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INTRODUCTION

Since the heart is a pulsatile pump, blood is expelled into the arterial system intermittently causing pressure pulses of blood, which is rapidly introduced into the arteries during systole, causing a large pressure pulse that progresses out into the arterial tree. The increased peripheral blood volume accompanying systole causes the arterial pressure in the periphery to increase to a peak value (systolic pressure). During diastole the peripheral run-off of blood exceeds the volume of blood entering the arterial system thereby allowing the blood pressure to decrease to a base value (diastolic pressure).  In the resting young adult, the systolic (SBP) and diastolic pressure (DBP) in the brachial artery at the cubital fossa are normally 110-130 and 70-90 mmHg respectively. This produces a mean pressure of about 100 mmHg.

 

 

 

Pulse pressure (PP) is the difference between SBP and DBP and lies in the range of 30 to 70 mmHg. PP provides information concerning stroke volume and arterial capacitance. Under normal conditions the PP is directly related to the volume run off to the periphery during diastole.

 

The arterial blood pressure is a measurement routinely employed for medical diagnosis since it provides a useful clue as to one’s cardiovascular status.  The primary determinants of blood pressure are flow and peripheral resistance.  The relationship can be expressed as follows:

   

 

The flow or more specifically, the cardiac output (Q_c) is a product of stroke volume (SV) and heart rate (HR). The peripheral resistance depends on the setting of the arterioles. The setting is determined by hormone and neural factors.  If the arterioles vasodilate, resistance will be minimal and visa versa.

The diagnostic value of blood pressure measurements during exercise is well established.  Adjustment to exercise demands the simultaneous co-operation of a number of processes concerned with oxygen delivery and consumption.  At the onset of exercise, metabolic changes in the active muscles cause an immediate dilation of the resistance vessels in the active muscles.  If the systemic arterial pressure is to be maintained (a condition necessary to insure peripheral flow) the volume of blood injected into the arterial tree must be increased by either 1) increasing the cardiac output, 2) reducing flow to other vascular beds or 3) a combination of the two.  Rapid increments in heart rate and stroke volume during exercise cause the SBP to increase immediately.  As exercise is increased, the SBP increases proportionally while DBP increases to a much lesser extent.  The net effect is an increasing pulse pressure indicating increased perfusion of the peripheral muscles.

 

Blood pressure measurements are valuable in assessing the safety of exercise. During maximal exercise, the systolic pressure seldom rises over 220 mmHg in the normal subject.  The DBP may increase 10 to 15 mmHg and the mean pressure may increase 10 to 20 mmHg. The typical cut-off values for blood pressure are SBP above 240 mmHg and DPB above 120 mmHg.

 

Blood pressure can be determined either indirectly or directly.  The direct method, the most accurate procedure, involves introducing a catheter into a peripheral artery and determining the pressure by means of a manometer.  The indirect method involves the use of a sphygmomanometer and stethoscope.  A cuff is wrapped around the medial region of the upper arm. The cuff is inflated to a pressure that is 30 mmHg above the expected systolic pressure.  This will completely occlude blood flow.  A stethoscope is lightly applied over the brachial artery in the cubital fossa while the cuff pressure is slowly released. Eventually, the blood pressure will become greater than the cuff pressure thereby allowing blood to pass the cuff.  As this occurs, a number of sounds (Korotkoff sounds) may be heard.  The sounds are divided into phases as follows:

 

 

The initial sound caused by turbulent flow is taken as the systolic pressure. The diastolic pressure occurs when the sound suddenly becomes muffled or disappears due to streamlined non-turbulent flow. In some disease states, such as aortic insufficiency, muffled sound can be heard down to cuff pressures of close to zero. Exercise also tends to produce an abnormally low disappearance point.  Sometimes the tapping sound doesn’t go away since blood is large and flowing.

 

Interaction of heart rate and blood pressure. As mentioned previously, heart rate is affected by both its rate of pumping (beats^.min^-1) and the force or resistance (mmHg) that it encounters. This power output of the heart is often referred to as the Rate Pressure Product (RPP) because of the multiplication of the two factors, systolic blood pressure and (SBP) and heart rate (HR). The RPP (RPP = SBP x HR) is not meant to reflect differences in stroke volumes between individuals but is an accurate reflection of the myocardial oxygen requirements (MVO₂). It should be recognized that the rate of myocardial fiber shortening is another important factor in MVO₂ that is not included in the RPP. 

Lab Assignment

 

In this lab you will be measuring blood pressure at rest and during exercise. The skills required to measure blood pressure are not technically difficult, but they do require practice.

 

Procedures  – Measuring Blood Pressure A stethoscope and a sphygmomanometer are used in the indirect measurement of systemic arterial blood pressure. All students will participate in the lab.     1.              Wrap the deflated cuff around the left arm. The lower margin of the cuff should be 2-3 cm above the antecubital fossa (i.e. elbow joint). The boundaries of the fossa can be seen and felt. The pronator teres muscle (arising from the lateral supracondylar ridge of the humerus) forms the lateral boundary. The tendon of the biceps brachii muscle, which inserts on the radial tuberosity of the radius, can be palpated as it passes downward into the fossa. The bicipital aponeurosis can be felt as it leaves the tendon to join the deep fascia on the medial side of the forearm.   2.              After the cuff is in place the brachial artery is located approx. 1 cm below the elbow joint beneath the bicipital aponeurosis. Given the variation in the point of origin of the radial and ulnar divisions of the brachial artery, locating the brachial artery may require first palpating its pulse in the antecubital fossa.   3.              Once the brachial artery has been located, the diaphragm of the stethoscope is then applied firmly over the artery and the cuff is inflated.           A.        Responses at Rest 1.     Have each subject rest quietly on the cycle ergometer and determine the heart rate and blood pressure. If the blood pressure is > 144/94 mmHg do not complete the exercise portion of this lab.   B.         Responses to Exercise 1.              Power output will be set at 300 kpm.min-1 (50 Watts) and the subject will exercise for 2 minutes.   2.              After 1 minute of exercise, immediately record HR and blood pressure while the subject continues to exercise for another 1 minute.   3.              After this first stage of exercise, power output will then be increased to 600 kpm.min-1 (100 Watts) and the subject will exercise for 2 minutes. After 1 minute of exercise, immediately record HR and blood pressure while the subject continues to exercise for another 1 minute.   4.              After this second stage of exercise, power output will then be increased to 900 kpm.min-1 (150 Watts) and the subject will exercise for 2 minutes. After 1 minute of exercise, immediately record HR and blood pressure while the subject continues to exercise for another 1 minute.   5.              After this third stage of exercise, power output will be decreased back to 300 kpm.min-1 (50 Watts) and the subject will exercise for 2 minutes. After 1 minute of exercise, immediately record HR and blood pressure while the subject continues to exercise for another 1 minute.

 

BLOOD PRESSURE AND EXERCISE – WORK SHEET

 

 

Name __________________________________  Age _____  Sex _____ Date _____________

 

 

PRIVATE	SBP (mm Hg)	DBP (mm Hg)	PULSE Pressure (mm Hg)	MAP (mm Hg)	HR (bpm)	RPP
Rest
300 kpm.min-1
600 kpm.min-1
900 kpm.min-1
300 kpm.min-1

 

 

 

Calculations:

1.              Calculate Pulse Pressure, Mean Arterial Pressure and Rate Pressure Product.

 

2.              Using the resting, exercise and recovery data, plot SBP, DBP, Pulse pressure and Mean Arterial Pressure.

 

3.              Review the graph and describe how SBP, DBP and mean arterial pressure changed as the exercise intensity increased.

 

4.              State the physiological mechanisms responsible for the changes observed in blood pressure and discuss how these changes were mediated.

 

5.              What does the RPP in the above table represent and why did it change with exercise?