Sam LO #1 - Anatomy
7. Describe the mechanisms (muscles, pressure and volumes) underlying spontaneous ventilation. Pressure (P) & Airflow to Lungs Air will flow area higher (P) → area lower (P) 1x respiratory cycle → inspiration (inhalation) + expiration (exhalation) o Inhal/exhalation involve s in vol of lungs creating pressure gradients moving air in/out of resp tract Ea lung lies w/in pleural cavity Parietal & visceral pleurae separated only by thin film pleural fluid can slide across ea other Comparable fluid bond btn parietal pleura & visceral pleura covering lungs → surface of ea lung sticks to inner wall of chest & superior surface of diaphragm o movements of chest wall/diaphragm directly affect vol of lungs o Vol of thoracic cavity s when diaphragm s position or rib cage moves: Diaphragm contracts & moves inferiorly ↑ volume of cavity Superior movement ribs ↑ depth & width of thoracic cavity 1. 2. 3. 4. 5. 6. 7.
1. 2. 3. 4. 5. 6. 7.
At start of breath, pressures inside & outside thoracic cavity = identical Thoracic cavity enlarges Pleural cavities & lungs expand to fill additional space ↑ vol ↓ (P) inside lungs Air enters resp passageways (P inside < P outside) Air continues entering until vol stops ↑ (Pi) = (Po) Thoracic cavity ↓ vol (P) ↑ inside lungs force air out of resp tract Inspiration Respiratory muscles contract Thoracic cavity expands ↓ in pleural pressure Transpulmonary pressure ↑ Lungs inflate Alveolar (P) < atmospheric (P) Air flows into the lungs
1. 2. 3. 4. 5. 6. 7.
no air moves in/out of lungs
Expiration Respiratory muscles relax Thoracic cavity ↓ Pleural pressure becomes less negative Transpulmonary pressure ↓ Lungs deflate Alveolar (P) > atmospheric (P) Air flows out of the lungs
Compliance Compliance = indication of expandability o ↓ compliance = ↑ force req’d to fill & empty lungs Factors affecting compliance: o Connective-tissue structure of lungs o Level of surfactant production o Mobility of thoracic cage At rest, muscular activity involved in ventilation ~3-5% of resting energy demand (normal, compliant lung) Pressure Changes during Inhalation & Exhalation Intrapulmonary Pressure Direction of airflow determined by r/ship btn atmospheric (P) & intra-pulmonary (P) o Intra-pulmonary (intra-alveolar) (P) = (P) measured inside resp tract at alveoli During quiet breathing, (P) diff relatively small Inhalation → Lungs expand, intrapulmonary (P) ↓ ~759mmHg -1mmHg (vice versa for expiration = +1mmHg) Size of pressure gradient ↑ with heavy breathing o Exhaling less forcefully against a closed glottis (Valsalva manoeuvre) causes reflexive s in BP & CO due compression aorta & vena cavae Internal (P) ↑ vena cavae collapse → ↓ venous return (VR) ↓ CO & ↓ BP → stimulation aortic & carotic baroreceptors → reflexive ↑ HR & peripheral VC Glottis opens (P) normalise ↑ VR & ↑ CO Due VC → sharp ↑ BP inhibiting baroreceptors → CO, HR & BP quickly normalise Intrapleural Pressure Intrapleural (P) = (P) measured in space btn parietal & visceral pleurae o Averages -4mmHg (can reach -18mmHg during powerful inhalation) o (P) below atmospheric due r/ship btn lungs & body wall Elastic fibres of lungs o Can’t recoil sign’f b/c not strong enough to overcome fluid bond btn parietal & visceral pleurae o Continuously oppose fluid bond & pull lungs away from chest wall & diaphragm lowering intrapleural (P) slightly Cyclical s in intrapleural (P) are responsible for respiratory pump → mechanism assist venous return to heart
1. 2. 3. 4. 5. 6. 7.
At start of breath, pressures inside & outside thoracic cavity = identical Thoracic cavity enlarges Pleural cavities & lungs expand to fill additional space ↑ vol ↓ (P) inside lungs Air enters resp passageways (P inside < P outside) Air continues entering until vol stops ↑ (Pi) = (Po) Thoracic cavity ↓ vol (P) ↑ inside lungs force air out of resp tract Inspiration Respiratory muscles contract Thoracic cavity expands ↓ in pleural pressure Transpulmonary pressure ↑ Lungs inflate Alveolar (P) < atmospheric (P) Air flows into the lungs
1. 2. 3. 4. 5. 6. 7.
no air moves in/out of lungs
Expiration Respiratory muscles relax Thoracic cavity ↓ Pleural pressure becomes less negative Transpulmonary pressure ↓ Lungs deflate Alveolar (P) > atmospheric (P) Air flows out of the lungs
Compliance Compliance = indication of expandability o ↓ compliance = ↑ force req’d to fill & empty lungs Factors affecting compliance: o Connective-tissue structure of lungs o Level of surfactant production o Mobility of thoracic cage At rest, muscular activity involved in ventilation ~3-5% of resting energy demand (normal, compliant lung) Pressure Changes during Inhalation & Exhalation Intrapulmonary Pressure Direction of airflow determined by r/ship btn atmospheric (P) & intra-pulmonary (P) o Intra-pulmonary (intra-alveolar) (P) = (P) measured inside resp tract at alveoli During quiet breathing, (P) diff relatively small Inhalation → Lungs expand, intrapulmonary (P) ↓ ~759mmHg -1mmHg (vice versa for expiration = +1mmHg) Size of pressure gradient ↑ with heavy breathing o Exhaling less forcefully against a closed glottis (Valsalva manoeuvre) causes reflexive s in BP & CO due compression aorta & vena cavae Internal (P) ↑ vena cavae collapse → ↓ venous return (VR) ↓ CO & ↓ BP → stimulation aortic & carotic baroreceptors → reflexive ↑ HR & peripheral VC Glottis opens (P) normalise ↑ VR & ↑ CO Due VC → sharp ↑ BP inhibiting baroreceptors → CO, HR & BP quickly normalise Intrapleural Pressure Intrapleural (P) = (P) measured in space btn parietal & visceral pleurae o Averages -4mmHg (can reach -18mmHg during powerful inhalation) o (P) below atmospheric due r/ship btn lungs & body wall Elastic fibres of lungs o Can’t recoil sign’f b/c not strong enough to overcome fluid bond btn parietal & visceral pleurae o Continuously oppose fluid bond & pull lungs away from chest wall & diaphragm lowering intrapleural (P) slightly Cyclical s in intrapleural (P) are responsible for respiratory pump → mechanism assist venous return to heart
