Cardiovascular response to
exercise
The Heart
Outline
• General cardiac responses to exercise
– Control of heart rate
– Control of stroke volume
– Blood pressure
– Distribution of blood flow
– Barroreceptors
• Adaptations to training
• Impact of the environment
Examples of work (METS)
•
•
•
•
•
Rest
Cycling <10 mph
Cycling >20 mph
Running (10 min/mile)
Running (6 min/mile)
1
6
16
10
16
METS=metabolic equivalent tasks
1 MET=resting energy expenditure= 3.5 mlO2kg-1 min-1= 1 Kcalkg-1 min-1
CO=5 L/min
vO2 content=15 ml
O2/100 ml blood
aO2 content=20 ml
O2/100 ml blood
Effects of Exercise on Blood
Pressure
MABP-RAP = CO  TPR
120
80
systolic
Pressure
(mmHg)
mean
diastolic
Impact of Dynamic and Isometric Exercise on
Arterial Blood Pressure
Dynamic
Static (isometric)
250
Blood Pressure (mmHg)
Blood Pressure (mmHg)
250
200
150
Systolic
Diastolic
100
50
0
200
Systolic
Diastolic
150
100
50
0
0
50
100
150
Work (W)
200
250
0
20
40
60
80
Time (sec)
100
120
140
Comparison of BP
Response Between
Arm and Leg
Ergometry
Why is blood pressure going up? I
thought we had sensors that control
blood pressure.
Arterial Baroreceptors
Cardiovascular Physiology. Berne and Levy 1972
Activation of Barroreceptor reflex
Response to an increase in arterial pressure
• Withdrawal of sympathetic tone
• Activation of parasympathetic tone
• Results:
– Decrease heart rate and contractility
– Arterial vasodilation
– Increase in venous compliance
Afferent nerve firing responds to absolute pressure
and rate of change in pressure
Baroreceptors adapt
ACUTE
75
(impulses/sec)
CAROTID NERVE
FIRING RATE
100
50
LONG TERM
25
0
0
100
200
ARTERIAL PRESSURE (mmHg)
Afferent and efferent neural baroreflex responses
Arterial Baroreflex Control of the Peripheral Vasculature in Humans: Rest and Exercise.
FADEL, PAUL Medicine & Science in Sports & Exercise. 40(12):2055-2062, December 2008
Afferent and efferent neural baroreflex responses to the application of
neck pressure (NP) and neck suction (NS)
Arterial Baroreflex Control of the Peripheral Vasculature in Humans: Rest and Exercise.
FADEL, PAUL Medicine & Science in Sports & Exercise. 40(12):2055-2062, December 2008
Schematic illustration of the effect of
exercise on arterial baroreflex
control of heart rate. Exercise resets
the relationship between arterial
pressure and heart rate upward and
to the right (OP = hypothetical
arterial baroreflex operating point).
Heart rate control during exercise by baroreceptors and skeletal muscle afferents.
OLEARY, DONAL Medicine & Science in Sports & Exercise. 28(2):210-217, February 1996.
3
Oxygen Demand
CO=5 L/min
vO2 content=15 ml
O2/100 ml blood
aO2 content=20 ml
O2/100 ml blood
Meeting oxygen needs during exercise
Fick equation
VO2 = Q  (CaO2 – CvO2)
VO2 = [HR  SV]  (CaO2 – CvO2)
VO2 = [BP  TPR]  (CaO2 – CvO2)
Fick equation
VO2 = Q  (CaO2 – CvO2)
Oxygen Extraction (E)
E=
CaO2 – CvO2
CaO2
VO2 = Q  CaO2 x E
Arterial and venous oxygen during exercise
O2Extraction
=(19-12)/19
=0.33
O2 Extraction
=(19.5-2)/19.5
=0.90
Heart rate and stroke volume
200
180
160
Heart rate
(bpm)
140
120
100
80
60
20
30
40
50
60
70
(% Vo2 max)
80
90
100
140
120
Stroke volume
(ml/beat)
100
80
60
0
20
40
60
(% Vo2 max)
80
100
22
20
18
16
Cardiac Output 14
(liters/min)
12
10
8
6
4
0
20
40
60
(% Vo2 max)
80
100
Heart rate
Estimate Maximal heart rate
=208-0.7 x (age year)
=208-0.7x54=170 bpm
Autonomic Nervous System
SNS
Nerves
Neurotran Distribution Effect
smitter
Cervical
Thoracic
Pregang:
ACH
Postgang:
NE
Pregang:
ACH
Post gang
ACH
PNS Vagus
and
lumbar
1(HR)
Heart,
Arteries & 1
Most veins 2
HR
Heart
Vessels of
Genitalia &
colon
The heart is under net vagal tone
120
110
100
Heart rate
(bpm)
Propranolol
90
80
Atropine
70
60
50
40
Propranolol
Atropine
Epinephrine
• Source: Adrenal medulla
• Increase heart rate and contractility (1),
• low concentrations vasodilation (2)
• high concentrations vasoconstriction (1), decrease
venous compliance (1)
Norepinephrine
• Source: Adrenal medulla
• Increase heart rate and contractility (1),
• Limited effect on 2
• At all concentrations vasoconstriction (1), decrease
venous compliance (1)
Determinants of Cardiac Output
• Heart rate
• Stroke volume
– Ventricular end-diastolic volume
– Contractility
– Afterload (aortic pressure)
Venus Blood Return to Heart
Return of blood to heart
• muscle pump
• one-way venous valves
• breathing
Increase Preload
Increase Afterload
Increase Contractility
Stroke volume
• End diastolic volume
– End-diastolic volume (Starling’s Law)
• End systolic volume
– Afterload
– Contractility
Time between beats
Increase in heart rate decreases filling
time
Heart rate control during exercise by baroreceptors and skeletal muscle afferents.
OLEARY, DONAL Medicine & Science in Sports & Exercise. 28(2):210-217, February 1996.
2
What would happen if you could not
increase adrenergic tone to the
heart during exercise?
Metaprolol= 1 antagonist
Ο average-trained
 endurance trained
J Appl Physiol 106: 486-493, 2009
Training and the CV system
VO2 = Q  CaO2 x E
= SV x HR x CaO2 x E
Training
Benefits seen after 3x week for 6
weeks
• 70% of max heart rate
> 30 min/bout
• Maintenance 2x week but maintain intensity
College Students
World Class
Athletes
Control
Bedrest
Trained
VO2 max (L/min)
3.3
2.4
3.9
5.3
Max Ventilation
(L/min)
191
201
197
219
Arterial O2
(mlO2/100 ml
blood)
21.9
20.5
20.8
22.4
Art-Ven O2
(mlO2/100 ml
blood)
16.2
16.5
17.1
18
Max. cardiac
Output (L/min)
20
14.8
22.8
30.4
Max Heart rate
(bpm)
192
197
190
182
Stroke Volume
(ml)
104
74
120
167
Directly measured cardiac pressure–volume curves for athletes and non-athletic controls
Note the marked improvement in both static and dynamic compliance in the endurance
athletes
Levine B D J Physiol 2008;586:25-34
Winder et al JAP 45:370,1978
Heart Adaptations to Training
Endurance
trained
Sedentary
Resistance
trained
1995 Marathon Training Data
(females)
VO2
5 mph
6 mph
RER
5 mph
6 mph
HR
5 mph
6 mph
VO2max
HRmax
*P < 0.05
Pre-training
30.7
35.5
Post-training
29.8
34.6
0.92
0.95
0.88*
0.92*
168
182
54.4
206
151*
167*
58.5*
198*
Adaptations to Training
Resting bradycardia
• Increased stroke volume
• Increased cardiac size and compliance
Increased blood volume
• Lower vascular resistance at any work load
• Improved flow distribution
• Improved oxygen extraction
• Improved heat tolerance
Training Heart Rates
• Low range
– Between 60-70% of maximal heart rate
– ~50-60% of VO2 max
• High range
– 90% of max heart rate
– 85-90% of VO2max
Thermal stress and exercise
Impact of duration of exercise
180
heart rate (BPM)
160
140
120
Stroke Volume (ml/beat)
100
cardiac output (%)
80
60
0
20
40
60
80
Duration of exercise ( min)
100
Rowell LR Ann Rev Physiol 54:75,1976
Rowell LR. Ann Rev Physiol 54:75,1976
Rowell LR. Ann Rev Physiol 54:75,1976