Laser Resistance – Technical

The article that I cited yesterday had some very important findings
that clearly showed that vessels upstream and downstream to the
treatment site could constrict and thus not be treated properly.
Interestingly, it showed that minimal photocoagulation with complete
blood flow stoppage for 24 hours could resume blood flow once the
emboli dislodged and `save' the vessel from proper treatment. In
essence, they were performing pure science to determine pulse
duration, pulse lag time and proper energy delivery to ensure that
the above did not occur so that laser treatment would be much more
effective. This surely does explain part of the reason why some
people may be more laser resistant than others.

It also shows that the treating physician must be on his toes to
follow the progress or lack of progress by varying the treatment
parameters. It also clearly illustrates the need for pre-flushing
patients as constriction of vessels occurred quite frequently during
treatment. Topical adenosine is now considered the most potent pre-
flushing topical dilator. Currently I am testing out adenosine at
5%, 10% and 15% in an evaporative gel base with a laser physician.
The laser physician who does not have rosacea lights up like a
Christmas tree for over one hour. Below are some excerpts from the
paper – the meat is in the second paragraph.

Regards,

Geoffrey
______________________________

Dr. Geoffrey Nase
Ph.D. Neurovascular Physiologist
http://www.drnase.com
______________________________


3.1 in vivo results

Initial studies were performed to determine promising 532 and 1064
nm laser parameters and interpulse spacing. The first series of
irradiations was performed with the 532 nm laser set to 10 Jcm-2,
the 1064 nm laser set to 40 Jcm-2 and comparatively long delays
between the 532 nm and 1064 nm pulses (70 – 150 ms). The green
radiant exposure was chosen to give > 50% probability of permanent
damage for these vessel sizes based on the earlier work of Barton et
al.24 using 532-nm only. Examination of the videotape post-
irradiation showed that the initial 532 nm pulse caused complete
stenosis of the vessel lumen of blood at these settings. The
stenosis occurred within the minimum resolvable time period (one
video frame, < 33 ms) of our technique. With no blood in the
irradiation zone, the only visible indication of the 1064 nm pulse
interacting with the tissue was a cylindrically symmetric
contraction and relaxation of the connective tissue in the
interaction region occurring over a period of several hundred
milliseconds. Post-irradiation, at these settings, the ends of the
vessels bordering on the interaction region were seen to be occluded
by dark flow-stopping coagula. The effect of 1064 nm irradiation
alone was ascertained in a separate series of experiments. Radiant
exposures of 15 Jcm-2 were seen to have no effect on any arterioles
or venules of 20 – 200 microns diameter, while radiant exposures of
42.5 Jcm-2 caused permanent damage of the larger arterioles and
venules (150 - 200 µm in diameter).

Based on these initial results, and the in vitro results given in
the next section, we concentrated this study on a parameter set with
overlapping laser pulses. The 1064 nm laser was set to a pulse width
of 4 ms, radiant exposure of 14.1 Jcm-2, and a delay of 6 ms after
the beginning of the 532 nm pulse. The 532 nm pulse width was set to
10 ms, and the radiant exposure varied from 4 to 11 Jcm-2. Both
lasers had spot sizes of 3 mm. This parameter space allowed direct
comparison with the earlier 532 nm-only work.24 Approximately 200
blood vessels were irradiated with this overlapping double pulse
configuration in this study. Response to laser irradiation included
no effect, embolized coagula, vessel constriction, enlargement,
complete stenosis, and fixed coagula blocking flow. After 24 hours,
some cases of vessel stenosis or occlusion from coagula resolved,
and blood began flowing normally again. In rare cases, a blood
vessel that appeared only partially constricted immediately after
irradiation was completely stenosed at 24 hours. Blood vessels that
had regions of complete stenosis or fixed coagula blocking flow were
considered permanently damaged, whereas constricted vessels that
still maintained some blood flow were not. The results of the probit
analyses are given in Figure 3. Separate probit analysis was
performed on arterioles and venules in each of three size
categories. Also shown for comparison are the probit results from
the earlier, green-only study. 24