Special Circulations Flashcards
Pulmonary circulation must accept the
Entire cardiac output
Pulmonary circulation works at
Low pressure and low resistance
Features of the pulmonary circulation
Low resistance- short wide vessels, lots of capillaries, arterioles have relatively little smooth muscle so lumen size T not constricted as much
Mean arterial pressure
12-15mmHg
Mean capillary pressure
9-12mmHg
Mean venous pressure
5mmHg
Adaptations of pulmonary circulation for efficient gas exchange
very high density of capillaries in alveolar wall - large sa
Short diffusion distance
What is V/Q
Ventilation perfusion ratio
Need to match for efficient oxygenation
Ideal = 0.8
How do you maintain V/Q
Diverting blood from alveoli which are not well ventilated
What is the most important mechanism ensuring optimal ventilation perfusion ratio
Hypoxia pulmonary vasoconstriction - regulates pulmonary vascular tone
Alveolar hypoxia results in vasoconstriction of pulmonary vessels
Poorly ventilated alveoli are less well perfused to optimise gas exchange. Effect is opposite to
That in systemic circulation
Chronic hypoxic vasoconstriction can cause
Right ventricular failure or chronic pulmonary hypertension
e.g. altitude or emphysema
Chronic increase in vascular resistance leads to
Chronic pulmonary hypertension
High afterload on right ventricle can lead to
Right ventricular heart failure
low pressure pulmonary vessels are strongly influenced by
Gravity
In upright position there is greater hydrostatic pressure on vessels in lower part of lung
Effect of exercise on pulmonary blood flow
Increased cardiac output
Small increase in pulmonary arterial pressure
Opens apical capillaries
Increase oxygen uptake by lungs
Capillary transit time is reduced as blood flow increases
Features of tissue fluid formation
Starling forces
Hydrostatic pressure pushes fluid out
Oncotic pressure draws fluid in (created by plasma proteins)
Capillary hydrostatic pressure is influenced more by
Venous pressure in the systemic circulation
Hypertension does not usually result in
Peripheral oedema
low capillary pressure minimises the formation of
Lung lymph
Increased capillary pressure causes
More fluid to filter out and oedema
Can get pulmonary oedema if
Capillary pressure increases (left atrial pressure rises to 20-25mmHg, mitral valve stenosis and left ventricular failure)
Principles of pulmonary oedema
Impairs gas exchange Forms mainly at base when upright Forms throughout lung when lying down use diuretics to relieve symptoms Treat underlying cause
Worse type of pulmonary oedema
Forms throughout lung when lying down
