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Chapter 8
Heart and Circulation
Figure 8.1 Basic structure of the heart. RA is the right atrium, RV is the right
ventricle; LA is the left atrium, and LV is the left ventricle. Basic pacing rates are
shown.
Deoxygenated
blood
Oxygenated
blood
Upper body
Right
atrium
Lung
Right
ventricle
Left
atrium
Left
ventricle
Lower body
Figure 8.2 The simplified circulatory system. The blood is delivered from the right
ventricle to the lung. The oxygenated blood from the lung is then returned to the left atrium
before being sent throughout the body from the left ventricle. Deoxygenated blood from the
body flows back to the right atrium and the cycle repeats.
Figure 8.3 In the top figure, the electrocardiogram (ECG) initiates the cardiac cycle. The
cardiac sounds are also shown. The bottom figure shows that ejection occurs when the
pressure in the left ventricle exceeds that in the arteries.
Event
Characteristics
Duration at 75 bpm
(0.8 second cycle)
Atrial diastole
Ventricular diastole
AV valves opened.
Semilunar valves close.
Ventricular filling.
0.4 seconds
Atrial systole
Ventricular diastole
AV valves open.
Semilunar valves closed.
Ventricular filling.
0.1 seconds
Atrial diastole
Ventricular systole
AV valves closed.
Semilunar valves open.
0.3 seconds
Blood pumped into aorta
and pulmonary artery.
Table 8.1 Duration and characteristics of each major event in the cardiac cycle.
Figure 8.4 A disposable surface electrode. A typical surface electrode used for
ECG recording is made of Ag/AgCl. The electrodes are attached to the patients’
skin and can be easily removed.
I
aVR
V4
V1
(a)
aVR
I
V1
V4
(b)
I
V1
aVR
V4
(c)
Figure 8.5 The electrocardiogram. (a) The normal ECG. (b) 1st degree AV block in which
the delay from the P wave to the Q wave is lengthened. (c) acute inferior myocardial
infarction (lack of blood flow to heart muscle, which causes tissue to die), in which the S–T
sement is depressed.
I
aVR
V1
V4
(d)
I
V1
aVR
V4
(e)
I
aVR
V1
V4
(f)
Figure 8.5 The electrocardiogram. (d) right atrial hypertrophy (increase in muscle mass of
the atria), in which V4 is large. (e) ventricular tachycardia (faster than normal heart rate)
with clear AV dissociation. (f) Wolff–Parkinson–White syndrome with atrial fibrillation.
RA
LA
Resistors
and switch
Monitor
RL
LL
Amp
ADC
Signal
processor
Printer
Storage
Figure 8.6 Block diagram of an electrocardiograph. The normal locations for
surface electrodes are right arm (RA), right leg (RL), left arm (LA), and left leg
(LL). Physicians usually attach several electrodes on the chest of the patients as
well.
Va
+
0.01 uF
22k
4.7k
10k
47k
10k
-
-
22k
150k
3.3M
1 uF
+
+
Vb
+
Vo
10k
50k
S1
3.3M
Figure 8.7 A circuit of an ECG amplifier. The instrumentation amplifier, located on the left of
the circuit provides a high input impedance and has a gain of 25 in the dc-coupled stages.
(From Webster, J. G. (ed.) Medical Instrumentation: Application and Design. 3rd ed. Copyright © 1998
by John Wiley & Sons. Reprinted by permission of John Wiley & Sons.)
I  II  III  0
Figure 8.8 Einthoven’s triangle. Lead I is from RA to LA, lead II is from RA to
LL, and lead III is from LA to LL.
Infusion
Balloon
Catheter
Pressure
port
Pressure
sensor
Figure 8.9. A system for cardiac pressure and flow measurement. The pressure is
usually measured with a catheter placed in the right side of the heart. An external
strain gage pressure sensor is also shown. (Adapted from Orth, J. L. 1995. System for
calculating compliance and cardiac hemodynamic parameters, US Patent, 5,423,323.)
Variables
Mean (SD)
Weight (kg)
70
Cardiac output (mL/s)
110
Heart rate (min–1)
76
Mean velocity, ascending aorta (mm/s) 16
LV end-diastolic volume (mL)
125 (31)
LV end-systolic volume (mL)
42 (17)
LV stroke volume (mL)
82 (20)
LV ejection fraction
0.67 (0.11)
LV mean wall thickness (mm)
10.9 (2.0)
Cardiac output (CO) = heart rate (HR)  stroke volume (SV)
Table 8.2 Some physiological variables. The data presented in this table are the
average values of a group of subjects.
CO 
|Q|
t1
 b cb  | Tb (t ) | dt
(m 3/s)
0
Q = heat injected in joules
b = density of the blood in kg/m3
cb = specific heat of the blood in J/(kgK)
Tb = temperature gradient function
Figure 8.10 The relationship of the temperature gradient and time.
Adapted from Baker, P. D., Orr, J., Westenskow, D. R. and Johnson, R. W. Method and apparatus for
producing thermodilution cardiac output measurements utilizing a neural network, US Patent, 5,579,778.
Figure 8.11 Simultaneous recording of motion mode (M-mode) and two dimensional
echocardiograms. The arrows on the right image indicates the position of the ultrasound beam
from which the M-mode recording was made. LVW = left ventricular wall, LV = left
ventricle, LA = left atrium, RV = right ventricle. (From College of Veterinary Medicine, Univ. of
Tennessee. 2003. M-Mode Echocardiography [Online] www.vet.utk.edu/)
(a)
(b)
(c)
Figure 8.12 2-D echocardiography of the long axis view of the right ventricle
(RV): (a) the ultrasonic beam angle through the heart, (b) the cross-sectional
diagram of the image and (c) the actual 2-D image. TV = tricuspid valve, AML =
anterior mitral leaflet. (Adapted from Rafferty, T. 1992. Transesophageal two-dimensional
echocardiography: www.gasnet.org/echomanual/html/2-d_echo.html).
M-mode echocardiography
Two-dimensional echocardiography
Excellent time resolution
Anatomical relationships
Accurate dimensional measurements Shape information
Timing of events against other
parameters
Lateral vectors of motion
Easy storage and retrieval
Easier to understand
Table 8.2a Relative advantages of echocardiographic examination techniques.
(Adapted from Roelandt, 1983)
Sound
Origin
1st sound
Closure of mitral and tricuspid valves
2nd sound
Closure of aortic and pulmonary valves
3rd sound
Rapid ventricular filling in early diastole
4th sound
Ventricular filling due to atrial contraction
Table 8.3 The heart sounds. The 1st and 2nd heart sounds are most prominent.
Characteristic
Type of murmur
Valve disorder
Systolic murmur
1st HSmurmur2nd HS
Whistling
Swishing
Stenotic semilunar valve
Insufficient AV valve
Diastolic murmur
2nd HSmurmur1st HS
Whistling
Swishing
Stenotic AV valve
Insufficient semilunar valve
Table 8.4 Timing of murmurs. For example, if the physician hears the 1st heart
sound, a swishing sound, and then the 2nd heart sound, the patient likely suffers
from AV valve insufficiency.
Figure 8.13 A stethoscope with bell and diaphragm modes. (Adapted from Mohrin, C. M., 1995.
Stethoscope. US Patent, 5,389,747. )
R
Electrode
C
-
V
+
Piezoelectric
sensor
Figure 8.14 The piezoelectric sensor generates charge, which is transferred to the
capacitor, C, by the charge amplifier. Feedback resistor R causes the capacitor
voltage to decay to zero.
xi
Deflection
vo
Time
vo max
vo max /e
Time
Figure 8.15 The charge amplifier
responds to a step input with an
output that decays to zero with a
time constant  = RC.
+
B
B
l
S
N
e

e = Blu
u
Figure 8.16 Principle of an electromagnetic flowmeter.
Oscillator
Scan head
Image plane
Skin surface
Blood vessel
Doppler
angle
Computer
RF
amplifier
Detector
AF
amplifier
F/V
converter
Figure 8.17 Ultrasonic flowmeter. The sensor at the scan head transmits the signal from the
oscillator and receives the reflected wave from the blood cells. The RF (radio frequency)
amplifier amplifies the received signal and the carrier frequency, then AF (audio frequency)
signal is produced by a detector. (Adapted from Picot, P. A. and Fenster, A. 1996. Ultrasonic blood
volume flow rate meter. US Patent, 5,505,204. )
Laser
Photodiode
Skin
Blood
vessel
Blood cell
Figure 8.18 Laser-Doppler flowmetry. Light that intercepts the red blood cells
experiences a Doppler frequency shift.
Pressure/mmHg
Figure 8.19 The sphygmomanometer detects arterial opening and closing that
occurs between systolic and diastolic pressures.
cuff
occluded
blood vessel
Figure 8.20 The pressure of the cuff occludes the blood vessel. When the arterial
pressure is greater than the pressure applied by the cuff, Korotkoff sounds are
created and blood pressure can be measured.
Figure 8.21 Top: Cuff pressure with superimposed Korotkoff sounds, which appear
between systolic and diastolic pressures. Bottom: the oscillometric method detects when
the amplified cuff pressure pulsations exceed about 30% of maximal pulsations. (From
Geddes, L. A. 1984. Cardiovascular devices and their applications. Copyright © by John Wiley &
Sons. Reprinted by permission of John Wiley & Sons.)
Ultrasonic
beam
Rotating
catheter
Ultrasonic
transducer
Blood
Arterial
wall
Figure 8.22 A catheter is inserted through the blood vessels. A rotating ultrasonic
transducer is attached at its tip and illuminates the walls.