Cardiorespiratory mechanics (30) Flashcards
What happens to the flow-volume loop in variable extra thoracic obstruction?
- blunted inspiratory curve
- otherwise normal
- obstruction to inspiration, but not expiration
What happens to the flow-volume loop in variable intrathoracic obstruction?
- blunted expiratory curve
- otherwise normal
- no obstruction to inspiration, but blocks air coming back/expiration
What is the significance of Poiseuille’s Law?
if you decrease radius by half, the resistance goes up 16 fold resistance=8.n.l/pi.r^4 fluid viscosity= n length of tube= L inner radius of tube= r
Why doesn’t resistance continue to increase as airways get smaller?
- resistance increases up to airway generation 4, then decreases
- bc we are increasing the cumulative cross-sectional area (inc. numbers)
What are some characteristics of systemic circulation?
- 60-70% of systemic blood is in venous system
- veins and venules are highly compliant
- small arteries and arterioles have extensive smooth muscle in their walls to regulate their diameters and resistance to blood flow
Why does pressure fall across the circulation?
due to viscous/frictional pressure losses
What is the equation for blood pressure/ mean arterial pressure?
MAP= cardiac output X resistance (TPR)
–> assumes steady flow, rigid vessels and that right atrial pressure is negligible
AND
MAP= diastolic blood pressure + 1/3 pulse pressure
(pulse pressure= SBP-DBP)
What is laminar flow?
- velocity of fluid is constant at any one point and flows in layers
- blood flows fastest closest to the centre of the lumen
What is turbulent flow?
- blood flows erratically, forming eddys, and is prone to pooling
- associated w/ pathophysiological changes to the endothelial lining of the blood vessels
What is elastance in terms of lung tissue?
its tendency to resist force and return to original shape/volume
What is compliance in terms of lung tissue?
willingness to distort its shape under pressure
What is the equation for compliance?
change in volume/change in pressure
What is the equation for elastance?
change in pressure/change in volume
What is the relevance arterial compliance in the aorta?
- Windkessel effect
- aorta stretches during systole and recoils during diastole
- prevents intermittent flow–> continuous flow bc elastic aorta
How does the body facilitate venous return?
- skeletal muscle pump e.g. when we walk, veins get squashed by muscles and pushes blood up
- respiratory pump e.g. when we breathe in, intrathoracic pressure decreases–> strethces open low pressure vena cava, increasing pressure gradient into right atrium–> improved venous return
When does varicosity occur?
incompetent valves–> dilated superficial veins in the leg (varicose veins)
When does oedema occur?
after prolonged elevation of venous pressure
What is a pathological example of the law of Laplace?
- aneurysms
- vessel walls weaken–> balloon-like distension
- inc. radius of vessel, so inward force exerted by muscular wall must also increase for the same internal pressure
- if muscle fibres have weakened, the force needed cannot be produced, so aneurysm continues to expand until it ruptures
Why is it easier to ventilate the base of the lung?
- lower transmural pressure
- tissue stretched by gravity
- more blood flows to base
What can a flow-volume loop show in a pulmonary function test?
peak expiratory flow- the peak y-axis
vital capacity- difference between x points
What does a COPD flow-volume loop look like?
- displaced to the left bc lungs fuller, but amount of air accessed is less
- decreased vital capacity and indented exhalation curve bc obstruction
What does a flow-volume loop look like in restrictive disease?
restrict ability of chest to expand, so lungs cannot fill as much
- displaced to the right
- narrower curve
What is conductance?
- willingness of airways to conduct air
- the conductivity of airways inc. w/ inc. volume
