hemodynamics

Question 1

stroke volume (SV)

Answer 1

volume ejected from the ventricles with each systolic contraction aroudn 70mls/ beat

Question 2

cardiac output (CO)

Answer 2

SV x HR

normal around 5L-6L in males

Question 3

what is cardiac index

Answer 3

used to normalize CO across population by accounting for size 
CI= CO/ BSA
BSA (body surface area)
normal value
 2.6-4.2L/min/m2

Question 4

wide range of HR

Answer 4

HR has the widest range of variability potential increases of 100-200%
SV can only increase 50%
this means that as HR increases filling time decreases and so CO is reduced,
this is seen with shock and abnormal rhythms

Question 5

preload (SV)

Answer 5

preload is the final stretching of the cardiac myocytes prior to contraction. stretch is the lengthening of sarcomeres at end diastole

Question 6

how is preload measure ?

Answer 6

cannot be measure directly so end diastolic volume (EDV) or end diastolic pressure (EDP) is used as a proxy.

Question 7

what does an increase in stretch within physiological limits do to the ventricle ?

Answer 7

the greater the stretch= stronger contraction

Question 8

what does the frank starling and venous return chart explains ?

Answer 8

the greater the stroke volume (more blood-max stretch ) the greater the contraction therefore it increases the blood venous return

Question 9

factors that can increase ventricular preload

Answer 9

• increase venous pressure 9decrease compliance or increase venous blood volume)
• increase ventricular compliance
• increase atrial inotropy (strength of contraction)
• increase outflow resistance and afterload
• decrease HR

Question 10

what is Afterload

Answer 10

afterload is the “load” against which the heart must contract to eject blood
under normal circumstances the greatest contributor to afterload pressure is aortic pressure

Question 11

afterload and stroke volume

Answer 11

an increase in SV= decrease in afterload

a decrease in SV= increase in afterload

Question 12

what does inotropy mean ?

Answer 12

Force of contraction or “Contractility” can be influenced independently from preload and afterload on a cellular level.

“Changes in inotropy are caused by cellular mechanisms that regulate the interaction between actin and myosin independent of sarcomere length”

Question 13

inotropy on stroke volume

Answer 13

increase in Inotropy= increase SV

reverse with a decrease in inotropy

Question 14

factors influencing inotropy

Answer 14

• ↑ sympathetic activation
• ↑ circulating catecholamines (adrenile)
• ↑ afterload (anrep effect)
• ↑ heart rate (bowditch effect)

Question 15

what is the anrep Effect ?

Answer 15

The Anrep effect is an autoregulation method in which myocardial contractility increases with afterload.
the hear is gonna squeeze harder with an increase afterload, compensatory effect in order to overcome resistance.

Question 16

what is the bowditch effect ?

Answer 16

an autoregulation method by which myocardial tension increases with an increase in heart rate.
inotropy increases as your heart rate increases, to compensate for the loss of filling time

Question 17

positives inotropes

Answer 17

increases inotropes
digoxin 
beta antagonist 
-dopamine 
-dobutamine 
-epinephrine 
-isoproterenol
phosphodiesterase inhibitors 
-milrinone

Question 18

negative inotropes

Answer 18

parasympatheric stimulation- vagus nerve (decreases heart rate) 
hypoxia
acidosis 
anesthesia 
increased potassium 
calcium channel blockers

Question 19

three methods to measure CO

Answer 19

ficks method
thermal dilution
dye dilution

Question 20

what is the ficks method concept

Answer 20

is the rearrange of the uptake of a oxygen this can determine on the factors of blood flow and the arterua venous contenc difference
VO2/ C(a-v)O2

Question 21

dye dilution method

Answer 21

makes use of phot spectrometry to analyze the concentration of dye over time .

Question 22

thermal dilution method

Answer 22

A Pulmonary Artery Catheter is inserted into a central vein
The proximal port lies in the right atrium
A known volume with a known temperature is injected
Eg. 10 cc of 0 degrees celcius
The end of the catheter has a temperature probe
This distal end is set to lie in the Pulmonary Artery
The RV functions as a mixing chamber