Bild 1

1
Microvascular Response to Iontophoretically
Applied Acetylcholine Investigated by Tissue
Viability Imaging
Joakim Henricson 1 Doctoral Stud., Gert Nilsson
2,3 Prof., Folke Sjöberg 1 Prof.
1 Department of Biomedicine and Surgery,
Linköping University Hospital, Linköping,
Sweden 2 Department of Biomedical Engineering,
Linköping University Hospital, Linköping,
Sweden 3 WheelsBridge AB, Lövbergsvägen 13, S-589
37 Linköping, Sweden
Introduction Increasing efforts are directed
towards the development of vascular models in
which the vessels and vascular effects are
investigated in a tissue environment
incorporating the influences of not only the
vessels themselves as in the case for the in
vitro models but also comprising nerve endings,
endothelial cells mechanical and humoral
factors. Acetylcholine delivered to skin tissue
by use of a small current (iontophoresis) and
blood flow assessment using laser Doppler
perfusion methodology offers such a model and has
been used extensively for more than ten years in
a multitude of experimental settings. We propose
a new technique called Tissue Viability Imaging
(TiVi), based on the method of polarization
spectroscopy of blood in superficial skin tissue,
with the ability to see through the surface of
the skin and collect spectroscopic information
about microvascular red blood cell
concentration. Aim To investigate the
microvascular response to iontophoretically
applied acetylcholine by using TiVi technology
and if possible present these results as dose
response curves.
Methods Eight healthy volunteers gave informed
consent to participate (male 4, mean age 23
years). Electrodes were attached to the volar
side of subjects forearms. Acetylcholine
dissolved in physiological saline to a
concentration of 10 mg/ml was anodally
iontophorised to evoke vascular response. TiVi
values were collected at a rate of one image
every 5 second at a distance of approximately 10
cm. Data was analysed using TiVi600 software by
WheelsBridge AB, Linköping, Sweden and GraphPad
Prism 4 by GraphPad Software inc.
Figure 1. Iontophoresis of acetylcholine.
Tissue Viability Imaging system in use.
Theory Iontophoresis is the facilitated
transport of charged substances over the skin by
the use of a small current (Figure 1). TiVi
technology uses linearly polarized light in the
visible region that is partly reflected by the
skin surface and partly diffusely scattered in
the dermal tissue matrix. The directly reflected
light retains its original linear polarization
state and is blocked by the orthogonally placed
filter over the detector and only linearly
polarized light backscattered from red blood
cells (RBCs) and other tissue is used for
analysis. Evaluation of the RBC concentration and
the associated tissue viability is possible since
the light absorption of the static tissue
components in dermis is smaller and less
dependent on wavelength than the light absorption
in RBCs (Figure 2).
Figure 2. Schematic of TiVi (RP Randomly
Polarized, LP Linearly Polarized).
Results Iontophoretic administration of the
endothelium dependent and vasodilating drug
acetylcholine in combination with TiVi technology
has shown promising results. The effect of the
drug can be measured by TiVi and presented as
dose response curves (Figure 3). Effective dose
50 was 2.2 mC (95 Ci 1.8-2.7 mC). These results
open up for new possibilities in pharmacological
in vivo studies of the cutaneous microvasculature
and comparison of obtained results to
corresponding in vitro studies.
Figure 3. Dose dependent vasodilatory effect of
iontophoretically applied acetylcholine measured
by TiVi (n8).
Correspondence Joakim Henricson, joahe_at_ibk.liu.se