Download Hypertension and Exercise

Hypertension and Exercise
due to hardening of arteries, excessive
peripheral resistance (enhanced nervous
tone or kidney malfunction)
 pressures of 250-300 for systole and >90
mm Hg for diastole
 aerobic exercise can modestly lower BP
 extent is unclear, but beneficial for
normotensive and hypertensive individuals

resting BP also lowers significantly,
possibly due to higher circulating
catecholamines after training 
decreased peripheral resistance to blood
flow, decreasing BP
 exercise may enhance sodium elimination
by kidneys

BP and Exercise
static and dynamic resistance exercise will
increase peripheral resistance to BF
 even at light loads, e.g., 25% 1RM
 potential for harm for those with heart and
vascular disease
 chronic resistance training does not
appear to increase resting BP, and can
blunt the response to a single bout
Steady State exercise
dilation of blood vessels in working
muscles will decrease TPR, increase BF
to working muscle
 may see a small rise in systole, 140-160
mm Hg, then levels off
 diastole may increase or decrease 10 mm
Hg, or remain unchanged

Graded Exercise
Increase in systole, mean, and diastole
with increase in Q
 greatest changes are in systole, diastole
may change only ~12%

Arm Exercise
systole and diastole significantly higher
than with leg exercise, even at same
intensity
 may be due to smaller vasculature,
increased resistance to flow
 heart will have to work harder

Recovery
after submax exercise, systolic pressure
can be temporarily (2-3 hrs) depressed
below pre-exercise levels
 B/c TPR remains low after exercise

Heart Blood Supply
has its own blood supply
 has dense capillary network
 @ rest, normal BF to myocardium is ~200250 ml, 5% of Q

Myocardial oxygen utilization
@ rest, 70-80% of oxygen is extracted
from the blood in coronary vessels
 in other tissues, @rest, ~25% of the
oxygen is extracted
 coronary BF will increase during exercise
to meet myocardial oxygen requirements,
can increase 4-6X above resting levels

Two ways to increase myocardial
BF
1. Increased myocardial metabolism causes
dilation of coronary vessels
2. Increased aortic pressure forces a larger
amount of blood into coronary circulation
 coronary BF is 2.5X greater during diastole than
during systole
 heart has limited ability to generate energy
anaerobically
Myocardial Metabolism
has a 3X higher oxidative capacity than
skeletal muscle
 have the greatest mitochondrial density,
well adapted for fat catabolism as primary
source of ATP resynthesis
 Figure 15-9 this is the substrate use of the
heart at rest, during exercise, and during
recovery


glucose, fatty acids, and lactate provide
energy for the heart
 during heavy exercise, with a large
concentration of lactic acid in the blood, the
heart can use lactate for 50% of its total
energy
 during prolonged submax activity, 70% of
energy comes from fatty acids
 metabolic patterns are similar for TR and
UNTR, but TR have a greater contribution of
fats to the total energy requirement
Rate-Pressure Product:
Estimate of myocardial work
increase in myocardial contractility and heart
rate will increase the demand for oxygen
 estimate myocardial workload and oxygen
consumption, use product of peak systole
and heart rate
 index of relative cardiac work
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called the double product, or rate-pressure
product
highly related to myocardial oxygen
consumption and coronary BF
RPP = SBP X HR
with training in cardiac patients, a higher RPP
can be achieved before ischemic symptoms
appear
this measure is used in coronary heart disease
patients
Blood Distribution
rapid adjustments are necessary during
exercise, possible by constriction and
dilation of smooth muscular bands of
arterioles
 additionally, venous capacitance
vessels stiffen
 can rapidly redistribute blood to meet
metabolic demand of exercise, while
preserving adequate flow and pressure
throughout the system

Regulation of Blood Flow
changing diameter of blood vessels is
most important factor regulating regional
flow
 resistance to flow changes with vessel
diameter (to the fourth power)
 reducing diameter by 1/2, causes flow to
decrease 16X

Local Factors
1 in 30-40 capillaries is open at rest
opening capillaries during exercise will
1. Increase muscle blood flow
2. Due to the increase in channels,
increased blood volume can be delivered
with only small increases in velocity of flow
3. Enhanced vascularization will increased
the effective surface for exchange
between blood and muscle cells
 local factors can increase the dilation of
arterioles and precapillary sphinchters
Local Factors
1. Decrease in oxygen supply
2. Increase in temperature
3. increase in carbon dioxide
4. increase in acidity
5. increase in adenosine
6. increase in ions of magnesium and potassium
 these are autoregulatory mechanisms
Neural factors
sympathetic and to small extent,
parasympathetic portions of autonomic
NS provide a central vascular control
 muscles contain sensory nerve fibers
which are sensitive to substances
released in local tissue during exercise:
causes vascular responses
 central regulation ensures that the area
with the most need for oxygen gets the
most blood flow

norepinephrine is the general
vasoconstrictor, and is released at
certain sympathetic nerve fibers
(adrenergic fibers)
 other sympathetic fibers can release
ACH, causing vasodilation (cholinergic
fibers)
 dilation of blood vessels is due more to
a reduction in vasomotor tone than to
an increase in action of either
sympathetic or parasympathetic dilator
fibers

Hormonal Factors
sympathetic nerves terminate in the
medullary portion of the adrenal gland
 with activation, epi is released in large
quantities, norepi in small quantities
 epi and norepi cause a constrictor
response, except in blood vessels of the
heart an skeletal muscle

during exercise, hormonal control is minor
in the control of regional BF
 BF is decreased to the skin, gut, spleen,
liver, and kidneys as a general response

Integrated Response in
Exercise
Nerve centers above the medullary region
are active both before and at the onset of
exercise to cause increases in the rate
and contractility of the heart, as well as to
change regional blood flow
 sympathetic cholinergic outflow plus local
metabolic factors acting on
chemosensitive nerves and on blood
vessels cause dilation in active muscles

this reduces peripheral resistance,
allowing for greater blood flow
 constriction adjustments will then occur
in less active tissues as exercise
continues, so that perfusion pressure
can be eliminated
factors influencing venous return:
1. action of muscle and ventilatory pumps
2. stiffening of the veins
3. increase in venous tone with an
increase in Q

Cardiac Output
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Q = HR X SV
primary indicator of the functional capacity
of the circulation to meet the demands of
PA
Four methods to determine Q:
 Direct Fick
 Q = O2 consumed/ (a-v)O2 Indicator
Dilution: examine an indicator dilution
curve
 CO2 rebreathing, indirect Fick
 Q = CO2 production/ (v-a)CO2 X 100
 Impedance
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SV
Preload
Afterload
Contractility
BP
Systemic Vascular Resistance (SVR)
Can index the values to body size