Chapter 8
Heart and CirculationHeart 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.
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.
Lower body
U pper body
Lefta trium
R ightatrium
Leftventric le
R ightventric le
O xygenatedblood
D eoxygenatedblood
Lung
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.
Table 8.1 Duration and characteristics of each major event in the cardiac cycle.
EventEvent CharacteristicsCharacteristics Duration at 75 bpm Duration at 75 bpm (0.8 second cycle) (0.8 second cycle)
Atrial diastoleAtrial diastole
Ventricular diastole Ventricular diastole
AV valves opened.AV valves opened.
Semilunar valves close.Semilunar valves close.
Ventricular filling. Ventricular filling.
0.4 seconds 0.4 seconds
Atrial systoleAtrial systoleVentricular diastole Ventricular diastole
AV valves open.AV valves open.
Semilunar valves closed. Semilunar valves closed. Ventricular filling.Ventricular filling.
0.1 seconds 0.1 seconds
Atrial diastoleAtrial diastoleVentricular systole Ventricular systole
AV valves closed.AV valves closed.
Semilunar valves open.Semilunar valves open.
Blood pumped into aorta Blood pumped into aorta and pulmonary artery. and pulmonary artery.
0.3 seconds 0.3 seconds
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 V1 V4
I aVR V1 V4
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
(a)
(b)
(c)
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.
(d)
(e)
(f)
I aVR V1 V4
I aVR V1 V4
I aVR V1 V4
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.
Resistorsand switch
Amp ADC
SignalprocessorMonitor
PrinterStorage
LA
LL
RA
RL
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.)
22k
10k
47k
22k
10k
-
+
-
+
10k
50k
-
+
1 uF
S1
-
+
3.3M
3.3M
150k
0.01 uF
4.7kVa
Vb
Vo
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.
0IIIIII
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.)
Balloon
Pressureport
Pressuresensor
Infusion
Catheter
Table 8.2 Some physiological variables. The data presented in this table are the average values of a group of subjects.
VariablesVariables Mean (Mean (SD)SD)
Weight (kg)Weight (kg) 70 70
Cardiac output (mL/s) Cardiac output (mL/s) 110 110
Heart rate (min–1) Heart rate (min–1) 76 76
Mean velocity, ascending aorta (mm/s) Mean velocity, ascending aorta (mm/s) 1616
LV end-diastolic volume (mL) LV end-diastolic volume (mL) 125 (125 (31) 31)
LV end-systolic volume (mL) LV end-systolic volume (mL) 42 (42 (17) 17)
LV stroke volume (mL) LV stroke volume (mL) 82 (82 (20) 20)
LV ejection fraction LV ejection fraction 0.67 (0.67 (0.11) 0.11)
LV mean wall thickness (mm) LV mean wall thickness (mm) 10.9 (10.9 (2.0) 2.0)
Cardiac output (CO) = heart rate (HR) stroke volume (SV)
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.
/s)(m |)(|
||CO 3
0 bbb1
t
dttTc
Q
Tb = temperature gradient function cb = specific heat of the blood in J/(kgK)b = density of the blood in kg/m3
Q = heat injected in joules
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/)
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).
(a) (b) (c)
Table 8.2a Relative advantages of echocardiographic examination techniques. (Adapted from Roelandt, 1983)
M-mode echocardiographyM-mode echocardiography Two-dimensional echocardiographyTwo-dimensional echocardiography
Excellent time resolution Excellent time resolution Anatomical relationships Anatomical relationships
Accurate dimensional measurements Accurate dimensional measurements Shape information Shape information
Timing of events against other Timing of events against other parameters parameters Lateral vectors of motion Lateral vectors of motion
Easy storage and retrieval Easy storage and retrieval Easier to understand Easier to understand
Table 8.3 The heart sounds. The 1st and 2nd heart sounds are most prominent.
SoundSound OriginOrigin
1st sound 1st sound Closure of mitral and tricuspid valves Closure of mitral and tricuspid valves
2nd sound 2nd sound Closure of aortic and pulmonary valves Closure of aortic and pulmonary valves
3rd sound 3rd sound Rapid ventricular filling in early diastole Rapid ventricular filling in early diastole
4th sound 4th sound Ventricular filling due to atrial contraction Ventricular filling due to atrial contraction
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.
CharacteristicCharacteristic Type of murmurType of murmur Valve disorderValve disorder
Systolic murmurSystolic murmur
1st HS1st HSmurmurmurmur2nd HS 2nd HS
WhistlingWhistling
Swishing Swishing
Stenotic semilunar valveStenotic semilunar valve
Insufficient AV valve Insufficient AV valve
Diastolic murmurDiastolic murmur
2nd HS2nd HSmurmurmurmur1st HS 1st HS
WhistlingWhistling
Swishing Swishing
Stenotic AV valveStenotic AV valve
Insufficient semilunar valve Insufficient semilunar valve
Figure 8.13 A stethoscope with bell and diaphragm modes. (Adapted from Mohrin, C. M., 1995. Stethoscope. US Patent, 5,389,747. )
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.
-
+
C
R
V
Electrode
Piezoelectricsensor
xi
Deflection
vo
vo max
vo max /e
Time
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
N S
B
u
+
e
l
Figure 8.16 Principle of an electromagnetic flowmeter.
e = Blu
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. )
Blood vessel
Doppler angle
Scan head
Skin surface Image plane
RF amplifier
Detector AF
amplifier F/V
converter
Computer
Oscillator
Figure 8.18 Laser-Doppler flowmetry. Light that intercepts the red blood cells experiences a Doppler frequency shift.
Laser Photodiode
Blood cellBloodvessel
Skin
Pres
sure
/mm
Hg
Figure 8.19 The sphygmomanometer detects arterial opening and closing that occurs between systolic and diastolic pressures.
cuffocc luded
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.)
Figure 8.22 A catheter is inserted through the blood vessels. A rotating ultrasonic transducer is attached at its tip and illuminates the walls.
Blood Arterial wall
Ultrasonic transducer
Ultrasonic beam
Rotating catheter