PROCEEDINGS OF THE PHYSIOLOGICAL SOCIETY UNIVERSITY COLLEGE LONDON AIEETING 25-26 .March 1991 These abstracts were accepted by Members of the ASociety present at the Meeting
i PhyIJ.il. (1991) 1 ,/. 43s t.Un.rsify ('ol4,,fy, London.lo(eetiny 2) PROCEED)INGS OF THE PHYSIOLOGICAL SOCIETY ,1.
142P
26 Jirlch 1991
DEMONSTRATIONS Apparatus for simultaneous flash photolysis and microfluorimetry D. Farquharsoni. Michael R. Duchen. R. J. Pearce anid T. .J. Biscoe I)epartmeit of Physiology. University College London, Gowcer Street. Londo?i IV'CJE 6BT We will demonstrate a sy-stem that directs the beam of a flash lamp through the epifluorescence port of an inverted Nikon microscope equipped for standard microfluorimetry. This effectively localizes the flash photolysis of photolabile caged compounds to the microscopic field. A flash lamp (Chadwick Helinuth) is mounted at right angles to the normal xenon source of the epifluorescence mnicroscope. A front silvered mirror is mounted so that it lies parallel to the xenon beam. Under these conditions, fluorescence signals are monitored as previously described (Biscoe & Duchen, 1990). An appropriately timed series of TTL pulses serve (i) to close an electronically operated slhutter (Uniblitz) in the light path to the photomultiplier tubes in order to protect them; (ii) to turn the mirror to 45 degrees using a servo controlled motor (Radio Spares); (iii) to flash the lamp; (iv) to reverse (i) and (ii). \\'e tlank the Wellcomne Trutst andl the Royal Society fo isuppwot. andl Di A.Guminey fol het advice. REFER EN(E Biscoe. T.J. & DuLChlell. M.R. (1990). J.
P,hysiol. 428.
39-59.
Iroceedtinql.s of 7he 1'hy.siol(xical Society UNIVERSITY COLLEGE LONDON MEETING 25-26 MARCH 1991
J. Physiol. (1991) V'ol. 438
.
143P
Use of the 'Sheffield' Electrical Impedance Tomography (EIT) system in imaging intracranial impedance changes with scalp electrodes in the anaesthetized rat David S. Holder Department of Physiology, University College London, Gower Street, London WC1E 6BT
EIT is a recently developed technique which enables the internal impedance of an object to be imaged with the use of a ring of external electrodes. Whilst several reconstruction algorithms and hardware designs are currently being developed, only one prototype design, the 'Sheffield' EIT system, is commercially available (see Webster, 1990). With this device, a ring of sixteen electrodes are placed around the object of interest. A constant current at 51 kHz is applied to an adjacent pair, and the inphase component of the resulting potential difference is measured serially from each adjacent pair of remaining electrodes. This is repeated for each electrode pair in turn; a complete data set is obtained in 79 ms, and 10 such sets are collected each second. An image is reconstructed on an IBM compatible 80186 microcomputer in 5 s by a single pass weighted back projection algorithm. This prototype method is rapid, relatively inexpensive and portable. Its disadvantages are: a relatively poor spatial resolution, images are of impedance changes with respect to a reference image, sensitivity falls off centrally, changes out of the electrode plane are included, and the algorithm assumes constant initial resistivity of the object. In impedance images made in a cylindrical tank 15 cm in diameter, the centre of a polythene rod 1.5 cm in diameter was localized to 3.9 ± 0.2 % of tank diameter (mean ± S.E.M., n = 9) of its true position, and a rod placed centrally could be discriminated from a second rod when their centres were 32 % apart. Images were also obtained with scalp electrodes placed in the fronto-occipital plane in adult Wistar rats. Post-mortem, a polythene rod, 2.4 mm in diameter, caused an impedance increase when placed vertically in the brain, but could not be discriminated from a second rod 6 mm away. In vivo, under anaesthesia with 1 % halothane, a peripheral impedance decrease occurred when scalp impedance was decreased by warming with a lamp. The technique appears to localize single impedance changes accurately in a medium of constant resistivity, but spatial resolution is substantially degraded in images made with scalp electrodes, where initial resistivity is non-uniform. This uvoi k was suppor ted by a Royal Society Univei sity Researc(?h Fellowship and equip)ment
grant.
RE FER ENC(E
Webster. J.G. (1990). Electrical Impedance Tomogiraphy. Bristol: Adain Hilger.
.Mletiny 2.-26 Jnirch PROCEEDINGS OF THE PHYSIOLOGI(AL SOCIETY J. Phy.diol. (1991) o1. 438 ('Uniresity
144P
(Colleye
Lond(lon
1991
The use of a laser Doppler flow meter to monitor pulpal blood flow in intact teeth of human subjects N. Vonigsavani and B. Alatthews Department of Physiology, School of Medical Sciences, Uin iiersity Walk. Bristol BSS ITI) It has been shown that records of pulpal blood flow can be obtained from intact teeth in human subjects using laser Doppler techniques (Olgart, Gazelius & Lindh-Stromberg, 1988). At first sight this seems surprising since when the same technique is applied to skin, its range is thought to be limited to the superficial 1-2 mm of tissue, yet the combined thickness of the enamel and dentine in human permanent teeth is about 2.0-3.5 mm. However, in preliminary experiments on teeth of similar size in pigs we confirmed that at least the major part of the records we obtained originated from the pulps of the teeth. The pigs were anaesthetized with thiopentone (10 mg/kg I.V. as required) and records were obtained before and after section of the pulps of the teeth. Thus enamel and dentine seem to be more transparent than skin. In the experiments to be demonstrated we have used techniques similar to those employed in the pigs to monitor blood flow in human maxillary incisors. The sensitivity of the flow meter (type AIBF31); AMoor Instruments, England) was increased above that normally used for skin so that the Brownian movement in the manufacturer's standard gave a reading of 160 perfusion units (PU) with an upper bandpass of 3.1 kHz. A specially modified flow meter probe was used. This was similar to a Moor Type P3 except that the length of the stainless steel shaft was reduced to 5 mm to make it more convenient to fix to teeth. A removable acrylic splint was made to fit the labial surfaces of the maxillary incisors of each subject. Over the centre of each tooth, a hole (diam. 1.6 mm) was drilled through the splint perpendicular to the enamel surface, with its centre approximately 2 mm from the gingival margin. Recordings were made with the tip of the probe inserted into this hole. Upper bandpass limits of 3.1 and 14.9 kHz were used. In each case a reading equivalent to zero flow was determined by recording from a white card with the position of the probe adjusted to give the same intensity of back-scatteied light as from the tooth. The values thus obtained were subtracted from the perfusion values recorded from the teeth. The average values recorded from each of 14 teeth in 8 subjects ranged from 2.2 to 22.7 P.U. (mean 7.2, S.D. 5.0, upper bandpass 14.9 kHz). It was found that covering the crown of the tooth and the adjacent mucous membrane with aluminium foil before inserting the splint, with just a small hole in the foil under the probe tip, increased the perfusion signal in every case (range 6.0-32.4, mean 14.2, S.D. 7.3). This irierease was significant (P < 0.001, paired t test). This effect is attributed to t.he foil reflecting back into the tooth some light which would otherwise have escaped from the surface and indicates that the instrument, even without the foil, could be detecting flow in vessels across the whole diameter- of the pulp and not just the superficial capillaries. EERE(NE R Ek
(lgart. L.. Gazelius B. & Lindh-Str6inberg. LT. (1988). IJt. Endod. J. 21. 30() 306.
i PhyIJ.il. (1991) 1 ,/. 43s t.Un.rsify ('ol4,,fy, London.lo(eetiny 2) PROCEED)INGS OF THE PHYSIOLOGICAL SOCIETY ,1.
142P
26 Jirlch 1991
DEMONSTRATIONS Apparatus for simultaneous flash photolysis and microfluorimetry D. Farquharsoni. Michael R. Duchen. R. J. Pearce anid T. .J. Biscoe I)epartmeit of Physiology. University College London, Gowcer Street. Londo?i IV'CJE 6BT We will demonstrate a sy-stem that directs the beam of a flash lamp through the epifluorescence port of an inverted Nikon microscope equipped for standard microfluorimetry. This effectively localizes the flash photolysis of photolabile caged compounds to the microscopic field. A flash lamp (Chadwick Helinuth) is mounted at right angles to the normal xenon source of the epifluorescence mnicroscope. A front silvered mirror is mounted so that it lies parallel to the xenon beam. Under these conditions, fluorescence signals are monitored as previously described (Biscoe & Duchen, 1990). An appropriately timed series of TTL pulses serve (i) to close an electronically operated slhutter (Uniblitz) in the light path to the photomultiplier tubes in order to protect them; (ii) to turn the mirror to 45 degrees using a servo controlled motor (Radio Spares); (iii) to flash the lamp; (iv) to reverse (i) and (ii). \\'e tlank the Wellcomne Trutst andl the Royal Society fo isuppwot. andl Di A.Guminey fol het advice. REFER EN(E Biscoe. T.J. & DuLChlell. M.R. (1990). J.
P,hysiol. 428.
39-59.
Iroceedtinql.s of 7he 1'hy.siol(xical Society UNIVERSITY COLLEGE LONDON MEETING 25-26 MARCH 1991
J. Physiol. (1991) V'ol. 438
.
143P
Use of the 'Sheffield' Electrical Impedance Tomography (EIT) system in imaging intracranial impedance changes with scalp electrodes in the anaesthetized rat David S. Holder Department of Physiology, University College London, Gower Street, London WC1E 6BT
EIT is a recently developed technique which enables the internal impedance of an object to be imaged with the use of a ring of external electrodes. Whilst several reconstruction algorithms and hardware designs are currently being developed, only one prototype design, the 'Sheffield' EIT system, is commercially available (see Webster, 1990). With this device, a ring of sixteen electrodes are placed around the object of interest. A constant current at 51 kHz is applied to an adjacent pair, and the inphase component of the resulting potential difference is measured serially from each adjacent pair of remaining electrodes. This is repeated for each electrode pair in turn; a complete data set is obtained in 79 ms, and 10 such sets are collected each second. An image is reconstructed on an IBM compatible 80186 microcomputer in 5 s by a single pass weighted back projection algorithm. This prototype method is rapid, relatively inexpensive and portable. Its disadvantages are: a relatively poor spatial resolution, images are of impedance changes with respect to a reference image, sensitivity falls off centrally, changes out of the electrode plane are included, and the algorithm assumes constant initial resistivity of the object. In impedance images made in a cylindrical tank 15 cm in diameter, the centre of a polythene rod 1.5 cm in diameter was localized to 3.9 ± 0.2 % of tank diameter (mean ± S.E.M., n = 9) of its true position, and a rod placed centrally could be discriminated from a second rod when their centres were 32 % apart. Images were also obtained with scalp electrodes placed in the fronto-occipital plane in adult Wistar rats. Post-mortem, a polythene rod, 2.4 mm in diameter, caused an impedance increase when placed vertically in the brain, but could not be discriminated from a second rod 6 mm away. In vivo, under anaesthesia with 1 % halothane, a peripheral impedance decrease occurred when scalp impedance was decreased by warming with a lamp. The technique appears to localize single impedance changes accurately in a medium of constant resistivity, but spatial resolution is substantially degraded in images made with scalp electrodes, where initial resistivity is non-uniform. This uvoi k was suppor ted by a Royal Society Univei sity Researc(?h Fellowship and equip)ment
grant.
RE FER ENC(E
Webster. J.G. (1990). Electrical Impedance Tomogiraphy. Bristol: Adain Hilger.
.Mletiny 2.-26 Jnirch PROCEEDINGS OF THE PHYSIOLOGI(AL SOCIETY J. Phy.diol. (1991) o1. 438 ('Uniresity
144P
(Colleye
Lond(lon
1991
The use of a laser Doppler flow meter to monitor pulpal blood flow in intact teeth of human subjects N. Vonigsavani and B. Alatthews Department of Physiology, School of Medical Sciences, Uin iiersity Walk. Bristol BSS ITI) It has been shown that records of pulpal blood flow can be obtained from intact teeth in human subjects using laser Doppler techniques (Olgart, Gazelius & Lindh-Stromberg, 1988). At first sight this seems surprising since when the same technique is applied to skin, its range is thought to be limited to the superficial 1-2 mm of tissue, yet the combined thickness of the enamel and dentine in human permanent teeth is about 2.0-3.5 mm. However, in preliminary experiments on teeth of similar size in pigs we confirmed that at least the major part of the records we obtained originated from the pulps of the teeth. The pigs were anaesthetized with thiopentone (10 mg/kg I.V. as required) and records were obtained before and after section of the pulps of the teeth. Thus enamel and dentine seem to be more transparent than skin. In the experiments to be demonstrated we have used techniques similar to those employed in the pigs to monitor blood flow in human maxillary incisors. The sensitivity of the flow meter (type AIBF31); AMoor Instruments, England) was increased above that normally used for skin so that the Brownian movement in the manufacturer's standard gave a reading of 160 perfusion units (PU) with an upper bandpass of 3.1 kHz. A specially modified flow meter probe was used. This was similar to a Moor Type P3 except that the length of the stainless steel shaft was reduced to 5 mm to make it more convenient to fix to teeth. A removable acrylic splint was made to fit the labial surfaces of the maxillary incisors of each subject. Over the centre of each tooth, a hole (diam. 1.6 mm) was drilled through the splint perpendicular to the enamel surface, with its centre approximately 2 mm from the gingival margin. Recordings were made with the tip of the probe inserted into this hole. Upper bandpass limits of 3.1 and 14.9 kHz were used. In each case a reading equivalent to zero flow was determined by recording from a white card with the position of the probe adjusted to give the same intensity of back-scatteied light as from the tooth. The values thus obtained were subtracted from the perfusion values recorded from the teeth. The average values recorded from each of 14 teeth in 8 subjects ranged from 2.2 to 22.7 P.U. (mean 7.2, S.D. 5.0, upper bandpass 14.9 kHz). It was found that covering the crown of the tooth and the adjacent mucous membrane with aluminium foil before inserting the splint, with just a small hole in the foil under the probe tip, increased the perfusion signal in every case (range 6.0-32.4, mean 14.2, S.D. 7.3). This irierease was significant (P < 0.001, paired t test). This effect is attributed to t.he foil reflecting back into the tooth some light which would otherwise have escaped from the surface and indicates that the instrument, even without the foil, could be detecting flow in vessels across the whole diameter- of the pulp and not just the superficial capillaries. EERE(NE R Ek
(lgart. L.. Gazelius B. & Lindh-Str6inberg. LT. (1988). IJt. Endod. J. 21. 30() 306.
