Cardiovascular System
• Composed of blood
, the heart
, and vasculatur e within which blood is pumped throughout the body a) Pulmonary Circulation
9 Concerning blood flow to, within and from the lungs b) Systemic Circulation
9 Concerning blood flow to, within and from the remainder of the body
9 Consists of tissue/organ specific circulation beds
(ex: renal, hepatic, skeletal muscle, etc.)
Figure 15.3a
Objectives
• Review of anatomy & blood flow
• Systemic and localized (within the heart) blood flow & blood pressure a) Rest, exercise & recovery
• CV regulation & integration
• Functional capacity of CV system
• Adaptations to exercise
Figure 15.1
Blood
• Water, clotting proteins, transport proteins, lipoproteins, glucose, FA, antibodies, waste products
•
Plasma
– the liquid component of blood & all of it’s non-cellular content
55% of whole blood (0.3ml O
2
)
<1% of whole blood
Hematocrit: 45% of whole blood (19.7ml
O
2
, 15g Hb)
1

• Blood volume ~ 5 L, but varies with: a) Body size b) Endurance training c) Exposure to extreme environments
• % distribution at rest
Figure 15.4
Arterial BP Classifications
Hemodynamics – BF & Resistance
• Pressure a) Blood flows from high → low pressure
• Resistance a) Length of the vessel b) Viscosity of the blood c) Radius of the vessel
9 A small change in vessel diameter can have a dramatic impact on resistance!
Resistance =
Length x viscosity
Radius 4
Blood Pressure
• Arterial blood pressure – reflects the combined effects of arterial blood flow per minute & the resistance offered by the peripheral vasculature
BP = Cardiac Output x Total Peripheral Resistance a) Systolic BP
9 Estimate of the work of the heart and the force that blood exerts on the arterial wall during ventricular systole b) Diastolic BP
9 Indicates the ease with which blood flows from the arterioles into the capillaries
9 Peripheral resistance
Hypertension
• Chronically elevated arterial BP
> 140 mmHg systolic
> 90 mmHg diastolic
• Treatment a) Exercise b) Drug therapy
2

Blood Pressure
(cont.) c) Mean Arterial Pressure – the average force exerted by the blood against the arterial walls during the entire cardiac cycle
MAP = Diastolic BP + [0.33(Systolic BP – Diastolic BP)] d) Relationship between BP, Cardiac Output & TPR
Cardiac Output = MAP / TPR
TPR = MAP / Cardiac Output
Blood Flow Continuum
• Arteries, arterial BP & arterioles
• Capillaries:
EXERCISE
REST
Blood Flow Continuum
• Venous system – serves as blood reservoirs
• Skeletal muscle pumps & venous pooling a) Application of an active cool down
Figure 15.5C
BF & Pressure in the Systemic
Figure 15.7
BP Response to Exercise
•
Resistance exercise
: a) Straining compresses vessels b) TPR ↑ c) Sympathetic nervous system activity, cardiac output, and MAP increase in attempt to restore muscle BF
Heavy resistance training intensifies the BP response
3

BP Response to Exercise
(cont.)
•
Graded Exercise
: a) Systolic pressure ↑ with increases in workload b) There is a linear relationship between workload and systolic BP c) Diastolic pressure remains fairly constant
BP Response to Exercise
(cont.)
• Upper Body Exercise a) Resistance to flow is increased with upper body exercise b) Smaller vessels in upper body compress more easily
• Recovery BP a) Following endurance exercise, there is a hypotensive response b) BP temporarily falls below normal resting values
The Heart’s Blood Supply
• Coronary circulation: a) Right and left coronary arteries branch off the upper ascending aorta b) RCA supplies predominantly the right atrium and ventricle c) LCA supplies the left atrium and ventricle and a small portion of the right ventricle
Myocardial O
2
Use
• At rest, myocardium extracts ~ 70–80% available
O
2 from the coronary vessels
• During exercise flow must increase to meet O
2 demand a) Flow may increase 5–7 times
• Vasodilation of the coronary vessels ↑ due to: a) Adenosine (byproduct of ATP breakdown) b) Hypoxia c) Sympathetic nervous system hormones
Measurement of Myocardial Work
• Rate Pressure Product:
Systolic BP x HR = RPP
• Myocardial Metabolism – reliant upon energy released from aerobic metabolism a) Myocardium has a significantly higher mitochondrial density compared to skeletal muscle
• Allows the heart to utilize available substrates depending on activity
Figure 15.13
4

Intrinsic Regulation
Figure 15.14
Time sequence (seconds) for electrical impulse transmission
Measuring Electrical Activity
Electrocardiogram (ECG or EKG)
Figure
16.1
Measuring Electrical Activity
Electrocardiogram (ECG or EKG)
5

Extrinsic Regulation
• Elicit changes in HR rapidly through nerves that directly supply the heart & chemical messengers that circulate in blood
•
Sympathetic
&
Parasympathetic
Neural Input
Extrinsic Regulation
(cont.)
• Sympathetic neural input: a) Localized – Stimulation of cardioaccelerator nerves causes the release of the catecholamines epinephrine
& norepinephrine
9 Accelerate SA node depolarization which increases HR
(chronotropic effect)
9 Increases contractility (inotropic effect) b) Systemically – Stimulation produces vasoconstriction (except coronary vasculature)
9 Release of norepinephrine by adrenergic fibers causes vasoconstriction
9 Vasomotor tone
Extrinsic Regulation
(cont.)
• Parasympathetic neural input: a) Localized – Stimulation of vagus nerves causes release of the neurohormone acetylcholine which slows sinus discharge & therefore HR
9 Slows sinus discharge & therefore ↓ HR
9 No effect on contractility
Figure 16.3
Rapid adjustments
(feed-forward
mechanisms) with the onset of exercise
Central Command Exercise Anticipation
Figure 16.6
Figure 16.10
6

Peripheral Input
•
Chemoreceptors: monitor metabolites, blood gases
•
Mechanoreceptors: monitor movement and pressure
•
Baroreceptors: monitor blood pressure in arteries a) Aortic arch & carotid sinus
Distribution of BF during Exercise
Local Factors within the Muscle
• Autoregulatory mechanisms allow for ↑ blood flow, ↑ blood volume with only a small increase in velocity, and ↑ effective surface area for gas & nutrient exchange a) Vasodilation induced by:
9 ↑ blood flow
9 ↑ temperature
9 ↑ CO2
9 ↑ acidity
9 ↑ adenosine, K + & Mg 2+
9 ↑ NO
Figure 16.7
Nitric Oxide
Hormonal Factors
• Adrenal medulla releases: a) Larger amounts of epinephrine and smaller amounts of norepinephrine b) Cause vasoconstriction (except in coronary & skeletal muscle)
• Minor role during exercise
7

Cardiac Output (Q)
• Q = HR x SV
• Methods of Measuring Q a) Direct Fick = (VO
2 ml·min -1 /a-vo
2 difference) x 100
Cardiac Output (Q)
• Q = HR x SV
• Methods of Measuring Q a) Direct Fick = (VO
2 b) Indicator dilution ml·min -1 /a-vo
2 difference) x 100 c) CO
2 rebreathing
• Q at rest a) Values vary depending upon:
9 Emotional state (central command via cardioaccelerator nerves & nerves modulating arterial resistance)
9 Posture b) Average male (70kg) ~ 5L · min -1 c) Average female (56kg) ~ 4L · min -1
~ 25% lower in females
• Untrained vs. Endurance trained characteristics of Q at rest
: a) Variation in resting HR
Rest
Q = HR x SV
Untrained: 5000 mL·min -1 = 70 b·min -1 x 71 mL·min -1
Trained: 5000 mL·min -1 = 50 b·min -1 x 100 mL·min -1 b) Mechanisms:
9 Increased vagal tone (parasympathetic) w/decreased sympathetic drive
9 Increased blood volume
9 Increased myocardial contractility and compliance of left ventricle
• Untrained (UT) vs. Endurance trained (ET) characteristics of Q during exercise
: a) Both UT & ET Q ↑ rapidly with onset of exercise
9 Subsequently a more gradual rise to meet exercise metabolic demands b) Variation between groups often observed as intensity ↑
Untrained:
Trained:
Maximal Exercise
Q = HR x
22,000 mL = 195 b·min -1 x
35,000 mL = 195 b·min -1 x
SV
113 mL·min -1
179 mL·min -1
• Mechanisms: a) Enhanced cardiac filling in diastole ( preload
) & a more forceful ejection caused by an ↑ in end diastolic volume (
EDV)
9 Starling’s Law: the greater the stretch, the more forceful the contraction ( contractility
) b) Greater systolic emptying
9 greater systolic ejection overcomes exercise-induced arterial blood pressures ( afterload ) c) Expanded blood volume & reduced peripheral resistance in tissues in ET individuals
8

CV Drift w/ Prolonged Exercise
• ↓ SV and coinciding a gradual ↑ in HR
• Proposed mechanisms: a) Progressive H tissues
2
O loss and a fluid shift from plasma to
9 Drop in PV decreases central venous cardiac filling pressure b) Increased core temperature c) Progressive increase in HR with CV drift during exercise ↓ EDV, subsequently reducing SV
Blood Flow Distribution @ Rest
Figure 17.3
Blood Flow Distribution & Exercise
1. Hormonal vascular regulation
2. Local metabolic conditions
Q & O
2
Transport
• Arterial blood carries ~ 200mL of O
2 blood per L of
• Resting conditions: a) If Q @ rest ~ 5L·min -1 , then 1000mL of O
2 available to the body each minute would be b) Resting oxygen consumption (VO
2
300mL·min -1
) ~ 250 to c) Leaves ~ 750mL of oxygen returning to the heart unused
Q & O
2
Transport
(cont.)
• Exercise conditions: a) Even during max exercise, Hb saturation remains nearly complete, so each L of blood carries ~ 200mL of O2
9 Ex: a max exercise Q of 16L x 200mLO
2
·L -1 ~ 3200mL b) Debate exists as to the real cause of a VO plateau
2 max
9 Q
9 O
2 extraction at the tissues
9 O
2 delivery
Central
Peripheral
Q & VO
2 max Association
Figure 17.4
9

O
2
Extraction: a-vO
2
Difference
• Exercise oxygen consumption increases by: a) Increased cardiac output b) Greater use of the O
2
9 Expanding a-vO
2 already carried by the blood difference
VO
2
= Q x a-vO
2 difference
From Rest to Exercise
Figure 17.5
• Factors affecting a-vO
2 exercise: difference during a) Central – diversion of blood flow to working tissues b) Peripheral
9 Increased skeletal muscle microcirculation increases extraction
9 Increase in capillary to fiber ratio
9 Cells ability to regenerate ATP aerobically
9 Increased # and size of mitochondria
9 Increased aerobic enzyme concentration
Cardiac Hypertrophy
Figure 21.7
Plasma Volume Expansion
• Up to 20% increase in PV (without changes in
[RBC]) after 3 to 6 aerobic exercise sessions
• Mechanisms: a) Directly related to increased synthesis and retention of plasma albumin
• Increased PV: a) Increases EDV, SV, O
2 transport, & temperature regulation during exercise
10

Heart Rate
Stroke
Volume
Figure 21.9
Cardiac
Output
Figure 21.10
a-v O
2 difference
Figure 21.11
Blood Flow Distribution
• BF shunting toward Type I fibers (oxidative) during submaximal exercise
• Better distribution from non-active areas
• Enlarged cross-sectional area of arteries, veins & capillary beds
• Myocardial BF: a) Increased perfusion capabilities b) Mitochondrial mass & density increased
• Reduction in BP
Figure 21.6
Figure 21.12
11