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Pulmonary Ventilation 1 David Taylor

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1 Pulmonary Ventilation 1 David Taylor

2  When you have worked through this you should be able to  Describe the relationships between airflow, pressure gradients and resistance – gas laws  Describe the mechanics of breathing – compare quiet versus forced  Reflect upon the integration of heart and lungs working together  Explain the nervous control of breathing Pulmonary ventilation 1

3  These slides are available with all my other lectures on my website  In the text books: Chapters 22,23 and 24 in Preston and Wilson (2013) Chapter 13 in Naish and Court (2014) Resources

4 Airflow, pressure gradients and resistance – gas laws

5  Changes in diameter of the airways  Autonomic control  Parasympathetic: ACh binds to M 3 receptors – bronchoconstriction  Sympathetic: Mainly by inhibiting ACh release but also through Noradrenaline on β 2 receptors  Endocrine: β 2 receptors are also sensitive to adrenaline  Irritants and allergens or inflammatory agents What affects resistance? Chapter 22 p in Preston and Wilson (2013) Chapter 13 p. 633 in Naish and Court (2014)

6 Mechanics of breathing “Passive”  The diaphragm contracts and this pulls down on the lungs – air enters.  The diaphragm lifts the lower ribs  External intercostal muscles contract also raising ribs  Normally breathing out is passive. Chapter 22 p. 268 in Preston and Wilson (2013) Chapter 13 p. 635 in Naish and Court (2014)

7  “Forced”  Inspiration can also use the accessory muscles  scalenes raise first two ribs,  sternomastoids raise the sternum  Additionally there is dilation of the upper airways  Expiration also uses the abdominal muscles  Rectus abdominis, transversus abdominis, internal and external oblique muscles  Internal intercostals pull ribs downward and inward Mechanics of breathing Chapter 22 p. 268 in Preston and Wilson (2013) Chapter 13 p. 635 in Naish and Court (2014)

8  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 and numbers

9 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

10  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

11  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

12  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

13 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 (dorsal) motor neurones Expiratory (ventral) motor neurones Scalene and sternomastoid External intercostals DiaphragmInternal intercostals Abdominal Chapter 24 p.298 and following in Preston and Wilson (2013) Chapter 13 p in Naish and Court (2014)


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