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Mechanics of Respiration & Work of breathing 24.9.24.pptx
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- 2. Ventilatory apparatus • Consistsof lungs and a pump mechanism • Pump mechanism: • Ventilates the lungs • Comprises of • 1: chest wall/ribcage surrounding the lungs • 2: respiratory muscles which are skeletal muscles.
- 3. Breathing/Pulmonary Ventilation • Breathing(pulmonary ventilation), consists of two cyclic phases: • Inhalation, also called inspiration - draws gases into the lungs. • Exhalation, also called expiration - forces gases out of the lungs.
- 4. Muscles That CauseLung Expansion and Contraction • lungs can be expanded and contracted in two ways: • (1) by downward and upward movement of the diaphragm to lengthen or shorten the chest cavity (vertical diameter) • (2) by elevation and depression of the ribs to increase and decrease the anteroposterior & lateral diameters of the chest cavity. • External and internal intercostal muscles control these 2 diameters.
- 5. A/ ROLE OFDIAPHRAGM (affects the vertical diameter of the ribcage) • Normal quiet breathing is accomplished almost entirely by movement of the diaphragm. • During inspiration: • contraction of the diaphragm • pulls the lower surfaces of the lungs downward. • There is an increase in vertical diameter of the chest. • Air is taken in to the lungs (air is inhaled)
- 6. • During expiration: •The diaphragm simply relaxes • The elastic recoil of the lungs, chest wall, and abdominal structures compress the lungs • Decrease in vertical diameter of the chest. • Compressed lungs expel the air.
- 7. • During heavybreathing the elastic forces are not powerful enough to cause the necessary rapid expiration, so that extra force is achieved mainly by contraction of the abdominal muscles, which pushes the abdominal contents upward against the bottom of the diaphragm, thereby compressing the lungs.
- 8. B/ ROLE OFRIB CAGE & Sternum (affects the anteroposterior & lateral diameter of the ribcage) • The second method for expanding the lungs is to raise the rib cage. • In the natural resting position the ribs slant downward ,allowing the sternum to fall backward toward the vertebral column.
- 9. • During inspiration,ribcage is moved upward(elevated forward and outwards. (increase in both anteroposterior and lateral diameters of the ribcage) • During expiration, ribcage is moved downwards (depressed) & backwards and inwards. (decrease in both anteroposterior and lateral diameters of the ribcage)
- 10. • When theglottis is open and no air is flowing into or out of the lungs, the pressures in all parts of the respiratory tree, all the way to the alveoli, are equal to atmospheric pressure, that is, 0 centimeters water pressure. • The normal atmospheric pressure is equal to 760 mmHg or 1 atm.
- 11. Inspiration • It isalso called inhalation or taking in of air • During inspiration the thoracic cage and lungs expands, • this results in a fall in intrapulmonary/ alveolar pressure relative to the atmospheric pressure. • As a result of this pressure gradient, the atmospheric air rushes into the lungs producing inspiration. • During normal quiet breathing inspiration is an active process. (because it requires an active skeletal muscular contraction- contraction of diaphragm and therefore requires ATP).
- 15. MUSCLES OF INSPIRATION: Main/primarymuscles: • Diaphragm (primary muscle of inspiration), increases vertical diameter of thoracic cage. • It is a thin skeletal muscle at the base of the chest that separates chest from the abdomen. • External intercostals, increase anteroposterior and transverse/lateral diameters of the thoracic cage. These are also skeletal muscles attached to the ribs and are chest elevators. Accessory Muscles • Scalene • Sternocleidomastoid • Serratus anterior • Elevators of scapulae • Pectoralis minor
- 16. Rib-cage/thoracic cage movementsduring inspiration • Bucket handle movement of Thoracic cage: • Contraction of external intercostals causes the central portion of the ribs to move upward and outwards to a more horizontal position. • This movement is called bucket handle movement and it increases the transverse/lateral diameter of thoracic/ribcage. • Pump handle movement of Thoracic cage: • Contraction of external intercostal muscles causes elevation of these ribs and upward and forward movement of sternum. • This movement is called pump handle movement. • It increases anteroposterior diameter of the thoracic cage.
- 18. Expiration • It isalso called Exhalation or taking out of air. • During expiration, opposite changes occur than inspiration. • Thoracic cavity decreases in size. • Lungs are compressed resulting in a raised intrapulmonary/alveolar pressure relative to the atmospheric pressure. • As a result, the air is pushed out of the lungs into the atmosphere producing expiration. • During normal quiet breathing expiration is a passive process. (because it does not require active skeletal muscular contraction and therefore does not require ATP.)
- 19. Sequence of eventsDuring Expiration relaxation of inspiratory muscles and elastic recoil of the lungs decrease in size of thorax (decrease in all diameters) Compression of lungs decrease in size of lungs increase in intrapulmonary/alveolar pressure (becomes + 1.2 mmHg) establishment of pressure gradient from alveoli to atmosphere start of expiration intrapulmonary/alveolar pressure becomes equal to atmospheric pressure end of expiration
- 22. Muscles of Expiration •Main muscles: • Internal Intercostals. These are skeletal muscles located between the ribs. These are chest/ribcage depressors. Work more during forced expiration. • Accessory muscles: • Abdominal muscles , rectus abdominis, external oblique, internal oblique and transversus abdominis. • These also work more prominently during forced expiration.
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- 24. WORK OF BREATHING •During normal quiet breathing, all respiratory muscle contraction occurs during inspiration; • Expiration is almost entirely a passive process caused by elastic recoil of the lungs and chest cage. • The respiratory muscles normally perform “work” to cause inspiration but not to cause expiration.
- 25. WORK OF INSPIRATION •Can be divided into three fractions: 1. That required to expand the lungs against the lung and chest elastic forces, called compliance work or elastic work; 2. That required to overcome the viscosity of the lung and chest wall structures, called tissue resistance work; 3. That required to overcome airway resistance to movement of air into the lungs called airway resistance work.
- 26. ENERGY REQUIRED FORRESPIRATION • During normal quiet respiration, only 3 to 5 per cent of the total energy expended by the body is required for pulmonary ventilation. • During heavy exercise, the amount of energy required can increase as much as 50-fold especially with: • increased airway resistance OR • decreased pulmonary compliance
- 27. Reading Material • Guytonand Hall • Jaypee • Mushtaq Physiology Vol 2