group 4_baseline heart rate & ecg

8/18/2019 Group 4_baseline Heart Rate & Ecg

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Physiology of theCirculatory

System: The baseline heart rate

and ECG

DE LA PAZ | DUQUE | GALAROSA | GONZALESGroup 4

4 Biology 6


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SUMMARY

The frog heart is made of three chambers, one ventricle and two atria.

Although it is similar to skeletal muscles, it is an involuntary muscle that

does not need to be stimulated by nerves to contract. This is due to the

action potentials that spontaneously begin in the pacemaker region inthe right atrium that spreads through the heart. An electrocardiogram

(ECG) was used to test the electrical activity in the heart. An ECG

translates the heart's electrical activity into line tracings. In this

experiment, the baseline heart rate and ECG of the frog was observed.

The baseline heart rate of the frog at room temperature is said to bearound 40 BPM, and it was found experimentally that the computed

baseline heart rate is 31.7460 BPM, and the baseline heart rate from

the data pad is 31.4273 BPM. The heart rate of the frog may be lower

than normal due to the lower temperature in the laboratory. For the

ECG, the tracing produced waves that consists of P waves, PRintervals, QRS complexes, ST segments, T waves, QT intervals, and,

at times, U waves.

Keywords: Circulatory system, heart, baseline heart rate,

electrocardiogram


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Introduction


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Frog Heart


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Frog Heart

▪ Ventricle: single chamber at the bottom of the heart

▪ Atria: two thin-walled chambers located above theventricle (darker red in color)

▪ Sinoatrial (SA) node

– Pacemaker of the heart

– Transmit electrical signals to make the heart contract ina rhythmic manner

▪ Aortic trunk

–Right side of the ventricle

– Less oxygenated blood: pulmocutaneous artery

– More oxygenated blood: Carotid, aorta

▪ Sinus venosus:

–Receives blood and delivers it to the right atria


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Circulatory System


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ECG

▪ An electrocardiogram (ECG) is a

machine that can be used torecord and display the electricalactivity of the heart

▪ Different peaks shown in an ECG

and each corresponds to voltagechanges in specific regions of theheart

▪ The ECG can be very helpful tothe lives of human beings


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ECG

▪ P wave: atrial depolarization

▪ QRS complex: atrial repolarization and ventriculardepolarization

▪ T wave: ventricular repolarization


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Methodology


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Set-up and Calibration

The Bridge Pod was plugged into the Pod Port onInput 1 of the PowerLab.

PowerLab was turned on. LabChart waslaunched from the computer.

“Frog heart settings” was opened and from theForce Channel Function pop-up menu, Bridge

Pod was selected.

The zeroing knob on the front of the Bridge Podwas turned until a reading of zero is seen in the

dialog preview window.

The mounting stand was set-up with theForce transducer mounted on the

micropositioner.

The force transducer cable was connected tothe back of the Bridge Pod.

A piece of strong thread about 36cm in lengthwas tied to the force transducer. A small,

barb-less hook was attached to the other endof the thread.

The patient cable was attached to the Bio Amp pocket on the PowerLab.

Three lead wires were attached to the Bio Amp Cable: Channel 1 positive and negative,

and Earth.


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Recording Baseline Heart Rate and ECG

A heartbeat waveform in the Force Channeland an ECG signal in the ECG channel were

seen.

The tension on the heart was adjusted withthe micropositioner when a weak signal in the

force channel was seen.

“ Autoscale" button was clicked from the

LabChart toolbox to scale all channels.

The heart was gently lifted from the animal’sbody cavity, and the other end of the thread

was tied to the force transducer.

The slack in the thread was reduced byadjusting the micropositioner on the mounting

stand.

Lead wire alligator clips were attached to thefrog to record the ECG. Positive- left forelimb;Negative- Right forelimb; Earth- right hindlimb.

In LabChart, the “Start” button was clicked andrecording was done for 30 seconds.


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Results and Discussion


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Determination of baseline heart rate

▪ asdf

Number of beats Time differential Calculated heart

rate

Heart rate from

data pad

32 beats 59.21 seconds 31.7460 BPM 31.4273 BPM


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Baseline heart rate

▪ The baseline heart rate or resting heart rate is the

number of contractions of the heart that occur in a singleminute while the body is at complete rest

▪ The baseline heart rate of a frog is said to be 40-50 BPM

▪ Amplitude and frequency of the heart beat varies

according to the size of the animal, the bigger the animalthe lesser the frequency

▪ Temperature influences the heart rate of frogs

– Frogs are ectotherms, animals that gains heat through

the environment– The heart rate of the frogs reflect their metabolic rate

which consequently increases with increasing bodytemperature and vice versa


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Baseline heart rate

▪ Temperature influences the heart rate of frogs

–In the experiment, the lower temperature in thelaboratory may have caused the baseline heart rate ofthe frogs to become lower than normal

▪ Changes in the environment influences the heart rate of

the frog– Changes in the general metabolism induces

bradycardia, or decreasing of the heart rate

– Shortage of oxygen supply or an excess carbon

dioxide also induces bradycardia– Exposure to nitrogen may cause an immediate

tachycardia, or increasing heart rate


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ECG


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ECG

Representation

P wave Atrial depolarization

PR

interval

Delay between atrial

depolarization and ventricular

activation

PR

segment

Conduction from the

atrioventricular (AV) node to

Purkinje fibers

QRS

complexVentricular depolarization

ST

segment

Electrical plateau of ventricular

activation

T wave Ventricular repolarization

QT

interval

Time interval for ventricular

depolarization and repolarization

U wave Late ventricular repolarization


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ECG

▪ Propagation of action potentials that causes the heart to

contract

▪ The ECG trace repeats with every heart beat and showsthe compilation of electrical activity or action potential ofthe heart

▪ P wave

– Represents atrial depolarization or atrial systole

– A heart beat begins with an action potential signal fromthe SA node

–The signal spreads to both atria causing the muscles ofthe atrium to depolarize and contract

– Slow cell-to-cell atrial conduction spreads thedepolarization slower and gives the P wave a rounded

deflection


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ECG

▪ PR interval

–Represents the time the impulse takes to reach theventricles from the SA node

– Begins at the onset of the P wave and ends at theonset of the QRS complex

–

Shows the delay between atrial depolarization andventricular activation

▪ PR segment

– Represents when the signal leaves the atria and enter

the ventricles though the AV node in the interatrialseptum, enters the bundle of His, and spreads throughthe bundle branches, and the Purkinje fibers that arefound along the ventricle walls

– Follows atrial systole and preceding ventricular systole


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ECG

▪ QRS complex

–Represents the depolarization of the ventricles andconsequently ventricular systole

– Immediately follows the P wave

– The sharp deflection of the complex is due to the fast

electrical impulse conduction done by ventricularconducting fibers, namely the bundle of His, bundlebranches, and the Purkinje fibers; and, the ventricularmuscle mass is greater than that of the atria

– Q wave: is the downward deflection following the P

wave– R wave: is the first upward deflection following the P

wave

– S wave: is the first downward deflection following the R

wave


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ECG

▪ QRS complex

– Atrial repolarization is not visible because it coincideswith the onset of ventricular depolarization

▪ ST segment

– Represents the electrical plateau of ventricular activity

– At this phase the ventricles are uniformly depolarized

– This segment is said to be isoelectric for there is no netelectric charge or difference in electrical potential

▪ T wave– Represents the ventricular repolarization, and

consequently, ventricular diastole


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ECG

▪ T wave

–Ventricular muscles recover from the influx of ions andare returning to their resting state

– At this point, more blood enters the ventricle inpreparation for its circulation into the arteries

▪ QT interval

– Represents the time interval for the ventricle todepolarize and repolarize

▪ U wave

– Represents the late repolarization of the Purkinje orventricular conducting fibers

– Is usually not seen on the ECG


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ECG

▪ An arrhythmia, also called dysrhythmia, is an irregular or

abnormal heartbeat

▪ Types of arrhythmia:

– Tachycardia: a fast heart rhythm

–

Bradycardia: a slow heart rhythm– Supraventricular arrhythmias: arrhythmias that begin

above the ventricles or in the atria

– Ventricular arrhythmias: arrhythmias that begin in the

ventricles– Bradyarrhythmias: slow heart rhythms that may be caused

by disease in the heart’s conduction system, such as theSA node, atrioventricular AV node or HIS-Purkinje network


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ECG

▪ Terms:

– Action potential: the point at which a cell becomes electricallyactivated

– Polarized: the resting electrical state of a cell

– Depolarization: change in electrical state of a cell due to the inflow

of positively charged ions– Repolarization: the return to the normal resting electrical state of a

cell following an action potential

– Isoelectric: the phase wherein the electrical charges through theheart are equal and there is no deflection that occurs on the ECGtrace

– Systole: phase of the heartbeat when the heart muscle contractsand pumps blood

– Diastole: phase of the heartbeat when the heart muscle relaxes

and allows the chambers to fill with blood


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Guide Questions


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What do you call the first sound heard as pressure is being

released from the cuff slowly? What does this sound

indicate?

The first sound heard is the systolic pressure. This

pressure indicates the pressure of the blood that is pumped

out by the heart where the blood starts flowing again in the

blood vessel after the flow has been disrupted by the

pressure applied on the sphygmomanometer cuff.


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Describe the basis for the delay between the arterial and

ventricular contractions.

The delay between the arterial and ventricular contractions

is due to the delay of the impulse conducted by the AV

node to let the ventricle to be fully filled with blood and

making sure that the atrium has already emptied its

contents to the ventricle before ventricular contractionoccurs.


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How did temperature affect heart rate? What do you

suppose is a consequence being a poikilotherm?

Heart rate, controlled primarily by different chemical

processes, increases as the temperature increases due to

the fact that temperature supplies heat and heat is

responsible for the atomic and molecular movement that

speeds up the reactions in the body. Poikilotherms, beingunable to regulate their own body temperature and adapt

only to their environment, cannot stabilize their metabolic

activities efficiently because of their inability to regulate

their own body temperature. Their heart rate can be veryactive on high environmental temperatures but their heart

rate could also not be very active due to low temperature in

the environment.


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What is Starling’s Law of the Heart? Does your data

support this law?

Starling’s Law of the Heart states that the heart has the

ability to change its force of contraction and therefore

stroke volume in response to changes in venous return,

simply put, as the heart wall increases in length more

volume of blood could be accommodated thus increasingthe stroke volume. The length-tension applied to the

ventricle stretches the cardiac sarcomere length thus

increasing the ventricular chamber therefore increasing the

stroke volume. Yes. The data obtained supports this law.


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Describe the mechanisms by which the following drugs

affect heart rate:

A. Acetylcholine

Acetylcholine (Ach) is a neurotransmitter that binds to

muscarinic cholinergic receptors which in turn activates G

proteins that results to hyperpolarization. Then,

hyperpolarization allows the passage of K ions by opening

K channels and thereby closing Na and Ca channels. Theclosing of the Na and Ca channels decreases the heart rate

significantly.


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affect heart rate:

B. Epinephrine

Epinephrine is a neurotransmitter that binds to adrenergic

receptors such as β1 receptors which in turn activates

cAMP where the depolarization frequency increases. Then,

depolarization opens up Na and Ca channels permitting a

spontaneous entrance of Na and Ca ions. The entry of Naand Ca ions generate an impulse that makes the heart rate

faster.


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affect heart rate:

C. Atropine & Acetylcholine

Atropine functions as cholinergic antagonist where it blocks

Acetylcholine receptors. If the Ach receptors are blocked,

the Ach neurotransmitter could not bind to muscarinic

cholinergic receptors that the process is halted before it

even began.


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References

1. ADInstruments. Physiology of the in situ amphibian heart. Retrieved on 6 April 2015,

from

http://jpkc.zju.edu.cn/k/554/preparation/experiment/pl/Frog%20Heart%20Protocol.doc.

2. Electrocardiogram: MedlinePlus Medical Encyclopedia. (2015). Retrieved on 6 April

2015, from http://www.nlm.nih.gov/medlineplus/ency/article/003868.htm.

3. Frog Electrocardiogram. (2013). Retrieved on 6 April 2015, from

http://www.iworx.com/documents/LabExercises/FrogECG.pdf.

4. Herbert, T.J. (2011). Cardiac muscle and circulation. Retrieved on 6 April 2015, from

http://www.bio.miami.edu/tom/courses/bil265/bil265goods/18_cardiac.html5. John, A.D. & Fleishr, L.A. (2006). Electrocardiography: The ECG. Anesthesiology

Clinics, 24, 697-715.

6. Kumar, S. (July 2007). ECG Tutorial for clinicians. Retrieved on 6 April 2015, from

https://cardionotes.files.wordpress.com/2008/02/ecg-tutorial-by-dr-satish.pdf.

7. Pal, G.K. & Pal, P. (2005). Textbook of practical physiology. (2nd ed.). Chennai, India:

Orient Longman Private Ltd.

8. Rastogi, S.C. (2005). Experimental physiology. Daryaganj, India: New Age

International (P) Ltd.

9. Sambo, J. (2012). Bio 22 Lab - Expt 19 (Group 4). Retrieved on 6 April 2015, from

http://www.slideshare.net/JenSambo/bio-22-lab-expt-19-group-4

10. Waitemata Cardiology. Electrocardiogram (ECG). Retrieved on 6 April 2015, from

http://wcardio.co.nz/newsite/electrocardiogram-ecg/.


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Physiology of theCirculatory

System: The baseline heart rate

and ECG

DE LA PAZ | DUQUE | GALAROSA | GONZALESGroup 4

4 Biology 6

group 4_baseline heart rate & ecg

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