Exam 2- Lectures 9-11 Flashcards
functions of cardiovascular system during exercise
- provide tissues with oxygen and nutrients
- remove carbon dioxide and metabolic waste products
- maintain body temperature
- transport hormones
Oxygen delivery =
cardiac output x arterial oxygen content
when does cardiac output increase?
in proportion to dynamic exercise intensity
what stays relatively constant during exercise?
arterial oxygen content (CaO2)
what do increases in oxygen delivery depend on?
increases in cardiac output
stroke volume =
end diastolic volume - end systolic volume
how do autonomic nerves affect HR?
- vagus (parasympathetic) activation lowers HR
- sympathetic nerves raise HR and cardiac contractility
how does oxygen consumption change with exercise?
- VO2 can increase from 1 MET to 12-20 in untrained to highly trained
- CO increases from 5-20 l/min in untrained (4x increase)
- O2 extraction can increase from 4 ml to 15-20 ml in untrained (3-4x increase)
arteriovenous oxygen difference
- represents the amount of oxygen transferred from the blood to the interstitial space and/or tissue
- a-v O2 difference = arterial O2 content - venous O2 content
BP =
CO x TPR
CO response during exercise
- depends on increases in SV and HR
- both increase at onset of exercise
- SV plateaus during moderate exercise, while HR increases linearly until maximal HR is reached
in most individuals, what is the further increase in CO during moderate to heavy exercise due to?
increases in HR
- often use HR as a surrogate marker for exercise intensity
change in heart rate –>
change in cardiac output –> change in oxygen delivery –> change in VO2 with increasing workload
what dominates heart rate at rest?
vagal activity with minor influence from SNS
Heart rate initial response to exercise
- rapid withdrawal of vagal (PNS) activity
- activation of SNS is slower
what happens as HR continues to rise above 100 b/m
- balance of vagal to SNS tone shifts more and more towards SNS dominant
- during maximal exercise, the HR response is very strongly dependent on SNS
why is there a decrease in HR max due to age?
the reduction in intrinsic HR and decrease in beta-adrenergic responsiveness
what are the consequences of increased heart rate during exercise
- decreased left ventricular filling time
- but filling is well maintained until close to max HR
what helps maintain filling time?
increased rate of relaxation with SNS stimulation
second consequence of an increase in HR during exercise
- can increased cardiac contractility and thus SV –> “treppe” or the force-frequency relationship
- at higher HR there is more calcium available to contractile proteins
- SV will increase as a result of increased contractility
major determinants of stroke volume
preload, after load, and contractility
what occurs to stroke volume during dynamic exercise
increases
can increase from 70 to 100 ml in the untrained
what is preload
ventricular wall tension at the end of diastole
what is used as a major index of preload?
end diastolic volume