cardio_hw_2006 - 16.423 Space Biomedical Engineering and...

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16.423 Space Biomedical Engineering and Life Support Cardiovascular Adaptation to Microgravity A series of pre-flight physiologic tests were performed on astronaut J.B. One test was the so-called “stand test”, in which the subject was asked to rise quickly from a supine to a standing position, and to remain standing quietly for 15–20 minutes (Figure 1). The electrocardiogram and arterial blood pressure were continuously monitored. Figure 1: A theoretical stand test is shown in Figure 2 for the case in which there are NO operational control systems. Heart rate and BP are plotted as functions of time for a short baseline period (lying) and the first 2 minutes after standing. The time of the change in posture is t = 0. s� i�n�)� -20� 0� 20� 40� 60� 80� 60� 70� 80� 90� A�B� m� -20� 0� 20� 40� 60� 80� 0� 10� 20� 30� 40� 50� 60� 70� 80� 90� H�e�a�r�t�R�a�t�e�(�b�e�a�t� /�m� 10�0� 12�0� 10�0� 11�0� 12�0� 13�0� 14�0� P�(�m� H�g�)� 10�0� 12�0� 10�0� 11�0� 12�0� 13�0� 14�0� T�i�m�e�(�s�e�c�)� T�i�m�e�(�s�e�c�)� Figure 2: HR and BP in stand test—no CV controls
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1. Compare the heart rate and blood pressure at time = + 100 sec to the baseline values at time = − 10 sec. What is the physiologic basis for the observed change in arterial BP?
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