Cardiorespiratory Mechanics :) Flashcards
what is laminar blood flow?
where velocity of the fluid is constant at any point, and flows in layers
where is laminar blood flow the fastest?
closest to the lumen
what is turbulent blood flow?
when blood flows erratically, forming eddys, and is prone to pooling
what changes is turbulent blood flow linked to?
pathological changes to the endothelial lining of blood vessels
what pressure differences causes inspiration?
Pressure of atmosphere > Pressure of alveoli
what pressure differences causes expiration?
pressure of atmosphere < pressure of alveoli
define compliance
tendency to distort under pressure
define elastance
tendency to recoil to its original volume
what is blood pressure the same as
mean arterial pressure
state the equation for blood pressure
Blood pressure (MAP) = Cardiac Output x Resistance
state the equation to calculate pulse pressure
pulse pressure = systolic blood presssure - diastolic blood pressure
state the equation for cardiac output
cardiac output = stroke volume x heart rate
state the equation for cardiac output
cardiac output = stroke volume x heart rate
state the equation for mean arteriole pressure
diastolic blood pressure - 1/3 (pulse pressure)
define airway transmural pressure
the pressure difference between the alveolar pressure and intrapleural pressure
define intrapleural pressure
pressure within pleural cavity
state the equation for compliance
Compliance = change in volume / change in pressure
state the equation for elastance
Elastance = change in pressure / change in volume
define perfusion
the passage of bodily fluids i.e blood through a system to an organ or tissue
what is the 2 key elements of the Law of Leplace?
the tension on the wall of a sphere is the product of the pressure x radius of the chamber
tension inversely proportional to thickness of wall
what initiates rapid ejection in the cardiac cycle
the opening of the aortic and pulmonary valves
what does fluid and air flow according to?
pressure gradient
state the poiseuille’s law equation
if you half the radius in poiseuille’s law what happens to flow
flow decreases 16 times
what is resistance inversely proportional to?
resistance => inversely proportional to r(to the power of 4)
in what generation does resistance in the lung peak?
generation 4
why does resistance begin to decrease after generation 4?
number of aiways start to cumulatively increase
what happens do the airways as the lung volume increases?
airways dilate
what increases the conductivity of airways
increasing lung volume
what component of arteries and arterioles regulate diameters and resistance to blood flow?
smooth muscle in walls
which out of arteries and veins acts as a reservoir for blood volume in body?
veins
why do we see a fall in pressure across circulation?
falls due to viscous (frictional) pressure losses
when arteries/arterioles are smaller, what happens to the resistance to flow?
resistance to flow increases
why is pulmonary circulation at a lower blood pressure than systemic circulation?
pulmonary circuit has a smaller distance
what does TPR stand for
total peripheral resistance
Blood pressure (MAP) = Cardiac Output x Resistance: what are some assumptions for this equation? (3)
- steady flow
- rigid vessels
- right arterial pressure is negligble
how is the regulation of blood flow achieved?
through resistance variation in vessels with a constant blood pressure
state 3 variables that increase resistance of a tube
- fluid viscousity (n,eta)
- the length of the tube (L)
- inner radius of the tube (r)
state the 2 types of blood flow
- turbulent
- laminar
how does blood pressure cuff deflation lead us to hear blood flow?
slow deflation of cuff causes turbulent flow => can be heard by stethoscope
at what speed does ventricular pressure fall when the aortic valve closes
rapidly
at what speed does aortic pressure fall when the aortic valve closes
slowly
why does aortic pressure fall slowly after the closing of the aortic valve?
the aorta and large arteries have elastic tissue = act as buffer to change pulse pressure
why is the large extrapulmonary airways supported with cartilage?
prevents airway collapsing in the case of -ve transmural pressure
state 2 structural properties of lung tissue
compliance
elastance
how does arterial compliance lead to continuous blood flow with controlled pressure? (stages)
blood enters artery => artery stretches => artery recoils in diastole but due to the stretch alongside aortic valve => artery becomes a reservoir for generating diastolic blood flow => continuous blood flow with controlled pressure
what will a decrease in arterial pressure impact and what will happen to blood pressure?
impact on diastolic blood flow => increase in blood pressure
what is a pulse?
the difference between systolic and diastolic blood pressure
state 2 pumps essential for venous return
- skeletal muscle pump
- respiratory pump
how does the skeletal muscle pump work in terms of venous return?
when muscles contract => squeezing veins due to valves it pushes blood upwards => when muscles relax it creates a negative pressure sucking blood forward
how does the respiratory pump work in terms of venous return?
diaphragm pulls down (-ve intrathoracic pressure => air flow) => hypercompliant veins dilate in presence of negative pressure => helping suck blood back into chest from head neck and abdomen
state 2 health problems that can impact venous return
- incompetent valves => dilated superficial veins in leg => varicose veins
- prolonged elevation of venous pressure = oedema
what is the pathology of aneurysmal disease?
vascular aneurysms = increase vessel radius => the inward force exerted by muscular wall must increase => if elastic muscle fibres weakened => force needed not produced => aneurysm expands until it ruptures
what happens to vessel walls over time
weaken
what does compliance depend on
vessel elasticity
at low pressure, which is higher venous or arterial compliance?
venous (as veins hold 70% of blood)
what is the link between compliance, transmural pressure and vessel volume?
Compliance = relationship between transmural pressure and vessel volume
how does venous compliance work and aid with storage of blood?
Increased smooth muscle contraction => decreased venous volume => increased venous pressure => changes in venous pressure distend (swell) veins and increase the volume of blood stored in them.
where are the air pockets smaller in the lung?
at the apex
does the apex of the lung need more or less air flow than the top of the lung
less
are ventilation and perfusion greater at the top or bottom of the lung?
bottom
why is there less ventilation at the top of the lung?
Pressure of the Pleural cavity = more -ve => greater transmural pressure gradient => also Alveoli are larger and less compliant => less ventilation
why is there more ventilation at the apex of the lung?
Pressure of the Pleural cavity = less -ve => smaller transmural pressure gradient => alveoli are also smaller and more compliant => more ventilation
why is perfusion lower at the top of the lung?
Lower intravascular pressure => less recruitment => greater resistance => lower flow rate
why is perfusion greater at the apex of the lung?
Higher intravascular pressure (gravity effect) => more recruitment => higher flow rate
why does the difference in ventilation between the apex and base of the lung vary more than perfusion?
perfusion involves liquid => heavily impacted by gravity
where is the maximum efficiency on the ventilation-perfusion graph?
When ventilation-perfusion crosses => ventilation-perfusion = 1
when there is no gravity, is there a preferred perfusion location?
no
