cardiorespitory mechanics Flashcards
what drives circulation in the rapid ejection part of the cardiac ejection
postive prressure
what causes heart sounds (s1 and s2)
SOUNDS OF VALVE CLOSING
what causes air to enter the lungs
diaphragm pulls down
decrease in thoracic pressure
what happens if you have a larger snokel
increase dead space
(increase distance from gas exchnage and ambient air)§
describe the relationship between reistance and radius
Resistance is inversely proportional to the fourth power of the radius
up to generation 4 the resistance to flow increase then decreases
Why doesn’t resistance continue to increase as airways get smaller?
although the airways get smaller, the amount of air decreases
lots of airways
relationship between lung volume and resistance
As the lung expands, the diameter of these vessels increases via radial traction of the vessel walls. Therefore, vascular resistance is low at large lung volumes. During lung collapse, there is increased resistance through the vessels due to the unopposed action of vessel elasticity.
what is Poiseuille’s Law
𝑅𝑒𝑠𝑖𝑠𝑡𝑎𝑛𝑐𝑒= 8ƞƖ /𝜋𝑟^4
- Fluid viscosity (ƞ, eta)
- The length of the tube (L).
- Inner radius of the tube
does the cinductivity of airways increase or decrease with volume
The ‘conductivity’ of the airways increases with increasing volume
what happens as the lung volume increases to airway size
Airways are not rigid pipes – they dilate as lung volume increases
what is the organistaion of vessels including viens arterie ect
arteries arteioles cappilliries venules veins
describe the change in surface are
increases to max at capiliry to then decrease
describe the mean pressure changes
pressure highest at arteries
massive reduction at atreioles
then decreases steadily
describe change in proportion of systemic volume
low at arteries
reduces more to capilies
then increases from venules to vein
which vessles are more resistance to flow
Small arteries and arterioles present most resistance to flow.
how does the pressure change accros ciruclation from systemic to pulmanory
Pressure falls across the circulation due to viscous (frictional) pressure losses.
high at systemic cos to push to whole body
low at pulmonary as only to lungs
how do arteries/arterioles regulate diameter
Small arteries and arterioles have extensive smooth muscle in their walls to regulate their diameters and the resistance to blood flow
why do veins act as a high resevior of blood
Veins and venules are highly compliant and act as a reservoir for blood volume
equation of blood pressure
Haemodynamic determinants of blood pressure
Blood pressure (MAP) = Cardiac output * Resistance
what are the key assumptions
steady flow (which does not occur due to the intermittent pumping of the heart)
rigid vessels
right atrial pressure is negligible
so only an approximate
how is regulation of blood achieved
Physiologically, regulation of flow is achieved by variation in resistance in the vessels while blood pressure remains relatively constant.
what is LAMINAR FLOW
flow in the same direction
Velocity of the fluid is constant at any one point and flows in layers
where does the blood flow the fastest
Blood flows fastest closest to the centre of the lumen.
slowest
towards the edge
TURBULENT FLOW
Blood flows erratically, forming eddys, and is prone to pooling
Associated with pathophysiological changes to the endothelial lining of the blood vessels..
what can be heard during deflation of the blood pressure cuff
Slow deflation of cuff causes turbulent flow which can be heard with a stethoscope
how to work out plse pressure
SBP-DBP
how to work out mean arterial pressure
DBP +1/3 pulse p
what causes the dichrotic notch
caused by closure of aortic valve
why do we have cartilangous airways
stop the airway collapsing in on its self
hard expiration should theoritcally cause our lung to collapse
This is why our large extrapulmonary airways are supported with cartilage
what is compliance
The tendency to distort under pressure
if it isvery compliant a small pressure causes a large change in volume so steep volume pressure line
𝑪𝒐𝒎𝒑𝒍𝒊𝒂𝒏𝒄𝒆= ∆𝑽/∆𝑷
elastance
The tendency to recoil to its original volume
high elastance means
small volume change requires large ellastance
𝑬𝒍𝒂𝒔𝒕𝒂𝒏𝒄𝒆= ∆𝑷/∆𝑽
what is the difference in pressure changes once the aortic valve closes
Once the aortic valve closes (A) ventricular pressure falls rapidly but aortic pressure falls slowly
why
This can be explained by the elasticity of the aorta and large arteries which act to “buffer” the change in pulse pressure.
The elasticity of a vessel is related to its compliance.
how are the arteries able to change a pulsiatile flow into a constant flow
During ejection, blood enters the aorta and other downstream elastic arteries faster than it leaves them
When the aortic valve closes, ejection ceases but due to recoil of the elastic arteries, pressure falls slowly and there is diastolic flow in the downstream circulation
(recoil of arteries)
If arterial compliance decreases (e.g. as arteries become stiffer with age). How would you expect blood pressure measurements to change?
remember blood pressure is 2 readings
systolic and diastolic
systolic increases - as the vessels will not stretch
diastolic decreases as the is no recoil pushing the blood
what are 2 Facilitated venous return mechanisms
skeletal muscle pump
respitory pump
Incompetent valves cause
dilated superficial veins in the leg (varicose veins)
Prolonged elevation of venous pressure (even with intact compensatory mechanisms) causes
oedema in feet/lower limbs
what is Aneurysmal disease
Over time, vessel walls can weaken causing a balloon-like distension
Pathological example of the Law of Laplace. Vascular aneurysms increase radius of the vessel. This means that for the same internal pressure, the inward force exerted by the muscular wall must also increase.
However, if the muscle fibres have weakened, the force needed cannot be produced and so the aneurysm will continue to expand …
often until it ruptures
This pathology and the underlying physical forces involved also holds for the formation of diverticuli in the gut.
when does venous compliance mean
its ability and willingness to change volume to a given pressure is greater than artery
how do you increase venous pressure
Increasing smooth muscle contraction (green arrow) decreases venous volume and increases venous pressure.
what is the ventilation differnce in the lung
ventilation at the base of the lung is greater than the top of the lung provided your standing up
head stand would cause it to invert
and perfusion
greater at the base Higher intravascular pressure (gravity effect) More recruitment Less resistance Higher flow rate
effective gas exchange requires
gas exchange occurs in the lungs between alveolar air and blood of the pulmonary capillaries. For effective gas exchange to occur, alveoli must be ventilated and perfused. Ventilation (V) refers to the flow of air into and out of the alveoli, while perfusion (Q) refers to the flow of blood to alveolar capillaries
how does the ventialtion/perfusion ratio chnage from apex to base
decrease
what is wasted ventilation
at the apex, the gas at the apex is not exchanged effictively as less perfusion
what is wasted perfusion
at the base more blood going passed the respitory exchange surface than what can particpate in gas exchange
