The ins and outs of respiratory physiology Reverend Dr David Taylor

 What do you know about breathing?  We all do it  It involves the cardiovascular system as well…  It is a process of allowing gasses (which?) to exchange between blood and air  It has active and passive phases (which are which?)  it is hard to stop doing it (why?)  In this lecture we will look at the relationship between the cardiovascular and respiratory systems and the control of breathing. Before the lecture

 By the end of this lecture you should be able to discuss:  The importance of matching ventilation and perfusion  The (local) ways in which perfusion is controlled  The inputs to the pathways which control breathing  The physiological control of breathing Learning outcomes

 Naish’s Medical Sciences (2009 edition)  Silverthorn’s Human Physiology (2010 edition)  Ganong’s Review of Medical Physiology (2010 edition)  But the subject is covered reasonably well in most basic texts I used the following texts

 (Alice Springer) becomes wheezy and short of breath, despite using her blue inhaler. Her neck and chest muscles are working hard, but she cannot get control of her breathing. The case....

 (Alice Springer) becomes wheezy and short of breath, despite using her blue inhaler. Her neck and chest muscles are working hard, but she cannot get control of her breathing. highlighting

 Ventilation (alveolar ventilation)  The volume of air (L/min) entering and leaving an alveolus (4L/min)  Perfusion  In this case, pulmonary blood flow (5L/min)  Both change with position in the lung  (range L/min) Some words

Ventilation/perfusion ratio (V/Q) Distance above bottom of lung Relative blood flow Top Left atrium Pulmonary venous pressure above atmospheric pressure No blood flow Flow is regulated by alveolar pressure V/Q=3.3 V/Q=0.8

 Take the obvious extremes  Lung is well ventilated but there is no perfusion  Lung is well perfused, but there is no ventilation  Both would be fatal. The importance of matching ventilation and perfusion

 If ventilation is poor  Local hypoxia (low O 2 )  Leads to vasoconstriction  So blood is diverted to other (better perfused regions of the lung) The (local) ways in which perfusion is controlled

 Receptors:  Central chemoreceptors (ventral surface of medulla) – increase rate and depth with ↑ CO 2  Peripheral chemoreceptors (carotid bodies, aortic arch) – increase rate and depth with ↓ O 2 or pH  Stretch receptors (bronchi) - inhibit rate  There are several others, but these are the most important for now. The inputs to the pathways which control breathing

The physiological control of breathing Emotions etc.,CO 2 O 2 and pH Higher centres Limbic system Medulla oblongata and pons Central chemoreceptors Peripheral chemoreceptors Afferent sensory neurones Inspiratory motor neurones Expiratory motor neurones Scalene and sternomastoid External intercostals DiaphragmInternal intercostals Abdominal