Lower Body Negative Pressure Learning Task
Lower Body Negative Pressure Device

This learning task will test your knowledge on the effects of lower body negative pressure on several cardiovascular variables.

The crew member is placed into the lower body negative pressure device; an instrument which looks somewhat like a large iron tube. The tube covers the astronaut from the feet to the waist, creating an airtight seal around the waist. A pump then sucks air from the tube which creates a negative pressure (- 50 mmHg for our purposes) inside the tube, and hence around the legs of the subject. This in effect pulls blood from the upper part of the body to the legs. The pressure is lowered for about 50 minutes. You have hooked up several instruments to the subject which allow you to measure or estimate the following variables: 
(the abreviation in the parentheses is the same as found on the chart) 

  • heart rate  (HR)
  • blood pressure (arterial pressure)
  • cardiac output
  • stroke volume  (SV)
  • total peripheral resistance (TPR)
  • norepinephrine spillover (MSNA, NE spillover)
  • cardiac sympathetic nervous system activity (CSNA)
If the crew member has this stress applied on earth, can you predict not only the direction of change for each of the above variables but also how quickly during the 50 minutes of LBNP these changes occur? 

Suppose this stress is applied to our crew member in space.  How will the cardiovascular responses change after 2,8 and 16 days of space flight? 

Keep in mind that many of the baseline values for some of these variables will change in space.  See the figure from Maillet et. al. for some of these changes. (Note: the chart will open in a new window.)

Lower Body Negative Pressure Learning Task Answer


Figure 2-8 of Rowell's book provides the cardiovascular responses found on earth.  As the pressure drops to -50 mmHg cardiac output, and stroke volume decline while heart rate and forearm vascular resistance(not shown) iincreases. Muscle sympathetic nerve activity increases. Blood flow to the arms but mostly the splanchnic region decreases.  Due to the long duration application of this stress, 50 minutes, the cardiovasculr system makes both quick and slow adaptations.