Pathophysiology
P-I-26. Diabetic vascular function: laser Doppler/TcPO2 — heating response
糖尿病の血管機能：レーザードップラー/TcPO2 — 加温反応
Laser Doppler Flow Measurement
- Uses a transmitter + receiver electrode → measures amount & frequency of reflected light
- Frequency shifts as objects move toward/away (Doppler phenomenon) → calculates blood flow from moving RBCs
- Measures blood flow in superficial skin
- Assesses blood flow response to physical changes (↑temperature, postprandial):
- ↑temperature → blood flow should ↑ significantly
- Eating → blood flow ↑ to certain (GI) areas
Transcutaneous Partial Oxygen Pressure (TcPO₂)
- Measures partial O₂ pressure at skin surface → indicates how much O₂ reaches tissue
- Too low → concern for cell viability; amputation considered (to avoid necrosis)
- O₂ sensor heats the underlying skin → augments local blood flow + makes epidermis more gas-permeable
Blood Flow Response to Heating (Normal)
- Early peak → due to axon reflex
- Followed by a long-term plateau → due to NO-dependent vasodilation
Changes in Diabetic Vascular Dysfunction
- Endothelial cells dysfunctional:
- Secrete vasoconstrictor mediators (ROS, TXA2)
- TXA2 → enhances thrombosis
- Adhesion molecules → ↑leukocyte attachment + inflammation
- Inflammation → ↑ROS + NF-κB
- Growth factors → ECM + smooth-muscle proliferation
- Underlies peripheral neuropathy in DM:
- ↓wound healing tendency
- ↑infection risk (high blood sugar favors bacterial growth)
- Weaker immune system, ulcer development
一問一答
▶What does laser Doppler flow measurement detect?
Blood flow in superficial skin, calculated from the frequency shift of light reflected by moving red blood cells (Doppler phenomenon).
▶What components does the laser Doppler probe use?
A transmitter and a receiver electrode that measure the amount and frequency of reflected light.
▶How should skin blood flow respond to increased temperature normally?
Blood flow should increase significantly with heating.
▶What does transcutaneous partial oxygen pressure (TcPO₂) measure?
The partial O₂ pressure at the skin surface, indicating how much oxygen reaches the tissue.
▶What does a very low TcPO₂ indicate clinically?
Concern for cell viability — amputation may be considered to avoid necrosis.
▶Why does the TcPO₂ sensor heat the underlying skin?
Heating augments local blood flow and makes the epidermis more gas-permeable, allowing accurate O₂ measurement.
▶What causes the long-term plateau in the normal blood flow response to heating?
NO-dependent vasodilation.
▶What vasoconstrictor mediators do dysfunctional endothelial cells secrete in diabetes?
Reactive oxygen species (ROS) and thromboxane A2 (TXA2).
▶What causes the early peak in the normal blood flow response to heating?
The axon reflex.
▶What effect does TXA2 have in diabetic vascular dysfunction?
It enhances thrombosis (as well as causing vasoconstriction).
▶How do adhesion molecules contribute to diabetic vascular dysfunction?
They increase leukocyte attachment and inflammation.
▶What is the link between inflammation and ROS/NF-κB in diabetic vessels?
Inflammation increases ROS and activates NF-κB, perpetuating endothelial damage.
▶What do growth factors promote in diabetic vascular dysfunction?
Extracellular matrix (ECM) deposition and smooth-muscle proliferation.
▶How does diabetic vascular dysfunction affect wound healing and infection?
It reduces wound healing and increases infection risk (high blood sugar favors bacterial growth), promoting ulcers.
▶What is the Doppler phenomenon as used in laser Doppler flowmetry?
The frequency of reflected light shifts as objects (RBCs) move toward or away from the probe, allowing blood flow to be calculated.
▶How does eating affect skin/regional blood flow as assessed by laser Doppler?
Postprandially, blood flow increases to certain (GI) areas.
▶Why is the heating-induced blood flow response blunted in diabetic vascular dysfunction?
Endothelial dysfunction reduces NO-dependent vasodilation, so the normal plateau rise in flow is impaired.
▶Why is TcPO₂ useful in deciding on amputation level?
It quantifies tissue oxygenation; very low values predict poor healing and non-viability, guiding amputation to a better-perfused level.
▶What is the axon reflex underlying the early heating peak?
Local heat stimulates sensory nerve endings, which antidromically release vasodilator neuropeptides causing a rapid rise in skin blood flow.
▶Why does endothelial dysfunction shift the balance toward vasoconstriction and thrombosis in diabetes?
Damaged endothelium secretes more ROS/TXA2 and less NO, favoring vasoconstriction, platelet aggregation, and clot formation.