F3.viii · Mechanics of Breathing

This Viva will examine your knowledge of respiratory physiology Q1: Draw the flow volume loop of the lung of a young adult male. Include tidal volume and submaximal efforts Dynamic tests of forced vital capacity are one of the most common types of respiratory function test that trainees will be exposed to. Candidates were expected to accurately label and discuss features of the flow volume loop including accurate axes, peak flow and its determinants and the effort dependent and independent parts of the loop. Pressures and flow characteristics in the airway during quiet expiration and forced expiration were sought. An adequate description of dynamic airways compression resulting in forced expiratory gas flow limitation was also required. Also asked were expiratory gas flow characteristics and lung volumes in chronic obstructive and restrictive lung disease. Finally the viva briefly explored knowledge of equipment that measures gas flow. Most candidates performed poorly in this viva. The main area of weakness was a lack of understanding of how pressure and flow change in the lungs during quiet and forced expiration. Also most candidates did not appreciate the importance of alveolar (lung) elastic recoil pressure in determining the pressure gradient for gas flow during quiet and forced expiration and how this depends on lung volume.