<prompt> A man connected to a body plethysmograph for estimation of FRC inspires against a closed glottis. Which of the following statements is true -The pressure in both the lung and the box increaseThe pressure in both the lung and the box decreaseThe pressure in the lung decrease, but that in the box increaseThe pressure in the lung increase, but that in the box decrease  <response>: Ans. c The pressure in the lung decrease, but that in the box increaseRef: Ganong, 25th edp.630Body plethysmography is based on the principle of Boyles Law which states that volume of a gas is inversely proportional to the pressure of that gas at constant temperatureReciprocal changes in Pressure and volume Boyles law during plethysmography During inspirationDuring expirationIn subjects LungVolume increasesPressure decreasesVolume decreasesPressure increasesIn boxVolume decreasesPressure increasesVolume increasesPressure decreases 