Download Cardiovascular Responses

Cardiovascular
Responses to Exercise
Chapter Learning Outcomes
• Graph and explain the pattern of response for the
major cardiovascular variables during short and
long-term, light to moderate submaximal aerobic
exercise.
• Graph and explain the pattern of response for the
major cardiovascular variables during incremental
aerobic exercise to maximum and during dynamic
resistance exercise
• Discuss the similarities and differences between
the sexes in the cardiovascular response to the
various classifications of exercise.
Cardiovascular Responses
to Acute Aerobic Exercise
• Increases blood flow to working muscle
• Involves altered heart function, peripheral
circulatory adaptations
– Cardiac output (A)
• Heart rate (C)
• Stroke volume (B)
– Blood pressure (D)
– Total peripheral resistance (TPR) (E)
– Rate pressure product (RPP) (F)
Figure 12.1, 12.4 & 12.7
Acute Responses to Submaximal
Aerobic Ex
Light to Moderate
Moderate to Vigorous
Steady State Exercise
output = requirements
• When the body can meet the metabolic and
physiological demands during submaximal
exercise, a “steady state” of equilibrium is
achieved at values above resting.
Acute Maximal Aerobic Ex
Cardiovascular Responses:
Cardiac Output (Q)
• Q = HR x SV
•Normal values
– Resting Q ~5 L/min
– Untrained Qmax ~20 L/min
– Trained Qmax 40 L/min
• Qmax a function of body size and aerobic
fitness
Cardiovascular Responses:
Heart Rate (HR)
• Normal ranges
– Untrained RHR: 60 to 80 beats/min
– Trained RHR: as low as 30 to 40 beats/min
– Affected by neural tone, temperature, altitude
• Anticipatory response: HR  above RHR
just before start of exercise
– Vagal tone 
– Norepinephrine, epinephrine 
Cardiovascular Responses:
Heart Rate During Exercise
• Directly proportional to exercise intensity
• Maximum HR (HRmax): highest HR achieved
in all-out effort to volitional fatigue
–
–
–
–
Highly reproducible
Declines slightly with age
Estimated HRmax = 220 – age in years
Better estimated HRmax = 208 – (0.7 x age in years)
Cardiovascular Responses:
Heart Rate During Exercise
• Steady-state HR: point of plateau, optimal
HR for meeting circulatory demands at a
given submaximal intensity
– If intensity , so does steady-state HR
– Adjustment to new intensity takes 2 to 3 min
• Steady-state HR basis for simple exercise
tests that estimate aerobic fitness and
HRmax
Cardiovascular Responses:
Stroke Volume (SV)
•  With  intensity up to 40 to 60% VO2max
– Beyond this, SV plateaus to exhaustion
– Possible exception: elite endurance athletes
• SV during maximal exercise ≈ double
standing SV
• But, SV during maximal exercise only
slightly higher than supine SV
– Supine SV much higher versus standing
– Supine EDV > standing EDV
Cardiovascular Responses:
Factors That Increase Stroke Volume
•  Preload: end-diastolic ventricular stretch
–  Stretch (i.e.,  EDV)   contraction strength
– Frank-Starling mechanism
•  Contractility: inherent ventricle property
–  Norepinephrine or epinephrine   contractility
– Independent of EDV ( ejection fraction instead)
•  Afterload: aortic resistance (R)
Cardiovascular Responses: Stroke
Volume Changes During Exercise
•  Preload at lower intensities   SV
–  Venous return   EDV   preload
– Muscle and respiratory pumps, venous reserves
• Increase in HR   filling time  slight 
in EDV   SV
•  Contractility at higher intensities   SV
•  Afterload via vasodilation   SV
Ventricular Contractility
Cardiovascular Responses:
Blood Pressure
• During endurance exercise, mean arterial
pressure (MAP) increases
– Systolic BP  proportional to exercise intensity
– Diastolic BP slight  or slight  (at max exercise)
• MAP = Q x total peripheral resistance (TPR)
– Q , TPR  slightly
– Muscle vasodilation versus sympatholysis
Cardiovascular Responses:
Blood Flow Redistribution
•  Cardiac output   available blood flow
• Must redirect  blood flow to areas with
greatest metabolic need (exercising muscle)
• Sympathetic vasoconstriction shunts blood
away from less-active regions
– Splanchnic circulation (liver, pancreas, GI)
– Kidneys
Cardiovascular Responses:
Blood Flow Redistribution
• Local vasodilation permits additional blood
flow in exercising muscle
– Local VD triggered by metabolic, endothelial
products
– Sympathetic vasoconstriction in muscle offset by
sympatholysis
– Local VD > neural VC
• As temperature rises, skin VD also occurs
–  Sympathetic VC,  sympathetic VD
– Permits heat loss through skin
Blood Flow Redistribution
Cardiovascular Responses:
Cardiovascular Drift
• Associated with  core temperature and
dehydration
• SV drifts 
– Skin blood flow 
– Plasma volume 
(sweating)
– Venous return/preload 
• HR drifts  to
• Compensate
• (Q maintained)
Cardiovascular Responses:
Fick** Principle
• Calculation of tissue O2 consumption
depends on blood flow, O2 extraction
• VO2 = Q x (a-v)O2 difference
• VO2 = HR x SV x (a-v)O2 difference
• VO2max = Qmax [(a-v)O2 diffmax]
**ExPhysRules
(who IS Fick?)
Cardiovascular Responses:
Blood Oxygen Content
• (a-v)O2 difference (mL O2/100 mL blood)
– Arterial O2 content – mixed venous O2 content
– Resting: ~6 mL O2/100 mL blood
– Max exercise: ~16 to 17 mL O2/100 mL blood
• Mixed venous O2 ≥4 mL O2/100 mL blood
– Venous O2 from active muscle ~0 mL
– Venous O2 from inactive tissue > active muscle
– Increases mixed venous O2 content
VO2max
• The highest amount of oxygen a person can
take in, transport and utilize to produce AP
aerobically while breathing air during heavy
exercise.
–
–
–
–
Blood lactate value > 8-9mmol/L
HR + 12bpm of predicted MHR (220-age)
Respiratory exchange ratio of 1.0-1.1
A plateau in oxygen consumption during incremental
exercise (rise < 2.1ml/kg/min in VO2 with an
increase in workload that represents a change in
grade of 2.5% while running at 7mph with 3 min
stages).
VO2max
•
•
•
•
THE measure of aerobic fitness
Laboratory assessment
Performance-based concept
Possible limitations of VO2max:
– Ventilation
– Blood flow
– Metabolic functions
• Lactic acid
• pH
• ATP availability
Respiratory Responses:
Ventilation During Exercise
• Immediate  in ventilation
– Begins before muscle contractions
– Anticipatory response from central command
• Gradual second phase of  in ventilation
– Driven by chemical changes in arterial blood
–  CO2, H+ sensed by chemoreceptors
– Right atrial stretch receptors
Respiratory Responses:
Ventilation During Exercise
• Ventilation increase proportional to
metabolic needs of muscle
– At low-exercise intensity, only tidal volume 
– At high-exercise intensity, rate also 
• Ventilation recovery after exercise delayed
– Recovery takes several minutes
– May be regulated by blood pH, PCO2, temperature
Figure 8.14
Respiratory Responses:
Estimating Lactate Threshold
• Ventilatory threshold as surrogate
measure?
– Excess lactic acid + sodium bicarbonate
– Result: excess sodium lactate, H2O, CO2
– Lactic acid, CO2 accumulate simultaneously
• Refined to better estimate lactate threshold
– Anaerobic threshold
– Monitor both VE/VO2, VE/VCO2
Ventilatory Equivalents
During Exercise
Respiratory Responses:
Limitations to Performance
• Ventilation normally not limiting factor
– Respiratory muscles account for 10% of VO2, 15%
of Q during heavy exercise
– Respiratory muscles very fatigue resistant
• Airway resistance and gas diffusion
normally not limiting factors at sea level
• Restrictive or obstructive respiratory
disorders can be limiting
Respiratory Responses:
Limitations to Performance
• Exception: elite endurance-trained athletes
exercising at high intensities
– Ventilation may be limiting
– Ventilation-perfusion mismatch
– Exercise-induced arterial hypoxemia (EIAH)
Respiratory Responses:
Acid-Base Balance
• Metabolic processes produce H+   pH
• H+ + buffer  H-buffer
• At rest, body slightly alkaline
– 7.1 to 7.4
– Higher pH = Alkalosis
• During exercise, body slightly acidic
– 6.6 to 6.9
– Lower pH = Acidosis
Respiratory Responses:
Acid-Base Balance
• Physiological mechanisms to control pH
– Chemical buffers: bicarbonate, phosphates,
proteins, hemoglobin
–  Ventilation helps H+ bind to bicarbonate
– Kidneys remove H+ from buffers, excrete H+
• Active recovery facilitates pH recovery
– Passive recovery: 60 to 120 min
– Active recovery: 30 to 60 min
Figure 8.16
Sex differences in CV responses
• FFM
• Blood volume & Heart Size
• O2 carrying capacity