Exercise: Cardiovascular Function
Michael L. Smith, Ph.D.
Reading:
• Handout on Exercise & Temperature Regulation
• Kladunde: 168-169, 198-205
Study Questions
• Review appropriate study questions after you have done sufficient
studying
Cardiac Output Distribution
Cardiac Output
Sk. Muscle
Renal
Skin
Splanchnic
Heart
Cardiac Output Distribution
20
Blood
Flow
(L/m)
Sk muscle
5
Sk muscle
coronary
renal
splanchnic
brain
Rest
coronary
renal
splanchnic
brain
Max
Exercise
Oxygen Consumption
• VO2 = Oxygen consumption = oxygen uptake
• VO2 = Cardiac output x oxygen extraction
• Is a function of O2 delivery (CO) and extraction (a-v O2 difference)
• Oxygen extraction = a-v O2 difference
• VO2max = Qmax x a-v O2 diff max
Oxygen Uptake Response to Exercise
max
Keys: VO2 will plateau
Oxygen Uptake
or VO2
VO2 max is std measure of
Aerobic fitness
Workload
(Treadmill speed & grade)
Cardiac Output Response to Exercise
Key: Q will plateau,
just like VO2
Cardiac
Output
VO2 and CO increase progressively
with progressive increases in
workload to a maximum. For each,
it plateaus at very high workloads
and this defines the maximum VO2.
Workload
(Treadmill speed & grade)
Venous Return Response to Exercise
Venous
Return
Venous return increases
progressively with progressive
increases in workload to a
maximum and plateaus at very high
workloads.
Key: VR will plateau,
just like Q
Workload
(Treadmill speed & grade)
Venous Return During Exercise
Skeletal Muscle Pump (#1)
 Vasodilation ( SVR)
 Venoconstriction

»

Venous compliance
Respiratory Pump
» Intrathoracic pressure fluxes
Cardiac Output Response to Exercise
Normally: Q is primary limit
To VO2—this is consistent
With this linear relation.
Cardiac
Output
NOTE: X axis is VO2 in this
graph, not treadmill workload,
thus there is not the plateau that
was seen with increases in
relation to workload.
rest
max
Oxygen Consumption
[ or VO2 ]
Stroke Volume Response to Exercise
May occur in high fit individuals
Stroke
Volume
Plateau at submaximal workloads:
WHY?
Workload
(Treadmill speed & grade)
Stroke Volume Response to Exercise
May occur in high fit individuals
Stroke
Volume
Plateau at submaximal workloads:
WHY?
Workload
(Treadmill speed & grade)
Stroke Volume Response to Exercise
What affects stroke volume & how??
• Venous return (skeletal muscle pump, venous compliance, MCFP)
• These factors contribute to the increase in venous return
• The muscle pump is the MOST IMPORTANT FACTOR!!
• Contractility
• Greaded increase in contractility with workload contributes to increases in SV
• Afterload
• Graded DECREASE due to progressive decrease in SVR (muscle vasodilation)
• Heart rate: Progressive increase in HR with workload
• The resulting decreased filling time LIMITS the increase in SV – causes the
plateaus seen on the previous slide
Ventricular
Volume
LV Volumes During Exercise
E
D
V
E
S
V
Workload
Stroke volume (EDV – ESV) increases progressively up to about 60% of
max workload. ESV decreases progressively due primarily to the
increasing contractility and EDV plateaus and decreases at high
workloads due to the decreasing filling time.
Heart Rate Response to Exercise
Heart Rate
Workload
Heart rate increases progressively with progressive increases in workload similarly to cardiac
output to a maximum and plateaus at very high workloads.
Heart Rate Response to Exercise
(Autonomic control)
SNA
PSNA
Workload
Heart rate increases initially mostly due to withdeawal of PSNA. This is the MAIN determinant of increased HR up to HR of about 100-110 bpm. At
higher workloads the increased HR is due more to nicreases in SNA.

Can a heart transplant patient exercise?
If so, how?
Heart rate?
We will discuss in class.
Cardiac Function: Net Effects
How do these change?
• Heart Rate
• preload
• contractility
• afterload
• stroke volume
• ejection fraction
Cardiac Function: Net Effects
How do these change?
• Heart Rate: increases progressively
• preload: increases up to moderate workloads then decreases due to
decreasing filling time
• contractility: increases progressively
•afterload: decreases progressively
• stroke volume: increases progressively then plateaus at high
workloads
• ejection fraction: Increases progressively
Increased contractility
Venoconstriction
Increased MCFP
Decreased SVR
During Exercise, what happens to…

PR Interval

T-P duration

QRS duration

AV nodal conduction velocity

Ejection duration

Duration of isovolumic contraction

Time between Aortic valve opening and closing

Rate of dP/dt of the ventricular pressure

SA Node resting membrane potential
A. Increase
B. Decrease
C. No change
During Exercise, what happens to…

PR Interval B

T-P duration B

QRS duration B

AV nodal conduction velocity A

Ejection duration B

Duration of isovolumic contraction B

Time between Aortic valve opening and closing B

Rate of dP/dt of the ventricular pressure A

SA Node resting membrane potential less negative
A. Increase
B. Decrease
C. No change
SVR Responses to Exercise
Systemic
Vascular
Resistance
What about the following resistances?
Renal
Splanchnic
Coronary
Cutaneous
Skeletal muscle
Workload
SVR Responses to Exercise
Systemic
Vascular
Resistance
What about the following resistances?
Renal increase
Splanchnic increase
Coronary decrease
Cutaneous depends on temp
regulation – decreased when
tempregulation kicks in
Skeletal muscle decrease
Workload
Resistances at near Maximum Exercise
[Hypothetical Examples]
Blood flow (L/m)
rest
Ex
Pressure Gradient
rest
Ex
Resistance
rest
Ex
Systemic
5
20
100
120
20
6
Renal
1
0.2
100
120
100
600
Splanchnic
0.8
0.2
100
120
125
600
Coronary
0.5
3.0
100
120
200
40
Cutaneous
0.3
??
100
120
333
???
Skeletal muscle 0.8
14
100
120
125
8.5
What happens to urine production?
Pressures
Arterial Pressure Responses to Exercise
S
M
D
Workload (VO2)
This represents the normal response. In patients with hypertension, the diastolic
decrease does not occur and will actually increase (a sign of pathology)
Net CV Effects during Exercise
ANS Effects:
↑ Sympathetic Nerve Activity
↓ Parasympathetic Nerve Activity
Ohm’s Law:
DP = Q x R
DP = (HR x SV) x R
DP = (HR x [EDV-ESV]) x R
Net CV Effects during Exercise
ANS Effects:
↑ Sympathetic Nerve Activity
↓ Parasympathetic Nerve Activity
Ohm’s Law:
DP = Q x R
DP = (HR x SV) x R
DP = (↑HR x [↑EDV- ↓ESV]) x ↓R
Oxygen Extraction During Exercise
(a-v O2 difference)
Oxygen
Extraction
(A-V O2 diff)
Workload
Blood O2 Content During Graded Exercise
Arterial
Oxygen
Content
Venous
Workload
Based on this figure, are the lungs limiting maximal VO2? Why?
Ventilatory Threshold
Exercise workload at which ventilation
and lactate accumulation begin to
increase at progressively greater rate
Ventilatory (lactate) Threshold
Ventilation
threshold (breakpoint)
Ventilation
Drives for ventilation:
Below V threshold
Central command from motor cortex
Reflex from muscles & tendons
Above V threshold
Additional contribution from acidosis
stimulating chemoreceptors
Workload (VO2)
What is the acid-base state?
Ventilatory (lactate) Threshold
What happens to the following at workloads higher than
the ventilatory threshold?
•
•
•
•
•
•
•
PaCO2
PaO2
arterial oxygen saturation
plasma lactate
muscle pH
plasma pH
plasma bicarbonate
Ventilatory (lactate) Threshold
What happens to the following at workloads higher than
the ventilatory threshold?
•
•
•
•
•
•
•
PaCO2 decreased
PaO2 increased due to hyperventilation
arterial oxygen saturation increased
plasma lactate increased
muscle pH decreased
plasma pH decreased
plasma bicarbonate decreased
Acid-Base state during Exercise
below vent threshold
Above vent threshold
Endurance Training Effects
Endurance Training Effects
• Heart rate
-- Reduced at rest
-- Reduced at any given submaximal absolute work
-- Similar at any given relative workload (% of max)
-- Similar maximal heart rate (~220 - age)
• Stroke volume
-- Increased at rest
-- Increased at all workloads
Training Effects: Heart Rate
70% max
HR
trained
70% max
Note: HR are equal at same
relative workload (% of max)
VO2
Training Effects: Heart Rate
Decreased resting heart rate:
Increased parasympathetic nerve activity and effect
Often some reduction in sympathetic activity
Can be some reduction in intrinsic heart rate (intrinsic rate of SA Node)
Same effects at ANY submaximal workload!!
Endurance Training Effects
• Cardiac output (Q)
-- Similar at rest and at any given submaximal workload
-- High workloads (above the untrained maximum)
Q increases progressively up to max
• Oxygen extraction
-- Greater extraction at submaximal and maximal workloads
Training Effects: Cardiac Output
Training effect
Q
VO2
Max
(UT)
Max
(T)
Endurance Training Effects
• Systemic vascular resistance
-- Similar at rest
-- greater decrease at progressive workloads
-- much less at maximal workloads
Why??
Distribution of cardiac output
-- The greater increases in Q at max go to the
skeletal muscle and the heart
Endurance Training Effects
• Blood volume
--up to 20% expansion of plasma volume
•Cardiac chamber size
--increased ventricular chamber size at rest and exercise
• Cardiac hypertrophy
--eccentric hypertrophy=proportional increase in chamber to
increase in mass (wall thickness)
--concentric hypertrophy= mostly an increase in mass (e.g. HTN)
Types of Hypertrophy
With regular dynamic exercise, an eccentric hypertrophy occurs which is
normal. KEY: The chamber increases in proportion to the wall thickness.
WHEREAS, with hypertension or aortic stenosis, a concentric hypertrophy
will occur resulting in a much thicker wall with minimal changes in the
chamber.
Endurance Training Effects
• Cardiac work (decreased…)
• Rate x Pressure product
= HR x MAP (or SAP)
Decreased at rest and submax work
(Know this!!)
• Capillary density
-- increased…….
Where?
What are effects on diffusion distance, O2 delivery etc.??
Endurance Training Benefits: The Heart??
• Decreased resting HR (decreased RPP)
• decreased work of heart at rest and any workload
• Increased capillary density
• reduced deliterious effects of ischemia
• Increased resting PSNA
• protection against ventricular dysrhythmias