Unit 3 Flashcards
Cardiac output is determined mainly by
Venous return
CO= VR (Also CO = SV X HR)
SV = stoke volume HR = heart rate
Factors that influence VR
Body metabolism (local flow and autoregulation) - VR is a summation of all local blood flows
Age
Body size
Gender (heart size)
Factors affecting heart rate
Autonomic innervation
Hormones
Fitness levels
Age
Factors affecting stroke volume
Heart size Fitness levels Gender Contractility Duration of contraction Preload (EVD) Afterload (resistance)
Stroke volume =
SV = EVD - ESV
Cardiac index increases from age ___-___
It decreases after age
0 - 10ish
10ish
CO will match VR via the following mechanisms:
Frank sterling’s mechanism (effects force of contraction) Bainbridge Reflex (effects rate of contraction) SA node stretch (effects rate of contraction)
Normal CO limit (at rest)
5 L/min
Maximum CO it can achieve
13 L/min
Cardiac output curve demonstrates:
The effectiveness of cardiac function at different levels of right atrial pressure (which reflects venous return)
Hyper-effective heart causes (More than normal amount of CO)
Sympathetic stimulation
Hypertrophy
Hypo-effective heart causes (less than normal amount of CO)
Hypertension
Sympathetic inhibition
Any heart pathology
Factors that decrease peripheral resistance
These can cause:
Beriberi (Thiamin deficiency)
Arteriorvenous fistula
Hyperthyroidism
Anemia
Cause pathologically HIGH cardiac output
Abnormal connection between an artery and vein
Arteriovenous fistula
Inability to hold O2 in the blood
Anemia
Too much fluid in the cardiac sac
Cardiac tamponade
Cardiac factors that can cause pathologically low CO
Myocardial infarction
Severe valve disease
Myocarditis
Cardiac tamponade
Peripheral factors cause it pathologically low CO
Decreased blood volume (hypovolemia)
Acute venous dilation (SNS suppression)
Large vein obstruction
Decreased metabolic rate of tissues (hypothyroidism)
When cardiac output falls too low, it is called:
Circulatory shock
Venous return curve plateau is due to
Low atrial pressures leading to vein collapse
The higher the right atrial pressure, the _____ venous return will be
Less
Venous return curve- mean systemic filling pressure
The venous return becomes 0 when the right atrial pressure rises to mean systemic filling pressure
If first atrial pressure is in the negatives, what happens to venous return
Increases until it gets to plateau
What happens to CO when sympathetic stimulation increases
It increases as right atrial pressure increases