Transcript Review of EKG’s

Blood Pressure—
The driving force
• Blood pressure (hydrostatic
pressure) is the force
exerted by the blood against
any unit area of vessel wall.
• Measured in millimeters of
mercury (mmHg). A pressure
of 100 mmHg means the
force of blood was sufficient
to push a column of mercury
100mm high.
• All vessels have it – but
we’re usually addressing
arteries when we refer to it.
Stephen Hales
1733
Blood Pressure Profile in the Circulatory
System
20
0
Systemic
Pulmonary
Circulatory pressure- averages 100mmHg
Arterial blood pressure-100-35mmHg
Capillary pressure- 35mmHg at beginning and 10-15mmHg at end
Venous pressure-15-0mmHg
•Large pressure drop across the arteriolar-capillary junction
Pulmonary viens
Capillaries
Large viens
40
Small viens
60
Venules
80
Capillaries
Pressure
(mmHg)
100
Pulmonary arteries
120
Measurement of Blood Pressure
• Auscultation:
– Art of listening.
• Laminar flow:
– Normal blood flow.
– Blood in the central axial
stream moves faster than
blood flowing closer to the
artery wall.
• Smooth and silent.
• Turbulent flow and
vibrations produced in the
artery when cuff pressure
is greater than diastolic
pressure and lower than
systolic pressure.
Measurement of Blood Pressure
(continued)
• Blood pressure cuff is
inflated above systolic
pressure, occluding the
artery.
• As cuff pressure is
lowered, the blood will
flow only when systolic
pressure is above cuff
pressure, producing the
sounds of Korotkoff.
• Korotkoff sounds will be
heard until cuff pressure
equals diastolic pressure,
causing the sounds to
disappear.
Measurement of Blood Pressure
(continued)
• Different phases in
measurement of blood
pressure are identified
on the basis of the
quality of the Korotkoff
sounds.
• Average arterial BP is
120/80 mm Hg.
• Average pulmonary BP
is 22/8 mm Hg.
Central Venous Pressure
•
Pressure in the right atrium is called
central venous pressure.
•
determined by the balance of the heart
pumping blood out of the right atrium
and flow of blood from the large veins
into the right atrium.
•
normally 0 mmHg, but can be as high
as 20-30 mmHg.
More vigorous heart contraction (lower
CVP).
Less heart contraction (higher CVP)
Factors that increase CVP:
increased blood volume
increased venous tone
dilation of arterioles
decreased cardiac function
Skeletal and respiratory pumps
•
•
•
Figure 15-9; Guyton and Hall
Your lab today and CVP
• Not holding breath—
• Raising arm- should
take smaller elevation
of arm for the blood in
your hand veins to
over come the
somewhat collapsed
veins in arm
Blood pressure
here becomes
greater and over
comes pressure in
downstream veins
Your lab today and CVP
• Holding valsalva
maneuver —
• Increases peripheral
venous pressure
(simulating elevated
CVP)
• Raising arm- should take
a higher elevation of arm
for the blood in your hand
veins to over come the
very collapsed veins in
chest
Blood pressure
here becomes
greater and over
comes pressure in
downstream veins
A decrease in blood pressure is detected by
baroreceptors found in the aortic arch and carotid
bodies. Afferent impulses are transmitted through
cranial nerve X and IX, respectively toward the
medulla oblongata for integration.
In the medulla oblongata the decreased rate
of action potentials arriving from cranial nerve
X and IX, stimulates the cardioacceleratory
and vasomotor centers within the medulla
oblongata.
Sympathetic outflow from the medulla
oblongata increases and stimulates
preganglionic cell bodies found at levels
(T1-T6).
The preganglionic cell body
transmits an action potential
through the preganglionic
fiber to the postganglionic
cell body found in the
sympathetic trunk
How is this reflex
arc different if too
much stroke
volume (i.e., too
much pressure) is
detected?
The postganglionic fiber
transmits an action potential to
the conductive fibers of the
heart that leads to increased
heart rate and contractility
Valsalva maneuver
•
•
•
•
•
subject conducts a maximal, forced expiration against a closed glottis and
holding this for at least 10 seconds.
pressure compresses the vessels within the chest.
Aortic compression results in a transient rise in aortic pressure (Phase I), which
causes a reflex bradycardia due to baroreceptor activation. Because the
thoracic vena cava also becomes compressed, venous return to the heart is
compromised, resulting in a large fall in cardiac output.
Peripheral venous pressure is increasing (bulging veins in hand/neck) simulates
elevated CVP; but really CVP is dropping
This leads to a secondary fall in aortic pressure (Phase II), and as aortic
pressure falls, the baroreceptor reflex increases heart rate.
Valsalva
Maneuver
• After several seconds, arterial pressure (both mean and pulse
pressure) is reduced, and heart rate is elevated. When the subject
begins breathing again, the sudden loss of compression on the aorta
can cause a small, transient dip in arterial pressure and further reflex
increase in heart rate (Phase III).
• When compression of the vena cava is removed, venous return
suddenly increases causing a rapid rise in cardiac output several
seconds later which leads to a transient increase in arterial pressure
(Phase IV).
• Arterial pressure overshoots during Phase IV because the systemic
vascular resistance is increased due to sympathetic activation that
occurred during Phase II. Heart rate reflexively decreases during
Phase IV in response to the transient elevation in arterial pressure.
• This can occur during bowel movements, lifting weights, etc.
• “RELEASE PHASE” is the part of the maneuver that can rescue
supraventricular tachycardia.