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26/02/2013
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Cardiac Output and Blood Pressure
Characteristics of Cardiac Ejection
Measurement of Cardiac Output
Blood pressure
Measurement of Blood Pressure
Cardiac Ejection
Quantity of blood ejected from the heart each cardiac cycle
Copyright © 2005 Pearson Education, Inc., Publishing as Benjamin Cummings
Ventricular contraction
Valves
NB: Ejection fraction: % EDV ejected with each stroke (approx. 65%).
A good index of ventricular function
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Turbulence vs. Laminarity
Blood normally flows in a
laminar fashion
Parabolic
flow
Blood flow is
steady/continuous
When flow becomes
turbulent a sound can be
heard
Sherwood fig. 9-19, p.319
Significance of Heart Sounds
1st - Closure of AV valves
2nd - Closure of SL valves
3rd - end of rapid filling
4th - the atrial sound
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Murmurs:
Valve malfunction
Stenotic valve
Insufficient valve-
Circulatory dynamics in valve disease
Aortic Stenosis and Aortic Regurgitation
Left ventricular hypertrophy
Increase in blood volume
Mitral Stenosis and Mitral Regurgitation
Pulmonary edema
Enlarged left atrium, atrial fibrillation
Increase in blood volume
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Measurement of Cardiac Output
Fick principle
the amount of a substance taken up by an organ per unit
time is equal to the product of blood flow and the difference
in the concentration of the substance in the
arterial and venous blood
CO = oxygen uptake (ml.min-1) / (CaO2- CvO2)
CvO2 = oxygen concentration in venous blood
CaO2 = oxygen concentration in arterial blood
Fick Principle- indirect
Oxygen consumption
Consumed oxygen calculated by assumed
oxygen consumption index
Indicator dilution
CO = I (mg) x 60 / C (mg/L) x t (sec)
Gases
Dyes
Temperature
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Measurement of Cardiac Output Cont.
Thoracic inductance
Change in stroke volume
dependent on stretch in
thorax
Thoracic impedance
Movement of blood alters
the electrical impedance
Calculate beat–to–beat CO
SV (ml) = L2/ Z2 x dZ/dt x t x 135
Imaging
Echocardiogram
Doppler
MRI
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Blood Pressure
The force exerted on the walls of blood
vessels by the blood
Depends on:
the volume of blood
compliance of vessel
Result of contraction
and relaxation of
heart
Systolic Arterial Pressure
maximum pressure exerted in arteries
when blood pumped into them during systole
(120mmHg)
Ejection period
Afterload
Exercise
Aortic compliance
Non-compliance
Ejection velocity
Stenosis
Exercise
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Diastolic Arterial Pressure
minimum pressure exerted in the arteries when
blood is draining off during diastole
(80mmHg)
Total Peripheral
Resistance
Heart Rate
Aerobic exercise
Resistance exercise
Arterial Pulse Wave
Systolic pressure: on ventricular contraction
Diastolic Pressure: on ventricular relaxation
Dicrotic notch: Rebound wave or “echo’ of valve closure
Sherwood Fig. 10-7, p. 350
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Mean vs. Pulse Pressure
Pulse pressure- pulse in an artery
Mean Arterial Pressure- main driving force of blood flow
PP = SBP-DBP
Average pressure
Regulated pressure
MAP = 1/3SBP + 2/3DBP
MAP = 1/3PP + DBP
During exercise MAP =
1/2PP + DBP
Blood Pressure: Mean Arterial Pressure
MAP = driving force of blood flow
Flow = ∆Pressure/ Resistance
MAP < normal
Hypotension
Inadequate blood flow to tissues
MAP > normal
Hypertension
Stress on heart and walls of blood vessels
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Central Venous Pressure
Pressure in large veins leading back to
heart
Pressure gradient
drives blood to
heart
Decrease in venous
pressure decreases
venous return
Sherwood Fig. 10-27, p. 364
Central vs. Peripheral Pulse Pressure
Longitudinal resistance
Arterioles =
high resistance
Veins =
low resistance
Sherwood Fig 10.9, p.345
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Central Venous vs.
Peripheral Pulse Pressure
Peripheral resistance
Changes in TPR
Resistance vs. Aerobic exercise
Non-compliance
Arterial system
Venous system
Measurement of Blood Pressure
Intra-arterial catheters
Palpation
Auscultation
Oscillometry
Application tonometry
Sherwood Fig. 10-8a, p. 344
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BP measurement: Auscultation
Fig. 10-8, p. 351
BP measurement: Oscillometry
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BP measurement: Tonometry
Summary
Cardiac Ejection
Turbulence
Heart sounds
Murmurs
Measurement of CO
Blood Pressure
Measurement of Blood Pressure
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