Cardio - Physio (Resistance, pressure, flow, & Cardiac/vascular function curves) Flashcards
Pg. 268-269 in First Aid 2014 or Pg. 255 in First Aid 2013 Sections include: -Resistance, pressure, flow -Cardiac and vascular function curves
What is the equation that relates resistance, pressure, and flow in the cardiovascular system? On what is this equation based?
Pressure gradient or driving pressure (deltaP) = Flow (Q) x Resistance (R); Ohm’s law (V = I*R or I = V/R)
What is/are the equation(s) that defines/characterizes resistance? To what factors does resistance relate, and how so?
Resistance = driving pressure (deltaP) / flow (Q) =( (8(eta)(viscosity) x length) / (pi)(radius)^4 ; See FA p. 255 for equation ; Based on equation, resistance is directly proportional to viscosity and vessel length & inversely proportional to radius to the 4th power
How do you calculate the total resistance of vessels in series? What about in parallel?
TOTAL RESISTANCE OF VESSELS IN SERIES = R1 + R2 + R3…; 1/TOTAL RESISTANCE OF VESSELS IN PARALLEL = 1/R1 + 1/R2 + 1/R3…
On what does viscosity mostly depend? What are 3 conditions in which viscosity is increased?
Hematocrit; (1) Polycythemia (2) Hyperproteinemic states (3) Hereditary spherocytosis
Again, on what does viscosity mostly depend? What is a condition in which viscosity is decreased?
Hematocrit; Anemia
Again, what is the Ohm’s law based equation that applies to the cardiovascular system? What role does pressure gradient play?
Q = deltaP / R; delta P = Pressure gradient, which drives flow from high pressure to low pressure
What accounts for most of the total peripheral resistance? In turn, what does/do this/these regulate?
Arterioles; Capillary flow
What effect does inotropy have on cardiac/vascular function curves?
Changes in contractibility –> altered CO for a given RA pressure (preload)
What are 2 examples of positive inotropy?
(1) Catecholamines (2) Digoxin
What are 2 examples of negative inotropy?
(1) Uncompensated heart failure (2) Narcotic overdose
What effect does venous return have on cardiac/vascular function curves?
Changes in circulating volume or venous tone –> altered RA pressure for a given CO. Mean systemic pressure (x-intercept) changes with volume/venous tone
What are 2 examples of increased venous return?
(1) Fluid infusion (2) Sympathetic activity
What are 2 example of decreased venous return?
(1) Acute hemorrhage (2) Spinal anesthesia
What effect does total peripheral resistance have on cardiac/vascular function curves?
Changes in TPR –> altered CO at a given RA pressure; however, mean systemic pressure (x-intercept) is unchanged
What is an example of increased TPR?
Vasopressers
What are 2 examples of decreased TPR?
(1) Exercise (2) AV shunt
What represents mean systemic pressure on cardiac/vascular function curves? How does venous return versus TPR affect mean systemic pressure?
Mean systemic pressure (x-intercept) changes with volume/venous tone; Mean systemic pressure (x-intercept) is unchanged with TPR
What does the intersection of cardiac and vascular function curves represent?
Intersection of curves = operating point of heart (i.e., venous return and CO are equal)
What are the axes for cardiac and vascular function curves?
x-axis: RA pressure or EDV; y-axis: Cardiac output/Venous return
Draw cardiac and vascular function curves in the following contexts: (1) operating point of heart (2) positive inotropy (3) negative inotropy.
See p. 269 in First Aid 2014 for graph on left
Draw cardiac and vascular function curves in the following contexts: (1) operating point of heart (2) increased volume/venous tone (3) decreased volume/venous tone.
See p. 269 in First Aid 2014 for graph in middle
Draw cardiac and vascular function curves in the following contexts: (1) operating point of heart (2) increased TPR (3) decreased TPR.
See p. 269 in First Aid 2014 for graph on right
In general, how do changes affecting cardiac and vascular function often occur? What are 2 ways in which this may happen? Give an example of each way.
Changes often occur in tandem, and may be (1) reinforcing (exercise increases inotropy & decreases TPR to maximize CO) or (2) compensatory (heart failure decreases inotropy –> fluid retention to increase preload to maintain CO)
