cardiovascular system - haemodynamics Flashcards
what is haemodynamics
Study of how blood flows through the cardiovascular system
blood flow is determined by what
physical factors:
- Blood pressure
- Resistance to flow
what does resistance to blood flow depend on
Vessel length and radius
Blood viscosity
Arrangement of vessels
what is Hydrostatic pressure exerted by
blood on walls of vessel
what is resistance
opposition to blood flow, principally due to friction between blood vessel walls & blood.
Pressure measured within major artery system measures
Millimetres of mercury (mm Hg)
whats Systolic BP
Maximum BP during contraction of ventricles
whats Diastolic BP
Minimum BP just before next contraction
name a method for measuring blood pressure
sphygmomannometer
explain what happens in a Sphygmomanometer
Inflate cuff
- Occlude artery – no sound (as no blood flow)
Slowly deflate
Listen for Korotkoff sounds
- Spurting blood - sound = systolic (pressure to allow blood through narrow vessel; mmHg)
- Further deflate – feint sound = diastolic (mmHg)
what is our arterial pulse
heart rate
explain how we have an arterial pulse
Sudden ejection of blood into the aorta
then
Transmission through the arterial system
then
Rhythmic expansion of arterial wall
what is tachycardia
rapid resting pulse >100 beats/min (bpm)
what is Bradycardia
slow resting pulse <60 bpm
(e.g., endurance-trained athletes)
what is venous return
Blood returns from periphery to the heart
explain the respiratory pump in terms of venous control
Pressure changes in thorax & abdomen during respiration
Inspiration —->low pressure in thorax —> draws blood into RA
explain the skeletal muscle pump in terms of venous control
Skeletal muscles contract in lower limbs
valves in veins contribute to return
Important difference between pulmonary & systemic circulation is what
the autoregulatory response to O2
explain the autoregulatory response to O2
Systemic circulation dilate if low O2
Pulmonary constrict!
- so bypass poorly functioning areas, to reach better ventilated areas of lung
Substances enter & leave capillaries by:
Diffusion (down concentration gradient)
- O2, CO2, Glucose, Amino acids
Transcytosis (vesicles in endothelial cells, for large lipid insoluble)
- Insulin, antibodies from maternal-foetal circulation
Bulk flow (high pressure to low)
- filtration OUT of capillaries & reabsorption IN
in capillary exchange, what are filtration and reabsorption promoted by
Filtration promoted by
- Blood hydrostatic pressure (heart)
- Interstitial fluid osmotic pressure
Reabsorption promoted by
- Blood colloidal osmotic pressure
Whether fluid leaves or enters it depends on what
net balance of pressure
explain Starling’s Law of Capillaries
volume of fluid & solutes reabsorbed = volume filtered
If filtration»_space;> reabsorption = OEDEMA (=excessive accumulation of fluid, usually causing swelling)
explain the fluid exchange across walls of capillaries
at arterial end:
- osmosis in
- blood pressure, and negative interstitial pressure out
venous end:
- osmosis in (1/10 vol to lymphatics so outside capillaries, 9/10 vol returns to capillaries)
- blood pressure and negative interstitial pressure
what can be used if a vessel is obstructed
Can use a Stent
names after charles stent
to overcome problem coronary obstruction
what can stents be used to do
open various ‘tubes’ within the body, with a balloon
explain what Inferior Vena Cava Filters are for
To prevent clots travelling up to the heart and on to the lungs
- pulmonary embolism
Inserted by surgery, remaining for ~1 month
For patients who cannot be given conventional therapy e.g., anticoagulants
Note: are different to stents.
when does a haemodynamic shock occur
when Failure of CV system to deliver enough O2 & nutrient to meet cellular metabolic needs
Cells switch from aerobic to anaerobic production of ATP
- lactic acid accumulates in body fluids
If shock persists, organs become damaged
- Death if untreated
name the 4 types of haemodynamic shock
Hypovolumic
Cardiogenic
Vascular
Obstructive
explain the Hypovolumic haemodynamic shock
decreased blood volume
- inadequate intake of fluid
- diabetes mellitus may cause much greater fluid loss in urine
- sudden haemorrhage
- excessive sweating
- diarrhoea
- vomiting
explain the cardiogenic haemodynamic shock
due to poor heart function
- heart attack - heart valve problems
explain the vascular haemodynamic shock
due to inappropriate vasodilation - anaphylactic shock (histamine release causes vasodilation)
- head trauma - septic shock (bacteria)
explain the obstructive haemodynamic shock
due to obstruction of blood flow
- e.g., pulmonary embolism (clot)
what happens if haemodynamic shock is mild
compensation by homeostatic mechanisms to prevent serious damage
explain the homeostatic responses to shock
- Activation of renin-angiotensin-aldosterone system (vasoconstrict, absorb H2O) so increase blood volume thus Blood Pressure (BP)
- Secretion of ADH (leads to as above)
- Activation of sympathetic ANS (vascoconstrict skin, abdominal viscera, not brain or heart) so increase heart rate & secretion of E & norE by adrenal medulla)
(E = Epinephrine = adrenalin; norE = norepinephrine = noradrenaline) - Release of local vasodilators (in response to hypoxia) e.g., K+, H+, lactic acid, adenosine, NO (NO = nitric oxide)
explain how to tell if shock is life threatening in terms of blood volume
If blood volume reduces >10-20%, shock life-threatening
describe some signs and symptoms of shock
Some easily predicted by the homeostatic responses:
Rapid resting heart rate
Weak, rapid pulse
Altered mental state
Sweating
Thirst
Reduced urine formation
Nausea
Acidosis (blood pH)
