Lecture 3 - Heamodynamics Flashcards
What are the 4 equations that you should know ?
Pulse Pressure (PP) = Systolic Blood Pressure (SBP) - Diastolic Blood Pressure (DBP)
Mean Arterial Pressure (MAP) = DBP + (SBP-DBP/3) = DBP + 1/3 PP
Cardiac Output (CO) = Heart Rate (HR) * Stroke Volume (SV)
MAP = CO * Total Peripheral Resistance (TPR)
what is the blood made of, and what changes its viscosity ?
RBC’s. Palsma. Buffy Coat
Serum is plasma without clotting factors
• Whole blood viscosity changes are relatively
uncommon – polycythaemia (RBCs),
thrombocythaemia (platelets) or leukaemia
(WBCs)
- “sludgey” thick blood – leading to dry
gangrene in peripheries
• Minor changes to plasma viscosity typically
from acute phase plasma proteins
(fibrinogen, compliment, c-reactive protein
(CRP) – result of inflammation – used to
measure plasma viscosity as indicator of
inflammation
• Now typically measure CRP clinically
what are the three types of blood flow
single file (bolus) flow
Laminar - smooth , maintains energy , in arteries and arterioles, venues and veins. there are concentric fluid layers and it is fastest in the middle
turbulent flow - disorganised and energy is lost, caused by a pressure increase, ie a clot or vessel branching. it makes an audible sound
what is flow ?
which direction does blood move ?
Fluid (blood) moves from an area of higher
to lower pressure – along a pressure
gradient
• Flow - volume transferred per unit time –
(L/min)
what happens if resistance increases in a vessel ?
K is the conductance, a measure of the ease of flow
R is the resistance to the flow - 1/K
if resistance increases and flow is maintained – pressure difference has to rise
what does a change in the blood pressure indicate ?
what is the relative pressures of blood vessels ?
a change in the resistance across a class of vessels
aorta an has a very high pressure and low resistance
the smallest arteries and arterioles contribute the greatest component of total peripheral resistance - the biggest pressure jump across a class of vessels
the arterioles are the seat of total peripheral resistance
pulmonary system has a lower resistance than the systematic resistance - vessels are shorter and wider
what is the velocity ?
flow is volume per unit time
velocity is distance per unit time
pressure is force per area
distance that blood will move in a given time (cm/s)
flow is related to the velocity and area
the lower the surface area of a vessel , the higher the velocity - so capillaries have the lowest velocity
what are normal values for the pressure
80 - 120 mmhg
below 70 mmhg organ perfusion becomes impaired
what is pulse pressure ?
what is a increased pulse pressure ? causes ?
The volume of blood ejected and the compliance of the arterial system govern pulse pressure
• Increased stroke volume during exercise with relative compliance of vessels will cause an increase in pulse pressure
• Basic measurements can inform us of important CVS function – stroke volume plus heart rate allows us to measure changes in cardiac output
• Pulse
What we feel is a shock wave that arrives slightly before the blood itself
if there is an increase in the pulse pressure then we have a bounding pulse - this can occur due to a bradycardia or vasodilation and hence decrease peripheral resistance - hot bath or pregnancy
pulse pressure is palpable
what are the factors that affect resistance to flow ?
diameter of vessel - very variable
length of vessel - does not change
viscosity - regulated within narrow range
due to the mathematics of posuiles law (1/r^4) - a small change in the radius will cause large changes to the flow and resistance
how does mean arterial pressure (MAP) change with exercise ?
systolic BP will rise due to an increase in cardiac output , but Total peripheral resistance falls (vasodilation) - so MAP stays constant
how do we measure blood pressure ?
use a pressure clamp just over the brachial artery to stop movement of blood through vessel
open the clamp gradually - blood moves when the pressure of the clamp is below systolic - this will create a turbulent flow which can be heard - is the SBP
flow returns to laminar flow, and hence sound stops when pressure of clamp matches the diastolic flow - DBP
Cuff size is important - too small - overestimate BP
too big - underestimate BP
sit upright, legs uncrossed, flat on ground, support arm, and take many values to determine a mean
unless stated otherwise - assume measurement is taken at the resting pressure
effects of gravity on blood pressure
not vital
pressure below level of the heart is greater and lower above level of heart is lower
Effects of gravity maintains a
pressure gradient allowing blood
flow from heart to foot when standing
• Pooling of blood occurs below the level of the heart upon standing in the venous system • Postural hypotension – dizziness upon standing – ↓stroke volume → transient arterial hypotension
