To study the mechanism of vasodilation induced by pulsed dye laser irradiation, we used an anesthetized rabbit model of femoral artery spasm Pulsed dye laser energy was delivered (1µs pulses at 2Hz for 10s at incremental energies of 2.5-40mJ/pulse) to the vessel via a 320µm core optical fiber introduced through a perpendicular side branch. Vessel internal diameter was measured by 12.5MHz ultrasound imaging at the fiber site of energy delivery, 1cm proximal, and 1cm distal. Change in diameter was measured after irradiation at 480 or 577nm.
| Wavelength | n | Proximal | Fiber | Distal | |
| 480nm | 6 | 0.12±0.10 | 0.17±0.08 | 0.12±0.12 | p=0.004 |
| 577nm | 6 | 0.28±0.20 | 0.35±0.21 | 0.27±0.23 | (480 vs 577nm) |
In 8 additional animals, the role of vessel perfusate was studied. Blood inflow was occluded and saline infused via a proximal side branch to match baseline flow. Laser energy at 480nm was delivered, then blood flow restored and energy again delivered.
| n | Fiber | Distal | ||
| Control | 4 | 0.02±0.08 | 0.00±0.07 | |
| Saline | 8 | 0.09±0.06 | 0.03±0.05 | p=NS (saline vs control) |
| Blood Following Saline | 8 | 0.31±0.16 | 0.29±0.20 | p<0.007 (blood vs saline) |
In summary; 1) pulsed dye laser mediated vasodilation occurs both antegrade and retrograde to blood flow,
2) 577nm irradiation (more avidly absorbed by blood) causes a greater effect than 480nm,
3) No significant dilation is seen when saline replaces the blood field.
We conclude that this vasodilation is a response to the absorption of laser
energy by blood, rather than a direct effect of light upon the vessel.
A. A. Ziskind, J. L. Caplin, and K. W. Gregory, "Vasodilation by pulsed laser requires the presence of a bloodfield," Circulation (Suppl. II) 80:II-523, 1989.