Microstructure and function of the heart Flashcards
What is the calculation for stroke volume?
SV= EDV-ESV
What is the calculation for Cardiac output?
CO= HRxSV
What is EDV?
End diastolic volume, volume of blood just before contraction
What is ESV?
End systolic volume, volume of blood after contracition (left overs)
What do increases in EDV do?
Increase in myocardial performance
What is the length-force realtionship?
As EDV increases, myocardial length increases, muscle starting length increases, increasing cross bridge formation, increasing myocardial contractiliy
What is stroke volume between?
Isovolumetric relaxation and isovolumetric contraction
How does the sympathetic NS cause contraction?
NA and the beta-1-receptor in cardiac muscle cells
How do hormones cause contraction?
Circulating A and NA
What are some symptoms of heart failure?
- Crackling sound- fluid in lungs
- Edema, specifically right side oedema, edema in periphery causing a clog increases hydrostatic pressure in the lower limbs increasing pressure
Why can myocardial infarction cause heart failure?
increase severity, decreased ventricular contractility and compliance
What is compliance?
STRECTH
not elasticity
What happens if there is a fall in contractility and why may this occur?
Smaller stroke volume as there is the same pressure buy smaller volume is ejected. this is due to the ventricle being flabby and weak. This can be due to illness
What happens in there is a fall in compliance?
Stroke volume falls as the ventricle is stiff and fibrotic
What is the ejection fraction?
Quantification of contraction as a percentage
EF= SV/EDV
What is the clinical importance of ejection fraction?
Measure of the ability of the ventricle to contract
- > 75%- could indicate hypertrophic cardiomyopathy
- 40-55% abnormal- but may be clinically insignificant
- 40%- HF- can be very low
What is preserved EFHF?
Diastoli heart failure. Heart muscles contract normally but the ventricles do not relax as they should during ventricular refilling
What is hypertrophic cardiomyopathy?
Thickening of the myocardium making the lumen of the left ventricle smaller therfore less blood. the compliance of the ventricle may also reduce. Ventricles ability to relax and fill with blood is reduced.
What is strain and why is it important?
The amount the muscle is stretched and it is important to the function
What is the sinusoidal wave pattern?
Shows the lengthening period and shortening period. Pressure volume loops.
What is the % where strain amplitude begins to affect power output?
12%
What also happens when strain amplitude changes?
Passive force increases- structural proteins resist overstretching of myofibrils
What is the length-force relationship?
With increased starting muscle length, increased net power. Until it reaches optimum. Then power decreases.
What is resting HR in a man?
70-90bpm
What is the theoretical max HR?
220
What happens in an aged heart?
Left ventricular thickening, increases in cardiomyocytes size, loss of cardiomyocytes, increase in extracellular matrix, decreased oxygen consumption, decreased maximum heart rate, reduction in cardiac function, decreases in ejection fraction and decreases in responsiveness to Beta-adrenergic stimulation.
