Atmospheric Pressure (P atm )– pressure exerted by the air/gases that surround the body

1. Atmospheric Pressure (Patm)– pressure exerted by the air/gases that surround the body -- respiratory pressure are always relative to Patm -- 760 mmHg at sea level Intrapulmonary Pressure (Ppul) -- pressure in the alveoli --fluctuates with breathing Intrapleural Pressure (Pip) --always about 4mmHg below Ppul -- difference created by adhesion between pleural membranes Transpulmonary Pressure --Ppul – Pip -- keeps the lungs open -- greater transpulmoray pressure = larger lungs.

2. Factors that can effect intraplueral pressure Pleural Membranes – serous fluid between visceral and parietal pleura cause them to adhere to each other --excessive fluid leads to an increase in Pip • Alveoli • Surface tension – attraction of water molecules within alveoli • --causes alveoli to collapse • --opposes adhesive force between membranes • Surfactant – secretion composed of lipoproteins • -- reduces surface tension and eases inspiration Lungs Elastic Recoil

3. Lungs at Rest When lungs are at rest, the pressure on the inside of the lungs is equal to the pressure on the outside of the thorax 19-16

4. Air Movements Boyle’s Law • Moving the plunger of a syringe causes air to move in or out • Air movements in and out of the lungs occur in much the same way 19-17

5. Inspiration • Intra-pulmonary pressure decreases to about 758mm Hg as the thoracic cavity enlarges • Atmospheric pressure forces air into the airways 19-18

6. Maximal Inspiration • Thorax at end of maximal inspiration • aided by contraction of sternocleidomastoid and pectoralis minor muscles Thorax at end of normal inspiration 19-19

7. Expiration • due to elastic recoil of the lung tissues and abdominal organs 19-20

8. Maximal Expiration • contraction of abdominal wall muscles • contraction of posterior internal intercostal muscles 19-21

9. Factors That Influence Ventilation • Airway resistance – friction between air and the respiratory passageways • -- Decreasing airway diameter increases resistance (asthma) • Alveolar Surface Tension • Compliance – ability of lungs to stretch due to pressure during inspiration • - decreases as lung volume increases • Decreased by airway obstructions and tissue destruction

10. Respiratory Volumes • Spirometry – measurement of air volume moved in and out of the lungs • respiratory cycle – one inspirations plus the following expiration • tidal volume – volume moved in or out during a normal breath • inspiratory reserve volume – volume that can be inhaled during forced breathing in addition to tidal volume • expiratory reserve volume – volume that can be exhaled during forced breathing in addition to tidal volume • residual volume – volume that remains in lungs at all times 19-22

11. Respiratory Capacities • inspiratory capacity = maximum amount of air that can be inhaled after a • resting expiration • functional residual capacity = volume of air in the lungs after a resting • expiration • vital capacity = maximum amount of air a person can expel after taking the • deepest breath possible • total lung capacity = total amount of air the lungs can hold

12. Respiratory Volumes and Capacities 19-24

13. Dead space – area where gas exchange does not occur anatomical – trachea, bronchi, bronchioles alveolar – nonfunctioning alveoli Physiological Dead Space – anatomical and alveolar dead space volumes

14. Alveolar Ventilation • alveolar ventilation rate • major factor affecting concentrations of oxygen and carbon dioxide in the alveoli • volume of air that reaches alveoli • tidal volume minus physiologic dead space then multiplied by breathing rate • minute ventilation • tidal volume multiplied by breathing rate • amount of air that is moved into the respiratory passageways per minute 19-25

15. Nonrespiratory Air Movements • coughing • sneezing • laughing • crying • hiccuping • yawning • speech 19-26