Equations To Know Flashcards
Compliance
Change in EDV/change in EDP
The law of Laplace?
Wall tension = pressure X radius/ 2 X wall thickness
What does negative pleural pressure do to cardiac output and ventricular emptying?
It will increase cardiac output by increasing preload
It will impede ventricular emptying by opposing the inward contraction of the ventricle
What is pulsus paradoxus?
When bp drops greater than 15 mmHg during inspiration. Means that the pleural pressure is pulling the ventricle outward when it should be going inward
What does positive pleural pressure do to ventricular emptying?
Enhances it because it facilitates the inward movement of the ventricle
What is vascular impedance?
It is the force that opposes pulsatile flow
Expressed in the proximal arteries such as the aorta
What is the principal afterload source of the LV.
Vascular impedance in the ascending aorta
What is the principal afterload force in the right ventricle?
The pulmonary arteries
What is vascular resistance?
The force that opposes steady flow
Expressed in the small terminal vessels
What is the equation for vascular resistance?
R= Pin-Pout/ Q
What is the equation for SVR?
SVR = MAP - RAP/ CO
What is the equation for pulmonary vascular resistance?
PulmVR= PAP - LAP/ CO
What is the Hagen-Poiseuille equation?
Q = change in pressure X (pi r4/8ul)
What does the Hagen-Poiseuille equation represent?
Steady flow through small rigid tubes
What is the resistance equation derived from the Hagen-Poiseuille equation?
R = 8ul/pi r4
This shows that radius is the single most important factor in determine resistance to steady flow in the peripheral circulation
What is the principal determination of the viscosity of blood?
The concentration of erythrocytes (hematocrit)
What is shear thinning?
The velocity of blood flow increases through small vessels causing an increase in plasma volume and decrease in blood viscosity
What is the relationship between blood viscosity and cardiac output?
Inverse - as blood viscosity decreases, cardiac output increases (disproportionately)
Why will cardiac output increases disproportionately?
Because as the flow rate increases as the viscosity drops, the viscosity gets even lower in response to the hemodilution
What is the equation for SO2?
Oxygenated Hb/total Hb
What is the equation for SvO2?
1- VO2/DO2
What is the equation for VO2?
CO X (CaO2-CvO2) X 10
What is the equation for CaO2?
1.34 X Hgb X SaO2
What is the equation for MAP.
map = CO X SVR/80 - CVP
What is the equation for calculating the amount of bicarbonate needing to normalize the ph?
0.2 X patients weight X base excess
