Huda is a 34-year-old dietician at an academic medical center. She believes in the importance of a healthy lifestyle and was happy when the division of cardiology recruited healthy female volunteers for a study on the cardiovascular responses to exercise. Huda met the study criteria (i.e. 25-40 years old, no medications, normal weight for height, normal blood pressure), and she was selected for participation. Control measurements were taken of Huda's blood pressure, heart rate, and arterial and venous PO2, her stroke volume was estimated. Huda then walked on the treadmill for 30 minutes at 3 miles per hour. Her blood pressure and heart rate were monitored continuously, and her arterial and venous PO2 were measured at the end of the exercise period
• Systolic blood pressure
control (pre-exercise) = 110 mm Hg
Exercise= 145 mm Hg.
• Diastolic blood pressure.
control (pre-exercise) = 70 mm Hg
Exercise= 70 mm Hg
• Heart rate
control (pre-exercise)= 75 beats /min
Exercise= 130 beats /min
• Stroke volume (estimated).
control (pre-exercise)= 80 ml
Exercise= 110 ml
• Arterial PO2
control (pre-exercise)= 100 mm Hg
Exercise= 100 mm Hg
• Venous PO2
control (pre-exercise)= 40 mm Hg
Exercise= 25 mm Hg
1. Describe the cardiovascular responses to moderate exercise, including the roles of the autonomic nervous system and local control of blood flow in skeletal muscle. What is the ultimate "purpose" of these cardiovascular responses?
2. What were Huda's mean arterial pressure and pulse pressure for the control and exercise periods, respectively?
3. What was her cardiac output for the control and exercise periods, respectively? Of the two factors that contribute to cardiac output (stroke volume and heart rate), which factor made the greater contribution to the increase in cardiac output that was seen when Huda exercised, or do these factors have equal weight?
4. What is the significance of the observed change in pulse pressure?
5. Why was systolic pressure increased during exercise? Why did diastolic pressure remain unchanged?
6. If Huda had been taking propranolol (a beta adrenergic antagonist), how might the responses to exercise have been different? Would her "exercise tolerance" have increased, decreased, or remained the same?
7. Early in the exercise period, Huda's skin was cool to the touch. However, at the peak of exercise, her skin was flushed and very warm to the touch. What mechanisms were responsible for these changes in skin color and temperature as the exercise progressed?
8. Arterial and venous PO2 were measured before and after exercise. Explain why venous PO2 decreased, but arterial PO2 did not?
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