced expiration, (D) Sta or beginning of inspiration
Answer is C. During active expiration, the abdominal muscles are contracted to force up the diaphragm and the resulting pleural pressure can become positive. Positive pleural pressure may temporarily collapse the bronchi and cause limitation of air flow Ref: guyton and hall textbook of medical physiology 12 edition page number:316,317,318