24 - Cardiac Function and Control Flashcards
For any volume of blood, pressure depends on 1) 2)
1) Compliance of the wall 2) Active tension in the wall
When is compliance important in blood pressure?
Diastole
When is active pressure important in blood pressure?
Systole
Is the right or left ventricle less compliant?
The left is thicker and therefore less compliant than the right
Which ventricle can generate more force?
The left
If more blood is pumped into the arterial system, what occurs in the venous system?
There is less blood
When can the pericardium become an important determinant of ventricular compliance?
When it stiffens (EG: inflammation, TB, pericarditis, cancers)
Normal end systolic volume
Between 65-150mL, but this can vary
Diastolic left ventricle pressure-volume curve
Systolic left ventricle pressure-volume curve
Normal total cardiac output
~5L/min
Normal stroke volume
~150mL
Normal early diastolic pressure
~5mmHg
How is a Frank Starling curve generated?
Fill left ventricle with blood, don’t let blood escape. As volume increases, with the same electric stimulation the ventricular pressure increases (due to increased force of contraction)
Ways to increase stroke volume 1) 2) 3)
1) Decrease heart rate 2) Increase end diastolic volume 3) Increase ventricular contractility
Frank Starling relationship
More stretch = more tension More end diastolic volume = more stroke volume
What does increased stroke volume reflect?
Increased LV pressure
What effect does increased heart rate have on stroke volume?
Decreased stroke volume (as lower end systolic volume)
Why can the heart appear smaller with exercise?
When heart rate increases, stroke volume decreases, as the time for diastole shortens (leads to decreased end diastolic volume)
Effect of increased heart contractility on LV pressure and volume
Mitral valve location
Between left atrium and left ventricle
Effect of acidosis on heart function
Impairs heart function
Effect of increased sympathetic stimulation on heart contractility
Increases contractility
Effect of parasympathetic activity on heart contractility
Parasympathetic nervous system not really related to heart contractility
Effect of hypercapnia on heart contractility
Leads to acidosis, which impairs cardiac function
Valves closed during systole
Tricuspid, mitral (bicuspid) valves.
Valves closed during diastole
Aortic valve
Valves closed during isovolumetric contraction
Tricuspid, bicuspid, aortic valves
Pressures and volumes of left heart during systole and siastole
Way to tell hen a murmur is in the cardiac cycle
Feel carotid. When it pulses, that is systole.
Where on the LV pressure loop are stroke volume, ESV and EDV?
How do we know that the heart has reserve maximum pressure?
Because the max pressure of the Starling curve is greater than that of the max pressure of the cardiac cycle loop
Effects of increasing heart contractility
Decrease end systolic volume, increase stroke volume
Effects of reducing compliance
Decreased stroke volume, decreased end diastolic volume
Effects of increased aortic pressure
Decreased stroke volume, increased end systolic volume
Afterload
Load encountered by ventricle as it begins contraction. Pressure applied by aortic hypertension, LV outflow tract obstruction
Preload
The stretch on myocyte fibres before contraction A volume (EDV) load imposed by increased venous return
