<prompt> Transthoracic compliance formula:-C Vt x RR PEEPC VAIv p - atmospheric pressureC VtPplt - PEEPC VtPk - Pplt  <response>: Various pressures in thoracic cage. 1. Intra pleural pressure - - Intra pleural pressure is the pressure of the fluid in the thin space bw the lung pleura the chest wall pleura - Its a slight negative pressure. - Normal pleural pressure at the beginning of inspiration is about - -5 cm H2O at rest - At rest - - 5cm H2O - At normal inspiration - - 7.5 cm H2O 2. Intra alveolar pressure - Pressure in alveolus - This is equal to atmospheric pressure. - It is considered to be zero at rest. Transpulmonary pressure - difference bw alveolar pleural pressure. Transthoracic pressure - Transthoracic compliance - Alveolar pressure - Atmospheric pressure 