UNIT TITTLE: BIOMEDICAL
INSTRUMENTATION III
UNIT CODE: EBM 511
ASSIGNMENT: BIOPAC
ELECTROCARDIOGRAPH LAB REPORT
ELECTROCARDIOGRAPH EXPERIMENT LAB REPORT
I. EXPERIMENTAL OBJECTIVES
1) To become familiar with the electrocardiograph as a primary tool for evaluating electrical events within the heart.
2) To correlate electrical events as displayed on the ECG with the mechanical events that occur during the cardiac cycle.
3) To observe rate and rhythm changes in the ECG associated with body position and breathing.
II. THEORY
The main function of the heart is to pump blood through two circuits:
1. Pulmonary circuit: through the lungs to oxygenate the blood and remove carbon dioxide; and
2. Systemic circuit: to deliver oxygen and nutrients to tissues and remove carbon dioxide.
Because the heart moves blood through two separate circuits, it is sometimes described as a dual
pump.
In order to beat, the heart needs three types of cells:
1. Rhythm generators, which produce an electrical signal (SA node or normal pacemaker);
2. Conductors to spread the pacemaker signal; and
1
, 3. Contractile cells (myocardium) to mechanically pump blood.
The Electrical and Mechanical Sequence of a Heartbeat
The heart has specialized pacemaker cells that start the electrical
sequence of depolarization and repolarization. This property of
cardiac tissue is called inherent rhythmicity or automaticity. The
electrical signal is generated by the sinoatrial node (SA node) and
spreads to the ventricular muscle via particular conducting
pathways: internodal pathways and atrial fibers, the
atrioventricular node (AV node), the bundle of His, the right
and left bundle branches, and Purkinje fibers (Fig 5.1).
When the electrical signal of a depolarization reaches the
contractile cells, they contract—a mechanical event called
systole. When the repolarization signal reaches the myocardial
cells, they relax—a mechanical event called diastole. Thus, the
electrical signals cause the mechanical pumping action of the
heart; mechanical events always follow the electrical events (fig. Fig. 5.1 The Heart
5.2).
The SA node is the normal pacemaker of the heart, initiating each electrical and mechanical cycle. When the SA node
depolarizes, the electrical stimulus spreads through atrial muscle causing the muscle to contract. Thus, the SA node
depolarization is followed by atrial contraction.
The SA node impulse also spreads to the atrioventricular node (AV node) via the internodal fibers. (The wave of
depolarization does not spread to the ventricles right away because there is nonconducting tissue separating the atria and
ventricles.) The electrical signal is delayed in the AV node for approximately 0.20 seconds when the atria contract, and then
the signal is relayed to the ventricles via the bundle of His, right and left bundle branches, and Purkinje fibers. The
Purkinje fibers relay the electrical impulse directly to ventricular muscle, stimulating the ventricles to contract (ventricular
systole). During ventricular systole, ventricles begin to repolarize and then enter a period of diastole (Fig. 5.2).
Although the heart generates its own beat, the heart rate (beats per minute or BPM) and strength of contraction of the heart
are modified by the sympathetic and parasympathetic divisions of the autonomic nervous system.
The sympathetic division increases automaticity and excitability of the SA node, thereby increasing heart rate. It also
increases conductivity of electrical impulses through the atrioventricular conduction system and increases the force
of atrioventricular contraction. Sympathetic influence increases during inhalation.
The parasympathetic division decreases automaticity and excitability of the SA node, thereby decreasing heart rate. It
also decreases conductivity of electrical impulses through the atrioventricular conduction system and decreases the
force of atrioventricular contraction. Parasympathetic influence increases during exhalation.
The Electrocardiogram (ECG)
Just as the electrical activity of the pacemaker is communicated to the cardiac muscle, ―echoes‖ of the depolarization and
repolarization of the heart are sent through the rest of the body. By placing a pair of very sensitive receivers (electrodes) on
other parts of the body, the echoes of the heart’s electrical activity can be detected. The record of the electrical signal is
called an electrocardiogram (ECG). You can infer the heart’s mechanical activity from the ECG. Electrical activity varies
through the ECG cycle as shown below (Fig. 5.2):
2
, 3
INSTRUMENTATION III
UNIT CODE: EBM 511
ASSIGNMENT: BIOPAC
ELECTROCARDIOGRAPH LAB REPORT
ELECTROCARDIOGRAPH EXPERIMENT LAB REPORT
I. EXPERIMENTAL OBJECTIVES
1) To become familiar with the electrocardiograph as a primary tool for evaluating electrical events within the heart.
2) To correlate electrical events as displayed on the ECG with the mechanical events that occur during the cardiac cycle.
3) To observe rate and rhythm changes in the ECG associated with body position and breathing.
II. THEORY
The main function of the heart is to pump blood through two circuits:
1. Pulmonary circuit: through the lungs to oxygenate the blood and remove carbon dioxide; and
2. Systemic circuit: to deliver oxygen and nutrients to tissues and remove carbon dioxide.
Because the heart moves blood through two separate circuits, it is sometimes described as a dual
pump.
In order to beat, the heart needs three types of cells:
1. Rhythm generators, which produce an electrical signal (SA node or normal pacemaker);
2. Conductors to spread the pacemaker signal; and
1
, 3. Contractile cells (myocardium) to mechanically pump blood.
The Electrical and Mechanical Sequence of a Heartbeat
The heart has specialized pacemaker cells that start the electrical
sequence of depolarization and repolarization. This property of
cardiac tissue is called inherent rhythmicity or automaticity. The
electrical signal is generated by the sinoatrial node (SA node) and
spreads to the ventricular muscle via particular conducting
pathways: internodal pathways and atrial fibers, the
atrioventricular node (AV node), the bundle of His, the right
and left bundle branches, and Purkinje fibers (Fig 5.1).
When the electrical signal of a depolarization reaches the
contractile cells, they contract—a mechanical event called
systole. When the repolarization signal reaches the myocardial
cells, they relax—a mechanical event called diastole. Thus, the
electrical signals cause the mechanical pumping action of the
heart; mechanical events always follow the electrical events (fig. Fig. 5.1 The Heart
5.2).
The SA node is the normal pacemaker of the heart, initiating each electrical and mechanical cycle. When the SA node
depolarizes, the electrical stimulus spreads through atrial muscle causing the muscle to contract. Thus, the SA node
depolarization is followed by atrial contraction.
The SA node impulse also spreads to the atrioventricular node (AV node) via the internodal fibers. (The wave of
depolarization does not spread to the ventricles right away because there is nonconducting tissue separating the atria and
ventricles.) The electrical signal is delayed in the AV node for approximately 0.20 seconds when the atria contract, and then
the signal is relayed to the ventricles via the bundle of His, right and left bundle branches, and Purkinje fibers. The
Purkinje fibers relay the electrical impulse directly to ventricular muscle, stimulating the ventricles to contract (ventricular
systole). During ventricular systole, ventricles begin to repolarize and then enter a period of diastole (Fig. 5.2).
Although the heart generates its own beat, the heart rate (beats per minute or BPM) and strength of contraction of the heart
are modified by the sympathetic and parasympathetic divisions of the autonomic nervous system.
The sympathetic division increases automaticity and excitability of the SA node, thereby increasing heart rate. It also
increases conductivity of electrical impulses through the atrioventricular conduction system and increases the force
of atrioventricular contraction. Sympathetic influence increases during inhalation.
The parasympathetic division decreases automaticity and excitability of the SA node, thereby decreasing heart rate. It
also decreases conductivity of electrical impulses through the atrioventricular conduction system and decreases the
force of atrioventricular contraction. Parasympathetic influence increases during exhalation.
The Electrocardiogram (ECG)
Just as the electrical activity of the pacemaker is communicated to the cardiac muscle, ―echoes‖ of the depolarization and
repolarization of the heart are sent through the rest of the body. By placing a pair of very sensitive receivers (electrodes) on
other parts of the body, the echoes of the heart’s electrical activity can be detected. The record of the electrical signal is
called an electrocardiogram (ECG). You can infer the heart’s mechanical activity from the ECG. Electrical activity varies
through the ECG cycle as shown below (Fig. 5.2):
2
, 3
