Survey
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Download The Cardiac Cycle
Transcript
Pulmonary Ventilation 1 David Taylor [email protected] http://www.liverpool.ac.uk/~dcmt Pulmonary ventilation 1 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 Resources These slides are available with all my other lectures on my website http://www.liv.ac.uk/~dcmt In the text books: Chapters 22,23 and 24 in Preston and Wilson (2013) Chapter 13 in Naish and Court (2014) Airflow, pressure gradients and resistance – gas laws As in so much physics and physiology: Δ𝑃 𝑉= 𝑅 So the pressure gradient and the resistance determine the flow per unit time. A word about resistance (Poiseuille’s Law) 8𝐿𝜂 𝑅= 4 𝜋𝑟 L is airway length, ƞ is viscosity (dependent on density) – Poiseuille’s law is for laminar flow Paradoxically the Pharynx is the site of greatest resistance Ask yourself, why not the bronchioles…. What affects resistance? Changes in diameter of the airways Autonomic control Parasympathetic: ACh binds to M3 receptors – bronchoconstriction Sympathetic: Mainly by inhibiting ACh release but also through Noradrenaline on β2 receptors Endocrine: β2 receptors are also sensitive to adrenaline Irritants and allergens or inflammatory agents Chapter 22 p. 273-274 in Preston and Wilson (2013) Chapter 13 p. 633 in Naish and Court (2014) 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) Mechanics of breathing “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 Chapter 22 p. 268 in Preston and Wilson (2013) Chapter 13 p. 635 in Naish and Court (2014) Some words and numbers 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 (V/Q range 3.3-0.8L/min) Ventilation/perfusion ratio (V/Q) Distance above bottom of lung 30 No blood flow V/Q=3.3 20 Flow is regulated by alveolar pressure 10 V/Q=0.8 0 Relative blood flow Pulmonary venous pressure above atmospheric pressure Top Left atrium The importance of matching ventilation and perfusion 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 (local) ways in which perfusion is controlled If ventilation is poor Local hypoxia (low O2) Leads to vasoconstriction So blood is diverted to other (better perfused regions of the lung) The inputs to the pathways which control breathing Receptors: Central chemoreceptors (ventral surface of medulla) – increase rate and depth with ↑ CO2 Peripheral chemoreceptors (carotid bodies, aortic arch) – increase rate and depth with ↓O2 or pH Stretch receptors (bronchi) - inhibit rate There are several others, but these are the most important for now. The physiological control of breathing Emotions etc., CO2 Higher centres Central chemoreceptors Limbic system O2 and pH Peripheral chemoreceptors Afferent sensory neurones Medulla oblongata and pons Inspiratory (dorsal) motor neurones Scalene and sternomastoid External intercostals Expiratory (ventral) motor neurones Diaphragm Internal intercostals Abdominal Chapter 24 p.298 and following in Preston and Wilson (2013) Chapter 13 p. 642-645 in Naish and Court (2014)
