Part 4 - Appendices
4.1. Level Control for the Reservoir |
|
Connecting the probe to the 'min' input the signal reaches the
NAND port, working as an inverter. The diodes connected to the port input are
protections for ESD and overvoltages. The
1MW resistance is a pulldown for node 4
when the signal is missing, i.e. when the level is lower than
the minimum expected. The capacitor at the input decouples the probe from
the DC voltage introduced by the resistor.
With the signal at the 'min' probe, the node 5 is at
high level due to the filtering done by the
1MW resistance
in parallel with the 100nF capacitor; the transistor connected to the second NAND
drives a buzzer.
The other 2 NAND ports are a Set/Reset flip-flop
driving the relay. In this way the valve is driven only
when the level cannot reach the 'min' probe, up to the reaching of the
'max' probe.
The probes are stainless steel wires fixed to
the holes at the top of the reservoir, as shown by the picture
in the chapter on the perfusion with blood.
The push-button of the 'min' signal is used to reload the max quantity of blood without
waiting for the reservoir to be empty.
For the circuit we developed a fiber-glass PCB (figures 97 and 98). The probes are connected
through a 3-pole connector: they can be easily replaced
without disassembling the circuit. The plastic box has a tool to be applied
to the oxygenator bar, and is waterproof: the switch, the buzzer, the fuse and the hole to
connect other types of valve (if necessary) are placed on the bottom part.
The valve has been fixed externally, in order to facilitate
maintenance work.
Fig.98: Circuit assembly
4.2. Relationships and Calculations for Morphometrical Data of the Vessels |
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Volume of the placenta | 488 cm3 |
Total volume of the villi | 240 cm3 |
% trunci vs total vol. | 2 |
% rami vs total vol. | 3.8 |
% ramuli vs total vol. | 21.4 |
% interm. mature villi vs total vol. | 26.2 |
% terminal villi vs total vol. | 36.5 |
Also the mean percentages of "lumina" of
trunci, rami and ramuli (26%), interm. mature villi (21%) and terminal villi
(45.2%) were available.
The lengths of the vessels of the trunci, of the 4 orders of
rami, of the mature interm. and terminal villi, of the 10 orders of ramuli were available too.
The number of vessels in parallel per each type and order of villi has
been obtained, knowing the numbar of trunci and of terminal villi, considering
dichotomic splitting where not differently mentioned by the description
of 3.1.7. paragraphs.
The dymensions of the chorionic vessels have been obtained by the previous literature
[45][25].
The table for the values to be used for the model was absolutely incomplete:
Vessels | stem | villi | ® | ||||||||
Arteries | cor. | rami | |||||||||
funicolus | I | II | III | IV | trunci | I | II | III | IV | ||
N | 2 | 2 | 50 | 400 | |||||||
r° | mm | 1750 | 325 | 275 | |||||||
l | mm | 520 | 30 | 30 | 30 | 30 | 5 | 10 | 20 |
¬ | stem | villi | villi | ||||||||||
ramuli | interm | ||||||||||||
I | II | III | IV | V | VI | VII | VIII | IX | X | mature | term. | sinus. | |
Nx1000 | 45000 | -- | |||||||||||
r° | 14 | 7.2 | 25 | ||||||||||
l | 1.1 | 1.1 | 1.1 | 1.1 | 1.1 | 1.1 | 1.1 | 1.1 | 1.1 | 1.1 | 0.45 | 1 | 0.1 |
We calculated the diameters of the missing vessels considering the hypothesis of
unchanged total area for the chorionic vessels (0.19 cm2) [25][45].
For the stem villi this hypothesis is no longer available:
we calculated the areas of rami e ramuli with the following formula:
4.3. Units of Measure |
|
Quantity | Unit | Symbol | LMTI |
Voltage | Volt | V | L2MT-3I-1 |
Current | Ampère | A | I |
Charge | Coulomb | C | TI |
Time | second | s | T |
Capacitance | Farad | F | L-2M-1T4I2 |
Resistance | Ohm | W | L2MT-3I-2 |
Inductance | Henry | H | L2MT-2I-2 |
Some of the units that are used in medicine do not
belong to this system: to make a correspondance between
hydraulic and electric quantities we have to convert them.
Quantity | Symbol | Unit | Relationship |
Length | l , r | cm | = 10-2 m |
Viscosity | m | cP | =10-3 Pa.s |
Pressure | P , k | mmHg | =133.3 Pa |
Flow | Q | cc/min | =6-1×10-7 m3/s |
Considering that
to convert the obtained data into SI units, they must be multiplied by the following constants:
4.4. Glossary |
|
aberration, chromatic | iridescence of image outlines caused by the different rifraction of each color. |
abruptio (placentae) | premature detachment of the placenta |
accuracy | matching level between a measurement and the real value being measured |
air chamber | closed reservoir, with pressurised air, connected to a pipe: it works as a damper |
amnios | thin membrane surrounding the fetus |
analogic | signal that can assume any value within a range |
anastomosis | confluence of two vessels |
aneurism | weakening of the wall of a vessel, generating a bulge |
bypass | vessel bypassing a vascular district |
capillary (vessel) | very thin vessels (from latin capilla = hair) |
chorion | external membrane around the embryo |
collapse | sudden decrease of pressione |
cotyledon | lobe of the placenta |
decidua | part of the uterine mucosa enveloping the ovule |
diffraction | phenomenon of wave propagation: a wave interferes with itself when running into an obstacle with dimensions comparable with its wavelength |
digital | signal whose amplitude can have a finite number of values |
endometrius | inner layer of the uterus |
(a)etiology | study of the causes of disease |
FFT | method for the calculation of the Fourier transform |
hemolysis | breaking of the membrane of the herythrocites |
heparin | anticoagulant |
mesenchima | connective tissue |
perfusion | continuous introduction of a liquid into a vessel |
precision | ratio between the measurement and the error introduced by the meter |
previa, placenta | placenta positioned in the low part of the uterus, prevents the normal birth |
rheology | science studying the deformation of materials and related strains |
sensitivity | ratio between the result of the measurement and the correspondent input signal |
sinusoid (of the terminal villi) | enlargement of a capillary of the terminal villi |
spectrum | series of frequences forming a signal |
stenosis | abnormal narrowing of a vessel or meatus |
strain-gauge | strain sensor used as transducer to measure strains or deformations |
tolerance | range of variation of the result of a measure |
transducer | tool able to make a conversion between different phisical quantities |
ultrasound | sound at high frequency, above the upper limit of human hearing. |
villus | final parts of the ramification of the placental vessels |
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