Session 8 Flashcards
How does the pulmonary circulation work?
With low pressure and low resistance
Describe the blood flow to the lungs
Brachial - part of systemic circulation, meets metabolic requirement of the lungs
Pulmonary - blood supply to the alveoli, required for gaseous exchange
What is the pressure in the RA?
0-8 mmHg
What is the pressure in the LA?
1-10 mmHg
What is the pressure in the aorta?
100-140mmHg
What is the mean arterial pressure?
12-15mmHg
What is the mean pressure in pulmonary capillaries?
9-12mmHg
What is the mean venous pressure?
5mmHg
What is the ventilation-perfusion ratio?
Ratio of the amount of air reaching the alveoli to the amount of blood reaching the alveoli.
What is the optimal V/Q ratio?
0.8
How is V/Q ratio maintained?
By diverting blood from the alveoli that aren’t well ventilated
What is hypoxic pulmonary vasoconstriction?
Ensures optimal ventilation perfusion ratio by constricting the pulmonary arteries. Poorly ventilated alveoli are less well perfused therefore gaseous exchange is optimised.
What happens in chronic hypoxic vasoconstriction?
RV failure. Can occur at high altitudes or as a consequence of lung disease –> chronic pulmonary hypertension. High after load on RV leading to RV failure.
What is transit time?
The time it takes RBCs to flow through capillary
How does tissue fluid form?
Hydrostatic pressure of blood within capillaries pushes fluid out Oncotic pressure (colloid osmotic pressure) draws fluid into the capillary
What influences capillary hydrostatic pressure?
Venous pressure in systemic circulation fluid tends to move out at the arterial end
How does oedema form?
Increased capillary pressure causes more fluid to filter out
How do you treat pulmonary oedema?
Give the patient diuretics to decrease blood volume which therefore decreases hydrostatic pressure.
What causes pulmonary oedema?
High capillary pressure (if it exceeds 20-25mmHg)
How much of the cardiac output does the brain use?
How much of the oxygen consumption of the body is attributed to the brain?
15% of CO
Grey matter consumes 20% of the oxygen of the body at rest
How is the brain supplied well?
High capillary density (large SA, decreased diffusion distance)
High basal flow rate
High oxygen extraction
Structure - anastomoses between basilar and internal carotid arteries
How can blood vessels respond to fluctuations in blood pressure?
Myogenic autoregulation - increase in BP leads to vasoconstriction, decrease in BP leads to vasodilation
What is hypercapnia?
What is hypocapnia?
Hyper - increased PCO2 leading to vasodilation
Hypo - decreased PCO2 leading to vasoconstriction
Panic/hyperventilation can cause hypocapnia and cerebral vasoconstriction leading to dizziness/fainting
What is cushing’s reflex?
A physiological nervous system response to increased intracranial pressure (ICP) that results in Cushing’s triad (increased blood pressure, irregular breathing, and a reduction of the heart rate). There is increased sympathetic vasomotor activity.
What forms the blood brain barrier?
Cerebral capillaries form a tight BBB.
What is the diffusion distance for myocardium?
9 micro metres
