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Mechanism

Sat, 12/22/2007 - 15:37 — oxygen

MECHANISM OF BREATHING: periodic exchange of gas from alveoli with fresh gas of the upper airways

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spontaneous ventilation
mechanical ventilation
anesthetic effects on ventilation

removal and elimination of carbon dioxide from the blood
Spontaneous ventilation

General:
alveolar pressure: is atmospheric and is greater than intrathoracic pressure during end expiration/inspiration
pleural pressure : used as a measure of intrathoracic pressure
transpulmonary pressure: equals alevolar pressure minus intrapleural pressure

End expiration
alveolar pressure: equal zero; no flow
intraplueral pressure: equals -5 cm H20
transpulmonary pressure equal +5 cm H20

Beginning inspiration
diaphragm contracts therefore chest cavity expands
pressure gradient allows gas to flow from the upper airways into the alveoli
alveolar pressure changes from 0 to -3 cm H20
intraplueral pressure changes from -5 cm H20 to -8 cm H20
transpulmonary pressure

End inspiration
new transpulmonary pressure sustains lung expansion
alveolar pressure returns to zero
intraplueral pressure remains decreased
transpulmonary pressure 5 cm H20

Beginning expiration
diaphragm relaxes
elastic recoil of the lung creates a pressure gradient
gas flow from alveoli to the upper airway

Alveolar pressure
intrapleural pressure returns to -5 cm H20
transpulmonary pressure no longer supports lung expansion

Mechanical ventilation
general: apply intermittent positive pressure to upper airways
inspiration: gas flows into the alveoli with positive pressure until the alveolar and upper airway pressure equal

Expiration
positive airway pressure is either removed or decreased
allows for reveral of pressure gradient (of inspiration)
airflow moves from alveoli into upper airway

Comments

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Sat, 09/12/2009 - 04:40 — nomzz

Ventilation is the term used

Ventilation is the term used for the movement to and from the alveoli. The two aspects of ventilation are inhalation and exhalation which are brought about by the nervous system and the respiratory muscles. The respiratory centers are located in the brain stem. The respiratory muscles are the diaphragm and the internal and external intercostal muscles. The diaphragm is a done shaped muscle below the lungs. When it contracts, the diaphragm flattens and moves downward. The intercostal muscles are found between the ribs. The external intercostal muscles pull the ribs upward and outward and the internal intercostal muscles pull the ribs downward and inward. Ventilation is the result of the respiratory muscles producing changes in the pressure within the alveoli and bronchial tree.actually i was surfing net to get data related to my projects of itil certification , testking pmp , mcse 2003 and in the meantime came here...And find this post different one!
There are three important pressure in respect to breathing:
atmospheric pressure- the pressure of the air around us. At sea level the atmospheric pressure is 760 mmHg, at higher altitudes the pressure is lower.
intrapleural pressure- the pressure within the potential pleural space between the parietal and visceral pleura. This space is a potential rather than a real space. Intrapleural pressure is always slightly below atmospheric pressure. This is called negative pressure because the elastic lungs are always tending to collapse and pull the visceral pleura away from the parietal pleura. The serous fluid, however, prevents separation of the pleural membranes.
intrapulmonic pressure- the pressure within the bronchial tree and alveoli. This pressure fluctuates below and above atmospheric pressure during each cycle of breathing.
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