CV IV Flashcards
Late diastole
Starts with atria relaxed and fills from veins
Both sets of chambers are relaxed and ventricles fill passively
Pressure in atria starts to exceed ventricle
AV valves open Passive filling 80%
Atrial systole
Atrial contraction forces small amount of additional blood
20% of ventricular filling due to atrial contraction
Lub
First heart sounds
Shutting of AV valves as ventricular blood tries to go back to atria
Sound is vibrations of wall as blood hits valve
Isovolumetric ventricular contraction
No change in volume
Pushes AV valves closed but doesn’t create enough pressure to open semilunar valves
Both valves closed and pressure builds
Ventricular ejection
Ventricle pressure rises exceeds pressure in arteries (aorta or pulmonary), semilunar valves open
Dub
Second heart sound
Closure of semilunar valves
Isovolumetric ventricular relaxation
Pressure in ventricles falls,blood flows back into cusps of semilunar valves and snaps them closed
What is the pressure volume loop
Another way to look at cardiac cycle of systemic
ESV
Blood left in ventricle after ventricular contraction, minimum amount
Safety reservoir
~65ml
EDV
Amount of blood in ventricle at end of diastole, after ventricular filling
Max volume
~135ml
A-A’
Late diastole
- starts at ESV
Big change volume because ventricle relaxing, no change in pressure
A’-B segment
Atrial systole
Slight increase in volume and blood
End diastolic volume
B-C segment
Isovolumetric contraction
Large increase in pressure
C-D segment
Ventricular ejection
- pressure rises
- pressure drops as ventricles relax but blood still flows
C-D segment is
Stroke volume
D-A segment
Isovolumetric relaxation
- pressure drops, no volume change
Pressure volume loop for RV
Short low pressure circuit
- ejects same amount of blood as systemic
- overall stroke volume same
- needs less pressure
- lower resistance (short, large diameter)
Wiggers diagram
Diagram has left ventricular volume, left and aortic pressures, ECG
D
Late diastole
C
Start of isovolumetric contraction
E
End diastolic pressure
A
Ventricle exceeds pressure in aorta
E to F
Ventricular ejection
B
Pressure in aorta starts to exceed ventricle, semilunar shuts
Stroke volume
Amount of blood ejected during a single ventricular contraction ~70ml
What is SV equation
EDV-ESV
What is ESV for
Provides safety margin, more forceful contraction will cause larger stroke
What is stroke volume modulated by
ANS, venous return, certain drugs
Ejection fraction
Percentage of EDV that is ejected from heart
Ejection fraction equation
SV/EDV
Cardiac output
Heart rate x stroke volume
Flow of blood delivered from one ventricle in a given time period (usually a minute)
Measure of cardiac performance
What happens when cardiac outputs of the pulmonary and systemic circuit are not identical
Blood pools in circuit feeding the weaker side
How much does CO rise during exercise
30-35L/min
Steve has EDV of 150ml, an ESV of 30ml and HR of 90bpm. What’s Steve’s CO
SV X HR
(EDV -ESV) X HR
(150 ml/b - 30ml/b) x 90 b/m
=10800 ml/min
10.8 L/min
How is cardiac output modified
- By adjusting HR
By parasympathetic or sympathetic - Adjusting stroke volume
What is SV directly related to
To force generated by cardiac muscle during contraction
As force of contraction increases, SV increases
What are 2 factors that determine amount of force generated by cardiac muscle
- Contractility of heart
- Length of muscle fibres at beginning of contraction
What is contractility of heart
Intrinsic ability of cardiac muscle to contract at any given fibre length and is function of Ca entering and interacting with contractile filaments
What is length of muscle fibres determined by
Volume of blood in ventricle at beginning of contraction (EDV)
What is contractility controlled by
Nervous and endocrine systems
Inotropic agent
Any chemical that affects contractility
Inotropic effect
Influence of Inotropic agent
Positive inotropic effect
Negative inotropic effect
Chemicals increasing contractility
Chemicals decreasing contractility
What causes positive inotropic effect
Norepinephrine, epinephrine
Sympathetic modulation
