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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 subject’s 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.
TiVi Value (A.U.)
150
100
50
0
-50
-100
10 -1.0
10 -0.5
10 0.0
10 0.5
10 1.0
10 1.5
Dose (mC)
Figure 3. Dose dependent vasodilatory effect of iontophoretically
applied acetylcholine measured by TiVi (n=8).
Correspondence: Joakim Henricson, [email protected]