Human Cardiovascular Function

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Rate

(bpm)

2. How do the values for systolic and diastolic blood pressures and heart rate as recorded by the auscultatory method and the Omron monitor compare? If they are different suggest why this might be.

The ausculotory method determines systolic and diastolic blood pressure using Korotkoff sounds. The stethoscope allows the observer to listen to each individual Korotkoff sound. The Omron automatic blood pressure monitor detects blood flow using an electrical pressure sensor. Using the Korotkoff sounds, the start and end points of systolic and diastolic pressure can be determined, and in turn the systolic/diastolic pressure can be easily predicted using the auscultatory method.

On the Result Sheet provided on the next page record the pulse rate and arterial blood pressure measurements made on the subject in your group.

3. Based on what you have learnt from the lectures, what is the immediate effect of a sudden change in posture from lying down to standing up on your blood pressure and why does this happen?

The sudden change in posture from lying down to standing up causes a drop in blood pressure. Suddenly standing up causes blood to pool at the distended veins. This results in a decrease in venous return as well as cardiac output. The end result is a decrease in mean arterial pressure.

4. What changes occur in the cardiovascular system shortly after changing posture from lying down to standing up and how are these changes brought about?

Shortly after, the arterial baroreceptor reflex is brought about. Baroreceptors detect and respond to stress changes. They are stimulated when the tunica externa that they are located in are deformed. When the blood pressure drops, the number of action potentials sent to the medulla is decreased. In turn, the sympatheyic nerve activity to the SA node increases, thus increase the heart rate. The heart muscle pumps with more force which increase the stroke volume. The increased stroke volume and heart rate leads to increased cardiac output. This cause the blood pressure to rise back to normal.

Effect of Posture and Exercise on Heart Rate and Arterial Blood Pressure

RESULT SHEET

BP

(systolic/diastolic; mmHg) Pulse rate

(beats/min)

At rest

5 min 7 min 9 min 5 min 7 min 9 min

Standing

0 min 1 min 3 min 0 min 1 min 3 min

Exercise

(low rate)

0 min 0 min

Exercise

(high rate)

0 min 2 min rest 4 min rest 0 min 2 min rest 4 min rest

5. How does exercise (work) affect your heart rate and blood pressure and what is the influence of the rate of exercise (work rate) on these changes? Comment on the size of the change in blood pressure during exercise in relation to the systolic pressure, the diastolic pressure and the mean arterial pressure.

Exercise increases your blood pressure and heart rate. Your heart rate increases because parasympathetic stimulation in decreased while sympathetic stimulation is increased. There is also an increase in circulating adrenaline. Stroke volume increases as venous return increases and the end-diastolic volume decreases. Increased adrenaline levels and sympathetic stimulation increases contractility. The diastolic pressure may not change and mean arterial pressure usually increases limitedly.

6. What effect would you expect training to have on (a) the increase in heart rate during exercise, and (b) how quickly it returns to normal after exercise?

The resting heart rate would be lower in trained people. Heart rate during sub-maximal exercise is lower in trained people compared to un-trained individuals. Heart rate also recovers much quicker in trained individuals.

THE ELECTROCARDIOGRAM (ECG)

In the space below place a copy of the recording of the ECG of yourself or one member of your group showing at least 4 or 5 cardiac cycles. Identify the P, QRS and T waves of the ECG.

NOTE: The ECG traces you will be recording will be through the LabTutor program. If you email the report page of the ECG exercise to yourself (by clicking the ‘email’ link in the report page of LabTutor), you will receive a Word document of all your graphs. Keep in mind that you will need to make any adjustments to your graph in the LabTutor interface before emailing a copy to yourself. If you are not able to do this in the lab practical, your experiment data will be available by logging into LabTutor from any Physiology computer.

Example ECG Traces

1. What do each of these waves of the ECG represent and at which stage of the cardiac cycle do they occur?

P wave – associated with atria activation, QRS complex – activation of the ventricles, T wave – repolarization of ventricles.

* P-R interval = time from beginning of P wave to start of QRS complex

* QRS interval = time from beginning to end of QRS complex

* QT interval = time from beginning of QRS complex to end of T wave

* RR interval = time from peak of one R wave to the peak of the following R wave.

2. Why does the QRS complex have the largest amplitude?

QRS complex illustrates the depolarisation of the ventricles of the heart. The ventricles are the heaviest components which cause them to contract with a larger force. Thus the voltage difference is largest in the ventricles. The QRS complex demonstrates the change in voltage through its amplitude i.e. a larger change in voltage = a larger amplitude

3. Explain why the ‘lub’ sound occurs at the time of the QRS complex

The depolarization of the ventricles indicated by the QRS