GP Dr as teacher cardio questions Flashcards
How long does a single heartbeat last?
0.8 seconds
How long does diastolic last for in a heartbeat?
How long does systolic last for in a heartbeat?
- 0.5s
- 0.3s
What are the 4 stages of the cardiac cycle?
1) Passive filling
2) Atrial contraction
3) Ventricular ejection
4) Isovolumetric ventricular relaxation
What is the pressure in atria + ventricles during passive filling?
Close to 0
What is the pressure in the aorta during passive filling?
80mmHg
What % of ventricular filling is due to passive filling?
80%
What on an ECG marks atrial contraction?
Between the P and QRS complex
What % of ventricular filling occurs due to atrial contraction?
20%
What is the normal end diastolic volume (after passive filling + atrial contraction)
130ml
What happens when ventricular pressure exceeds atrial pressure?
AV valves (tricuspid + mitral) shit
What is the 1st heart sound due to?
Closure of the AV valves
At the time of the 1st heart sound, is the aortic valve open/closed?
It is STILL closed at time of 1st heart sound
What is isovolumetric contraction (i.e. of the ventricles)?
- when all 4 heart valves are shut and tension (pressure) within the ventricles rise
(increase in tension around a CLOSED VOLUME)
What stage on an ECG marks ventricular contraction?
After the QRS complex (between S and T)
What happens when ventricular pressure exceeds aortic/pulmonary pressure?
- aortic/Po valves open
When the aortic/Po valves open is this a loud/silent event?
silent
What is end stroke volume (ESV)?
- the volume of blood left behind in each ventricle once stroke volume has been ejected (upon opening of aortic + Po valves)
What is the normal ESV?
~65ml
How do you calculate SV (vol ejected by ventricle per heartbeat)?
SV = EDV - ESV
What is a normal SV?
~ 70ml (130-65)
What happens to the aortic pressure upon opening of aortic/Po valves
Aortic pressure rises
What on the ECG represents ventricular repolarisation?
T wave
What happens to the ventricles upon repolarisation?
Pressure falls
Ventricles relax
What happens when ventricular pressure is less than aortic pressure?
Aortic/Po valves shut
What produces a 2nd heart sound?
Closure of aortic/Po valves
What is a DICROTIC NOTCH?
The vibration of the aortic valves upon closure creates a little rise in the aortic pressure curve
What is isovolumetric ventricular relaxation?
Once the aortic/Po valves close, the pressure within the ventricles falls in a CLOSED BOX (all 4 valves are closed)
(tension falls around a closed volume)
What happens when ventricular pressure < atrial pressure?
AV valves open
-silent event
What happens when AV valves open?
Beginning of passive filling
NEW CARDIAC CYCLE
What is central venous pressure?
Measure of pressure of central veins close to heart?
What does JVP measure?
Indication of right atrial pressure
RA pressure gives us an idea of what the central venous pressure is
What are the names of the 3 letters when measuring JVP?
a, c, v
On a JVP meausrement, what do the following letters represent?
- a
- c
- v
a) rise in JVP as atria contract
c) rise in JVP as tricuspid valve bulges into atrium during ventricular contraction
v) increase in JVP during atrial filling - release as AV valves open
What % of total body weight is water? (i.e. in a 70kg person)?
60% (42L)
What fraction of body water is
a) extracellular?
b) intracellular?
a) 1/3 (14L)
b) 2/3 (28L)
Of extracellular water, what % of it is:
a) Plasma?
b) interstitial?
a) 25% (3L)
b) 75% (11L)
What is interstitial fluid?
Water that bathes body cells
- acts as a go between blood + body cells
Why is blood flow slow through the capillary bed?
- to increase time for gas/nutrient exchange
What regulates flow of blood through the capillary bed in MOST tissues?
TERMINAL ARTERIOLES
What regulates flow of blood through capillary beds in SOME tissues (e.g. mesentery)
Pre-capillary sphincter
In a capillary, what do water filled pores in the membrane permit?
- movement of WATER SOLUBLE SUBSTANCES
- e.g ions/glucose/Amino acids
In a capillary, what is moved across the membrane by VESICULAR TRANSPORT?
- EXCHANGEABLE PROTEINS
- e.g hormones
How do lipid soluble substances (e.g. GASES) diffuse through capillary membranes?
- by diffusion across endothelial membrane
Can plasma proteins pass in/out of capillaries through the endothelial wall?
Give an example of a plasma protein
- NO: STAY INTRAVASCULAR
Albumin; plasma proteins are produced by the liver
What is BULK MOVEMENT/
- in capillaries, fluid movement follows a pressure gradient
What law (from rest physiology) does the movement of gases/solutes in and out of capillaries follow?
- FICK’S LAW OF DIFFUSION
- Diffusion across a sheet is proportional to surface area but inversely proportional to thickness
What is transcapillary fluid flow?
Flow of fluid is passively driven by PRESSURE GRADIENTS ACROSS CAPILLARY WALL
What is ultra-filtration?
- exchange across capillary wall is essentially PROTEIN FREE PLASMA
How do you calculate net filtration pressure?
forces favouring filtration - forces opposing filtration
What is a filtration coefficient and what does it do?
- relates to permeability of wall to fluid
- also affects NET FILTRATION PRESSURE
What 2 things calculate net filtration pressure?
1) forces favouring filtration - forces opposing filtration
2) filtration coefficient (permeability of wall to fluid)
