Infrasound refers to sound waves or vibrations with a frequency below the audibility range of the human ear. Even though infrasound cannot be heard, it can produce physiological effects in humans. Mechanical science engineers in China studied the impact of infrasound on a person’s blood pressure and heart rate (Journal of Low Frequency Noise, Vibration and Active Control, Mar. 2004). Six university students were exposed to infrasound for 1 hour. The table gives the blood pressure and heart rate for each student, both before and after exposure.

a. Compare the before and after mean systolic blood pressure readings using a 99% confidence interval. Interpret the result.

b. Compare the before and after mean diastolic blood pressure readings using a 99% confidence interval. Interpret the result.

c. Compare the before and after mean heart rate readings using a 99% confidence interval. Interpret the result.

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INFRASOUND Systolic Pressure Diastolic Pressure (mm Hg) Heart Rate (mm Hg) (beats/min) Student Before After Before After Before After 1 105 118 60 73 70 70 2 113 129 60 73 69 80 106 117 60 79 76 84 4 126 134 79 86 77 86 113 115 73 66 64 76 3.