428
5 Laser Specklometer, Speckle-Optical Diagnostics and Laser …
to the wavelength in the tissues, forward scattering prevails and only a small amount
of the light (0.1%) is diffused backward with red blood cells [44, 45, 84, 161].
In this case, the light scattered from deeper areas of skin does not reach the
inverse skin surface as a result of high absorption. This is the main reason why the
measurements were conducted with He–Ne laser as it gives the possibility to estimate
namely the capillary blood flow [84]. Movement of erythrocytes illuminated with a
coherent light source emits fluctuations of the light scattered from the capillaries.
Frequency of fluctuations of the scattered irradiation is shifted relative to frequency
of irradiations of the laser at the value proportional to the velocity of the blood flow
and depends on the orientations of capillaries relative to the direction of the inclined
and scattered light. The light scattered from the motionless tissues is not shifted in
frequency [162]. Typical boiling frequencies of the speckle-structure formed by the
laser irradiation scattered of the surface tissues are in the range from 0 to 10 kHz and
change at a different blood filling [44].
As far as we are concerned, there are two peculiarities, which give this possibility
to divide motions of speckles caused by the blood flow and shift of the body.
Firstly, the study of microcirculations is usually concentrated not on determination of absolute indices of the blood flow, but on their temporal changes as a
result of any tests. Meanwhile, the muscular tone and other factors, which influence
involuntary body movements, are supposed to be stationary and do not influence
the measured value. A typical example of such dynamics is the procedure of reactive hyperemia. Its essence is in the fact that parameters of a normal blood flow are
estimated from the spectrum, then the artery is compressed, the blood flow stops,
measurements are conducted (in this case, the spectrum is practically the same as the
spectrum formed by the shift of the body), and finally the cuff is removed. The blood
flow increases dramatically and then sinks gradually to the normal level. In other
studies, microcirculation is increased with an injection of tuberculin or with warming
ointments [163].
Secondly, blood cells make common translational motion with the body surface
as well as they have their own velocity and on the whole, unlike other diffusers,
their velocity distribution must be shifted into the range of great values. Fluctuations
formed by this diffuser will have high frequency. Experiments prove that spectra,
which correspond only to the changes of mobility of the body, are characterized by
lower frequencies [164] and the blood flow by higher frequencies [78].
Resulting characteristics can reflect the inclination of the spectral curve in some
way [44]. In particular, changing of such parameter was ascertained as a ratio of the
level of the spectral density at high- and low-frequency HLR = f
2
L f
2
U for a test of
reactive hyperemia where f L = 40 Hz and f H = 640 Hz.
The study was conducted on change of blood flow intensity in patients who suffer
from arterial occlusion before and after an operation [163].
The use of multi-channel registration and digital processing of signal gives the
possibility to obtain the microcirculation map, which reflects changes in the blood
flow intensity in the area of skin under study [75, 86].
5 Laser Specklometer, Speckle-Optical Diagnostics and Laser …
to the wavelength in the tissues, forward scattering prevails and only a small amount
of the light (0.1%) is diffused backward with red blood cells [44, 45, 84, 161].
In this case, the light scattered from deeper areas of skin does not reach the
inverse skin surface as a result of high absorption. This is the main reason why the
measurements were conducted with He–Ne laser as it gives the possibility to estimate
namely the capillary blood flow [84]. Movement of erythrocytes illuminated with a
coherent light source emits fluctuations of the light scattered from the capillaries.
Frequency of fluctuations of the scattered irradiation is shifted relative to frequency
of irradiations of the laser at the value proportional to the velocity of the blood flow
and depends on the orientations of capillaries relative to the direction of the inclined
and scattered light. The light scattered from the motionless tissues is not shifted in
frequency [162]. Typical boiling frequencies of the speckle-structure formed by the
laser irradiation scattered of the surface tissues are in the range from 0 to 10 kHz and
change at a different blood filling [44].
As far as we are concerned, there are two peculiarities, which give this possibility
to divide motions of speckles caused by the blood flow and shift of the body.
Firstly, the study of microcirculations is usually concentrated not on determination of absolute indices of the blood flow, but on their temporal changes as a
result of any tests. Meanwhile, the muscular tone and other factors, which influence
involuntary body movements, are supposed to be stationary and do not influence
the measured value. A typical example of such dynamics is the procedure of reactive hyperemia. Its essence is in the fact that parameters of a normal blood flow are
estimated from the spectrum, then the artery is compressed, the blood flow stops,
measurements are conducted (in this case, the spectrum is practically the same as the
spectrum formed by the shift of the body), and finally the cuff is removed. The blood
flow increases dramatically and then sinks gradually to the normal level. In other
studies, microcirculation is increased with an injection of tuberculin or with warming
ointments [163].
Secondly, blood cells make common translational motion with the body surface
as well as they have their own velocity and on the whole, unlike other diffusers,
their velocity distribution must be shifted into the range of great values. Fluctuations
formed by this diffuser will have high frequency. Experiments prove that spectra,
which correspond only to the changes of mobility of the body, are characterized by
lower frequencies [164] and the blood flow by higher frequencies [78].
Resulting characteristics can reflect the inclination of the spectral curve in some
way [44]. In particular, changing of such parameter was ascertained as a ratio of the
level of the spectral density at high- and low-frequency HLR = f
2
L f
2
U for a test of
reactive hyperemia where f L = 40 Hz and f H = 640 Hz.
The study was conducted on change of blood flow intensity in patients who suffer
from arterial occlusion before and after an operation [163].
The use of multi-channel registration and digital processing of signal gives the
possibility to obtain the microcirculation map, which reflects changes in the blood
flow intensity in the area of skin under study [75, 86].