CV LAB Circulation in Human Subjects

Transcription

1 Part I: Measurement of Blood Pressure CV LAB Circulation in Human Subjects 1. Introduction: Form teams of two and take each other s blood pressure. Enter the data in the Table Page. Measurement of human blood pressure is usually made by the indirect method in which the blood pressure is estimated from the influence of externally applied pressure on the blood flow through a limb. Wrap the blood pressure measuring cuff (approx. 12 cm breadth) around the upper arm of the subject. Place the stethoscope head gently in the antecubital fossa over the brachia artery (identified by sensing the pulse). Can you hear any sound without inflating the cuff? By squeezing the bulb (with the side vent valve closed), which is attached to the cuff and the manometer, raise the cuff pressure to approximately 160mmHg. Lower the cuff pressure gradually (2-4 mm Hg per sec) by opening slightly the vent valve; watch the mercury level in the manometer while listening through the stethoscope. The pressure at which the sound first appears (sharp, tapping sound) is the systolic pressure. With progressive decreases of cuff pressure, the sound first becomes louder, and the thudding sounds gradually fade and become muffled. The pressure at which this muffling occurs is taken as the diastolic pressure. Usually the sound disappears a few mm Hg below the point of muffling. Release the cuff pressure completely and wait for 10 seconds before making another measurement. What would be the effect of using a cuff that is too large or too small? Should one use a cuff of different size for the obese subject or for a small child? 2. Comparison of Methods of Blood Pressure Measurement. With the subject sitting, determine the blood pressure by using the auscultatory method described above. In addition, also determine the pressure at which the radial pulse begins during gradual deflation of the cuff (palpation method). Take three readings for each method of determination, alternating one with the other. Before beginning the palpation measurement, count the pulse for 15 seconds and record the pulse rate per minute. During each blood pressure measurement, also note the pressure at which the mercury column begins to oscillate. Compare the systolic pressure determined by auscultation with the readings obtained by palpation and visual observation of oscillation. Explain the differences. Can you determine the diastolic pressure by palpation? 3. Effects of Body Position on Blood Pressure and Pulse Rate. Allow the subject to lie flat for 3 minutes, then make three blood pressure measurements by auscultation and take the pulse rate three times. Let the subject stand up, and take four blood pressure and pulse rate measurements in quick succession (approx. 1 minute intervals). Compare the systolic pressure, diastolic pressure, pulse pressure (PP = systolic pressure - diastolic pressure) and pulse rate in different positions. Explain the differences.

2 Blood Pressure Measurements Systolic/Diastolic Pulse Pressure at Pressures Rate which oscillation (mm Hg) (per min) begins (mm Hg) Comparison of methods Auscultatory 1 / Auscultatory 2 / Auscultatory 3 / Mean / Palpatory 1 Palpatory 2 Palpatory 3 Mean Body positions Supine 1 / Supine 2 / Supine 3 / Mean / Standing 1 / Standing 2 / Standing 3 / Standing 4 / Mean (2,3,4) /

3 4. Effects of Exercise on Blood Pressure and Pulse Rate: (One subject per table). After measurement of blood pressure and pulse rate in the control state (quiet standing), the subject performs 30 deep knee bends in 30 seconds, with the blood pressure cuff wrapped around his upper arm but disconnected from the manometer. Immediately at the end of the exercise, connect the cuff to the manometer, and determine blood pressure and pulse rate as soon as possible. Repeat these measurements (Note the time of measurement) until the values return to control levels. Using the control data and the first measurement obtained immediately after exercise, calculate the effects of exercise on stroke volume, cardiac output and total peripheral resistance by using the following assumptions: (a) the control cardiac index (cardiac output per unit body surface area) is 3.3 L/min/m 2, (b) the effect of exercise on stroke volume is proportional to its effect on pulse pressure, and (c) the mean arterial pressure equals [diastolic pressure + (pulse pressure/3)]. Calculation of Cardiac Output, Stroke Volume and Total Peripheral Resistance Control Exercise Measured Data Systolic pressure (SP, mm Hg) Diastolic pressure (DP, mm Hg) Pulse rate (HR, per min) Body surface area 1 (SA,M 2 : estimate from hgt./wt.) Calculated results Pulse pressure (PP = SP-DP, mm HG) Control cardiac output (CO c = 3.3 SA, L/min) Control stroke volume (SV c = CO c /HR c, ml) Exercise Stroke volume (SV E = SV c x PP E /PP c, ml) Exercise Cardiac output (CO E = SV E x HR E, L/min) Mean Arterial Pressure [MAP = DP + (PP/3), mm Hg] Total peripheral resistance (TPR=MAP/CO, mm Hg-sec/ml) Hemodynamic Effects of Exercise (percent of control): 100 HR E /HR c = % 100 SV E /SV c = % 100 CO E /CO c = % 100 MAP E /MAP c = % 100 TPR E /TPR c = % 1 Surface Area (cm 2 ) = Wt X Ht X Weight (Wt) is in kilograms, and height (Ht) is in centimeters. From DuBois and DuBois. Arch. Internal. Med. 17:865, 1916

4 Part II: Cold pressor test: Record blood pressure and pulse rate from right arm to 1 min intervals until a stable reading is obtained. Continue the recording and perform the cold pressure test by placing left hand and lower forearm in a basin containing equal parts of water and ice for 2 min. After removal of the hand from the basin, continue the recording for 3 more min. What is the effect of cold pressure test on blood pressure and heart rate? Control 1 min (in ice) 2 min (in ice) 3 min 4 min 5 min Blood Pressure (systolic/diastolic ) Pulse Rate (/min) Part III: Study of Skin 1.The Red Reaction. Draw a blunt instrument firmly across the forearm. The lighter flush of an arteriolar flare may be seen peripheral to the red reaction. 2.The Triple Response. Draw a blunt instrument 6 to 7 times over the same area of the skin. Look for local vasodilation, the flare, and local edema. 3.Veins. Examine the veins of the hand and then allow the hands to hang at the side. Note the size of the veins. What is the effect on the veins of opening and closing the fist several times? Raise the hand slowly from the subject s side. At what level do the veins collapse? What is the effect on the veins of the forearm and hand of applying a blood pressure cuff to the arm inflated to a pressure of 40 mm Hg for 3 to 5 minutes?

5 PART IV: Electrocardiography: Each electrocardiographic lead is labeled with the initials of the extremity to which it must be attached. The chest lead is designated similarly. In order to record the standard leads I, II and III, and leads avr, av1 and avf, it is only necessary to turn the dial to the leads desired. When recording the chest leads, the dial is turned to V, and electrocardiographic recordings are obtained by moving the chest lead to each of the standard sites, V1-6, as follows: V 1 - Fourth intercostal space at right sternal border V 2 - Fourth intercostal space at left sternal border V 3 - Halfway between V 2 and V 4 V 4 - Fifth intercostal space at mid clavicular line V 5 - Anterior axillary line at the same level as lead V 4 V 6 - Mid axillary line at the same level as leads V 4 and V 5 1. Identify P, QRS and T in each lead. 2. Use a stethoscope to listen to the heart sound at the apex. What is the relationship between electrocardiographic waves and the heart sounds? 3. With the use of Einthoven s triangle, determine the direction of the QRS axis from the mean QRS amplitudes in leads I and III. 4. Measure and calculate the following parameters from lead II: Chart speed = 25 mm/sec; 1mm = 0.04 sec R-R interval = mm PR interval = sec. QRS duration = sec. QT interval = sec. Ventricular rate = (25 60)/R-R =?/min This formula is derived from the following: time between beats (sec) the number of beats (per min) = (R-R interval)/(chart speed) = 60 seconds/time between beats

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