Research Question (RQ) How does the position of the arm (cuff) in relation to the heart, affect the blood pressure[1] of non-diabetic, female, 16 year olds, in terms of Systolic Pressure[2] and Diastolic Pressure[3]?

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IB Biology

Human Physiology – Circulatory System – Open Investigation

Planning A

Research Question (RQ)

How does the position of the arm (cuff) in relation to the heart, affect the blood pressure of non-diabetic, female, 16 year olds, in terms of Systolic Pressure and Diastolic Pressure?

Hypothesis

It is known that there are many factors that influence blood pressure and blood pressure readings one of which will be explored in this experiment – the affect of the position of the monitored extremity (cuff) in relation to the heart.

Blood pressure readings may be influenced by body position because of variation in the vertical distance between heart and cuff level.’ (CAVELAARS Marinel; et al. – 2000)

 It is hypothesised that blood pressure will increase as the position of the monitored arm moves from ‘Below the Heart’ to ‘In Line With the Heart’ to ‘Above Heart’ in a proportional manner. To investigate this, the systolic pressure and diastolic pressures (mmHg) will be measured when the monitored arm is in various positions.

In line with this prediction, literature states that, ‘When the blood pressure (BP) is measured, the arm should be at the level of the heart’ (STEPHEN S.EHRLICH, M.D., - 2004) and that the values thus produced will be the true blood pressure values.’ Therefore the blood pressure values calculated with the monitored arm ‘In Line With the Heart’ will be treated as the control values and the other values will be analysed in relation to this control as that is the advised method for blood pressure measurement.

Past studies into pulse oxygenation (SpO2) have shows that, ‘by merely changing the position of the monitored extremity, the SpO2 can change by up to six percent. In this study, the arm was raised 90 degrees from surpine and this resulted in a highly significant decrease in SpO2 with elevation of the monitored arm.’ (Cooke, J., Johansen, J., 2000)

It is expected that the systolic and diastolic pressures values in this experiment, will change in a similar fashion to the SpO2 values in the Pulse Oxygenation experiment, as a result of moving the monitored arm. Thus it is hypothesised that when the monitored arm is held above the heart, the systolic and diastolic pressures will be lower than the control.

The systolic and diastolic blood pressure measured with the arm perpendicular to the body was significantly lower than with the arm in a parallel position.(UCSD Medical Researchers - 2004)

In line with this, it is hypothesised that the systolic and diastolic blood pressure values for when the monitored arm is parallel to the body (‘Below the Heart’), will be significantly higher than the control.

The hypothesised trend of the subjects’ systolic and diastolic pressures (mmHg) is illustrated in the Graph below.

Graph 1: The hypothesised trend of the subjects’ systolic and diastolic pressures (mmHg)

Variables

Independent variable

  • Position of Arm
  • Above Heart
  • In Line With Heart (Control)
  • Below Heart

Dependent variable

  • Blood Pressure
  • Systolic Pressure (mmHg)
  • Diastolic Pressure (mmHg)

Controlled variables

  • Environmental conditions
  • Testing Procedures/Method
  • 16 year old Subjects
  • Female Subjects
  • Non-Diabetic Subjects

Planning B

Apparatus and Materials:

  • 3 x CASCADE Blood Pressure Monitor (pressure 0~200mmHg)
  • 3 x JEX103 Stopwatches
  • Paper Data Collection Table
  • Writing Utensils
  • 10 x Non-Diabetic, 16 year old, Female Subjects:

Method:

  1. The CASCADE Blood Pressure monitor is fixed on the non-dominant wrist of the subject – positioned as outlined in the directions.
  2. Standing, the subject then held their arm above their heart (parallel to their body – directly above their head) for 3 minutes.
  3. After 3 minutes, the Blood Pressure of the subject was measured 3 times. The systolic and diastolic pressure values for this arm position were then recorded in the paper data collection table under the heading – ‘directly above heart’. These values were measured while the subject was still standing.
  4. Standing, the subject then held their arm at heart level – perpendicular to their body with a slight bend in the elbow – for 3 minutes.
  5. After 3 minutes, the Blood Pressure of the subject was measured 3 times. The systolic and diastolic pressure values for these arm positions were then recorded in the paper data collection table under the heading – ‘at heart level’. These values were measured while the subject was still standing.
  6. Standing, the subject then held their arm down by their side – parallel to their body – for 3 minutes.
  7. After 3 minutes, the Blood Pressure of the subject was measured 3 times. The systolic and diastolic pressure values for these arm positions were then recorded in the paper data collection table under the heading – ‘down by side’. These values were measured while the subject was still standing.

*        This method was repeated for each subject so that there were three trial values for each of the three positions of the arm. This resulted in three values for both systolic and diastolic pressures for each subject.

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Method for controlling variables:

  • Environmental conditions:
  • The aim to control the environmental conditions is to carry out the tests under similar weather conditions. The experimental tests were also run at roughly the same time of day so as not to disadvantage the participants.
  • Testing Procedures/Method and Equipment used
  • The same method will be followed and same equipment used for each test so that the errors can be minimised. The positioning of the blood pressure device was positioned by the same person, so as to minimise the errors involved with ...

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