Download Linear System for Quantitating Hydrogen at a Platinum Electrode

Linear System for Quantitating Hydrogen
at a Platinum Electrode
By EDWARD S. HYMAN, M.D.
ECENTLY, Clark and Bargeron 1 ' 2 introduced the use of hydrogen as a simple
tracer substance in the circulation, detecting
it by means of an intravascular platinizedplatinum electrode. With the electrode at the
tip of a cardiac catheter in the right heart,
the appearance time of hydrogen introduced
into the left side by inhalation can readily be
recorded. A left-to-right shunt can be detected by a short circulation time. The shunt
can be further localized by positioning the
electrode in the right heart. The short circuit
is not detected upstream to the shunt. These
observations have been amply confirmed and
have been extended to the injection of hydrogen-saturated saline or blood to detect rightto-left shunts in a similar fashion.3"6 The
hydrogen has been without toxieity and, in
left-to-right shunts, it offers sensitivity exceeding that of other methods. 3 " 5 It can be
repeated many times with ease and without
drawing blood for analysis.
Should it be possible to quantitate the hydrogen as well as detect it, it would then be
possible to use the method to estimate the magnitude of the shunts and perhaps to estimate
flow rates and other parameters by established
indicator (dye)-dilution techniques. 7
The " e " of the reaction H ? ^ 2 H + + 2e is
commonly estimated by a high impedance circuit, for example, pH or oxidation potential.
Clark and Bargeron introduced the signal
from the platinum electrode directly into a
standard recorder of one megohm impedance.
A higher impedance system gives more nearly
the full logarithmic response,
H
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but its use does not allow quantitation. 3 " 5 The
Dr. Hyman is affiliated with the Bio-chemistry
Research Laboratory at the Touro Infirmary, New
Orleans, Louisiana.
Beceived for publication April 27, 1961.
Circulation Retearch, Volume IX, September 1SB1
major difficulty is the minimal detectability.
There is no zero in a logarithmic system. Each
10-fold rise in the concentration of HS will
give a 61-mv. signal. Thus, an error of 0.0001
per cent for 0.001 per cent in minimum detection will reflect as an error of 3 per cent
for 30 per cent in an estimate. A linear registration would allow quantitation. Should the
reaction H2 ^ 2H+ + 2e be estimated by a
very low impedance circuit, each H2 gives 2e,
and the relationship is linear.
Methods
The method should be differentiated from the
polarograph commonly used to estimate oxygen.
Although the oxidizing potential of oxygen is
several hundred millivolts higher than that of
blood, the reduction of oxygen even at a platinum
catalyst is very slow, and potential of oxygen is
not expressed.8 Thus, in the polarograph this
reduction is induced by imposing approximately
—0.6 volts on the platinum electrode. By contrast,
hydrogen, potential of which is several hundred
millivolts below that of blood, is rapidly oxidized
at a platinum catalyst. The reaction is spontaneous
and need not be induced by an imposed voltage.
Hence, a simple, low impedance current measuring
device is all that is necessary to measure hydrogen.
It is noted that a platinum electrode without the
imposed voltage does not "poison" in blood as does
that in the polargraph.
The circuit in figure 1 has been found satisfactory.9 A single PNP transistor is used in a
"common emitter" circuit. The electrons from
the platinum electrode (Pt°) flow to the base
of the transistor, across the base-emitter junction
to B + . This results in an amplified replica of the
current flowing through the transistor's emittercollector circuit. The amplification depends on the
"h PE " of beta of the transistor. This amplified
current goes through the collector-load resistor.
The voltage across this resistor is linear with the
weak current originating in the platinum electrode.
The potentiometer slide (S) is set so that its
voltage equals the base voltage plus the reference
electrode (Ref.) voltage. This is easily done by
choosing the setting at which the output of the
circuit is equal to the output with the electrodes
disconnected. At this setting, the electromotive
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Figure 1
Transistor circuit. The six-volt battery consists of
four penlight cells. These can be reversed for an
NPN transistor. The connections for the platinum
(Pt°) and reference (Ref.) electrodes are marked.
The potentiometer slide (S) is set at about 0.3
volts depending upon the electrodes used. See text.
% Saturated with Hjdrog»i
force (EMF) of the electrodes is equal, and there
is no appreciable current through them. Above or
below this setting, the EMF of the electrodes is
unequal, and a current flows in one direction or
the other. The circuit becomes an amplifying
polarograph. Although the response to hydrogen is
the same above or below null setting, the zero
drift is minimal at this setting. For short
observations, it has been found unnecessary to
compensate the transistor for temperature.
Results
In vitro curves in figures 2, 3, and 4 were
obtained using a vibrating platinum electrode
and a calomel half-cell supported in a beaker
of solution. Starting with a measured quantity of plasma in a beaker as zero hydrogen,
the data were obtained by adding increments
of hydrogen-saturated saline or plasma via
syringe and needle. The estimate of concentration was corrected for the increase in volume. The output voltage of the transistor
circuit was observed on a Heathkit vacuumtube voltmeter (model V 7A) set at zero voltage for the hydrogen-free plasma.
Figure 2 represents a sensitive range. The
2X508 transistor has a current amplification
of about 125 times. A 6,800-ohm collector resistor was used. Concentration of hydrogen
Figure 2
The output of the transistor circuit in millivolts
plotted against the concentration of hydrogen in
terms of per cent saturated. Range: 0 to 3.3 per
cent saturated.
in terms of per cent saturated is plotted
against the output of the circuit in millivolts.
Eight points from 0 to 3.3 per cent lie in a
straight line. Figure 3 shows two straight
lines. The first is the continuation of figure 1
using the same transistor and collector load.
This same curve remains linear to the limit
of the circuit at a little over 9 per cent saturation with hydrogen. The second line in
figure 3 shows the effect of changing to a transistor with lower amplification. The 2N190
transistor has an amplification of about 35.
Zero and eight other points up to 25 per cent
saturation fall close to a straight line. Figure
4 demonstrates the range from 0 to 100 per
cent saturation. The reduced slope of the line
was achieved by using a smaller collector resistor (2,200 ohms). This straight line does
not intercept the point 00, probably due to
the difficulty in rapidly preparing dilutions
over this wide a range with the technique
used.
Circulation Research. Volume IX, September 1961
LINEAR SYSTEM FOR QUANTITATING HYDROGEN
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Figure 3
Millivolts versus per cent saturated icith hydrogen.
The steeper slope is with the higher gain transistor
(2N508) used in figure 2 in the range from 0 to
9 per cent saturated. The curve with the lesser
slope ivas obtained by substituting the lower gain
2N190 transistor in the same circuit. Itange: 0
to 25 per cent.
In vivo observations were made using the
same platinum-tipped intraeardiac catheters
as were used in previous studies.3"5 The reference calomel half-cell was wrapped in gauze,
attached to the skin with adhesive tape, and
wet with saline. The output of the transistor
circuit was introduced into a 1-megohm recorder. The tip of! the catheter was lodged in
the pulmonary artery of a dog under pentobarbital sodium (Nembutal) anesthesia. Successive quantities of hydrogen-saturated saline were rapidly injected intravenously in a
random sequence- Figure 5 is a plot of the
area in arbitrary units of the response curve
against the volume of the hydrogen-saturated
saline injected. This empirical response curve
has an area essentially linear with quantity
of hydrogen injected.
A platinum-tipped catheter was inserted
Circulation Retearch. Volume IX. September 1961
Jt Saturated «lth Hjdrogen
Figure 4
Range is 0 to 100 per cent, using the lower gain
2N190 transistor and a lower collector load (2,200
ohms).
into the aorta of a dog under pentobarbital
sodium anesthesia. The dog was given successive inhalations of hydrogen in a manner
and depth similar to that in previous studies.3"5 The response of the platinum by way
of the transistor circuit was recorded. The
catheter was removed and calibrated with
zero- and 100-per-cent-saturated blood. Assuming the linear relationship demonstrated
in figure 4, the concentration of hydrogen in
the aortic blood was estimated to vary from
20 to 50 per cent saturated, varying with the
depth of the inhalation.
Discussion
A simple method has been described to
quantitate hydrogen at a platinized platinum
electrode. I t is neither the polarographic
method nor the potentiometrie method. Because the oxidation of hydrogen at a platinum
black electrode is spontaneous, the forced reaction of the polarograph is unnecessary, and
the resultant drift in blood is avoided. The
method employs a simple, low impedance cur-
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3ml
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5 ml
4 ml
7ml
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Area under curve of response versus volume of hydrogen-saturated, saline given intravenously to a dog. The signal originated from a platinum electrode at the tip of an
in tru cardiac catheter in the pulmonary artery.
rent measuring device which tests the battery
consisting of a platinum-hydrogen half-cell
versus a calomel reference half-cell much like
an ammeter is used to test a flashlight battery.
The system described gives a linear response
to the concentration of hydrogen at the platinum electrode. This offers quantisation. It
is simple and stable.
The response of the system is dependent
upon the area and the quality of the colloidal
platinum black deposited. Platinum black
deposited from approximately 3 per cent
chloroplatinic acid has been used because of
its sensitivity. Recently, it has been found
that a platinum '' grey, : ' formed by cathodizing 5 per cent PtCl 2 + 5 per cent ZnS0 4 and
dissolving the deposited zinc in dilute HC1.
responds equally but much faster. The slope
of the response curve may be tailored by the
choice of component values iu the circuit.
The equilibrium time of this electrochemical
reaction is rapid, but not instantaneous. The
response curve looks less sharp with the linear
system than with the logarithmic. This may
be an artifact of the logarithmic response iu
which small changes are amplified at lower
concentrations and are unnoticed at higher
concentrations. Figure 5 shows that there is
an empirical relationship of area to quantity
injected. The slope is probable less than theoretical, and quantitation of a rapid injection
of hydrogen could not be based on the full or
absolute response of the electrode.
There are three possible ways of circumventing the lack of an instantaneous response.
First is an empirical calibration such as in
figure 5. Second is the correlation of the
slope of onset of response with the concentration. The latter could be recorded electrically.
The third method is the use of a continuous
infusion technique, taking advantage of two
fortuitous circumstances. One is the obserCirculalion Rrnrarch. Volumr IX. Srptrmber 1961
LINEAR SYSTEM FOR QUANTITATING HYDROGEN
1097
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vatiou that inhalation of hydrogen causes a
prolonged, virtual plateau of hydrogen concentration in the aorta and probably a somewhat continuous infusion through a left-toright shunt. The other is the observation that
dissolved hydrogen injected in a peripheral
vein is not detected beyond the normal lung
capillaries. If detected, it is via a shunt. This
lends itself to a continuous infusion technique
using hydrogen in saline.
Summary
With a low impedance, transistor measuring
circuit, the response of a platinum-platinum
black electrode to hydrogen in solution is
found to be linear with concentration. Hydrogen in solution can be quantitated by this
circuit. This offers the possibility of quantitation of hydrogen by an intravascular platinum electrode. It may now be possible to
quantitate, as well as detect, intracardiac
shunts and repeat the observation without the
withdrawal of blood.
Addendum
that this chlorine-treated surface is very sensitive to
gaseous oxygen and could serve as a transducer to
register changes in pOj in a similar circuit.
Since submitting this paper, it has been found that
a smooth platinum surface can be made at least as
active as platinum covered with platinum black. This
is done by anodizing the platinum in acidified 10 per
cent KC1 for several minutes and then removing the
deposited chlorine either by cathodizing the platinum
in the same solution, or by several exposures to gaseous hydrogen. The procedure probably removes some
impurities from the surface of the platinum. The
smooth platinum surface has the advantage of no
loss of sensitivity by mechanical removal of colloidal
platinum. It gives a very rapid response with a return to base lino even quicker than the " z i n c " preparation upon removal of the signal. It is noted further
Detection of right to left shunts with an
arterial potentiometric electrode. Circulation
22: 949, 1960.
Circulation Research. Volume IX. September 1SS1
References
1. Ci/AEK, L. C, JR., AND BARGERON, L. M.: Left
to right shunt detection by an intravascular
electrode with hydrogen as an indicator. Science
130: 709, 1959.
2. CLARK, L. C, JR., AND BARGERON, L. M.: Detec-
tion and direct recording of right to left shunts
with a hydrogen electrode catheter. Surgery
46: 797, 1959.
3. HYMAN, A. L., HYMAN, E. S., QUIROZ, A., AND
GANTT, J.: Comparison of the platinum-
rhodium-hydrogen electrode, dye dilution, and
oxygen methods in detecting shunts. Surg.
Forum 11: 150, 1960.
4. HYMAN, A. L., HYMAN, E. S., QUIROZ, A., AND
GANTT, J . : Hydrogen-platinum electrode system
in detection of intravascular shunts. Am. Heart
J. 61 (no. 1): 53, 1961.
5. HYMAN, A. L., HYMAN, E. S., QUIROZ, A., AND
GANTT, J.: Hydrogen-platinum electrode sys-
tem (abstr.). Circulation 22: 766, 1960.
6. CLARK, L. C, JR., BABGERON, L. M., LYONS, C,
BRADLEY, M. N., AND MCARTHUR, K. T.:
7. MAYO ASSOCIATION : Symposium on diagnostic ap-
plications of indicator-dilution curves recorded
from right and left sides of the heart. Proceedings of the Staff Meetings of the Mayo
Clinic 33 (no. 22): 535, ,1958.
8. HYMAN, E. S.: Cause of failure of the artificial
heart-lung. Tr. Am. Soc. Artificial Internal
Organs 5: 257, 1959.
9 HYMAN, E. S.: Simple linear system to quantitate
hydrogen at a platinum surface (abstr.). Clin.
Res. 9 (no. 1): 15, 1961.
Linear System for Quantitating Hydrogen at a Platinum Electrode
EDWARD S. HYMAN
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Circ Res. 1961;9:1093-1097
doi: 10.1161/01.RES.9.5.1093
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