Posture and Blood Pressure Regulation: Integrative PhUn for High School Students Anna E. Stanhewicz, Rebecca S. Bruning, and Lacy M. Alexander Department of Kinesiology, Noll Laboratory, The Pennsylvania State University, University Park, PA ABSTRACT For PhUn week 2012 we worked with the 11 th and 12 th grade Anatomy and Physiology class at State College Area High School to share a hands-on lab activity about postural changes and blood pressure (BP) regulation. The session began with a discussion about BP. Students were prompted to answer questions about why BP was important and what challenges the circulatory system might face that would prevent blood from getting to the brain or other organs that need it. The class then broke into groups to make and test hypotheses about how posture would affect BP. Using a sphygmomanometer, each group measured sitting BP and heart rate (HR) for one subject. The subjects then laid down for 3 minutes and each group recorded a supine BP and HR. The subjects then stood up and each group recorded BP and HR immediately and again after 3 minutes of standing. We then discussed the results as a class and drew conclusions about how changes in posture affect BP and how the cardiovascular system responds. This activity introduced and investigated BP regulation, emphasized hypothesis formation and testing, and worked well with high school students who had a background in biology and health science. KEY QUESTION: HOW IS BLOOD PRESSURE CREATED AND MAINTAINED? Blood pressure is the force exerted by blood against the blood vessel walls. It is determined by how much blood is pumped, or cardiac output, and the peripheral resistance created by the blood vessels. When extra stressors are placed on the system, cardiac output and peripheral resistance balance each other to maintain a safe blood pressure. Blood pressure = cardiac output x peripheral resistance INTRODUCTION Vocabulary Terms: Stroke Volume (SV) – the volume of blood (in milliliters) that your heart expels with each beat. Cardiac output (CO) – the volume of blood (in liters) your heart pumps in one minute. Average resting cardiac output is 5 liters per minute. Cardiac output is equal to heart rate times stroke volume: CO = HR x SV Peripheral resistance – resistance to blood flow created by your blood vessels. Peripheral resistance goes up when your vessels get narrower and goes down when your vessels get wider. Mean Arterial Pressure (MAP) – the average pressure during a cardiac cycle in millimeters of mercury (mmHg). MAP determines the rate of flow through the blood vessels and can be calculated: MAP = diastolic pressure + (1/3)*(systolic pressure – diastolic pressure) Example: If resting blood pressure measured with a sphygmomanometer is 120/80 mmHg MAP = 80mmHg + (1/3)*(120mmHg – 80mmHg) MAP = 93 mmHg Figure 1. Schematic representation of variables that effect blood pressure used with the activity to help students understand and explain their results. LAB EXERCISE: EFFECT OF POSTURE ON BLOOD PRESSURE REGULATION Posture has a large influence on the mechanisms that maintain blood pressure. When we stand up, gravity pulls blood into the vessels in our legs, making it harder to get blood up to the brain. Heart rate, stroke volume and peripheral resistance have to adjust quickly to maintain a safe blood pressure. You will need: A stopwatch A sphygmomanometer A stethoscope A pillow Getting Started: Before you begin, collect some resting baseline data from your subject. Have your subject sit in a chair for 3 minutes, then measure heart rate and blood pressure. Heart rate ____________________________________ Systolic blood pressure _________________________ Diastolic blood pressure _________________________ Calculate mean arterial pressure _________________ LAB EXERCISE: EFFECT OF POSTURE ON BLOOD PRESSURE REGULATION Next, have your subject lie down on the table (pillow under their head) for 3 minutes then measure their heart rate and blood pressure. Heart rate ____________________________________ Systolic blood pressure _________________________ Diastolic blood pressure _________________________ Calculate mean arterial pressure _________________ Hypothesis 1: What do you think will happen to blood pressure immediately when your subject stands up? What will happen to heart rate? Hypothesis 2: What do you think will happen to blood pressure after three minutes of standing? What will happen to heart rate? Inflate the blood pressure cuff before your subject moves. Have your subject stand up and immediately record heart rate and blood pressure. Heart rate ____________________________________ Systolic blood pressure _________________________ Diastolic blood pressure _________________________ Calculate mean arterial pressure _________________ Wait three minutes, then record heart rate and blood pressure again. Heart rate ____________________________________ Systolic blood pressure _________________________ Diastolic blood pressure _________________________ Calculate mean arterial pressure _________________ Students collecting supine blood pressure and heart rate data on their subject. ACKNOWLEDGEMENTS A very special thanks to Jessica Kutz, Daniel Craighead, Christian Conlon, and Nathan Garvin for their help with this activity; to Dr. Tammy Gilmour and the students at State College Area High School for celebrating PhUn week with us; and to the APS for making PhUn week possible. Contact : Anna