Cardiac output and blood pressure Flashcards
What is the CO?
Volume of blood pumped out by heart per unit of time; l/min; SV*HR
What is the typical values for SV, HR and thus CO at rest?
SV = 80ml HR = 70bpm CO = 5.6 l/min
What is the relationship between workload and HR?
HR has linear relationship
What is the relationship between workload and SV?
Increases, plateaus, then decreases; as HR increases above peak SV, there’s less time for ventricles to fill, decreasing SV
What is predominant way that elite athletes alter their CO being max effort exercise?
By increasing SV
What are three ways that HR is controlled?
ANS, hormones, and body temperature
What is the effect of parasympathetic stimulation on the HR?
Nerve endings secrete ACh @ SAN and AVN; ACh is inhibitory on cardiac muscle, hyperpolarising membranes and causing depolarising drift to become slower = slower SAN rhythm
What is the effect of sympathetic stimulation on the HR?
Nerve endings secrete NE @ SAN, AVN, and cardiac muscle; NE is excitatory on cardiac muscle, depolarising membranes further, causing depolarising drift to become faster = faster SAN rhythm. NE also shortens AVN delay, myocyte action potential, and increases speed of relaxation
What hormones increase HR?
NE and Epi in bloodstream act on beta receptors, increasing HR
How does temperature affect pacemaker rate?
Cold temperatures cause decrease, whilst warmer temperatures cause increase
What are the two ways that SV are controlled?
Force by which muscle cells contract; arterial pressure against which they have to eject blood
What are the two processes that regulate the force of contraction of the heart?
Length-tension properties of cardiac muscle cells; effects of hormonal influence on the contractility of cardiac muscle
How does hormonal activity affect the contractility of the cardiac muscle?
Sympathetic nerve activity and circulating catecholamines increase contractility = greater SV
How does venous return influence SV?
Increased venous return increases end-diastolic volume = increased SV
What law describes the relationship between end-diastolic volume and SV?
Starling’s law of the heart
What is the driving force for flow within the CV system?
Pressure; gradient is present between arteries and veins; pressure must be high enough to create flow but not too high to put excessive stress on CV system
What is the difference in the blood pressure maintenance in the veins and arteries?
Arteries have a pulsalite blood pressure due to the pressure oscillations of the heat; veins have a continuous blood pressure due to the loss of forward energy (mainly due to friction)
How is blood pressure measured clinically?
Cuff pressure; sound of artery opening and closing continuously
What would happen if the cuff pressure was below diastolic pressure?
Blood would flow freely and no sound would be heard
What would happen in the cuff pressure was above systolic pressure?
Blood would not flow, and no sound would be heard
What must the cuff pressure be in order or blood pressure to be heard?
Must be between diastolic ans systolic pressures (diastolic < cuff < systolic)
What is mean arterial pressure?
Diastolic pressure + (systolic-diastolic)/3
What value is MAP closer to?
Diastolic, as lasts almost twice the duration of systole
What is the normal value for blood pressure?
120/80; ~95mmHg MAP
Why does blood pressure vary?
MAP increases with age as arteries become stiffer due to loss of elasticity; women typically have lower blood pressure than men; pressure in foot is higher than in head due to hydrostatic pressure; painful stimulus, sex, and being awake and mobile more likely to cause increased blood pressure than rest/sleep
What is the effect of dynamic exercise on MAP?
Remains relatively steady; increase in systolic pressure, decrease in diastolic pressure; sympathetic activity constricts vessels not related to exercise and dilates vessels to skeletal muscles, so total peripheral resistance is almost constant
What is the effect of static exercise on MAP?
MAP dramatically rises; both systolic and diastolic increased; sympathetic activity constricts vessels and increases total peripheral resistance
What physiological factors determine MAP?
MAP = CO*TPR
What is TPR?
Sum of resistance in organs of the body
