1. L. Rogule. Bachelor work “ Optiskā metode ādas rekapilarizācijas laika noteikšanai” , Riga, 73p

(2011).

2. E. Kviesis-Kipge, E. Čurkste, J. Spigulis, L. Eihvalde. Real-time analysis of skin capillary-refill

processes using blue LED. Proc. SPIE, Vol.7715, 7715231-5 (2010).

REFERENCES

This prototype device was made for contact (in vitro) use on human

to measure capillary blood refill time. The main idea is to make pressure on

finger tip or nail (it’s not excluded to use other human body parts) with this

device moving tip part, then to take pressure off and after some time to

finish measurement. The pressure value is displayed during measurement.

At the end of measurement user gets capillary refill time value. This time

could be used to detect dehydration or hypothermia in tissues.

Abstract

Financial supports from European Social Fund, project

#2009/0211/1DP/1.1.1.2.0/09/APIA/VIAA/077 is highly appreciated.

ACKNOWLEDGEMENTS

CONCLUSIONS

Blue polarized light (450 nm) is used to irradiate skin, then

backwards coming light signal is detected through orthogonally orientated

polarizer (signal from the skin capillaries layer comes depolarized to the

photodiode, but still polarized light from the skin surface is filtered). Blood

amount change in capillaries is the reason for more or less absorbed light on

tissue, so without pressure finger tip is red and blue light absorption is high,

but when blood is out (under pressure), finger becomes white and blue light

absorption is low (but reflection high). The signal intensity changes are

evaluated before and after applied pressure. So it’s possible to measure, how

fast blood returns into capillaries.

How it works

Device construction

The device consists of mechanical and electronic parts: body,

transparent moving tip with blue LEDs, photodiode and amplification

circuit, pressure sensor that is connected to the tip with damping element,

and main signal processing electronic circuit with LCD display, battery

and buttons.

Figure 1. Blue light penetrates in capillaries depth of skin,

but not deeper, so there isn’t any needless information

about bigger blood vessels.

Figure 2. Device for capillary blood refill time

assessment.

Capillary blood refill time curve is showed in fig.4., as we see it in

computer DataScope program (device is absolutely autonomic, but we use

DataScope for checking the signal shape). The yellow curve is the signal,

but red is the derivation of yellow signal. Red signal 2 keen pikes are found

start and finish points of refill time process. Signal is strongly filtered to

reduce the pulse noise.

Signal curve

Fig.4 shows light intensity (yellow curve) changes during the time

at measurement process. It is allowed to prepare finger for measurement

before point one, then at point 1 device gives sound signal to make

pressure on finger, at point 2 pressure is appied and is kept for few seconds

until next sound signal at point 3. After taking pressure away at point 3, the

blood refill begins with blood overshoot utill point 4. Then signal starts to

normalize. When point 4 is found, capillary blood refill time is showed on

display and measurement is finished.

Fig.4. Signal of capillary blood refill time in DataScope.

1,8 1,9

1,3 1,2

1,6

2,7

1,9

2,3 2,2

1,3

2,0 2,0 2,1

3,5

4,1 4,0

3,5 3,3

4,3

2,9

0,0

1,0

2,0

3,0

4,0

5,0

6,0

7,0

Vecums

tim

e, s

2 3 3 3 3 5 5 5 5 12 14 14 15 3 6 10 11 13 15 17 age,years

Patients without dehydr. symptoms

Snmid ≈ 0,5s

Patients with dehydr. symptoms Snmid ≈ 0,9s

Measurement results

Clinical measurements were made for kids with and without

dehydratation symptoms (2 fingers of both hands were used for

measurements) (fig.5). Most kids from first group show refill time under 2

s, but most from second group above 3 s. There are also some kids from

first group in risk category (blue columns). High standart deviations could

mean not precise measurements because of moving patient or really

different refill time at various human fingers. Usually, cold fingers gives

higher refill time values, so it’s recommended to measure warm fingers at

room temperature.

Figure 3. Capillary blood refill time measurement

process.

Fig.5. Capillary blood refill time of patients with and without dehydratation symptoms.

Working capillary blood refill time device was made and clinically

tested. Measurement results show that patients with water lack in body

have higher refill time than patients without such problems.

.

Device for Measurements of Capillary Blood Refill Time

E.Laksa, J. Zaharans, J. Spigulis and L. Eihvalde

University of Latvia, Institute of Atomic Physics and Spectroscopy, Riga, Latvia