17. Pulmonary Circulation Flashcards
Where does pulmonary and bronchial circulation come from and end?
- Pulmonary - right ventricle => left atrium
* Bronchial - thoracic aorta => pulmonary veins
How do pulmonary arteries compare to systemic arteries?
- Greater lumen:wall thickness ration (thinner wall)
- More distensible
- Greater compliance
- Lower pressure
- Same cardiac output
- Smaller pressure gradient
- Less resistance (10% of systemic)
What are the functions of the pulmonary circulation?
- Gas exchange
- Metabolism of vasoactive substances e.g. ACE in pulmonary endothelium is involved in the formation of Angiotensin II and degradation of bradykinin
- Filtration of blood - elimination of small emboli (air bubbles moved out, fatty plaques and thrombi enzymatically degraded), filters before systemic circulation
What is a pulmonary shunt and give an example?
- Circumstances associated with bypassing the respiratory exchange surface
- Bronchial circulation - goes through the left side of the heart twice, and still bypasses the respiratory exchange surface (1% of CO)
- Foetal circulation - Foramen Ovale & Ductus Arteriosus (following the path of least resistance)
Give 2 examples of heart defects related to a disruption in pulmonary circulation
- Atrial Septal Defect/Patent Foramen Ovale - mixed venous blood moves from right to left atrium (mal-correction after birth)
- Ventricular Septal Defect - more of a congenital defect
What would an increase in cardiac output lead to in the pulmonary circulation if it was rigid?
- Increased MAP
- Increased hydrostatic pressure
- Fluid pushed into interstitial space
- Pulmonary oedema
- Decreased pulmonary function
Why does an increase in cardiac output not lead to pulmonary oedema?
- Distensible - MAP doesn’t increase much
- Increased perfusion to hypoperfused capillary beds
- No detriment to pulmonary function
What is vascular recruitment?
- Increased use of the vascular beds which were not being used because there wasn’t enough pressure to access them
- Unequal perfusion still present (basal more perfused due to gravity)
What effect does inspiration and expiration have on the vessels associated with the alveoli?
• Inspiration - alveoli expand - alveolar vessels compressed - extra-alveolar vessels relieved due to space • Expiration - chest becomes smaller - extra-alveolar compressed - alveolar vessels relieved of pressure
(both impact pulmonary circulation resistance dramatically)
What is the (systemic and) pulmonary vascular response to hypoxia?
• Systemic - vasodilation • Pulmonary - vasoconstriction - low oxygen - oxygen-sensitive potassium channels close - decreased potassium efflux - cell reaches threshold membrane potential - depolarisation => calcium influx - Vasoconstriction
When is the pulmonary vascular response to hypoxia useful?
- High altitude - only perfusion of ventilated alveolus to avoid wasted perfusion
- Foetal development - blood flows through shunts rather than unnecessarily flowing through the pulmonary circuit (first breath increases alveolar PO2 and dilates pulmonary vessels)
When is the pulmonary vascular response to hypoxia detrimental?
- COPD
- Reduced alveolar ventilation and air trapping
- Increased resistance in pulmonary circuit
- Pulmonary Hypertension
- Right ventricular hypertrophy
- Congestive Heart Failure
What is the pressure of fluid moving out of a vessel in a healthy person?
1 mmHg
What effect does hypoproteinaemia have on oedema?
- Less proteins
- Less pulling force
- More fluid remains in the interstitium
- Oedema
What effect does an infection (accumulating in the interstitium) have on oedema?
- More proteins and leukocytes in the interstitium
- Pulling force into the interstitium
- More fluid leaves the capillaries
- Oedema
