Ambulatory Blood Pressure Monitoring of High School Students in Test

Ambulatory Blood Pressure Monitoring of High School Students in Test-Taking Circumstances

Monitoring ambulatory blood pressure as a means of diagnosing hypertension has grown in the last thirty years from an obscure technique to a common clinical practice. A major purpose of research involving ambulatory blood pressure monitoring is to investigate factors that effect blood pressure. This study was the first designed to use ambulatory blood pressure monitoring to evaluate the blood pressure response to a test-taking situation in a population of high school students.

1) Systolic and diastolic blood pressure and heart rate will be higher in subjects during a test period than during the remainder of the school day, and

2) The blood pressures and heart rate recorded during the test period on the test day will be higher than those recorded during the same subject period on the non-test day.

Surprisingly, no studies have yet been performed to determine the effects that taking tests may have on cardiovascular parameters in subjects in a high-school population. This study was designed to do so. Some of these parameters examined in this study were blood pressure (systolic and diastolic), and heart rate. Blood pressure is the pressure or tension of the blood within the arteries, maintained by the contraction of the left ventricle, the resistance of the arterioles and capillaries, the elasticity of the arterial walls, as well as the viscosity and volume of the blood (Stedman’s Medical Dictionary, 1976). Blood pressure is expressed in millimeters of mercury (mmHg). Systolic blood pressure is the pressure during or resulting from systolic contraction of a cardiac chamber; more specifically, the highest arterial blood pressure reached during any ventricular cycle (Stedman’s Medical Dictionary, 1976). Diastolic blood pressure is the pressure during or resulting from diastolic relaxation of a cardiac chamber; more specifically, the lowest arterial blood pressure reached during any ventricular cycle (Stedman’s Medical Dictionary, 1976). The heart rate is also a parameter that is usually measured during cardiac testing and is the rate of the heart’s beat, recorded as the number of beats per minute (Stedman’s Medical Dictionary, 1976).

Hypertension is a problem that greatly affects the adult population of the world, and can be defined as high arterial blood pressure (Stedman’s Medical Dictionary, 1976) dependant upon age and gender. High values are generally described as systolic blood pressure of 140 mmHg or greater, diastolic blood pressure of 90 mmHg or greater, or taking antihypertensive medication (Joint National Committee on the Prevention, Detection, Evaluation, and Treatment of High Blood Pressure, 1997). It is important to note that while the number of teenagers who suffer from hypertension is much lower than that of adults, it is still a problem (Joint National Committee on Prevention, Evaluation, and Treatment of High Blood Pressure, 1997).

Hypertension in teens is defined as systolic or diastolic blood pressure higher than the ninety-fifth percentile for gender and age (Loggie and Sardegna, 1997).

Systolic Blood Pressure (mmHg)			Diastolic Blood Pressure (mmHg)
Age	Male	Female	Age	Male	Female
14	132	130	14	85	85
15	135	131	15	86	86
16	138	132	16	87	86
17	140	132	17	89	86

Table 1. Cutoff (ninety-fifth percentile) for hypertension by age and gender (Loggie and Sardegna, 1997).

Although most teens are normotensive under usual ambulatory and clinical conditions, blood pressure can rise significantly during times of stress. This pattern may continue into adulthood and contribute to heart disease and other effects of hypertension later in life. Therefore, it is important to study cardiovascular responses to everyday stress in high school-aged teens. This study examined how the blood pressure of high school students responds to test-taking, a stressful situation into which students are regularly placed.

Subjects included ten (10) high school students at Cherry Hill High School East, a suburban public school in Cherry Hill, New Jersey. Subjects were all juniors (grade 11) enrolled in at least three (3) honors or AP (Advanced Placement) level courses and were selected by volunteering. There were five (5) female (2 Asian-American) and five (5) male (2 Asian-American, 1 African-American) subjects.

All measurements of diastolic blood pressure, systolic blood pressure, and heart rate were collected using the SpaceLabs Ambulatory Blood Pressure Monitor 90207 (Figure 1). Subjects wore the cuff on their non-dominant arms so that writing would not be hindered.

The SpaceLabs model 90207 uses the oscillometric method of measurement. This method is an ambulatory blood pressure recording technique using the measurement of oscillations of pressure in a sphygmomanometer cuff during its gradual deflation (Pickering, T.G., and Blank, S.G., 1990). Measurement time is generally between thirty-five and fifty seconds. The physical properties are 1.1 inches x 4.5 inches x 3.4 inches and 12.2 ounces with four AA batteries (Manufacturer’s Material, SpaceLabs Medical Inc., 1992). The device therefore causes minimal disturbance to the subject.

Figure 1. SpaceLabs 90207 ambulatory blood pressure monitor (SpaceLabs Medical Inc., 1992).

The SpaceLabs’ Model 90121-1 Report Management system is used for data recording. Data is transferred directly from the monitor to an IBM-compatible computer by use of a cable (SpaceLabs Medical Inc., 2000).

The device is fairly quiet when taking readings. However, it was recommended that subjects wear baggy shirts in order to muffle the sound and hide the monitor if they so desired.

The SpaceLabs model 90207 has been validated for use in adults under the protocol of both the British Hypertension Society (BHS) and the Association for the Advancement of Medical Instrumentation (AAMI) (Marquez Contreras et al., 1998). However, it was not well validated in children and adolescents (aged 6 to 18) (Mayoral Sanchez, 1994). The device satisfies the criteria for the measurement of systolic but not diastolic blood pressure under the protocol of both the BHS and AAMI (Marquez Contreras et al., 1998). A noted source of error was kinked tubing due to the fact that the cable was too long for the patient (Belsha et al., 1996). As a result of that finding, tubing was adjusted to body size during this study in order to decrease error.

Subjects were interviewed at the end of each day to determine if there were any unusual factors that might have influenced readings. The only significant factor noted was that the monitor often failed to take successful readings between periods when the subjects were walking in the halls.

Volunteers filled out a survey including the following information: age, height, weight, gender, ethnicity, and class schedule. These factors were taken into account during the evaluation of data.

Subjects were monitored on two full school days (8:00 a.m. to 2:30 p.m., divided into eight periods of forty-two minutes with four minutes between periods). On one of these days, the test day, the subject took a test in one of four academic subject areas (science, mathematics, English, or history). The subject took no tests on the other day, the non-test day, which was used as control.

On each day, the monitor was initialized and put on the participant (Figure 2) during homeroom (8:00 to 8:10 a.m.) and an initial reading was taken. Thereafter, readings were taken every twelve minutes until 2:30 p.m. At that time, the device was removed and data was transferred from the monitor to a computer for storage and analysis. Whether or not the test day preceded or followed the non-test day was not a considered factor.

Students were excused from physical education on both days of monitoring in order to protect the device from damage and to reduce any physical activity that would yield incorrect readings.

After a participant had completed both days of recording, systolic blood pressure, diastolic blood pressure, and heart rate readings taken during the test were compared with readings taken at the same time on the non-test day. Mean systolic and diastolic blood pressures and heart rate data from the test day were compared with the data recorded during the test period itself. Matched pair T-tests were performed for both sets of data. A p-value less than 0.05 was considered statistically significant.

The mean systolic blood pressure, diastolic blood pressure, and heart rate were found for each school period. The mean values for the test period were compared with the mean values over the entire test day (including from the test period). The mean values for the test period were also compared with the mean values from the same period on the non-test day. The p-values from these matched pair T-tests are as follows:

	Test Period	Non-Test Period	p-value
Systolic BP	121.47±10.46	117.19±10.69	0.029
Diastolic BP	72.24±6.10	69.62±7.48	0.136
Heart Rate*	84.05±14.01	76.38±9.44	0.003

	Test Period	Test Day	p-value
Systolic BP	121.47±10.46	119±9.60	0.017
Diastolic BP	72.24±6.10	71.69±5.17	0.219
Heart Rate	84.05±14.01	84.15±12.72	0.532
data given as mean ±variance p-values are from matched pair t-tests * : extreme outlier omitted

TABLE 2: Comparison of data from test period with data from non-test period and entire test day, respectively.

There were statistically significant differences between the mean heart rates (p=0.003) and mean systolic blood pressures (p=0.029) during the test period and the non-test period. There was also a statistically significant difference between the mean systolic blood pressure during the test period and the mean systolic blood pressure throughout the entire test day (p=0.017).

The difference between the mean diastolic blood pressures during the test period and the non-test period was not statistically significant (p=0.136). Also not statistically significant were the differences between the mean diastolic blood pressure (p=0.219) and mean heart rate during the test period compared to the entire test day (p=0.532).

There are several limitations to any study involving ambulatory blood pressure and others more specific to this proposed study. Ambulatory blood pressure monitors are not able to accurately record the blood pressure level during strenuous physical activity (Mallion et al., 1999). To do so accurately would require the use of an intra-arterial monitor, which is invasive (and therefore not appropriate for this study).

Another limitation is that measurements may only be taken once every fifteen to twenty minutes when recording takes place over a twenty-four hour period. When readings are taken more frequently, subjects often become uncomfortable and not able to tolerate the extended recordings needed for the study (White, 1990). Because subjects only wore the cuff for a period of six hours, it was determined that taking readings at twelve-minute intervals was most appropriate.

Time constraints allow only a small number of students to be tested. There were only two monitors available for use during the study, limiting only two students to be monitored per school day. This was further limited by the need to test every student on both a test day and non-test day.

There is the possibility that having an ABP monitor on may increase the stress associated with taking a test. This could cause a blood pressure and/or heart rate response to the test-taking to appear more dramatic.

The study showed that systolic blood pressure and heart rate but not diastolic blood pressure were higher during the test period than during the non-test period. Also, systolic blood pressure, but not heart rate or diastolic blood pressure was higher during the test period than the rest of the day. The results of this study verified both hypotheses because at least one of the variables being tested increased during testing relative to both the rest of the test day and to the same period on the non-test day. The small sample size may be why diastolic blood pressure was not found to be significantly higher when subjects were taking tests.

Additionally, similar studies performed using subjects from different populations within high schools would be of interest. Results from further investigations may differ from the results of this study. As this was the first study of its nature, it is recommended that the model used for this study be used in the future when performing other investigations involving ambulatory blood pressure in high school populations. It is important to do further research in this almost unexplored field in order to maximize potential health treatments for adolescents.

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