CC9: Cardiac output 2 Flashcards
What is a normal stroke volume?
60-100ml/beat
SV index = 33-47ml/beat/m^2
What is a normal cardiac output?
4-8L/min
Cardiac index = 2-4L/min/m^2
What is the Fick principle?
-As blood goes through organs, there is a reduction in O2 and increase in CO2
-As blood goes through lungs, there is an increase in O2 and a decrease in CO2
What is cardiac index?
Cardiac output/Body surface area
What is the Fick formula?
What is the VO2 max of the average, untrained, healthy male and female?
Male = 35-40mL/kg/min
Female = 27-31mL/kg/min
How do calculate BSA?
How do calculate VO2?
VO2 = 125 x BSA
What are the ways of measuring VO2
Direct:
-Measure using respiratory techniques
Indirect:
-Predict from regression equations
-Derive from normal tables
Fick principle in systemic circulation
Fick principle in pulmonary circulation
What are the direct respiratory techniques for measuring VO2?
Spirometry
-Expired gas returned via soda lime filter
-Reduction in gas volume due to consumption of oxygen
Metabolic cart
-Inspired O2 volume/concentration and expired O2 volume/concentration measured by:
-Mass spectrometer
-Paramagnetic analyser
Fick formula in body
Fick formula in lungs
What is oxygen content (CaO2)?
CaO2 = the total amount of O2 in the blood, both attached to Hb and dissolved in the plasma
What is Hufner’s factor?
-Combining power of Hb
-1 gram of Hb can combine maximally with 1.34ml O2
How much O2 is dissolved in the plasma?
-Small amount of O2 is dissolved into plasma
-This increases when inspired air contains more oxygen than normal room air
-At PO2 = 100mmHg,
dissolved O2 = 0.3ml/100ml plasma
-Generally, dissolved O2 is not significant
What is oxygen capacity?
-Maximum amount of oxygen able to be carried by haemoglobin (ml/g)
How to calculate Oxygen capacity and content?
O2 capacity = Hb x 1.34
O2 content = O2 capacity x saturation
Calculate CaO2 and CvO2
CaO2 = 13 x 1.34 x 0.98
CvO2 = 13 x 1.34 x 0.61
What does low A-V O2 difference indicate?
-High CO - well oxygenated blood moves rapidly through the capillary
-Septic shock - cells extract less O2
What does high A-V O2 difference indicate?
-Low CO - slow blood flow
-Increased VO2 - tissues extracting more O2
What is the effective pulmonary blood flow?
-The amount of deoxygenated blood pumped to the lungs that the lungs can ‘effectively’ oxygenate
What is an example of ‘ineffective’ pulmonary flow?
-Child with left to right shunting through PDA
-Extra blood pumped to lungs is already fully oxygenated
-The lungs cannot further oxygenate this ‘red’ blood
What is vascular resistance?
-The resistance that must be overcome to push blood through the circulatory system and create flow
What is the SVR?
Systemic vascular resistance
-The resistance offered by the peripheral circulation
-Also called Total Peripheral Resistance (TPR)
What is the PVR?
Pulmonary vascular resistance
-The resistance offered by the vasculature of the lungs
What is the formula for resistance?
Vascular system parameters
Formula for SVR
SVR = Systemic vascular resistance
Ao = Mean aortic pressure
RA = Mean right atrial pressure
SBF = Systemic blood flow (Qs)
Formula for PVR
PVR = Pulmonary vascular resistance
PA = Mean pulmonary artery pressure
LA = Mean left atrial pressure
PBF = Pulmonary blood flow (Qp)
What is normal SVR and SVRi?
SVR = 10.0-16.3 HRU
SVRi = 24.6-30 HRU
What is normal PVR and PVRi?
PVR = 1.9-3.2 HRU
PVRi = 3.2-3.6 HRU
What increases/decreases SVR?
Increased by:
-aortic valve stenosis
-elevated BP
-polycythemia
Decreased by:
-use of vasodilators
How do you normalise vascular resistance for body surface area?
SVRI = SVR x BSA
-Multiply vascular vascular resistance by body surface area
What do you do to HRU value to get Absolute Resistance Units (ARU) dynes/sec/cm^-5
HRU x 80 = ARU
Relationship between PVR and PHT
-PHT is often the result of increased PVR
-To test for reversible increase in PVR breathe 100% O2
-In reversible disease this will cause dilation of pulmonary vasculature
What are the guidelines for vascular resistance ratio?
Vascular resistance ratio = PVR/SVR
<0.25 normal
0.25-0.75 mild pulmonary vascular disease
0.45-0.75 moderate pulmonary vascular disease
>0.75 severe pulmonary vascular disease
>1.0 corrective surgery unsuccessful (transplant instead)
