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Tilt Testing with Combined Lower Body Negative Pressure: a "Gold Standard" for Measuring Orthostatic Tolerance
Published on: March 21, 2013
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Bone microvascular flow differs from skin microvascular flow in response to head-down tilt.
Michelle Howden1, Jamila H Siamwala1, Alan R Hargens2
1Department of Orthopedic Surgery, University of California, San Diego, California.
Journal of Applied Physiology (Bethesda, Md. : 1985)
|July 1, 2017
Summary
Microgravity simulation via head-down tilt (HDT) significantly increases tibial bone microvascular flow but not skin microvascular flow. This differential response in blood perfusion may impact healing processes in astronauts.
Area of Science:
- Space Physiology
- Cardiovascular Research
- Microcirculation
Background:
- Microgravity conditions may impair lower extremity microvascular function, affecting wound healing and bone repair.
- Understanding the physiological response to simulated microgravity is crucial for astronaut health.
- Previous research has not clearly defined the differential responses of bone and skin microvascular flow to head-down tilt (HDT).
Purpose of the Study:
- To quantify the rate of change in skin and bone microvascular blood flow in response to varying degrees of head-down tilt (HDT).
- To test the hypothesis that tibial bone and overlying skin microvascular flows increase at different rates during HDT.
Main Methods:
- Seventeen subjects underwent simultaneous measurement of tibial bone and skin microvascular blood flow using photoplethysmography (PPG).
- Measurements were taken in randomized order across sitting (control), supine, 6°, 15°, and 30° HDT postures.
- Blood flow was analyzed for significant changes across different postural conditions.
Main Results:
- Tibial bone microvascular flow significantly increased with greater HDT angles, rising from 0.77 V (sitting) to 1.95 V (supine) and further to 3.74 V (15° HDT) and 3.91 V (30° HDT).
- Skin microvascular flow increased from sitting (0.703 V) to supine (2.19 V) but showed no significant change from supine to any HDT posture.
- Bone microvascular flow demonstrated a significantly higher increase with increasing HDT compared to skin microvascular flow.
Conclusions:
- Bone microvascular flow in the leg responds more robustly to simulated microgravity (HDT) than cutaneous blood flow.
- The distinct perfusion responses suggest potential mechanisms for bone density loss observed in astronauts, while skin integrity is maintained.
- These findings highlight differential tissue responses to microgravity, with implications for understanding and mitigating impaired healing in spaceflight.
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