Average adult CO :
Average adult CO Using average values
HR = 75 beats/min
SV = 70 ml/beat
CO = 75 x 70 = 5250 ml/min
What is total blood volume?
5 liters
The entire blood volume passes through each side of the heart in less than 1 minute
How can CO change? :
How can CO change? Any change in SV or HR will cause a change in CO
For example
Injection of several units of IV fluid increases blood volume
With more blood going back to the heart, preload (stretch) is greater and heart contracts harder
When heart contracts harder, SV goes up
Changes due to SV :
Changes due to SV sv changes
Degree of stretch (preload) - to a point, stretched fibers contract harder (more SV)
Contractility - epinephrine (sympathetic NS) leads to more Ca+2 release to fibers = harder contraction
Afterload - high blood pressure in aorta and Pulmonary trunk puts back pressure on ventricles to reduce SV
CO changes due to HR :
CO changes due to HR Autonomic nervous system
Parasympathetic (decrease HR)
Sympathetic (increase HR)
Chemical regulation
Hormones (ex. Epinephrine)
Ions (Na+ K+ Ca+2) - ex. Potassium hyperpolarizes heart muscle fibers (further from threshold)
CO and Blood Pressuresystolic/diastolic (120/80) :
CO and Blood Pressuresystolic/diastolic (120/80) Pressure in the system is based on the rate that fluid enters the system (CO) and the amount of resistance that fluid encounters (PR):
PRESSURE = CO x PR
Slide 7:
Blood pressure control Short term controls
Immediate effects are usually seen in vascular tone (PR) and Cardiac Output
Long term controls
Most effects of this type involve changes in blood volume