Magneto- and electrophosphenes: A comparative study

The purpose of this study was to compare the threshold values for magnetophosphenes and electrophosphenes under identical experimental conditions. Such comparisons between the phosphene types would increase our knowledge of the mechanism of the interaction between magnetic fields and electric current, respectively, and excitable tissue. The phosphenes were generated in the frequency range 10–45 Hz at moderate magnetic flux densities [up to 40 mT (400 G)] and electric currents up to 0.3 mA, respectively. The first part of the study was devoted to the problem of how electrode location and consequent current directions influence the threshold values of electrophosphenes. In the second part a comparison was made of the threshold values for electrophosphenes and magnetophosphenes under identical experimental conditions apart from the stimulation method. With electric-current stimulation in different directions no great differences were obtained with regard to the mean value for the threshold values within the frequency range 10–30 Hz. However, from 30 Hz upwards a significant difference developed between the threshold values for some of the curves. When generating electrophosphenes and magnetophosphenes we found significant differences in the threshold values between approximately 25 and 45 Hz. Both types of phosphenes had a concurring sensitivity maximum at 20 Hz. The deviations between the curves may be due, among other factors, to the generation of different current paths in electrical and magnetic stimulation, respectively.     

A model of the electrical volume conductor in the region of the eye in the ELF range.

Electrical and magnetic phosphenes are irritations of the eye caused by electric currents or magnetic fields. These are well known effects initially investigated in the early 1900s. Available estimations of the current densities in the eye, based on the assumption of a homogeneous volume conductor, show low thresholds. These outdated thresholds are still an important cornerstone when justifying today's limit values for extremely low-frequency (ELF) fields specified by statutory regulations. In vitro measurements of the complex conductivity of cattle eye are carried out for the ELF range (5-2000 Hz) separated for the different tissues of the eyeball. They do not show peculiarities at 20 Hz which is the threshold minimum for the phosphene generation. The reported conductivity data of the eye region show variations of two orders of magnitude regarding the electrical conductivity of the individual tissue layers. Starting with these new data, a model of the orbita is introduced describing the eye and its periphery as an electrically inhomogeneous volume conductor. This model contains small-scale structures which are expected to behave as good electrical conductors yielding regions of higher field values within the eye. Therefore, earlier models assuming a homogeneous volume conductor can be regarded as oversimplistic.     

Development of a platinized platinum/iridium electrode for use in vitro

Silver/silver chloride (Ag/AgCl) electrodes possess excellent electrical properties for measuring the electrical activity of gastrointestinal smooth muscle but exert toxic effects on this tissue in vitro. We thus developed a platinum electrode for use in vitro, the construction of these electrodes relying upon the formation of a glass-platinum/iridium seal. The platinum/iridium (Pt/Ir) electrodes were platinized using a current density of 0.45 mA mm⁻². The electrode impedance at 0.01 Hz showed a minimum with platinization current-time products greater than 500 mA s mm⁻². However, deposits in excess of 600 mA s mm⁻² were readily removed by mechanical abrasion and proved unsatisfactory. Optimal platinization was obtained with a deposit of platinum-black corresponding to a current-time product of 550 mA s mm⁻². Optimally-platinized electrodes (geometric surface area 0.11 mm²) had a stable and reproducible potential with a drift of less than 1 μV min⁻¹ and a lower impedance than optimally chlorided silver electrodes (geometric surface area 0.46 mm²) at frequencies higher than 0.25 Hz. The platinized Pt/Ir electrodes were used to record the electrical activity of gastrointestinal smooth muscle in vitro.     

Electrical stimulation of the human eye in different adaptational states

1. Experiments are described in which the phosphene produced by passing alternating current of frequency 100 Hz through the eye is matched with a patch of light having the same apparent size.2. Matches of this type have been made against different background light intensities, and at various times after a strong retinal bleach.3. To match the phosphene under particular conditions of this type, it is found that the patch must be set some 1.5 log td brighter than its own threshold under the same conditions. Exceptions to this rule occur with very bright backgrounds, or very soon after bleaching.4. The increment threshold for a small spot of light on the phosphene in the dark is some 0.5 log td higher than for the same spot on a patch of light matched in appearance to the phosphene under the same conditions.5. The process linking electrical stimulation of the eye to firing of fibres in the optic nerve is deduced to be substantially unaffected by the state of adaptation of the eye, save perhaps in the exceptional conditions described in (3).6. It is therefore argued that this phosphene is the result of stimulation both of the retinal visual pathways lying central to the variable-gain element commonly accepted to explain the facts of dark adaptation, and also of the input to this element that is supposed to alter its gain.     

Impedance of a goat eye lens

The complex electrical impedance of a goat eye lens is studied in the frequency range 10mHz−10Hz at room temperature, using a computer-controlled AC impedance system. AC impedance software (model 368, version 2.2) is employed to determine the total impedance and capacitance of the eye lens at various frequencies. A Cole-Cole plot of the eye lens material is drawn between the real component of impedance Z′ and the imaginary component Z″ for each excitation frequency that shows a perfect arc of a semicircle, with its centre lying below the abscissa at an angle of 35°. The half-angle ϕ between R₀ and R_∞ is found to be 55°, which mathematically demonstrates the selective permeability of the eye lens. Using graphical analysis of the Cole-Cole plot, characteristic frequency f_c and distribution factor α are observed to be 1Hz and 0.77, respectively. At characteristic frequency, capacitance and total impedance are found to be 1.14μF and 9.08kΩ. The effect of electrode polarisation on capacitance is corrected, based on Fricke's power function. The observed electrical parameters are then used to explain the multiple current path through various tissue compartments. Further, an attempt is made to explain the results on the basis of a possible dipolar model.     

Magnetophosphenes: a quantitative analysis of thresholds

Low-frequency and transient magnetic fields of moderate flux densities are known to generate visual phenomena, so-called magnetophosphenes. In the present study, time-variable very low frequency (10–50 Hz) electromagnetic fields of moderate flux density (0–40 mT) were used to induce magnetophosphenes. The threshold values for these phosphenes were determined as a function of the frequency of the magnetic field both in normal subjects and colour defective ones. Maximum sensitivity occurred at a frequency of approximately 20–30 Hz, and with broad-spectrum light the threshold flux density was 10–12 mT. The threshola values were found to be dependent upon the intensity and the spectral distribution of the background light. Sensitivity decreased during dark adaptation. In certain respects deutans differed from subjects with normal colour vision. Possible mechanisms for generation of magnetophosphenes are discussed. The present magnetic threshold curves show a close resemblance to corresponding curves obtained by electric stimulation at various frequencies provided the electric thresholds are divided by the a.c. frequency. These problems are under current investigation in our laboratory. This is in full agreement with the assumption that the fluctuating magnetic field affects retinal neurons by inducing currents which polarise synaptic terminals.     

Empirical correlation of triggered activity and spatial and temporal re-entrant substrates with arrhythmogenicity in a murine model for Jervell and Lange-Nielsen syndrome

KCNE1 encodes the β-subunit of the slow component of the delayed rectifier K⁺ current. The Jervell and Lange-Nielsen syndrome is characterized by sensorineural deafness, prolonged QT intervals, and ventricular arrhythmogenicity. Loss-of-function mutations in KCNE1 are implicated in the JLN2 subtype. We recorded left ventricular epicardial and endocardial monophasic action potentials (MAPs) in intact, Langendorff-perfused mouse hearts. KCNE1 ^−/− but not wild-type (WT) hearts showed not only triggered activity and spontaneous ventricular tachycardia (VT), but also VT provoked by programmed electrical stimulation. The presence or absence of VT was related to the following set of criteria for re-entrant excitation for the first time in KCNE1 ^−/− hearts: Quantification of APD₉₀, the MAP duration at 90% repolarization, demonstrated alterations in (1) the difference, ∆APD₉₀, between endocardial and epicardial APD₉₀ and (2) critical intervals for local re-excitation, given by differences between APD₉₀ and ventricular effective refractory period, reflecting spatial re-entrant substrate. Temporal re-entrant substrate was reflected in (3) increased APD₉₀ alternans, through a range of pacing rates, and (4) steeper epicardial and endocardial APD₉₀ restitution curves determined with a dynamic pacing protocol. (5) Nicorandil (20 μM) rescued spontaneous and provoked arrhythmogenic phenomena in KCNE1 ^−/− hearts. WTs remained nonarrhythmogenic. Nicorandil correspondingly restored parameters representing re-entrant criteria in KCNE1 ^−/− hearts toward values found in untreated WTs. It shifted such values in WT hearts in similar directions. Together, these findings directly implicate triggered electrical activity and spatial and temporal re-entrant mechanisms in the arrhythmogenesis observed in KCNE1 ^−/− hearts.     

Acoustic transmission of the aortic component of the second heart sound within the ascending aorta of dogs

The spectral characteristics of the acoustic transmission of the aortic component of the second heart sound within the ascending aorta was studied using a Millar dual-micromanometer catheter. The tip micromanometer was located close to the aortic valve leaflets while the second micromanometer was located 3 cm above the aortic valve. The frequency response of the transmission properties (amplitude and phase) of the blood and the aortic wall was modelled by an equivalent acoustic transmission system. The signal recorded by the tip micromanometer located near the aortic valve was considered to be the input signal of the equivalent system and the signal recorded by the second micromanometer was used as the output signal. Results of the spectral analysis of the input and output signals show that the acoustic transmissibility of blood in the ascending aorta is high at 20 Hz (the attenuation is negligible). Between 20 and 60Hz, the transmissibility decreases at a rate of −3dB per octave while between 60 and 120 Hz it decreases at a rate of −14dB per octave. Above 120Hz the transmissibility is low and the resulting attenuation is greater than 20 dB. The phase of the transfer function is shifted by −60°g at 20Hz and decreases at a mean rate of −2·0°Hz⁻¹ between 20 and 100Hz and −0·75°Hz⁻¹ up to 400Hz. The phase velocity of the sound transmission is relatively constant (5·5ms⁻¹) between 40 and 100Hz and increases up to 9ms⁻¹ at 300Hz.     

Effect of luminance level on electro-encephalogram alpha-wave synchronisation

A control system for the remote activation of electronic devices, based on alpha-wave synchronisation, must be robust over a wide range of lighting conditions. This study investigates the effect that low light levels have on the increase in amplitude of the occipital alpha-wave component of the human electro-encephalogram spectrum in response to eye closure. Measurements of the time required for the amplitude of the occipital alpha wave to increase above a predetermined threshold, upon eye closure, were taken from 21 subjects and at four illuminances, ranging from 2×10⁻¹ lx to 2×10⁻⁵ lx. The light source used to provide these illuminances was a featureless, uniformly illuminated white paper that subtended 30° of the visual field. Statistical analysis showed that the time to exceed threshold (TTET) upon eye closure was not independent (p<0.001) of illuminance, and that the main source of this lack of independence occurred at the lowest illuminance, 2×10⁻⁵ lx. At this luminance, the median TTET value was 15.0 s. However, at 2×10⁻⁴ lx, the median value of the TTET was 4.2 s. This is a sufficiently short time for device activation, and therefore a control system based on alpha-wave synchronisation is functional at very low light levels.     

Vestibular thresholds for yaw rotation about an earth-vertical axis as a function of frequency

Perceptual direction detection thresholds for yaw rotation about an earth-vertical axis were measured at seven frequencies (0.05, 0.1, 0.2, 0.5, 1, 2, and 5 Hz) in seven subjects in the dark. Motion stimuli consisted of single cycles of sinusoidal acceleration and were generated by a motion platform. An adaptive two-alternative categorical forced-choice procedure was used. The subjects had to indicate by button presses whether they perceived yaw rotation to the left or to the right. Thresholds were measured using a 3-down, 1-up staircase paradigm. Mean yaw rotation velocity thresholds were 2.8 deg s⁻¹ for 0.05 Hz, 2.5 deg s⁻¹ for 0.1 Hz, 1.7 deg s⁻¹ for 0.2 Hz, 0.7 deg s⁻¹ for 0.5 Hz, 0.6 deg s⁻¹ for 1 Hz, 0.4 deg s⁻¹ for 2 Hz, and 0.6 deg s⁻¹ for 5 Hz. The results show that motion thresholds increase at 0.2 Hz and below and plateau at 0.5 Hz and above. Increasing velocity thresholds at lower frequencies qualitatively mimic the high-pass characteristics of the semicircular canals, since the increase at 0.2 Hz and below would be consistent with decreased gain/sensitivity observed in the VOR at lower frequencies. In fact, the measured dynamics are consistent with a high pass filter having a threshold plateau of 0.71 deg s^-1 and a cut-off frequency of 0.23 Hz, which corresponds to a time constant of approximately 0.70 s. These findings provide no evidence for an influence of velocity storage on perceptual yaw rotation thresholds.

Efficacy and safety of the reciprocal pulse defibrillator current waveform

The efficacy and safety of a new defibrillating current waveform, consisting of a low-tilt 5 ms trapezoidal pulse followed closely by a second identical pulse of opposite polarity, was tested in seven isolated, perfused, working canine hearts suspended in an isoresistive, isotonic shock bath at 37°C. The efficacy and safety of the reciprocal pulse was compared with a single 5 ms pulse, a single 10 ms pulse, and a dual (unidirectional) 5ms pulse waveform. The mean threshold average current densities for the 5 ms single pulse, 10 ms single pulse, dual 5 ms pulse, and reciprocal pulse (absolute values) were 40, 38, 36 and 37 mA cm⁻², respectively. The corresponding mean threshold energy densities in the shock bath were 2·8, 2·9 and 3·1 mJ cm⁻³. Despite the differences in threshold current density among the waveforms, no differences in safety factor (shock strength for 50 per cent postshock depression divided by threshold shock strength) were found among the waveforms. The current safety factors were 5·4, 5·4, 5·6 and 5·5 for the 5 ms single pulse, 10ms single pulse, dual unidirectional pulse and reciprocal pulse, respectively. The corresponding energy density safety factors were 25, 27, 29 and 27. Thus the use of this reciprocal pulse waveform provides no advantage in efficacy or safety over waveforms of the same total duration.     

Alternating current electrophoresis of human red blood cells

An a.c. electrophoretic technique in the frequency range between 2–10 Hz, using a rectangular chamber design, has been developed for measuring the surface electric charge density of human red blood cells. With the a.c. approach, mobility can be determined rapidly, electrode polarization is minimized and the construction of the chamber simplified. For frequencies under 10 Hz and a chamber thickness of 150 μm, a theoretical analysis of the electroosmotic flow profile shows that it is almost identical to the d.c. case. With the a.c. method and using a 0.145 N NaCl solution buffered with NaHCO₃, the mobility of red cells measured at the lower stationary level is found to be −1.07±0.02 (S.D.) μmsec⁻¹ V⁻¹ cm. The zeta potential and charge density calculated from the mobility are −14.03±0.26 (S.D.) mV and −3603±69 (S.D.) esu cm⁻², respectively.     

The impact of exercise intensity on the release of cardiac biomarkers in marathon runners

We sought to determine the influence of exercise intensity on the release of cardiac troponin I (cTnI) and N-terminal pro-brain natriuretic peptide (NT-proBNP) in amateur marathon runners. Fourteen runners completed three exercise trials of the same duration but at exercise intensities corresponding to: (a) a competitive marathon [mean ± SD: heart rate 159 ± 7 beat min⁻¹, finish time 202 ± 14 min]; (b) 95% of individual anaerobic threshold [heart rate 144 ± 6 beat min⁻¹] and; (c) 85% of individual anaerobic threshold [heart rate 129 ± 5 beat min⁻¹]. cTnI and NT-proBNP were assayed from blood samples collected before, 30 min and 3 h post-exercise for each trial. cTnI and NT-proBNP were not different at baseline before each trial. After exercise at 85% of individual anaerobic threshold cTnI was not significantly elevated. Conversely, cTnI was elevated after exercise at 95% of individual anaerobic threshold (0.016 μg L⁻¹) and to an even greater extent after exercise at competition intensity (0.054 μg L⁻¹). Peak post-exercise values of NT-proBNP were elevated to a similar extent after all exercise trials (P < 0.05). The upper reference limit for cTnI (0.04 μg L⁻¹) was exceeded in six subjects at competition intensity. No data for NT-proBNP surpassed its upper reference limit. Peak post-exercise values for cTnI and NT-proBNP were correlated with their respective baseline values. These data suggest exercise intensity influences the release of cTnI, but not NT-proBNP, and that competitive marathon running intensity is required for cTnI to be elevated over its upper reference limit.     

60 Hz ventricular fibrillation thresholds for large-surface-area electrodes

The paper describes a series of animal experiments in which large-surface-area disk electrodes were used to study the current density required for ventricular fibrillation. The electrical currents were introduced to the heart both by applying the electrodes directly to the heart and by applying the electrodes to the surface of the chest near the heart. The electrode areas studied ranged from 1000 to 30 000 mm². The results show that, for large-area electrodes, fibrillation thresholds are determined by current density. The thresholds approach a constant value of 3·5 μA mm⁻²     

Closed-chest cardiac stimulation with a pulsed magnetic field

Magnetic stimulators, used medically, generate intense rapidly changing magnetic fields, capable of stimulating nerves. Advanced magnetic resonance imaging systems employ stronger and more rapidly changing gradient fields thant those used previously. The risk of provoking cardiac arrhythmias by these new devices is of concern. In the paper, the threshold for cardiac stimulation by an externally-applied magnetic field is determined for 11 anaesthetised dogs. Two coplanar coils provide the pulsed magnetic field. An average energy of approximately 12kJ is required to achieve closed-chest magnetically induced ectopic beats in the 17–26kg dogs. The mean peak induced electric field for threshold stimulation is 213 Vm ⁻¹ for a 571 μs damped sine wave pulse. Accounting for waveform efficacy and extrapolating to long-duration pulses, a threshold induced electric field strength of approximately 30 Vm ⁻¹ for the rectangular pulse is predicted. It is now possible to establish the margin of safety for devices that use pulsed magnetic fields and to design therapeutic devices employing magnetic fields to stimulate the heart.     

Assessment of the humane aspects of electric lancing of whales by measurement of current densities in the brain and heart of dead animals

The potential physiological effects of the electric lance are assessed, as used in Japanese whaling operations. Current densities are measured in the brains and hearts of six whales to which a controlled current of 5 A is applied by two electrodes inserted at various sites in the carcasses. The whales vary in size from 1.8 m (200 kg) to 16 m (40 t). The minimum current density in the brain necessary to cause depolarisation of neurones is estimated to be 10 mA cm⁻² and to cause ventricular fibrillation is estimated to be 0.5 mA cm⁻². No current densities exceeding 4.8 mA cm⁻² are recorded in the brain. Very few recordings of current density from the heart are above 0.5 mA cm⁻², and they occurr only when electrodes are in optimal positions. When electrodes are placed as in whaling operations, no whale over 3 m in length would receive current densities in the heart or brain sufficient to cause permanent dysfunction. It is concluded that electric lancing is ineffective as a secondary method of killing whales and that the current densities recorded could cause pain and suffering to an already distressed animal.     

Finite element modeling of drug distribution in the vitreous humor of the rabbit eye

Direct intravitreal injection of drug is a common method for treating diseases of the retina or vitreous. The stagnant nature of the vitreous humor and surrounding tissue barriers creates concentration gradients within the vitreous that must be accounted for when developing drug therapy. The objective of this research was to study drug distribution in the vitreous humor of the rabbit eye after an intravitreal injection, using a finite element model. Fluorescein and fluorescein glucuronide were selected as model compounds due to available experimental data. All required model parameters were known except for the permeability of these compounds through the retina, which was determined by fitting model predictions to experimental data. The location of the intravitreal injection in the experimental studies was not precisely known; therefore, several injection locations were considered, and best-fit retinal permeability was determined for each case. Retinal permeability of fluorescein and fluorescein glucuronide estimated by the model ranged from 1.94×10⁻⁵ to 3.5×10⁻⁵ cm s⁻¹ and from 0 to 7.62×10⁻⁷ cm s⁻¹, respectively, depending on the assumed site of the injection. These permeability values were compared with values previously calculated from other models, and the limitations of the models are discussed. Intravitreal injection position was found to be an important variable that must be controlled in both experimental and clinical settings.     

Two-point calibration procedure of the forced oscillation technique

The forced oscillation technique is usually calibrated by loading the measuring device with a known impedance. A correction function is calculated, relating the measured and reference impedances at each frequency. However, this one point calibration procedure does not account for transducer asymmetry. A procedure has previoously been presented to circumvent this problem: in addition to one known reference impedance, the callbration was repeated with the system occluded (infinite impedance). The aim of the present study was to evaluate a variant of this procedure, in which instead of resorting to an extreme condition imposing high requirements on the flow measuring system, two reference loads of 4 and 50 hPal⁻¹s were measured, thus covering the range of impedances obsereved in children and infants (a two-point procedure). The calibration procedure was performed with these two impedances and evaluated with a third impedance of ∼ 17 hPal⁻¹ s. The results of three calibration procedures were compared: one-point, two-point and a previously reported calibration procedure. Impedances consisted of sintered glass and mesh wire screens mounted in glass or polyvinyl tubes. For low impedance values, in the range of 4 to 17 hPal⁻¹s, measured and predicted values were similar for the three calibration procedures at frequencies from 4–52 Hz, although with the one point calibration procedure there was some underestimation above 44 Hz. With the highes load, especially above 32 Hz, marked discrepancies between measured and predicted values were observed with the one-point calibration procedure and the previously reported calibration procedure. Under these circumstances the two-point procedure is preferred.     

Effect of ageing on the ventilatory response and lactate kinetics during incremental exercise in man

We investigated the effects of age on breathing pattern, mouth occlusion pressure, the ratio of mouth occlusion pressure to mean inspiratory flow, and venous blood lactate kinetics during incremental exercise. Mouth occlusion pressure was used as an index of inspiratory neuromuscular activity, and its ratio to mean inspiratory flow was used as an index of the “effective impedance” of the respiratory system. Nine elderly male subjects [mean (SD) age: 68.1 (4.8) years] and nine young male subjects [mean (SD) age: 23.4 (1.3) years] performed an incremental exercise test on a bicycle ergometer. After a warm-up at 30 W, the power was increased by 30 W every 1.5 min until exhaustion. Our results showed that at maximal exercise, power output, breathing pattern, and respiratory exchange values, with the exception of tidal volume and the “effective impedance” of the respiratory system, were significantly higher in the young subjects. The power output and oxygen consumption values at the anaerobic threshold were also significantly higher in the young men. At the same power output, the elderly subjects showed significantly higher values for minute ventilation, respiratory equivalents for oxygen uptake and carbon dioxide output (CO₂), mean inspiratory flow, occlusion pressure and lactate concentration than the young subjects. At the same CO₂ below the anaerobic threshold (0.5, 0.75, 1.00 and 1.25 l · min⁻¹), minute ventilation and lactate concentration were also significantly higher in the elderly subjects. We observed a significantly higher minute ventilation at CO₂ values of 0.5, 0.75, 1.00 (P < 0.001) and 1.25 l · min⁻¹ (P < 0.05) in the elderly men, and a significantly higher lactate concentration at CO₂ values of 1.00 (P < 0.05) and 1.25 l · min⁻¹ (P < 0.01). In conclusion, the ventilatory response in elderly subjects is elevated in comparison with that in young subjects, both below and above the anaerobic threshold. This study demonstrates for the first time that this ventilatory increase, both below and above the threshold, is partly due to an increased lactate concentration. Received: 30 March 1999 / Accepted: 24 June 1999     

Standardization of the resistance to external cophasal powerline interference for grounded electrocardiographs with the patient's circuits insulated from ground

Conclusions 1. It is possible to simulate the aggregate composed of the interference sources, the interference receiver (the person undergoing the ECG examination), the coupling circuits between the interference sources and the person, and also the circuits between the person and surfaces at ground potential by equivalent current and voltage interference generators. The corresponding internal admittance and internal impedance of the interference generators in the majority of examination situations are determined by the patient's electrical capacity. The values of the generator current and the interference current are equal to the interference current through a grounded person. The values of the generator voltage and the interference voltage are equal to the potential of the patient with respect to ground for the condition that no electrically-conducting objects or electrical circuits of any sort are in contact with him. The highest values of interference current and voltage encountered fairly often under actual examination conditions are, respectively, equal to 0.5·10⁻⁶ A and 13 V. The patient's capacity that corresponds to the most adverse examination conditions with regard to interference is equal to 120 pF. 2. Similating examination conditions with current and voltage interference generators makes it possible to evaluate the resistance of grounded ECGs to external electrical cophasal power-line interference in terms of parameters that are known respectively as the “equivalent resistance of cophasal interference” and the “cophasal rejection factor.” The equivalent resistance of cophasal interference is the ratio referred to the input of an ECG of the differential interference voltage to the interference current causing it that is conducted to the patient's cable from the interference current generator through the equivalence of the electrode-to-skin resistances. The cophasal rejection factor is the ratio referred to the ECG input of the differential interference voltage to the cophasal voltage causing it that is conducted to the patient's cable through the equivalent of the patient's capacity and the equivalents of the electrode-to-skin resistances. When the peak-to-peak value of the differential interference voltage referred to the ECG input is equal to 0.02 mV, which corresponds to a peak-to-peak interference on the recording of 0.2 mm with an ECG sensitivity of 10 mm/mV, the requirements that were found for the parameters of the interference resistance are, correspondingly, ≤ 14 Ω and ≤ 0.5·10⁻⁶. All-Union Scientific-Research Institute of Medical Instrument construction, Moscow. Translated from Meditsinskaya Tekhnika, No. 3, pp. 27–34, May–June, 1977.