A Digital Timing System for a Small Animal Respiration Pump
EDISS AND DAVID F. BIGGS
CHRISTOPHER
A digital timing system has been developed to control the airflow from a respiration pump used in small animal pulmonary measurements. Three separate periods of up to 10 set may be selected with millisecond resolution using thumbwheel switches. A modular design using CMOS technology minimized the number of intercqnnections among the various parts of the system. A larger number of timing channels, longer time periods, and greater time resolution may be achieved by directly extending the existing design. Key Words:
Pulmonary flow resistance; Respiration pump
INTRODUCTION Measuring pulmonary flow resistance and dynamic pulmonary elastance or compliance in small rodents, such as rats or guinea pigs, is a common procedure in many
laboratories.
acting
skeletal
shorter-acting interfering piration
Often,
muscle agent,
with
such as succinylcholine, the animals.
to direct
seal to prevent
by a single
injection
or given
to prevent
Both techniques
to maintain
in the pump
an effective
are paralyzed
such as pancuronium,
measurements.
via a pump
employed
animals
relaxant,
respiratory
require
Standard
small
rodent
of a
movements
the use of artificial
As tidal volumes
res-
are small, any valves
the flow of air must be sensitive
leaks.
of a long-
an infusion
and still provide
ventilators’
valves
have
significant closing and opening times that can give rise to surprisingly large artifacts in flow rate and pressure signals recorded from the animals’ tracheas (Figure I). These spurious signals result in errors during resistance and dynamic compliance that reduce way of ensuring is to employ
rapid and complete
solenoid-operated
in Figure 2 (Gael
measurements their sensitivity
valve opening
and closing
valves. A typical experimental
and Biggs, 1987;
of pulmonary and reliability.
Biggs and Ladenius,
without
flow One
“bounce”
arrangement
is shown
1990). These valves need
a
timer to drive their power supply and to ensure that they open and close at the right times. We report the design of a simple reliable timing device for driving solenoid-operated
valves. The device
up to two valves. Also, analog-to-digital
From the
permits
a wide
it can be used to provide
degree
of flexibility
in driving
gating signals for integrators
and
converters.
Faculty of Pharmacy
and Pharmaceutical
Sciences,
University
of Alberta,
Edmonton,
Alberta,
T6G 2N8. Address of Alberta, Received
reprint
requests
Edmonton, August
to: Mr. C. Ediss, Faculty of Pharmacy
Alberta,
1, 1990;
T6G 2N8,
revised
and Pharmaceutical
Sciences,
University
Canada.
and accepted
October
3, 1990. 171
Journalof Pharmacological Methods 25, 171-177 (1991) Q 1991 Ekevier
Science Publishing
Co., Inc., 655 Avenue of the Americas. New York. NY 10~0
0160.5402/911$3.50
172
C. Ediss and D. F. Biggs
1 cm Hz0 i
+3s
___*(
FIGURE 1. The effect of optimising valve opening and closing on flow rate artifacts. No optimization (a), valve timing optimized (b). DESIGN The block
diagram
shown
in Figure 3 indicates
the modular
nature
of the com-
ponents required to control the pump. A reference signal generated by the beginning of a pump cycle creates a trigger signal and starts a I-ms clock. The six identical counters accumulate these clock pulses and provide an output when a time has
Small Animal Respiration Pump
Kuhnke 65 Solenoid Valve (Inflation)
Val idyne MP45-28 Pressure Transducer
Val tdyne MP45-28 Pressure Transducer
233
(
Flow
rate
(
)
)
Pressure
Pump
Animal I
Fleisch 0000 Pneumotachograph
Harvard Apparatus
Kuhnke 65 233 Solenoid Valve ( Exhaust
681 Rodent Respirator
FIGURE 2.
elapsed
equal to the thumbwheel
a setting arranged
settings.
arrangement.
Thus, with four thumbwheels
per timer
of 1000 corresponds to a time interval of 1 sec. The driver circuitry is so that a solenoid opens when the start time has elapsed after the begin-
ning of a pump The I-ms drivers
Block diagram of a typical experimental
)
cycle, and closes after some longer
clock
and the trigger
(Figure 5) were
constructed
circuitry
(Figure
stop period. 4) together
on a single printed
circuit
with board
the solenoid using conven-
tional techniques. The electronics associated with each timer digit (Figure 6) were attached directly to the corresponding thumbwheel switch. Two small single-sided printed circuit boards
accommodated
each 4510 counter
and pull-up
resistors within
the width
Timers (4 Decade
FIGURE 3.
Pairs)
Block diagram of the digital timing system.
Inflation
(9
173
174
C. Ediss and D. F. Biggs
12 16 3
III 13
12 4
5
r
‘Opf
L
’
FIGURE 4.
UGN
3501T
Clock and trigger circuitry.
mm) of a thumbwheel. Four of these digits were stacked together to control the time period required. The individual digits were linked through connectors mounted on a small mother board. Only five signals (Reset, Clock, Output, Ground and +I2 VI were required between each four-decade assembly and the remainder of the electronics. Figure 7 illustrates the compact nature of this arrangement. The three channel system shown in Figure 8 includes a conventional power supply and light-emitting
diodes
to indicate
the time duration
generated
by each timer.
Small Animal Respiration Pump
Start
stop
I
4
Decade
Preset
Counter
I+
I
4
Decade
Preset
Counter
h
oid
FIGURE 5.
Output circuitry for one channel of the timer.
.-.----
_E3 4-l:,
12 A
4 !5 1
FIGURE 6.
Four-decade preset counter.
175
176
C. Ediss and D. F. Biggs
FIGURE 7.
The compact four-decade
counter module.
RESULTS The complete pump controller (Figure 8) measures 11 in wide, 5 in high and 9 in deep. Although not completely waterproof, its compact size and unventilated enclosure is compatible with the mixed biological and electrical environment of the typical pharmacological workbench. The use of thumbwheel switches allows the direct visual display of the timing periods. This permits more exact recording of experimental conditions than would be possible with an analogue device. DISCUSSION The device reported here can be adapted to any motor-driven respiration pump; a Harvard Small Animal Respiration Pump was used in our experiments. We used a Hall-effect device attached to the pump rotor to provide the “start” signal, however, other systems could be used equally easily. Valve bounce was absent in our system if Kuhnke solenoid-operated valves were used. However, we found that it was important to optimize open and close times for each valve individually. Thus, some degree of overlap such that both valves were open simultaneously for a short
Small Animal Respiration Pump
FIGURE 8.
time
improved
motor.
One
The complete solenoid valve controller.
signal to noise ratios,
benefit
times. This is especially
important
in Figure 1 confirm that transient timizing the opening and closing reliable
in 18 months
of the butyl
rubber
much as is found
is that it is possible
to permit
when expiration
longer
in the classic Otto expiration
4-stroke
than inspiration
is passive. The waveforms
shown
flow rate artifacts can be greatly reduced by opof solenoid valves. The system has proven 100%
of use. The only maintenance
required
has been replacement
seals of the valves.
REFERENCES Gael V, Biggs DF (1987) Comparison of the bronchoconstrictor and cardiovascular effects of some tachykinins in guinea pigs. fife Sci 40:1007-1015.
Biggs DF, Laden& RC (1990) Capsaicin selectively reduces airway responses to histamine, substance P and vagal stimulation. Fur / fharmacol 175 : 29-33.
177
EDISS AND DAVID F. BIGGS
CHRISTOPHER
A digital timing system has been developed to control the airflow from a respiration pump used in small animal pulmonary measurements. Three separate periods of up to 10 set may be selected with millisecond resolution using thumbwheel switches. A modular design using CMOS technology minimized the number of intercqnnections among the various parts of the system. A larger number of timing channels, longer time periods, and greater time resolution may be achieved by directly extending the existing design. Key Words:
Pulmonary flow resistance; Respiration pump
INTRODUCTION Measuring pulmonary flow resistance and dynamic pulmonary elastance or compliance in small rodents, such as rats or guinea pigs, is a common procedure in many
laboratories.
acting
skeletal
shorter-acting interfering piration
Often,
muscle agent,
with
such as succinylcholine, the animals.
to direct
seal to prevent
by a single
injection
or given
to prevent
Both techniques
to maintain
in the pump
an effective
are paralyzed
such as pancuronium,
measurements.
via a pump
employed
animals
relaxant,
respiratory
require
Standard
small
rodent
of a
movements
the use of artificial
As tidal volumes
res-
are small, any valves
the flow of air must be sensitive
leaks.
of a long-
an infusion
and still provide
ventilators’
valves
have
significant closing and opening times that can give rise to surprisingly large artifacts in flow rate and pressure signals recorded from the animals’ tracheas (Figure I). These spurious signals result in errors during resistance and dynamic compliance that reduce way of ensuring is to employ
rapid and complete
solenoid-operated
in Figure 2 (Gael
measurements their sensitivity
valve opening
and closing
valves. A typical experimental
and Biggs, 1987;
of pulmonary and reliability.
Biggs and Ladenius,
without
flow One
“bounce”
arrangement
is shown
1990). These valves need
a
timer to drive their power supply and to ensure that they open and close at the right times. We report the design of a simple reliable timing device for driving solenoid-operated
valves. The device
up to two valves. Also, analog-to-digital
From the
permits
a wide
it can be used to provide
degree
of flexibility
in driving
gating signals for integrators
and
converters.
Faculty of Pharmacy
and Pharmaceutical
Sciences,
University
of Alberta,
Edmonton,
Alberta,
T6G 2N8. Address of Alberta, Received
reprint
requests
Edmonton, August
to: Mr. C. Ediss, Faculty of Pharmacy
Alberta,
1, 1990;
T6G 2N8,
revised
and Pharmaceutical
Sciences,
University
Canada.
and accepted
October
3, 1990. 171
Journalof Pharmacological Methods 25, 171-177 (1991) Q 1991 Ekevier
Science Publishing
Co., Inc., 655 Avenue of the Americas. New York. NY 10~0
0160.5402/911$3.50
172
C. Ediss and D. F. Biggs
1 cm Hz0 i
+3s
___*(
FIGURE 1. The effect of optimising valve opening and closing on flow rate artifacts. No optimization (a), valve timing optimized (b). DESIGN The block
diagram
shown
in Figure 3 indicates
the modular
nature
of the com-
ponents required to control the pump. A reference signal generated by the beginning of a pump cycle creates a trigger signal and starts a I-ms clock. The six identical counters accumulate these clock pulses and provide an output when a time has
Small Animal Respiration Pump
Kuhnke 65 Solenoid Valve (Inflation)
Val idyne MP45-28 Pressure Transducer
Val tdyne MP45-28 Pressure Transducer
233
(
Flow
rate
(
)
)
Pressure
Pump
Animal I
Fleisch 0000 Pneumotachograph
Harvard Apparatus
Kuhnke 65 233 Solenoid Valve ( Exhaust
681 Rodent Respirator
FIGURE 2.
elapsed
equal to the thumbwheel
a setting arranged
settings.
arrangement.
Thus, with four thumbwheels
per timer
of 1000 corresponds to a time interval of 1 sec. The driver circuitry is so that a solenoid opens when the start time has elapsed after the begin-
ning of a pump The I-ms drivers
Block diagram of a typical experimental
)
cycle, and closes after some longer
clock
and the trigger
(Figure 5) were
constructed
circuitry
(Figure
stop period. 4) together
on a single printed
circuit
with board
the solenoid using conven-
tional techniques. The electronics associated with each timer digit (Figure 6) were attached directly to the corresponding thumbwheel switch. Two small single-sided printed circuit boards
accommodated
each 4510 counter
and pull-up
resistors within
the width
Timers (4 Decade
FIGURE 3.
Pairs)
Block diagram of the digital timing system.
Inflation
(9
173
174
C. Ediss and D. F. Biggs
12 16 3
III 13
12 4
5
r
‘Opf
L
’
FIGURE 4.
UGN
3501T
Clock and trigger circuitry.
mm) of a thumbwheel. Four of these digits were stacked together to control the time period required. The individual digits were linked through connectors mounted on a small mother board. Only five signals (Reset, Clock, Output, Ground and +I2 VI were required between each four-decade assembly and the remainder of the electronics. Figure 7 illustrates the compact nature of this arrangement. The three channel system shown in Figure 8 includes a conventional power supply and light-emitting
diodes
to indicate
the time duration
generated
by each timer.
Small Animal Respiration Pump
Start
stop
I
4
Decade
Preset
Counter
I+
I
4
Decade
Preset
Counter
h
oid
FIGURE 5.
Output circuitry for one channel of the timer.
.-.----
_E3 4-l:,
12 A
4 !5 1
FIGURE 6.
Four-decade preset counter.
175
176
C. Ediss and D. F. Biggs
FIGURE 7.
The compact four-decade
counter module.
RESULTS The complete pump controller (Figure 8) measures 11 in wide, 5 in high and 9 in deep. Although not completely waterproof, its compact size and unventilated enclosure is compatible with the mixed biological and electrical environment of the typical pharmacological workbench. The use of thumbwheel switches allows the direct visual display of the timing periods. This permits more exact recording of experimental conditions than would be possible with an analogue device. DISCUSSION The device reported here can be adapted to any motor-driven respiration pump; a Harvard Small Animal Respiration Pump was used in our experiments. We used a Hall-effect device attached to the pump rotor to provide the “start” signal, however, other systems could be used equally easily. Valve bounce was absent in our system if Kuhnke solenoid-operated valves were used. However, we found that it was important to optimize open and close times for each valve individually. Thus, some degree of overlap such that both valves were open simultaneously for a short
Small Animal Respiration Pump
FIGURE 8.
time
improved
motor.
One
The complete solenoid valve controller.
signal to noise ratios,
benefit
times. This is especially
important
in Figure 1 confirm that transient timizing the opening and closing reliable
in 18 months
of the butyl
rubber
much as is found
is that it is possible
to permit
when expiration
longer
in the classic Otto expiration
4-stroke
than inspiration
is passive. The waveforms
shown
flow rate artifacts can be greatly reduced by opof solenoid valves. The system has proven 100%
of use. The only maintenance
required
has been replacement
seals of the valves.
REFERENCES Gael V, Biggs DF (1987) Comparison of the bronchoconstrictor and cardiovascular effects of some tachykinins in guinea pigs. fife Sci 40:1007-1015.
Biggs DF, Laden& RC (1990) Capsaicin selectively reduces airway responses to histamine, substance P and vagal stimulation. Fur / fharmacol 175 : 29-33.
177
