L17. Physiological Consequences of Increased Movement of Fluid Across Pulmonary Capillaries Flashcards
Is the pulmonary circuit low or high in pressure and resistance? Why?
the pulmonary circuit is a low pressure and a low resistance system. This is because it mainly works at the level of the heart and across relatively small distances.
What is the normal pulmonary pressure?
PAP: ???
Mean Pressure: 15mmHg
What is the advantage of the pulmonary system having a low pressure?
There is a reduced tendency for fluid to leak out of the capillaries into the alveolar space
What is the consequence of the low pulmonary pressures?
The right heart is substantially thinner than the left heart: it pumps the same amount (CO) but under less much less work.
Does pulmonary arterial pressure increase with exercise (increased CO)?
PAP remains relatively stable for physiological/mild pathological changes in CO due to compensatory mechanisms. Despite increases in capillary volume with increasing CO, pulmonary vessels are able to dilate to decrease pressure
Decreasing CO in pathologies can be compensated for by vasoconstriction.
“The pulmonary circuit acts as a reservoir for blood” Explain what is meant by this term. Give 2 examples.
The pulmonary circuit needs to accommodate for the same CO as the systemic (whole body) blood.
1. In the supine position: blood drains back into the heart and the pulmonary circulation
2. In Inspiration: intrathoracic and intrapleural pressure decreases and this negative pressure is transferred to the heart. Thus the lower pressure in the pulmonary circuit leads to a decrease in volume returning to the left atrium, and decreased CO and decreased systemic pressure.
Thus on inspiration systemic pressure is lower than in inspiration.
What are the 2 major pathologies on the pulmonary circuit?
- Pulmonary Oedema
2. Pulmonary Hypertension
What is the anion gap? What is the normal range?
The anion gap is the relationship between the common electrolytes of the body:
Na + K = Cl + HCO3
Normally: <15
What is the difference between metabolic vs. respiratory acidosis?
Metabolic acidosis is due to increases in acids such as lactic acid (so CO2 levels remain normal) while respiratory acidosis is due to problems with ventilation meaning that CO2 tends to be high these cases (compensated for by HCO3 buffering capacity).
What is pulmonary oedema? What are the 4 factors that affect the balance?
Fluid movement across the AC membrane (into the alveolar spaces).
- Hydrostatic Pressure (the fluid pressure inside the capillaries)
- Osmotic pressure: The protein concentrations
- Permeability of the membrane (especially affected in inflammation)
- Lymphatic Flow Obstruction (cancer)
What is the mechanism for interstitial fluid passage out of the lungs? What is the normal rate?
Interstitial fluid drains into the lymphatic circulation which prevents alveolar fluid accumulation. The flow rate is about 20 mL/hour
What mechanical changes to the lung occur as a result of pulmonary oedema?
Decreased Lung Compliance
Decreased lung volumes (restrictive)
Increased airway resistance
Increased work of breathing
What changes to gas exchange occur as a result of pulmonary oedema?
Diffusion impairment leading to V/Q mismatch and shunting
What changes to arterial blood gases (partial pressure) occur due to pulmonary oedema?
Decreased PaO2 Increased PaCO2 (thus decreased pH) If severe then decreases by large amount to the point of respiratory failure
What changes to pulmonary circulation occurs as a result of pulmonary oedema?
Increases in pulmonary vascular resistance which leads to increased pulmonary pressure on the heart (back flow) = cor pulmonale
