Lecture 4 – Respiration III

Mechanics of ventilation pressure gradient between

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Mechanics of Ventilation Pressure gradient between the airway opening and alveoli determines rate of inspiratory  or expiratory flow how is the gradient generated? You are not maintaining a constant rate of flow It reciprocates – in and out Muscle contraction that results in changes in the volume of the thoracic cavity Reciprocating flow is MECHANICAL It is all muscle contraction How does this relate to lung volume? Transmural pressure determines lung/chest volume The difference in alveolar and atmospheric pressures determines the direction and  magnitude of flow Components Elasticity of lung  Elasticity of chest wall Elasticity - bigger and smaller with changes of pressure The chest wall has elasticity separate from lung elasticity Not necessarily affected by the same pressure
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Muscles Will drive the change in pressure Airways Pleurae and intrapleural space Intrapleural pressure Hooks everything together Respiratory Muscles when the diaphragm contracts, the base of the thoracic cavity is pulled downward and  the volume increases 11 th  and 12 th  ribs and lumbar vertebrae connection this change in volume is what determines the pressure gradient Boyle’s Law: p1v1 = p2v2 The causal sequence If the lung volume is made to change this causes the volume of the alveoli and the palv  to change which results in the bulk from of air into/out of the lung The lung volume depends on Transpulmonary pressure Is the difference between alveolar pressure and that within the (intrapleural space) One of two transmural pressures This sets the lung volume Set across the wall (visceral pleura) Always calculate as the alveolar pressure minus the intrapleural pressure (in-out) If this pressure drops, the pressure gradient gets steeper and this lung will expand
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