MEASUREMENT OF LEG VOLUME IN SIMULATED LAUNCH AND MICROGRAVITY (Adapted from Human Physiology in Space, by Lujan & White)
BACKGROUND A headward fluid shift during spaceflight results in a so-called “puffy-face, bird-leg” appearance. This fluid shift actually begins pre-launch, when astronauts are in a reclined seating position with legs up, and is believed to be related to a variety of subsequent cardiovascular and body-fluid changes.
The net fluid shift can be estimated in several ways, one of which is to estimate the loss of fluid volume in the legs over time. In turn, one way to measure this fluid volume loss is by measuring the circumference of the leg(s) at several points and then calculating volume as if each segment were a truncated cone. For any two measurement sites, as shown in the diagram to the right, the estimated volume of the idealized truncated cone in between is:
2 2 Volume = h [(R1 + R1R2 + R2 ) 3],
where h is the height of the segment and R is radius at a given site. The radius is determined from a measurement of circumference by the equation:
R = Circumference 2
Final leg volume is calculated by summing the volume of each segment.
MATERIALS Measuring tape, in millimeters or ruler and non-elastic string Watch or clock with second hand Chair (optional) or other way to elevate legs Washable marking pen
GENERAL PROCEDURE 1. Pick at least two sites on the subject’s bare leg (e.g., A & D above), preferably four (e.g., A & B plus B & C to focus on the thigh or A & B plus D & E to focus on upper and lower leg). Describe their location (e.g., “upper thigh” or “biggest part of calf”) and illustrate it in your report. 2. Mark spots with a washable pen on the front and back of the leg when the subject is standing (before the experiment begins), trying to make the marks so they define a horizontal plane 3. Make observations after having the subject stand at rest (i.e., legs as relaxed as possible) for 10 minutes 4. Make observations after having the subject recline 10 minutes, with legs elevated and relaxed. Legs can be elevated by placing the feet on a chair, against the wall, or on a large stack of books. Be sure to record the amount of leg elevation.
Col R.D. Reed, USAF Academy For Further Thought: How might tensing leg muscles (instead of relaxing as directed) affect results? Other factors or possible experimental variables to consider in evaluating results include:
Number of subjects tested Number and location of sites used on leg Subject height and weight Measuring technique Subject sex (if female, phase of menstrual cycle) Thickness of tape/string Subject leg shape Degree of leg elevation Subject level of leg musculature and fat Duration of each test condition Subject state of hydration Room temperature Subject pre-experiment activity (exercising, eating, etc.) Other?
OBSERVATIONS TO RECORD 1. Subject height, weight, and sex as basic background variables 2. Heart rate (timed for 60 seconds each, 2 times during the last 23 minutes of each condition) 3. Leg circumference at each site (measured during the last 12 minutes of each condition) a. At least 2 measurements per site under each condition b. Always measure in the same way & at the same place(s) c. Do not indent the skin when measuring circumference 4. Vertical distance between sites, so volume can be calculated 5. Visual observations of subject’s face and leg appearance (skin, fullness of veins, etc.) 6. Any reported sensations by the subject pertinent to possible fluid shifts
CALCULATE 1. Heart rate under each condition 2. Estimated volume of leg under each condition (or, at least, of the total segment studied)
RESULTS 1. What was the effect of leg elevation on heart rate? A headward fluid shift might be expected to temporarily increase stroke volume. If cardiac output is to be roughly maintained, what might you expect to happen to heart rate? 2. What was the effect of leg elevation on leg or leg-segment volume? Did results support that there was a headward fluid shift? 3. What were the visual and subjective effects of leg elevation? Did these support that there was a headward fluid shift?
For Further Thought: What is the more valid physiological “baseline” on Earth for comparison to changes seen in space, standing or lying supine? How might your results compare to those in a classical 6o head-down tilt, bed rest study to simulate microgravity? MEASUREMENT OF LEG VOLUME: DATA SHEET
BACKGROUND DATA
Subject Height ______inches Weight ______pounds Sex: M / F
Other Possibly Pertinent Data?
LEG SITE SELECTION (Describe and mark)
Site 1:
Site 2:
Site 3:
Site 4:
Height of segment(s): Site ____ to Site ____ = ______mm Site ____ to Site ____ = ______mm
STANDING DATA: Actual Duration = ______minutes (target = 10 minutes)
Item Measurements Comments? 1 2 3 (if needed)* Heart Rate (beats/minute) Circumference, Site 1 (mm) Circumference, Site 2 (mm) Circumference, Site 3 (mm) Circumference, Site 4 (mm) Facial Appearance:
Leg Appearance:
Any Significant Sensations:
* You may want to do a third reading if the first two vary significantly
LEGS-ELEVATED DATA: Actual Duration = ______minutes (target = 10 minutes)
Describe Degree/Kind of Elevation:
Item Measurements Comments? 1 2 3 (if needed) Heart Rate (beats/minute) Circumference, Site 1 (mm) Circumference, Site 2 (mm) Circumference, Site 3 (mm) Circumference, Site 4 (mm) Facial Appearance: Leg Appearance:
Any Significant Sensations: