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Unformatted text preview: 1 Pulmonary Physiology • Respiratory neurons in brain stem – sets basic drive of ventilation – descending neural traffic to spinal cord – activation of muscles of respiration • Ventilation of alveoli coupled with perfusion of pulmonary capillaries • Exchange of oxygen and carbon dioxide Respiratory Control System Perfusion-----> Nerve Impulses Nerve Impulses Ventilation Diffusion Force, displacement Pco2, Po2, pH Mechanoreceptors Blood Respiratory membrance Lung & Chest Wal Respiratory Muscles Spinal Cord Respiratory center-Medul a Chemoreceptors Cerebral Cortex Respiratory Centers • Located in brain stem – Dorsal & Ventral Medullary group – Pneumotaxic & Apneustic centers • Affect rate and depth of ventilation • Influenced by: – higher brain centers – peripheral mechanoreceptors – peripheral & central chemoreceptors Muscles of Ventilation • Inspiratory muscles- – increase thoracic cage volume • Diaphragm, External Intercostals, SCM, • Ant & Post. Sup. Serratus, Scaleni, Levator Costarum • Expiratory muscles- – decrease thoracic cage volume • Abdominals, Internal Intercostals, Post Inf. Serratus, Transverse Thoracis, Pyramidal Ventilation-Inspiration • Muscles of Inspiration-when contract ⇑ thoracic cage volume (uses 3% of TBE) – diaphragm • drops floor of thoracic cage – external intercostals – sternocleidomastoid – anterior serratus – scaleni – serratus posterior superior – levator costarum – (all of the above except diaphragm lift rib cage) Ventilation-expiration • Muscles of expiration when contract pull rib cage down ⇓ thoracic cage volume (forced expiration • rectus abdominus • external and internal obliques • transverse abdominis • internal intercostals • serratus posterior inferior • transversus thoracis • pyramidal – Under resting conditions expiration is passive and is associated with recoil of the lungs 2 Movement of air in/out of lungs • Considerations – Pleural pressure • negative pressure between parietal and visceral pleura that keeps lung inflated against chest wall • varies between -5 and -7.5 cmH 2 O (inspiration to expiration – Alveolar pressure • subatmospheric during inspiration • supra-atmospheric during expiration – Transpulmonary pressure • difference between alveolar P & pleural P • measure of the recoil tendency of the lung • peaks at the end of inspiration Compliance of the lung • Δ V/ Δ P • At the onset of inspiration the pleural pressure changes at faster rate than lung volume- z hysteresis z • Air filled lung vs. saline filled lung – Easier to inflate a saline filled lung than an air filled lung because surface tension forces have been eliminated in the saline filled lung Pleural relationships-lung & chestwall forces Effect of Thoracic Cage on Lung • Reduces compliance by about 1/2 around functional residual capacity (at the end of a normal expiration) • Compliance greatly reduced at high or low lung volumes...
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- Spring '11
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