106

Electroencephalograohy and Clinical Neurophysiology, 40 (1976) 106--108 © Elsevier Scientific Publishing Company, Amsterdam -- Printed in The Netherlands

Technical contribution A THERMOELECTRIC PROBE F O R FOCAL CORTICAL H Y P O T H E R M I A * A.D. ROSEN **

Health Science Center, State University of New York, Stony Brook, N.Y. 11794 (U.S.A.) (Accepted for publication: August 4, 1975)

In the past several years localized hypothermia has been employed by several investigators to produce a reversible functional block of various structures within the central nervous system of small animals. The technique most c o m m o n l y used requires the pumping of a coolant through a thin-walled tube (Banet and Segvin 1967; Vastola et al. 1969; Skinner 1970). The purpose of this paper is to describe a small, easily constructed device which does not require circulating collants and which may be operated in contact with the cortical surface during recording with high impedance microelectrodes.

Methods and results The basis of this device is a thermoelectric module consisting of multiple junctions of dissimilar conductors. Passage of current through this device will result in a drop in temperature on one side of each junction and a rise in temperature on the other side (Peltier effect). The junctions are electrically in series and thermally in parallel. For a detailed discussion of the theory of operation of Peltier devices the reader is referred to the descriptions by Bird and Yamamura (1971) and Brown et al. (1973). The specific device used is capable of producing a temperature differential of 58 ° C (Model 801-3959-01, Cambridge * This work was supported under Veterans Administration Research Project 7570-01. ** Reprint requests to: Neurology Service, Veterans Administration Hospital. Northport, N.Y. 11768.

Thermionic Corp., Cambridge, Mass.). Fig. 1 shows the mechanical construction of the entire device. A probe, consisting of a silver rod soldered to a copper plate, is thermally coupled to the cold side of the thermoelectric module with a thin layer of zinc oxide loaded silicon grease. A brass heat sink through which water flows is coupled to the h o t side of the module. All three components (probe, thermoelectric module and heat sink) are clamped together in a lucite block which, in turn, is held on an electrode carrier. The face of the probe, i.e. that portion which will contact the cortical surface, measures 5 mm square and has a small thermistor cemented onto its center to permit continuous monitoring of cortical temperature. The battery operated thermistor bridge circuit uses a 50 pA, center zero, meter for temperature readout {Fig. 2). To calibrate, the probe is first cooled to 0°C and the 20 k~2 potentiometer adjusted for " 0 " meter reading. The probe is then warmed to 50°C and the 10 k~2 potentiometer adjusted for a " + 5 0 " meter reading. Battery drain for the bridge is negligible. Power for the thermoelectric module is provided by a 1.25 V, 23 Ah NiCd battery (Everready R23). When n o t switched to power the module, this battery receives a trickle charge from a single phase rectifier made up of a 6.3 V filament transformer and a silicone diode. When the battery is being charged, the thermoelectric module is grounded. The rate and degree of cooling is a function of the current delivered to the thermoelectric module. At the

107

THERMOELECTRIC PROBE

DOo

~0

Fig. 1. Mechanical construction of probe. A. Lucite clamp. B. Brass heat sink. C. Thermoelectric module. D. Copper plate with zinc oxide/silicone coating. E. Silver probe. F. Probe face with thermistor.

m a x i m u m current o f 5 A the device will lower the t e m p e r a t u r e o f the c or t ex in c ont a c t with the probe by 15°C in 30 sec. Lesser degrees of cooling are possible by switching in one of f o u r series resistors which are set to provide currents of 2.5, 1.5, 1.0 or 0.5 A. In actual use, m a x i m u m current is used to rapidly lower the temperature; then the current is reduced appropriately to maintain it at the desired level. Freeze lesions may be pr oduced if the device is operated at m a x i m u m current for periods in excess of 90 sec. The precise dimensions of the probe are n o t critical. The silver rod may be constructed to suite one's specific needs. Larger probes will, however, cool more slowly.

Summary A simple, non-mechanical device is described which permits rapid cooling (or freezing) of discrete cortical areas in small animals.

I



Resume

Sonde thermo-~lectrique pour hypothermie corticale locale L ' a u t e u r ddcrit un syst~me simple, non m~canique, qui p e r m e t le refroidissement (ou le gel) rapide d'aires corticales discr~tes chez de petits animaux.

108

A.D. ROSEN

SW2

= •



117V Ac •

SWI

']i tl/' j

R2

CHG

R1

-k

~

I

I I

R1

R2

! I I I I I I

801-3959"-0!

1"25V-- I

"J,,,

I

OHM, 12W

10

ee

--

•>

I

~ '.,~ •

1OHM,12 W 1 ,' ,12 ,, 3 " ,12 3 " 12

~ G~B35JI C ~

~ 1"SV 5K~ Fig. 2. Control circuit.

References Banet, M. and Segvin, J.J. A thermode for rat brain. Electroenceph. clin. Neurophysiol., 1967, 23: 572-573. Bird, G.S. and Yamamura, A. The cambion thermoelectric handbook. Cambridge Thermionic Corp., Cambridge, Mass., 1971. Brown, P.B., Maxfield, B.W. and Moraff, H. Electronics

for neurobiologists. The M.I.T. Press, Cambridge, Mass., 1973. Skinner, J.E. A cryoprobe and cryoplate for reversible functional blockade in the brains of chronic animal preparations. Electroenceph. clin. Neurophysiol., 1970, 29: 204--205. Vastola, E.F., Homan, R. and Rosen, A. Inhibition of focal seizures by moderate hypothermia. Arch. Neurol. (Chic.), 1969, 20: 430--439.

A thermoelectric probe for focal cortical hypothermia.

106 Electroencephalograohy and Clinical Neurophysiology, 40 (1976) 106--108 © Elsevier Scientific Publishing Company, Amsterdam -- Printed in The Net...
161KB Sizes 0 Downloads 0 Views