L-20 regulation Of COP And VR Flashcards
What is cardiac output
Volume of blood ejected from ventricles each minute
Formula of COP
SV x HR
What is the stroke volume
Volume of blood ejected from the ventricles each beat
How much blood does the ventricle receive during diastole
130-140 ml
End diastolic volume
How much blood is ejected each systole
60-70 ml
Stroke volume
How much blood remains in the ventricle
60-70 ml
End systolic volume
Cardiac output(figure)
4.9-5.2 liters/min
What is the ejection fraction and its figure and how is it calculated
Assesses efficiency of heart
Stroke volume/end diastolic volume
60-70%
How can we inc cardiac output
Inc stroke vol
Inc heart rate
Or both
What are the factors determining the stroke volume
Preload: vol at end of diastole
Afterload: resistance left ventricle must overcome from aorta
Contractility
How can the preload affect venous return
Position Skeletal muscle pump Valves in veins Abdominal thoracic pump Venomotor tone Residual pressure Ventricular suction
How can position affect venous return
In supine position The pressure gradient between the veins in the right atrium tends to return the blood back to the heart with no effect of gravity and this disappears in standing position
How can the skeletal muscle pump affect the venous return
Skeleton muscles contract and squeeze on the vein making the blood flow upwards increasing the Venous return
How can the valves in veins and vascular sheath affect venous return
As of the artery pulsates blood in adjacent vein is displaced upward to the heart which increases the COP and heart beats more powerfully then this massaging action is increased and so the VR increases
How can the abdominal thoracic pump affect venous return
During inhalation the thoracic cavity decreases and presses on the abdominal cavity which causes the vena cava to return more blood
How can the venomotor tone affect Venous return
Sympathetic alpha 1 adrenoreceptors receptors
Can cause Veno constriction or Veno dilation
Sympathetic tone decreases with old age
How can residual pressure affect venous return
Whenever there is a difference in pressure between two location fluid flows from the region of high-pressure to that of low pressure
Pressure in arteries is greater than veins so pressure gradient drives the blood from arteries to veins and increases venous return
Define residual pressure
Pressure from left side of the heart which is ultimately responsible for pushing of blood behind towards the right side of the heart
(Vis a tergo)
How can ventricular suction affect venous return
▪️Pressure in right atrium is normally about zero mmHg
▪️During ventricular contraction the atrial ventricular ring is pulled down as a result of this the atria expands
▪️This creates a negative pressure in the right atrium and the negative pressure is also created during sudden rush of blood from Atria to ventricle
▪️this negative pressure exerts suction effect on the great veins and draws blood into the atrium(vis a fronte)
