Pathophysiology
P-I-27. Diabetic vascular function: laser Doppler/TcPO2 — reactive hyperaemia
糖尿病の血管機能：レーザードップラー/TcPO2 — 反応性充血
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 response to ↑temperature (→ ↑flow significantly) and postprandial changes (→ ↑flow to GI areas)
Transcutaneous Partial Oxygen Pressure (TcPO₂)
- Measures partial O₂ pressure at skin surface → how much O₂ reaches tissue
- Too low → concern for cell viability; amputation considered to avoid necrosis
- Fluid placed in a ring between the sensor and skin
Post-Occlusive Reactive Hyperemia
- Occlude an artery ≥ 2 min (cuff inflated above systolic pressure) → release pressure → overshoot of blood flow → skin perfusion quickly returns to baseline
- In diabetes → no reactive hyperemia (endothelial dysfunction):
- Reduced endothelial response to vasodilators
- ↓NO production + ↑NO degradation
- ↓prostacyclin → ↑vasoconstrictors
Veno-Arterial Reflex
- Setup: both legs on the bed, measure leg perfusion → suddenly drop one leg to the ground → sudden ↑venous pressure
- Healthy: to prevent fluid outflow into the interstitium → sudden drop in arterial pressure (protective vasoconstriction)
- Diabetic: opposite → arterial pressure increases
- Pathomechanism: insufficient microcirculation → can lead to edema
一問一答
▶What does laser Doppler flowmetry measure and how?
Superficial skin blood flow, calculated from the frequency shift of light reflected by moving red blood cells (Doppler phenomenon).
▶What endothelial changes explain the loss of reactive hyperemia in diabetes?
Reduced endothelial response to vasodilators, decreased NO production with increased NO degradation, and reduced prostacyclin with increased vasoconstrictors.
▶What is post-occlusive reactive hyperemia?
After occluding an artery for ≥2 min and releasing the cuff, blood flow overshoots and then quickly returns to baseline.
▶What happens to reactive hyperemia in diabetes?
It is absent/blunted because of endothelial dysfunction.
▶How is post-occlusive reactive hyperemia produced?
A cuff is inflated above systolic pressure for at least 2 minutes, then released.
▶What does TcPO₂ measure, and what does a too-low value imply?
It measures partial O₂ pressure at the skin surface (tissue oxygenation); a very low value raises concern for cell viability and possible amputation to avoid necrosis.
▶Why is fluid placed in a ring between the TcPO₂ sensor and the skin?
To create a sealed, conductive interface that allows accurate measurement of O₂ diffusing through the skin.
▶What is the veno-arterial reflex test setup?
Both legs rest on the bed and leg perfusion is measured; then one leg is suddenly dropped to the ground, causing a sudden rise in venous pressure.
▶What is the healthy veno-arterial reflex response when a leg is lowered?
Arterial pressure drops (protective vasoconstriction) to prevent fluid leaking into the interstitium.
▶What is the abnormal (diabetic) veno-arterial reflex response?
The opposite of normal — arterial pressure increases instead of decreasing.
▶What is the pathomechanism and consequence of an abnormal veno-arterial reflex in diabetes?
Insufficient microcirculation regulation, which can lead to edema.
▶How long must the artery be occluded to elicit reactive hyperemia?
At least 2 minutes.
▶Why does blood flow overshoot after releasing the occluding cuff?
Ischemia triggers vasodilation (metabolic + endothelial), so on reperfusion flow transiently exceeds baseline before normalizing.
▶How does reduced NO contribute to absent reactive hyperemia in diabetes?
Less NO is produced and more is degraded, so endothelium-dependent vasodilation needed for the hyperemic overshoot fails.
▶What is the role of prostacyclin, and how is it altered in diabetes?
Prostacyclin is a vasodilator; in diabetes it is decreased while vasoconstrictors increase, impairing vasodilatory responses.
▶Why are reactive hyperemia and the veno-arterial reflex useful tests in diabetes?
They non-invasively reveal endothelial and microvascular dysfunction before overt complications appear.
▶What is the underlying theme linking all these diabetic vascular function tests?
They detect endothelial dysfunction and impaired microvascular regulation in diabetes.
▶Why does the veno-arterial reflex normally protect against edema?
On dependency, reflex arterial vasoconstriction limits the rise in capillary pressure, preventing fluid filtration into the interstitium.
▶Why does the cuff need to be inflated above systolic pressure for the occlusion test?
To completely stop arterial inflow and create true ischemia, which is required to provoke the subsequent hyperemic response.
▶Why might diabetic microvascular dysfunction ultimately cause edema?
Loss of protective vasoconstriction on dependency raises capillary pressure, driving fluid into the interstitium.