Laser Doppler Flowmetry (LDF)
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study of skin may be undertaken to provide primary knowledge about
cutaneous tissue or to use the skin as a surrogate organ for the
investigation of microcirculatory events. Essentially, there are no other
easilly accessible microvascular beds in humans, making cutaneous flow
studies of great importance. Measures of laser-Doppler flow (LDF) have
recently allowed ready access to the superficial dermis and therefore have
dominated studies of cutaneous microcirculation.
surface area of dermal capillaries provides for approximately 30 M2
of endothelial coverage. Blood flow, usually averaging 10-20 ml/min/100 g,
may vary from 1 to 200 ml/min/100 g, indicating a remarkable plasticity of
regulatory control in this vascular bed. The skin therefore is highly
vascular and very accessible. However, the key question confronting any
study of surrogate tissues including laser
Doppler studies of cutaneous microvasculature is: Does information
obtained from cutaneous microcirculation correlate with changes in
coronary, renal or muscle vascular beds, which are ultimately produce
myocardial infarction, insulin resistance, hypertension, and progression
of renal failure? There is positive evidence: Thus, it has been
demonstrated that cutaneous microvascular dysfunction correlates with
blood pressure and insulin resistance. Patients with cardiac allograft
vasculopathy or with coronary three-vessel disease have been found to
exhibit abnormalities of cutaneous microcirculation. Diabetic patients
show cutaneous microangiopathy which is more pronounced in those with
advanced retinopathy. Furthermore, cutaneous microcirculatory responses
are blunted in patients with angiographically demonstrated coronary artery
disease. These are all studies relating to changes in flow due to altered
local microvascular factors which is primarily how we will employ such
These data suggest that the investigation of cutaneous
microcirculation using laser-Doppler flowmetry may adequately mirror the
state of microcirculation in other vascular beds.
In experiments LDF
can only be used to determine relative changes in blood flow in
subjects. Typically, Doppler flows are indexed to the maximum flow
achievable with sodium nitroprusside microdialysis.
We use a point source or an integrating probe
employing continuous coherent laser light at a wavelength of 780 nm which
is sampled at a similar sample rate of 200 sps for consistency with other
signals interfaced through an A/D converter (DATAQ) using custom softwware.
LDF is measured in arbitrary perfusion units (pfu).
have combined LDF measurements with thermal hyperemia and with reactive
hyperemia measurements to provide physical stimuli to the system. Also,
LDF may be combined with such techniques as local iontophoresis of
biologically active chemicals and medications and the flow response
assessed. More powerful methods include combining LDF with microdialysis
techniques which, in addition to being more robust than iontophoresis in
terms of locally delivering biochemicals, are also capable of sampling the
interstitium for endogenous substances. .