Computer
Diurnal Blood Pressure Variation
9
Blood pressure is determined by the output of the heart and the resistance to flow in the vascular
system. These, in turn, are affected by factors such as the levels of certain hormones (renin,
angiotensin II, aldosterone, cortisol, epinephrine, and norepinephrine), physical activity,
emotional or physical stress, salt intake, and smoking. Blood pressure usually reaches a high at
6 am and a low between 2 and 4 a.m. Small peaks and valleys occur every one to two hours
throughout the day. For this reason, health care providers measure blood pressure at random
times on multiple occasions before diagnosing hypertension, or elevated blood pressure.
Nearly one in three American adults has high blood pressure, and of those who have high blood
pressure one-third do not know that they have it. Uncontrolled hypertension increases the risk of
stroke, mental impairment, heart disease and kidney disease. The following table shows the
guidelines set forth by the Joint National Committee on Prevention, Detection, Evaluation, and
Treatment of High Blood Pressure in 2003.
Blood Pressure
Category
140/90 or higher
High
120–139/80–89
Pre-hypertension
119/79 or below
Normal
When hypertension is diagnosed, a clinician may prescribe lifestyle changes (e.g., diet, exercise,
stress reduction). If these are ineffective, medication is recommended. Different categories of
medication act on the heart, peripheral vascular system, central or peripheral nervous system, or
hormonal system to lower the blood pressure.
In this experiment, you will take multiple blood pressure readings over the course of two or more
days and analyze the variability in these readings.
Important: The equipment used in this experiment is for educational purposes only and should
not be used to diagnose blood pressure disorders.
OBJECTIVES
In this experiment, you will

Obtain graphical representation of blood pressure measured at different times of the day.
 Analyze the variability of blood pressure readings individually and as a class.
 Correlate your findings with variables that may have influenced your blood pressure.
MATERIALS
computer
Vernier computer interface
Human Physiology with Vernier
Logger Pro
Vernier Blood Pressure Sensor
9-1
Computer 9
PROCEDURE
1. Connect the Blood Pressure Sensor to the Vernier computer interface. Open the file
“09 Diurnal Blood Pressure” from the Human Physiology with Vernier folder.
2. Attach the Blood Pressure Sensor to the blood pressure cuff if it is not
already attached. There are two rubber tubes connected to the cuff. One
tube has a black Luer-lock connector at the end and the other tube has a
bulb pump attached. Connect the Luer-lock connector to the stem on the
Blood Pressure Sensor with a gentle half turn.
3. Attach the blood pressure cuff to the upper arm, approximately 2 cm above
the elbow. The two rubber hoses from the cuff should be positioned over
the biceps muscle (brachial artery) and not under the arm (see Figure 1).
4. Have the subject sit quietly in a chair and avoid moving his or her arm or
hand during blood pressure measurements.
Figure 1
5. Click
to begin data collection. Immediately begin to pump until the cuff pressure
reaches at least 160 mm Hg. Stop pumping. The cuff will slowly deflate and the pressure will
fall. During this time the pulse and the systolic, diastolic, and mean arterial pressures will be
calculated by the software. These will be displayed on the computer screen. When the blood
pressure readings have stabilized (after cuff pressure drops below 50 mm Hg), click
to
end data collection and release the pressure from the cuff.
6. Store your data by choosing Store Latest Run from the Experiment menu.
7. Choose Text Annotation from the Insert menu. Label the run with the date and time it was
taken.
8. Enter the pulse and the systolic, diastolic, and mean arterial pressures in Table 1. These
values are also stored on Page 2 of the experiment file.
9. Save the experiment file as instructed by your teacher.
10. To collect additional data, open your experiment file and repeat Steps 2–9. Take at least 6
readings over 2 or more days. The readings taken during any one day should be separated by
at least 3–4 hours. Different times of the day should be represented in your data (i.e., early
morning, late morning, afternoon).
11. Complete Table 2 using either the data that was stored on Page 2 of your experiment file or
the data you recorded in Table 1.
12. Compile class data to complete Table 3.
9-2
Human Physiology with Vernier
Diurnal Blood Pressure Variation
DATA
Table 1–Individual Data
Run
Time of day
(hour: minute)
Systolic
pressure
(mm Hg)
Diastolic
pressure
(mm Hg)
MAP
(mm Hg)
Pulse (bpm)
Table 2–Individual Data
Blood pressure
reading
Maximum
∆ Blood pressure
Minimum
Systolic (mm Hg)
Diastolic (mm Hg)
MAP (mm Hg)
Pulse (bpm)
Table 3–Class Average Data
Time of day
Systolic
(mm Hg)
Diastolic
(mm Hg)
MAP
(mm Hg)
Pulse
(bpm)
Early morning (6–8 a.m.)
Mid-morning (8–10 a.m.)
Late morning (10–12 p.m.)
Early afternoon (12–2 p.m.)
Mid-afternoon (2–4 p.m.)
Late afternoon (4–5 p.m.)
Human Physiology with Vernier
9-3
Computer 9
DATA ANALYSIS
1. At what time of day did you record your highest blood pressure? Lowest? How much
variation was there between these two readings? It is common to see a higher blood pressure
in the early morning hours. Do your findings agree with this? Do the class average readings
agree with this?
2. List any factors that may have affected your blood pressure at the various times at which it
was measured (i.e., relation to lunch, physical activity, stress, smoking).
3. According to your data, does it appear that the blood pressure is dependent on pulse? Explain
your findings based on the factors that determine blood pressure, as listed in the Introduction
to this experiment.
4. By what percent did your systolic blood pressure vary? Use the following equation to
calculate this value:
Blood Pressure
 100%
Minimum Blood Pressure
5. Find the percent change in your diastolic pressure, MAP, and pulse using similar equations.
6. Calculate the percent change from the upper limit of normal for systolic and diastolic blood
pressures (seen in the chart on the first page of this experiment) and the lower limit of
hypertension.
7. Your patient, Mrs. Jones, is visiting you for her annual physical. Her blood pressure is mildly
elevated. What should you recommend to her as a course of action?
9-4
Human Physiology with Vernier
Diurnal Blood Pressure Variation
8. Adrenalin (epinephrine) is used to treat acute asthma attacks, severe allergic reactions, and
shock. What would you anticipate would happen to blood pressure and pulse after a shot of
epinephrine has been given?
9. Blood pressure is directly related to (1) heart rate, (2) resistance in the peripheral blood
vessels, (3) blood volume, and (4) levels of stress hormones, among other factors. For each of
the following classes of medicines, describe which of these four factors is affected:
a. calcium channel blockers dilate arterioles
b. diuretics cause a loss of fluid from the body
c. angiotensin-converting enzyme inhibitors stop conversion of angiotensin I to angiotensin
II, which is a potent constrictor of blood vessels
d. beta blockers inhibit the sympathetic nervous system
EXTENSIONS
1. Continue blood pressure measurements beyond the hours prescribed in this experiment (i.e.
between every class period/hourly/late at night, etc.).
2. Measure blood pressure before and after playing a fast-paced video game for 10 minutes.
Human Physiology with Vernier
9-5