F ‘08 P. Andrews, Instructor

 Respiration  Exchange of gases between an organism and it’s environment  Pulmonary (external) respiration Occurs in lungs  Cellular (internal) respiration Occurs in peripheral capillaries Is the exchange of respiratory gases between RBCs and tissue Produces CO2  Ventilation  The mechanical process that moves air into and out of lungs

 The thorax Moves air in and out Oxygen and CO 2 are exchanged Also contains heart, major vessels, trachea, bronchi, lungs, mediastinum

 Ventilations are controlled by a series of centers in the brain and blood vessels  Main control center – medulla oblongata Connected to respiratory muscles via VAGUS NERVE  Additional control center – pons Apneustic center Pneumotoxic center

 Stretch receptors  Decrease inspiratory stimulus

 In the medulla and carotid bodies and arch of the aorta  Stimulated by changes in O 2 and CO 2 as well as pH

 Hyoxemia is a profound stimulus of respiration in a normal person  People with COPD retain CO 2 – have chronically elevated PaCO 2  Peripheral chemoreceptors become used to this; CNS stops using PaCO 2 to regulate.  A default mechanism – HYPOXIC DRIVE – is activated  Increased respiratory stimulation when PaO 2 falls; inhibited respiratory stimulation when PaO 2 climbs

 Sternocleidomastoid muscles  raise upper rib and sternum  Intercostal muscles contract  elevate ribs and increase anterior-posterior dimension  Diaphragm is the primary muscle of respiration – it contracts and flattens  increases volume of cavity.  Pressure in cavity becomes less than atmospheric  air rushes in to alveoli to equalize pressure

 Muscles relax…  Diaphragm moves upward  Ribs and sternum move inferiorly  Ribs move closer together in inferior and posterior position  Thoracic volume decreases  Intrathoracic pressure increases

 Changing volume and pressure of thoracic cage also helps with  Pumping blood to and return from systemic circulation  Affects BP and pulse strength  Normally, systolic BP and pulse strength fall during inspiration, rise during exhalation

 Adults – 12 – 24 breaths per min.  Children – 18 – 24 breaths per min.  Infants – 40 – 60 breaths per min.

 Total lung capacity – TLC  ~ 6 L  Tidal Volume – V T  ~ 500 ml (5 – 7 ml/kg)  Dead space volume – V D ~ 150 ml  Alveolar Volume – V A ~ 350 ml  Minute volume - V min