Physiology Lab 2 Final

Exercise 1: ECG and pulse at rest 1. Today in class, you measured an electrical signal (ECG) produced by the heart. In your own words, describe as completely as you can the structures and processes that produces the QRS complex in the ECG you measured today.  During once cardiac cycle, electrical current flows from the SA node through the atria to the AV node, and then from the AV node through the AV bundle, bundle branches, and Purkinje fibers to ventricular muscle. For the heart to contract, a pacemaker potential in the SA node must first reach a threshold by the slow leakage of sodium and rapid influx of sodium and calcium. The QRS complex is caused by the potentials generated when the ventricles depolarize before contraction, that is, as the depolarization wave spreads through the ventricles. It is also during this wave that the atria repolarize, known as atrial T wave, but is usually obscured because of the much larger QRS complex. 2. List the physiological processes that take place between the QRS complex and the arrival of the pulse wave at the finger.  It can be observed from the data that the pulse wave is at its lowest in every highest peak of the QRS complex. This means that there is a delay in the recording of the peak of systolic pressure and the pulse wave. Exercise 2: The Pulse 3. Suggest some reasons for the differences in pulse amplitude from subject to subject.  The differences in pulse amplitude from subject to subject may be because of factors such as body type or physique, caffeine or stimulant level in the person’s circulatory system, drugs or medications take, stress level, emotional state, presence of atherosclerosis, presence of disease process such as hypertension, hyperthyroidism, diabetes mellitus, and placement of the finger pulse transducer. Exercise 3: Palpation of arterial pulses 4. When you feel a pulse, do you feel (a) the blood flow, (b) the pressure wave, or (c) brief changes in diameter of the artery due to the pressure wave?  The blood flowing through the veins is the physiological process happening when you feel a pulse. 5. Anatomical sites where a pulse can be palpated often correspond to “pressure points” for stopping hemorrhage in first-aid treatment. Why?  Pressure point is referred to as a point where a blood vessel can be compressed against underlying bone to slow blood flow and control bleeding. These points often correspond to where a pulse can be palpated and these points are the main arteries which have greater pressure. By applying pressure to these points, blood 1

flow will be cut off to the distal part of the pressure point, thus preventing too much blood loss. 6. Why can ulnar pulse not usually be felt?  All systemic arteries arises branch from the aorta. The ulnar artery arises from the subclavian artery and the brachial artery. Since blood flowing from the heart to the ulnar artery, which is distal and smaller, travels longer, the pulse will already be weak and usually not felt. Anatomically, the ulnar artery is small and deep, making it harder to be palpated. 7. Doctors are trained to assess various aspects of a pulse: the rate, rhythm, amplitude and quality. For example, the rate might be 72 beats per minute, rhythm regular or irregular, amplitude full and quality “thread” or collapsing. Based on your experiences in the lab today, which of these parameters do you think would be easy to assess, and which would be difficult?  The parameters that can be easily examined by palpation on the characteristics of a pulse would be the rate, rhythm and quality. The amplitude of a pulse is harder to determine just by palpation because a waveform recording must be recorded in order to differentiate the amplitude of a pulse. Exercise 4: Arterial anastomoses in the hand 8. In your own words, describe why the pulse in the fingers disappeared when the brachial artery was compressed?  The brachial artery is the main artery in the arm and when this is compressed, blood flow to the more distal upper limb or the forearm and fingers will be cut off causing the pulse to disappear. 9. Did the pulse disappear completely when the radial or ulnar artery alone was compressed? If not, why not?  When one of the radial or ulnar artery is compressed, the pulse will not completely disappear because of anastomoses of the arteries wherein if one area of supply will be cut off, the other side takes over. 10. There is much anatomical variation from person to person, but in most people, blood flow to the fingers is derived mainly from the ulnar artery, with a smaller contribution from the radial artery. On the basis of your results, does the subject seem to conform the general rule?  Yes, the subject conforms to the rule. Exercise 5: The effect of cold on the pulse 11. In your own words, describe the effect cold had on the pulse? 2

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The effect of cold application on the pulse is to decrease its blood flow and pulse wave amplitude by causing vasoconstriction of the blood vessel.

12. Many mammals have the ability to restrict blood flow to the extremities in cold temperatures. Does your data support this general observation?  Yes, the cold application caused vasoconstriction in order to conserve heat of the body and direct blood to the major organs of the body for optimum functioning during cold temperatures.

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