Lecture 3- Haemodynamics Flashcards
haemodynamics definition
can be defined as the factors that govern blood flow (the movement of fluid between two points) and is dependent upon the relationship between cardiac output, blood pressure and resistance.
what dictates delivery of blood
metabolic demand
blood moves from
relative high to low pressure regions
blood is made up of
plasma, serum and red blood cells
serum is
plasma without clotting factro
fluid collected from unclotted blood is called
plasma
fluid collected from clotted blood is called
serum
what can cause blood viscosity (thickness) to change
Polcythaemia (RBC) Thrombocythameia (platelets) Leukaemia (WBC)
viscous blood leads to
dry gangrene in peripheries
minor changes ot plasma viscosity arise due to
acute phase plasma proteins
examples of acute phase plasma proteins
Fibrinogen Compliment C-reactive protein (CRP)
mean arterial pressure (MAP) =
CO X TPR
pulse pressure=
Systolic pressure (SBP)- DBP
CO=
HR xSV
thickest vasculature and widest lumen
aorta and vena cava
thinnest vasculature and narrowest lumen
capillary and venules
blood usually flows through vessels in a
very organised and streamline fashion- laminar flow
laminar flow
Is smooth, silent, maintains energy and typical of most arteries, arterioles, venues and veins
turbulent flow
disorganised, energy lost, not in streamline, irregular movement of blood, noisy.
pressur and turbulence
Pressure increase beyond which flow can match its linearly
turbulent flow occurs due to
stenosis- occlusion of blood vessel
direct measurement of blood pressure is
precise but invasive and technically demanding
indirect measurement of blood pressure is
convenient, non invasive and can be carried out by anyone with minimal training
principles of indirect blood flow rely on
changes in type of flow- laminar and turbulent
thrill
is what can be felt when stenosis causes turbulent flow
bruit
is what can be heard when stenosis causes turbulent flow
creating turbulent flow during auscultation
Changes from laminar to turbulent flow create sound which can be heard and used to estimate BP –>Korotkoff sounds
Korotkoff sounds
are produced underneath the distal half of the blood pressure cuff. The sounds appear when cuff pressures are between systolic and diastolic blood pressure, because the underlying artery is collapsing completely and then reopening with each heartbeat.
outline how BP is estimated by auscultation
- Place the cuff over the bare upper arm with the artery mark positioned directly over the brachial artery.
- Measure in both arms, often a difference- use the higher as reference arm
- Sat comfortably, upright with legs uncrossed and flat on the ground
- Arm supported
- Repeated several times- mean taken of two closest values
- Measurement taken at the level of heart (brachial) and RESTING
if cuff is too small
overestimate BP
if cuff is too big
underestimate BP
blood flow refers to the
movement of blood through a vessel, tissue or organ (expressed in volume of blood per unit of time (L/min))
blood flow is initiated by the
contraction of the ventricles
ventricular contraction ejects blood into he
major arteries resulting in flow from region of higher pressure to region of lower pressure as blood encounters smaller arteries, arterioles, then capillaries, then venues and veins for the nervous system
flow -
L/min
pressure =
force per unit area - mmHg (SI unit is pascal)
pressure is highest in
arteries (nearest aorta) and lowest in veins
resistance is the
measure of ease of flow (TPR)
higher the TPR
the higher the arterial pressure - narrow lumen - vasoconstriction
lower pressure
wider lumen
the lower the resistance =
the higher the flow at said perfusion pressure
the higher the resistance=
the lower the flow at said perfusion pressure
resistance to flow factors (3)
diameter length of vessel viscosity
resistance in pulmonary circulation is
much lower than systemic system due to having shorter and wider vessels
resistance in aorta is
low- large diameter and relatively short in length - highest pressure
Pressure in small arteries and arterioles contribute the
greatest component of TPR –> arterioles are the seat of TPR
velocity=
distance fluid moves in a given time (cm/s)
velocity reduces from
the aorta to the capillaries - gives capillaries optimum time for diffusion of nutrients
velocity and area in capillaries
cross-sectional area is vast (thousand time greater than aorta) - velocity of capillary level much slower than aorta - velocity increases again as vessels merge into larger veins and into vena cava
mean arterial pressure (MAP) represents
Represents the “average” pressure of blood in the arteries, that is, the average force driving blood into vessels that serve the tissues.
MAP equation
diastolic BP + ((systolic-diastolic BP) / 3)
normal range of MAP
70–110 mm Hg
if BP falls below
60mmHg for an extended time, BP will. not be enough to perfuse organs- ischameai
blood pressure is
The force exerted by blood upon the walls of the blood vessels or the chambers of the heart.
where is blood pressure usually obtained from
brachial artery
systolic pressure
(typically around 120 mm Hg) reflects the arterial pressure resulting from the ejection of blood during ventricular contraction or systole
diastolic pressure
(around 80 mm Hg) represents the arterial pressure of blood during ventricular relaxation or diastole
pulse
Shock wave that arrives slightly before the blood itself. After blood is ejected from the heart, elastic fibers in the arteries help maintain a high-pressure gradient as they expand to accommodate the blood, then recoil. This expansion and recoiling effect, known as the pulse, can be palpated manually or measured electronically.
pulse indicates
heart rate
what can cause a hounding pulse (indicates strength of ventricular contraction and CO)
heart block (Bradycardia) vasodilation (decrease TPR) Elite athletes (systole increases and diastolic decreases)
pulse pressure
difference between the systolic pressure and the diastolic pressure is the pulse pressure. For example, an individual with a systolic pressure of 120 mm Hg and a diastolic pressure of 80 mm Hg would have a pulse pressure of 40 mmHg.
PP =
SBP-DBP
Pulse pressur should be at least
25% of the systolic pressure
low or narrow PP
In patients with a low stroke volume, which may be seen in congestive heart failure, stenosis of the aortic valve, or significant blood loss following trauma.
high or wide pulse pressure
is common in healthy people following strenuous exercise, when their resting pulse pressure of 30–40 mm Hg may increase temporarily to 100 mm Hg as stroke volume increases.
persistently high pulse pressure above 100 mm Hg
may indicate excessive resistance in the arteries and can be caused by a variety of disorders- can degrade the heart, brain, and kidneys, and warrant medical treatment.
