A&P2 Lecture 3 - influence of exercise

winniesmith1's version from 2017-03-13 14:00

Section 1

Question Answer
What is blood flow the volume of blood that flows through any tissue in a give time period (ml/min)
What is total blood flow known as cardiac output (L/min).
How do you calculate CO=SV * HR
What is stroke volume=amount of blood pumped into the circulatory system from the left ventrivle during systole.
What is average resting CO 5L/min
What is average resting stroke volume70 ml/min
Why would higher EDV result in higher SVThe more blood returned to the heart, the more blood will be pumped out of the heart. -SV will be higher. -Frank-starling mechanism
Why would higher ESV result in lower SVThe less able the heart is to squeeze the blood out of the heart, the more blood will be left in the heart after systole

Section 2

Question Answer
What are the 3 key factors influencing SVpreload, afterload and contractility. (also heart size, fitness levels, gender, duration of contraction)
How do you work out stroke volumeEDV-ESV
What is preloadThe initial stretching of the cardiac myocytes prior to contraction. Related to muscle sarcomere length.
How do you work out preloadEDV used as an index of preload, as it depends directly on venous return to the heart. As sacromere length cannot be determined in the intact heart.
What happens to preload when venous return to the heart is increasedEnd diastolic pressure (EDP) and volume of the ventricles are increased  Stretches the sarcomeres  Increased preload
What happens to preload when venous return to the heart is decreasedE.g., blood loss, EDP and volume of the ventricles are decreased  Shorter sacromere lengths  Reduced preload
Does changes in preload affect SVYes. Increase preload stretches cardiac fibres and initiates strong contraction.
What does myocyte stretching causethe heart to contract more forcefully. Enables heart to eject the additional venous return, thereby increasing SV.
Why does stretching cause the heart to contract more forcefullyStretch-dependent force generation.‚ Intrinsic factor of cardiac contractility ‚ Increased number of interactions between actin and myosin generates increased force

Section 3

Question Answer
What is afterloadthe amount of tension that the contracting ventricle must produce to force open the semilunar valve and eject blood.
How do the blood vessels contribute to afterloadAfterload increases with increased resistance to blood flow out of the ventricle
What does increased afterload meanreduced ventricular contraction = greater ESV
What is ESVvolume of blood left in the heart after systole.
How does afterload affect SVDue to aortic resistance. LV must generate enough force to overcome this resistance to be able to eject blood into circulation. Increased afterload = increased ESV= decreased SV.
How does afterload alter the frank-starling mechanism curve-An increase in afterload lowers SV and increases LVEDP (C) ‚ Heart failure ‚ Poor contractility -Lower afterload increases SV and lowers LVEDP (B) ‚ Healthy heart

Section 4

Question Answer
What is inotropycardiac contractility. force of muscle contraction
How does increased contractility alter SV Stretch-independent force generation. Increased inotropy (e.g. exercise) increases the force of contraction of the heart --> SV increased.
How does decreased contractility affect SVDecreased inotropy (heart failure) decreases the force of contraction of the heart. SV reduced.

Section 5

Question Answer
What are chronotropy effectsthose that effect heart rate
What factors affect heart rateAutonomic innvervation (SNS and PNS), Hormones (adrenaline), Fitness levels (help attenuate age-associated increase in HR), Age (ageing increases HR)
Does heart rate fluctuate?yes. Beat to beat fluctuations exist in resting heart rate. HR not a 'metronome' value. Due to push and pull of ANS
Which HR nerve is associated with the sympathetic NSAccelerator nerve
Which HR nerve is associated with parasympathetic NSVagus nerve
What does irregular HR include‚ Atrial fibrillation: Irregular and fast heart rate ‚ Tachycardia :Overly fast heart rate. Classified as arrhythmias
What is high HRV associated withbeing healthy. Increased ability of the ANS to adapt to sudden changed placed upon it.
What is low HRV associated withpoor cardiac outcomes.

Section 6

Question Answer
Where does the blood flow go during rest50% of blood goes to the metabolically active tissue. Resting skeletal muscles get 15%
Where does the blood flow go during exerciseBlood is redirected to the metabolically active skeletal muscle  Up to 25X more blood flow to active muscle during exercise
What happens to the blood vessels during exerciseNeurohumoral factors regulate blood flow by causing vasconstriction and vasodilation.
How does the CV centre control blood vessels during exerciseIncreased sympathetic stimulation and epinephrine  Vasoconstriction in the blood vessels of the skin (early onset of exercise) and viscera: Alpha adrenergic receptors  Vasodilation of blood vessels in skeletal muscles :beta-adrenergic receptors
When skeletal muscle is resting, what % capillaries are open20-25%
During exercise what percentage of capillaries are open100%.
Why are all capillaries open during exerciseAs metabolic demand of the local tissue is high. Lactic acid, high CO2, potassium ions cause precapillary sphincters to relax. Enables increased flow of blood for exchange.

Section 7

Question Answer
How does the onset of exercise effect blood flow to the skinSympathetic stimulation causes some decrease in the blood flow through the skin.
How does prolonged exercise effect blood flow to the skinIncreasing body temperature due to increased muscular activity stimulates temperature receptors in the hypothalamus. Decreases firing of sympathetic nerve fibres (Results in vasodilation of blood vessels in the skin, skin turns red, excess heat is lost).
How does exercise effect preload and venous return-Skeletal muscle pump (increase venous return/preload/SV). Increased sympathetic stimulation of heart. -Elevated HR. Increased SV and HR = increased CO
How does the skeletal muscle pump work/effected during exercise.-Veins compressed in a cyclic fashion -Greatly increases venous return to the heart ‚ Increased preload and hence increased SV

Section 8

Question Answer
What happens to blood pressure during dynamic exerciseMean arterial pressure (MAP) usually increase by 20 to 60mmHG.
Why does MAP increase-Due to increased CO -Higher pressure needed to push the increased CO (blood flow) to working muscles
How is MAP calculatedMAP= DBP + (SBP - DBP)/3
What happens to SBP (systolic blood pressure) during dynamic exerciserises more sharply with exercise. -Increased CO = increased LV systolic pressure ‚ Greater force and pressure needed to deliver increased blood flow (CO) to the working muscles.
What happens to DBP (diastolic blood pressure) during dynamic exerciseremains almost unchanged. Large muscle mass recruited during dynamic exercise ‚ Lots of heat generated by contracting muscles  Causes vasodilation – decreases resistance. -Thus, despite increased CO, DBP remains unaltered.

Section 9

Question Answer
What is post exercise hypotensionA single bout of dynamic exercise causes a prolonged reduction in arterial pressure lasting nearly 2 hrs in healthy individuals. Occuring after exercise bouts of 30-60 mins at moderate intensity.
What is post-exercise hypotension associated withmarkedly reduced vascular resistance.Lots of nitric oxide produced during exercise. Nitric oxide is a potent vasodilator.
How is blood pressure effected by chronic endurance exercise trainingMAP is chronically lowered over time with regular aerobic exercise training: Weight maintenance and repeated bouts of exercise thought to cause resetting of BP to a new lower value.
How is HR controlled/effected during exerciseIncreased O2 consumption during exercise. Decreases O2 and increases CO2 blood concentration ‚ Detected by chemoreceptors ‚ Dilation of veins occurs ‚ Increased venous return  Increases pressure in the heart  Detected by stretch and pressure receptors in heart. -CV centre responds, signals SNS to increase HR and force (inotropy) of heart.
What happens to heart rate during exerciseHR increases linearly with increasing exercise intensity. With increased exercise intensity, the contribution of the SNS to HR increases and the PNS decreases.

Section 10

Question Answer
How do you calculate max HRoften as 220-age = MHR bpm (accurate within +/- 15 bpm). Better to measure it
Describe heart rate variability during physical exerciseAs % of max heart rate increases, heart rate variability decreases.
Compare trained vs untrained heart ratepost training heart rate is lower for a given exercise intensity/speed. Heart has become a more efficient pump
How long does the transition from rest to short duration submaximal exercise 4 mins to reach a steady state.

Section 11

Question Answer
Describe cardiovascular changes during prolonged exerciseDehydration & sweating --> plasma vol, blood vol and venous return decreases. HR increases to try to maintain CO and exercise intensity
What happens to stroke volume during increasing exercise intensitySV plateaus at 40% (VO2peak) 100-130 ml/min. However chronic endurance training alters this relationship
Why does stroke volume plateau at 40%Attributed mainly to a decrease in the diastolic filling time (due to increased HR) that occurs during exercise of increasing intensity.
Why does the effect of increased exercise on stroke volume alter with endurance trainingthe proposed mechanisms for the progressive increase in SV are enhanced diastolic filling, enhanced contractility, larger blood volume, and decreased cardiac afterload
What happens to blood volume in response to endurance exercise trainingit increases, after 2-4 weeks. Primarily due to increase in plasma volume. Some increase in RBC volume also (Associated with increased water intake and decreased urine volume output ‚ Increased anti-diuretic hormone and aldosterone  Cause kidneys to retain or reabsorb water).
What does an increase in plasma volume doincreases preload --> ^EDV --> ^SV

Section 12

Question Answer
What happens to resting CO in an athleteResting and submaximal HR decreases. SV is increased at rest, and is therefore higher during maximal exercise ƒ Contractility of the heart is increased. -Less beats needed to provide same CO ‚ Due to increased SV and contractility
Max CO in untrained and trainedUntrained = 20L/min. Trained = 30-35L/min due to higher SV for given HR.
How does an athlete's heart differ from untrainedIncreased heart size (hypertrophy) Electrical: bradycardia (slower HR). Structural: increased chamber wall thickness and cavity size. Functional: Enhanced diastolic filling. Augmentation of stroke volume
How does an aerobic athletes heart differIncreased LV cavity and LV wall ‚ Associated with repeated bouts of high venous return that accompanies exercise ‚ Increased preload and EDV
How does an anaerobic athletes heart differ Increased LV wall thickness ‚ Associated with repeated bouts of forcing the LV to eject against an elevated mean arterial pressure during exercise training  Increased afterload
What does cardiomyopathy cause-Thickening of the LV wall -LV cavity reduced -Inefficient pump