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