CVS Flashcards
What is the function of the CVS?
To transport through its pump and vessels by joining the pulmonary and systemic circulations, to work in series.
What may be the cause for a difference in the R CO compared to the L CO?
Blood loss or pooling
What are the pressures with the systemic, pulmonary and venous circulations?
Systemic - 90mmHg
Pulmonary - 25mmHg
Venous - 0mmHg
Why do vascular beds run in parallel?
To ensure that all the capillaries receive blood with the same level of oxygenation. It also allows changes in flow to one organ without affecting the others.
What is the value of Pao2 and Paco2 on leaving the LV given normal alveolar ventilation?
Pao2 = 13kPa Paco2 = 5kPa
What is absolute pressure?
As all the pressures in the body are higher than atmospheric pressure, but the measures used absolute is the total of atmopheric + mean BP
What is the function of the heart’s pumping action?
To receive blood from the venous system at low pressures of 0mmHg due to resistance and to IMPART PRESSURE onto the blood in order to eject it into the systemic circulation.
What stages occur during systole?
Ventricular contraction and ejection
What stages occur during diastole?
Ventricular relaxation and filling
What is CO?
The volume of blood ejected per minute = 5L/min.
CO = HR x SV
LCO=RCO
What is the average SV and HR?
SV = 70ml HR = 70bpm
What is the pulse pressure?
The difference between the pressures during diastole and systole within the aorta = 30-50mmHg
PP=SP-DP
What does PP show?
The force that the heart generates on contraction. The larger the PP, the greater the force.
How can PP be measured?
Via BP or arterial line. It varies with each beat.
How is mean ABP calculated and what does it show?
Indicates oxygenation to the brain. Should be >60mmHg.
mean ABP = (SP-DP)/3 + DP
Why is PP divided by three in mean ABP?
During a cardiac cycle, the heart is in diastole 2/3 of the time and in systole for 1/3.
What determines ABP?
Resistance to flow
Blood volume in the arterial system
ABP = CO x TPR
What is TPR?
The resistance to flow in all systemic vasculature
Why does the pressure fall throughout the system?
Due to increased resistance in the arteries and capillaries.
What effect does vasodilation and vasoconstriction have on TPR?
Vasodilation = decreases TPR = increased flow Vasoconstriction = increased TPR = decreased flow
What controls vasoconstriction/dilation?
Sympathetic N and local factors
Which organs have an autoregulatory range that is not affected by systemic vasodialtion/constriction?
Brain, Kidney and Heart
How much blood is in a 70kg pt?
5L - All the blood passes through the heart once per minute (CO=5L.min)
What happens if VR doesn’t equal CO?
A coordinated response is initiated to maintain ABP. If the response is too slow it causes light headedness.
How can CO be increased and why is it needed?
To increase CO must increase VR: -Increase HR via cardia stimulation -Vasoconstrict to force more VR -Increase water retention through kidneys = increased BP
