Cardiorespiratory Mechanics Flashcards
What does pressure help generate?
Flow
What marks the start of the rapid ejection phase of the heart cycle?
Opening of the aortic and pulmonary valves mark the start of this phase
What happens during rapid ejection?
As ventricles contract pressure within them exceeds pressure in aorta and pulmonary arteries. Semilunar valves open, blood pumped out and the volumes of ventricles decrease.
How would a graph during inspiration and expiration look like for time against
- Palv (cmH2O)
- flow rate (L/s)
- vol change (mL)
What counts as fluid?
air, blood, filtrate, lymph
How do fluids flow?
according to a pressure gradient
What leads to inspiration?
Patm> Palv with patent airways
What happens to Ppl during inspiration and expiration?
Inspiration-> Ppl decreases (Pleural pressure decreases)
Expiration-> Ppl increases
Pleural pressure
Why does pleural pressure decrease during inspiration?
During inspiration, the diaphragm contracts and the thoracic cavity increases in volume. This decreases the intra-alveolar pressure so that air flows into the lungs.
What does diameter affect?
resistance to flow
What is a flow volume loop used for?
Flow volume loops are an advanced diagnostic
test and can be extremely useful and discriminatory between potential diagnoses
What does Boyle’s law state?
What does Poiseuille’s law state?
What is the difference between having a long or shorter snorkel?
(think dead space)
TLC= total lung capacity
TV= tidal volume
What is resistance inversely proportional to?
the fourth power of the radius (poiseuille’s law)
What happens to airways as lung volume increases?
they dilate
What happens to the conductivity of the airways as volume increases?
It increases
Volume of blood is greatest in which blood vessel?
The veins
How would you compare the
- Total SA
- Mean pressure
- proportion of systemic blood volume
for all the blood vessels?
What do small arteries and arterioles have to regulate their diameters?
extensive smooth muscle in their wall to regulate their diameters and the resistance to blood flow
What are the three layers of the walls of arteries and veins?
Intima (innermost)
Media
Adventitia
How would you describe veins and venules?
highly compliant and act as a reservoir for blood volume
Why does pressure decrease across the circulation?
due to viscous (frictional) pressure losses
What blood vessels present the most resistance to flow?
small arteries and arterioles
What is the theoretical relationship between MAP, CO and PVR?
Blood pressure (MAP)= Cardiac output (CO) x Resistance (PVR)
What is the relationship between MAP, CO, PVR?
It is an approximation
Why is the relationship between MAP, CO, and PVR and approximation?
because it assumes:
1) steady flow (which does not occur due to the intermittent pumping of the heart)
2) rigid vessels
3) right atrial pressure is negligible
Physiologically, how is the regulation of flow achieved?
by variation in resistance in the vessels while blood pressure remains relatively constant
What does resistance of a tube to flow depend on?
fluid viscosity
length of the tube
inner radius of the tube
What happens when you half the radius?
decrease the flow x16, increase resistance x16
What is blood pressure?
a product of cardiac output (blood entering system) and total peripheral resistance (size of tubes in system)
What organs have the same cardiac output before and after exercise?
kidney
brain
skin
What is the rest cardiac output and what is the exercise cardiac output?
5L/min and 20L/min
What happens to the skin during exercise and why?
It becomes warm due to high SA:V, the tummy becomes cold because it does not have a high SA:V
What are the types of blood flow?
Turbulent and laminar
What is laminar blood flow?
What is turbulent blood flow?
- slowest pace and less momentum
- can happen as velocity decreases
How do you calculate pulse pressure?
systolic blood pressure - diastolic blood pressure
PP= SBP- DBP
What causes the dichrotic notch?
closure of the aortic valve
What does slow deflation of a BP cuff cause?
turbulent flow- which is hear with a stethoscope
How can you calculate MAP?
MAP= DBP + 1/3PP
mean arteriole pressure = diastolic blood pressure + 1/3 pulse pressure
During hard expiration how is our extrapulmonary airways supported?
with cartilage
Using collapsible tubes, what does the pre inspiration and mid-inspiration look like?
Using collapsible tubes, what does the end-inspiration and hard experiation look like?
What can happen to severe transmural pressures?
can collapse to small-to-medium airways
What is compliance?
The tendency to distort under pressure
How do you calculate compliance?
delta V/ delta P
What is elastance?
The tendency to recoil to its original volume
How do you calculate elastance?
delta P/ delta V
Why do ventricular and aortic pressures differ?
The elasticity of a vessel is related to its what?
Its compliance
During ejection, how does blood enter the aorta?
During ejection, blood enters the aorta and other downstream elastic arteries faster than it leaves them (40% of SV/ stroke volume is stored by the elastic arteries)
What happens when the aortic valve closes?
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
What is a natural way of arterial compliance decreasing?
as arteries become stiffer with age
How is venous return facilitated?
Skeletal muscle pump
Respiratory pump (negative pressure facilitating venous return)
What do incompetent valves in veins cause?
dilated superficial veins in the leg (varicose veins)
What does prolonged elevation of venous pressure cause?
(even with intact compensatory mechanisms) causes oedema in feet
What is an 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.
For the same pressure change, but a greater volume change what happens to compliance?
compliance increases
What is greater, arterial or venous compliance?
venous compliance, it is 10 to 20 times greater than arterial compliance at low pressures
What is the relationship between transmural pressure and vessel volume called and what does it depend on?
the relationship is compliance and it depends on vessel elasticity
This is a graph for compliance curves for a vein, describe it.
Increasing smooth muscle contraction (green arrow) decreases venous volume and increases venous pressure.
Most blood volume is stored in the veins.
Relatively small changes in venous pressure distend veins and increase the volume of blood stored in them.
Describe ventilation across the lungs.
- assumption thorax is upright
Describe perfusion across the lungs.
assume the thorax is upright
What happens as you reach the bottom of the lungs?
air pocket size is smaller at the bottom
blood will therefore flow better at the bottom of the lung
more perfusion and ventilation
more extreme relationship because of gravity
When are the lungs the most efficient?
When perfusion= ventilation
What is Pa, PA, and Pv?
pulmonary arterial pressure
alveolar pressure
pulmonary venous pressure
What is the difference between Pa, PA, Pv in the three different zone of the lungs?
Are veins or arteries more compliant?
veins
Where does ventilation vary more than perfusion?
between the base and apex of the lungs
