Haemodynamics Nov2 M2 Flashcards
Average number of cells for a capillary and reason
1 capillary for every cell on avg -> large number of capillaries surrounding cell = are very close to all parts of the cell = large flow in cell
Qualitative definition of diffusion
Spontaneous movement of particles caused by random thermal motion
Definition (in words) for flux and for flow that don’t come from prof (for understanding)
Flux = Rate of volume flow across a unit area (per second) in m3/sm2. Flow = Volume of fluid which passes in some area(per second) in m3/s.
Prof definition/formula for flux and units for flow
Flux = Flow/Area = D x concentration gradient. Flow is in mol/s
Meaning of a concentration gradient and of D in flux formula + complete formula
Concentration gradient = (Cout- Cin)/d must divide by the distance D = diffusion coefficientFlux (mol/s for prof) = D x(Cout- Cin)/d
Flow formula in terms for flux and complete
Flow = flux x area. Flow = D x(Cout- Cin)/d x A
How much oxygen a person uses every minute + What principle rules the movement of air from outside of our airways to our alveoli
200-250 mL of oxygen/minute = what we use. Bulk flow responsible formovement of air to our alveoli (and not diffusion)
Other name for bulk flow and 4 steps to get outside air to our cells
Convective flow. Convection from the outside to the alveoli -> Diffusion to the capillaries -> Convection from lung capillaries to tissue capillaries -> Diffusion from blood to tissue
All transportwithinthe cardiovascular system OR the respiratory system is done through _________________. ll transportbetweenhe cardiovascular system AND the respiratory system is done through _________________
convection, diffusion
Haemodynamics definition and 4 concepts to understand it
Volume, Flow, Pressure, Resistance
Avg blood volume, def. of 1 unit of blood, characteristics of the reference individual
5L blood in body. 1 unit of blood = 450 mL (amount at donation). Ref. individual = 70 kg young healthy male lying flat on his back.
Blood distribution in the body when lying flat
60% in vein/venules, 10% in arteries, 10% in capillaries, 10% in heart, 10% in lungs
Other name for the venous system and other name for its vessels and why
Capacitance system and capacitance vessels. Because most blood in venous system when lying flat (has a capacity to hold stuff)
Other name for the arterial system and why
Resistance system because resistance to flow of blood from ventricles is mainly in the arterioles and small arteries
Flow output from the left/right heart : Name and value
Cardiac output. 5000 mL/min
Name and value for the flow that goes from the lungs to the left heart and for the flow that goes from the organs to the right heart. Reason for this value
Venous return. 5000 mL/min. Must be same as cardiac output because of conservation of mass
Method for flow measurement and conventional physiology units
Pump blood or fluid through a vessel that is not in the body. Collect volume that exits vessel (V) and record time (T). Flow = V/T. In mL/min or L/min.
How do we compare the flow for different organs
You normalize per unit of mass and so flow is calculated in mL/min/100g
What influences the flow (2). Give units and how these units give the units of flow
Cross-sectional area or flow velocity (flux). F = area x velocity = A x v. Certain volume moving through a tube at 1 cm/sx A gives you the volume of the cylinder of blood that travelled in 1 sec in cm3/s.1 cm3(1 cc - cubic centimeter) = 1 mL
Formula of flow is F = A x v. Small correction that must be done and why
F = area x mean velocity because not all blood travels at the same velocity at all points in a cross section
How vessels chance as they get further from the heart ? And when they get closer to the heart ? Name for this pattern
Increase in number, become smaller in diameter and shorter in length. Opposite when getting closer to heart (less numerous, larger diameter, longer in length). Pattern = Vascular tree
Kind/categories of vessels in the vascular tree starting from the left ventricle and note about branching
Aorta, arteries, arterioles, capillaries, venules, veins, vena cava (sup and inf). There is branching within each category (arteries -> smaller arteries -> smallest arteries before arterioles)
Why is there a very complex arterial branching in the kidneys
To facilitate diffusion. A shorter distance for O2 (all cells near a capillary) = greater gradient
How total cross-sectional area varies as we go down in levels of branching and how total flow varies with each level of branching ? How do we calculate these
Total cross sectional area increases (add up all vessels’ cross sectional area in one level of branching = total cross-sectional area). Total flow at each level of branching is the same. Add flow from each vessel of one level of branching = total flow
What can be deduced if flow is the same in all levels of vascular tree but cross-sectional area increases.
F = v x A. Mean velocity decreases with level of branching -> By the time blood gets to capillaries, it moves very slowly
Other advantage of a high total cross sectional area
Total blood vessel wall area increases. More surface area for gas/molecule diffusion to take place
Advantage of low flow velocity (in the capillaries for ex)
Allow time for gas/molecules to diffuse through capillary membrane. If RBC went fast through capillary, they wouldn’t have time
Summary of 3 advantages (and explanation) for a branching network like the vascular tree
- High total cross-sectional area (less resistance, less effort from the heart, smaller heart) 2. High total surface area (greater diffusion area) 3. Low flow velocity (more time to allow diffusion)
Definition of pressure (formula) and 3 units (SI + 2 practical units)
Pressure = Force/Area. S.I : Pascal (Pa) = newton/m2Practical units : cm H2O or mmHg
Pressure units used for arterial BP and venous BP. and normal values
BP in arteries : use mmHg (normal BP is 120/80 mmHg). BP in veins : use cm H2O (central venous pressure is 5-10 cm H2O)
How to have pressure without flow ? Characteristics of the pressure
Yes. Take a bag with saline connected to a tube, plug it, squeeze the bag -> P w/o F. Pressure is uniform and exerted in all directions
Bag of saline linked to a tube. How to find flow in one portion of the tube + what happens if this system is closed
Add up the forces acting on the portion. F = PxA from one side and F=PxA from other side. Closed system -> Forces equal in magnitude and opposite in direction (because P same everywhere)-> Net flow of 0.
In the pressurized saline bag-tube system, where does the pressure energy come from ? + Proof
Comes from work applied (energy) ofsqueezing the bag -> became pressure energy. Proof : Making a hole in the system would have fluid flow out without any other work necessary
What does the heart do that is analogous to the bag-tube saline system
Ventricles pumping pressurize the system and store energy in it, which starts flow
Bag-tube saline system : If we open the end of the tube what happens
P inlet (bag/tube fork) > P outlet (where tube open and pressure gradient determines flow direction. Fluid flows out
Bag tube saline system : How to find flow in one portion of the tube and what happens if the tube is open
Calculate F=PxA on both side of the section of interest. On the closed side, pressure is greater so force from closed side > force from open side -> flow outwards
Bag tube saline system : In perfect world/conditions, how would the fluid move outwards and what happens IRL
The fluid would accelerate (force being applied). IRL, internal friction in the opposite direction due to the viscosity of the fluid keeps the flow rate constant
How to determine fluid pressure in middle of the tube + How pressure changes in the tube as fluid flows out ? Why
Mean of Pinlet and Poutlet. Flow out -> Pressure falls in tube due to pressurized energy given up to overcome frictional forces
How pressure varies down the vascular tree (aorta vs venae cavae for ex) and what this is helpful for
Falls down. Aorta : 100 mmHg. Venae cavae: 5 mmHg. This fall in pressure keeps the flow at some level
Hydrostatic pressure definition, + other simple def. + value in space
Pressure exerted by fluid at equilibrium at any given point within the fluid due to the force of gravity.. i.e. Pressure of fluid when it is not moving. In space, no hydrostatic pressure because no gravity
Formula for hydrostatic pressure and derivation from situation of fluid in a standing tube
P = force/area = mass x acceleration / area = density x volume x acceleration / area = density x height x area x accel. / area = (density)(g)(h)
How hydrostatic pressure inused for medical practice on Earth + reference point
density and g are disregarded so only use height -> cm of H2O. 1 cm H2O = 0.98 kPa
In standing cylinder of 10 cm of water, top pressure, bottom pressure and how to find pressure in middle or any point
Top pressure = 0 cm H2O (but not exactly because there is air around, we’re not in space). Bottom = 10 cm H2O. Middle = 5 cm H2O. Only need to check height of fluid above the point
Atmospheric pressure, atm PO2 and meaning of atm P
760 mmHg (101.3 kPa). PO2 atm = 150 mmHg. Atm pressure = pressure of square inch area column of air from earth surface to stratosphere.
First measurement of hydrostatic pressure : method used
Tube stuck in coronary artery of horse, blood squirts up until reaches max height. Mark height.
In first hydrostatic P measurement experiment, why blood eventually stops moving up the tube + give height of stop and pressure measured
HP at bottom of column eventually equals blood P in the horse. 280 cm observed so approx arterial BP of 280 cm H2O (water density approx = blood density)
Conversion of pressure from cm H2O to cm Hg and why these units became popular
1 cm Hg = 14 cm H2O. cm Hg became used because Riva-Rocci invented the mercury sphygmomanometer
How to use sphygmomanometer + why wedon’t use it anymore
Wind cuff around arm and pump black rupper connected to reservoir of mercury until mercury height stops changing. Stopped used because Hg is a neurotoxin
