Cardiovascular System Response and Adaptation to Exercise

Question 1

Introduction

Answer 1

• response describes short term changes which accompany exercise (acute phenomenon)
• adaptations come thru regular training (chronic)
• knowledge of this area crucial to: understand role of exercise physiology in healthcare, fitness, and human performance; interpret diagnostic and functional testing; prescribe exercise in health and disease

Question 2

Summary of Acute Cardiovascular Response to Aerobic Exercise

Answer 2

• HR
• SV
• CO
• arteriovenous oxygen difference
• blood flow
• BP
• maximal oxygen consumption

Question 3

Heart Rate

Answer 3

• increase in linear fashion during submax dynamic exercise with work rate and oxygen uptake
• max attainable HR typically decreases with age: 220 - age is typically max HR but variance is considerable (SD +/- 10 bpm)
• magnitude of HR response related to age, body position, fitness, type of activity, presence of disease, medications, blood volume, environmental factors such as temp, humidity, or altitude

Question 4

Stroke Volume

Answer 4

• equal to difference between EDV and ESV
• EDV dependent upon: HR, filling pressure, ventricular compliance
• ESV dependent on contractility and afterload (amt of blood ejected per ventricular contraction or beat)
• curvilinear increase with exercise
• for most individuals SV reaches near max at 50% aerobic capacity and increase only slightly thereafter
• world class endurance athletes often display increased SV beyond 50% of aerobic capacity

Question 5

Cardiac Output

Answer 5

• product of SV x HR
• increases linearly with increased work rate
• resting value of about 5 L/min which increases 4-8 times with exercise
• increase in CO during exercise due to increased HR and SV at intensities up to 50% of VO2max and increases thereafter almost entirely secondary to increased HR
• maximum values for CO depend on many factors: age, posture, body size, presence of disease, level of conditioning

Question 6

Arteriovenous Oxygen Difference

Answer 6

• reflects difference in oxygenation in blood
• at rest: arterial blood ~20 ml O2/100ml/dl; venous blood ~15 ml O2/100ml/dl
• thus difference is 5 ml
• approximates an O2 use coefficient of 25%
• during exercise to exhaustion: venous oxygen level decreases to 5 ml O2/100ml/dl or lower
• thus widens a vO2 difference
• corresponds to a use coefficient of ~75%

Question 7

Blood Flow

Answer 7

• SM receives a 15-20% of CO at rest
• remainder goes to viscera, heart, brain, etc
• SM receives as much as 85-90% of CO during max exercise: selectively delivered to working MU; shunted away from skin, visceral, hepatic and renal vascular beds
• myocardial BF increases 4-5 times
• supply to CNS remains at resting levels

Question 8

Blood Pressure

Answer 8

• directly related to CO and peripheral vascular resistance
• thus provides noninvasive means to measure hearts pumping capacity
• response to exercise measured manually with cuff and stethoscope

Question 9

Blood Pressure Response to Aerobic Exercise

Answer 9

• systolic BP: linear increase with exercies intensity; 8-12 mmHg per MET (1 MET=3.5 mlO2/kg/min); max levels typically reach 190-220 mmHg; aerobic max > 260 mmHg contraindicated
• diastolic BP: remains unchanged or decreases slightly; thus pulse pressure (SBP-DBP) generally increases proportionally to intensity; if DBP increases during exercise ventricular filling not very effective and should slowly stop exercise

Question 10

Abnormal BP Response

Answer 10

• SBP that fails to increase or decrease with change in intensity may indicate plateau or decrease in CO (not good)
• terminate exercise testing if participant demonstrates exertional hypotension: SBP toward end of test below baseline standing level and/or SBP decreases 20 mmHg or more during exercise after initial rise
• this response shown to correlate with myocardial ischemia, left ventricular dysfunction or increased risk of cardiac events
• one study men with max SBP < 140 mmHg: 15 fold increase in annual rate of sudden death compared with those whose pressures > 200 mmHg

Question 11

Maximal Oxygen Consumpton

Answer 11

• VO2max most widely recognized measure of CP fitness/function
• defined as highest rate of oxygen transport and use achieved at max physical exertion
• may be expressed as VO2 = HR x SV x (a-VDO2) where a-VDO2 is arteriovenous oxygen difference
• apparent VO2 magnitude affected by both central factors and peripheral factors
• VO2max may be expressed in 2 ways: absolute or relative
• absolute value reflects total body energy output and caloric expenditure
• relative allows more fair comparison: individuals have different body masses, large absolute O2 consumption secondary to large muscle mass
• contrast the increase in O2 transport and use: 10 fold increase for sedentary guy, 23 fold increase for WC endurance athlete
• increased aerobic capacity derives primarily from increased max CO: greater relative increase in HR and SV rather than increased peripheral O2 extraction
• thus VO2max virtually defines heart’s pumping capacity

Question 12

Cardiovascular Responses to Dynamic Aerobic Exercsie

Answer 12

• steady state: condition which energy expenditure is balanced with energy required
• the factors responsible for energy supply reach a level of elevated equilibrium

Question 13

Short-Term, Light to Moderate Submaximal Aerobic Exercise

Answer 13

• following variables increase rapidly at onset of exercise and reach steady state within 2 minutes: CO, SV, SBP, rate pressure product (RPP)
• peripheral resistance decreases rapidly then plateaus
• DBP remains relatively unchanged

Question 14

Long-Term, Moderate to Heavy, Submaximal Aerobic Exercise

Answer 14

• cardiovascular drift: changes in observed CV variables that occur during prolonged, heavy submax exercise without a change in workload
• linked to increased body temperature during prolonged exercise
• following variables increase rapidly: CO, SV, HR, SBP, rate pressure product
• SBP and TPR may drift downward with prolonged, heavy exercise

Question 15

CV Response to Aerobic Exercise

Answer 15

• decrease in TPR: allows greater blood flow to working muscles; prevents excessive rise in SBP
• BV decreases during heavy aerobic exercise: biggest loss is during 1st 10 minutes of activity; 10% loss not uncommon

Question 16

Incremental Exercise to Maximum

Answer 16

• GXT
• following variables increase in rectilinear fashion: CO, HR, SBP, RPP
• stroke volume increases initially then plateaus at 40-50% VO2max in normally active adults and kids
• DBP remains relatively constant throughout incremental exercise to max
• TPR decreases rapidly with onset of exercise: reaches lowest value at max exercise

Question 17

Sex Differences During Dynamic Aerobic Exercise

Answer 17

• pattern of CV response to aerobic exercise is the same for both sexes
• males typically have higher max values for CO, SV, SBP at max exercise, VO2max
• most differences are attributable to body size and hear size differences between sexes and greater hemoglobin concentration in males

Question 18

Responses of Children to Dynamic Aerobic Exercise

Answer 18

• pattern of CV response in kids is similar to adults
• but kids have lower values at absolute workload and at maximal exercise: CO, SV, SBP
• most differences attributable to lesser body size and heart size

Question 19

Responses of Elderly to Dynamic Aerobic Exercise

Answer 19

• CV responses change with aging
• mac CO, SV, HR, VO2max decrease with age
• linked to decreased efficiency of myocardium
• max SBP, diastolic BP, mean arterial pressure increase with age
• these are linked to less elasticity in peripheral vascular system

Question 20

Cardiovascular Response to Static Exercis

Answer 20

• characterized by modest increase in HR, CO
• characterized by exaggerated increases in SBP, DBP, MAP
• commonly known as pressor response: rapid increase in both systolic and diastolic pressure during static exercise-influenced by amount of muscle involved in static exercise
• volume response: increase in volume stress when you regularly exercise aerobically

Question 21

CV Response to Dynamic Resistance Exercise

Answer 21

-results in modest increases in CO, increase in HR, little change or decrease in SV, large BP increase

Question 22

Summary of CV Response to Exercise Chart

Answer 22

-know this chart

Question 23

Physiological Adaptations in Myocardium with Training

Answer 23

• increased calcium transport efficiency in SR
• increase myocardial fiber mass
• increased capillary/fiber ratio
• increased coronary artery size
• increased myocardial contractility
• conflicting data on new collateral vessels

Question 24

Physiological Adaptations in the Heart with Training

Answer 24

• decreased RHR: largely secondary decrease intrinsic HR
• decrease HR at any given workload: largely secondary to decreased SNS tone
• increased volume leading to increased CO: long term rather than short term effect; largely secondary to ventricular contractility
• increased LV chamber size: secondary to aerobic exercise such as run, walk, bike; greater wall thickness changes with max anaerobic work
• increased heart rate reserve (HRR): fx of PMHR and RHR; karvonen THR = INT(HRR) + RHR…40 yo individual RHR=60 bpm; HRR = PMHR - RHR= 180-60=120; THR=.7(120) + 60 =144 bpm
• the more aerobically fit bigger the HRR

Question 25

Cardiovascular Adaptations with Training

Answer 25

• increased VO2max; increased CO, decreased systemic peripheral resistance at max workload
• increased lactate clearance capacity
• decreased SBP at rest and during exercise
• decreased BP at rest in hypertensives
• most studies show 20% +/- 10% increase VO2max: healthy subjects, greatest relatively increase among previously unfit
• at fixed submax work rate, physically trained: work at lower % VO2max; have greater reserve after training
• increased max SV and CO traditionally regarded as primary reason for change
• effect of chronic training on ANS –> decreased myocardial demand at rest and during exercise
• exercise bradycardia attributable to intracardiac change (increase SV during submax work) and extracardiac change (alterations in trained SM)
• results in decreased HR and SBP at rest, any fixed oxygen uptake, any submax work rate
• recent research shows improved coronary endothelial function
• function increases with 4 weeks of training in pts with asymptomatic CAD
• may help explain some of cardioprotective function of exercise
• pts may benefit via: augmented coronary blood flow, increased myocardial perfusion, increased plaque stabilization or combination thereof