9.6 Pulmonary Circulation and its determinants Flashcards
What are the factors that affect diffusion?
Thickness of membrane
Diffusion coefficient
Total SA of respiratory membrane
Pressure gradients
What pathological causes results in membrane thickening?
Lung oedema
Lung fibrosis due to inflammation
What pathological causes results in reduced membrane surface area?
Emphysema
Lung resections
What is the driving force for diffusion?
difference in the partial pressures in capillary and alveolus
What is the gas exchange dependent on?
ventilation, perfusion (CO) and Hb concentration
What causes vasoconstriction of pulmonary vessels?
Low PAo2 High PAco2 decreased pH Alpha adrenergic action Thromboxane A2 Angiotensin Leukotrienes Neuropeptides Serotonin Endothelin Histamine Prostaglandins
What cases vasodilation of pulmonary vessels?
High PAo2 Nitric oxide Beta adrenergic action Prostcyclin AcH Bradykinin Dopamine Adenosine
What is the V/Q when ventilation is > and < perfusion
> perfusion V/Q > 1
< Perfusion V/Q < 1
What occurs in hypoventilation?
Inadequate ventilation and Alveolar partial pressures reach those in the blood and there will be vasoconstriction and bronchodilation
What occurs in hyperventilation?
inadequate perfusion and there will be vasodilation and bronchoconstriction
How does ventilation change across the lungs?
Ventilation increases from apex to base
Describe ventilation at the apex of the lung
Intrapleural pressure is more negative
Greater transmural pressure gradient
Alveoli larger and less compliant
Less ventilation
Describe ventilation at the base of the lung
Intrapleural pressure less negative
Smaller transmural pressure gradient
Alveoli smaller, more compliant
Greater ventilation
Describe perfusion at the apex of the lung
Lower intravascular pressures
Less recruitment, distension
Higher resistance
Less blood flow
Describe perfusion at the base of the lung
Greater vascular pressures
More recruitment, distension
Lower resistance
Greater blood flow
