An ultra-high common-mode rejection ratio (CMRR) AC instrumentation amplifier for laplacian electrocardiographic measurement.

Laplacian electrocardiograms (LECGs) localize the moment of activation (MOA) of the heart noninvasively at a nearby point on the chest surface. Tripolar concentric ring (TCR) electrodes provide small, but well-defined, site-specific second spatial derivative signals of the potential on the chest surface for studying the activation sequence of the myocardium. A battery-powered, modified AC instrumentation amplifier (IA) was used as preamplifier to obtain signals with a high common-mode rejection ratio (CMRR). The authors' direct-coupled quasi-high-pass IA has high input impedance and high CMRR, without the need to match capacitors and resistors. The amplifier circuit and two lithium cells were integrated with the substrate for the TCR sensor to minimize inductive pickup by the leads. Combining the natural ability of the TCR electrodes to reject common-mode signals with the high CMRR of the IA made it possible to obtain LECG signals in real time with good signal-to-noise ratio (SNR). The authors observed and recorded the MOAs from 16 sites in a 4-by-4 matrix from the left side of the thorax of each subject. Beat-by-beat changes were observed from one subject showing episodes of bigeminal rhythm. The authors were able to obtain localized signals representing the right and left ventricles from surface TCR electrodes in real time.

Fractionated premotor, motor, and ankle dorsiflexion reaction times in hemiplegia.

Ten hemiplegic subjects completed 20 rapid dorsiflexions of their afflicted and nonafflicted limbs. Electrodes were attached to the tibialis anterior and the gastrocnemius muscles and electromyograms were recorded for their premotor time, motor time, and simple reaction time during ankle dorsiflexion and plantar flexion of their lower limbs. The fractionated components of reaction time, namely, premotor time and motor time, of both legs were statistically compared. It was found that the premotor time of the subject's stroke-affected limb was significantly slower than the premotor time of the nonaffected limb (control), with no differences between their associated mean motor times. These results supported the hypothesis that a stroke has a deleterious affect upon the central, premotor time processing centers and has no disruptive influence upon the peripheral motor time. Comparing the fractionated components of reaction time (premotor time and motor time), with simple reaction time, the former provided a more sensitive and valid method to detect possible injurious side effects of a stroke upon the brain's neuromotor transmission centers and subcenters, and their peripheral, stimulus, response network.

Conductivities of pig dermis and subcutaneous fat measured with rectangular pulse electrical current.

We examined experimentally the relationship between perpendicular and tangential electrical conductivities, sigma, and peak current density J, in pig skin dermis and subcutaneous fat specimens by using a four-electrode measuring system with rectangular pulse electrical current (RPEC). We also investigated the relationship of the conductivity, sigma, vs. pulse rate, f. The rates were selected at 8, 32, 64, and 128 pulses per second (pps), and the pulse width was fixed at 140 microseconds. These values are often used in vivo to enhance cutaneous regeneration with RPEC stimulation. It was found that the conductivities may be approximated to be [equation: see text] for the skin dermis and [equation: see text] for the subcutaneous fat in the conditions of this experiment. These findings implies that the conductivities of pig skin dermis and subcutaneous fat are anisotropic, i.e., sigma x = sigma y not equal to sigma z. It was also found that the conductivities are independent of current density and pulse rate in the current range from 20 microA/cm2 to 120 mA/cm2.

In vivo 3-D distributions of electric fields in pig skin with rectangular pulse electrical current stimulation (RPECS).

We developed stimulating and detecting electrodes. We experimentally examined three dimensional (3-D) distributions of electric fields in living pig skin under and around the stimulating electrodes with the detecting electrodes and rectangular pulsed electrical current stimulation (RPECS). We verified our previous physical assumption, E approximately I/(A sigma dz), in the skin under the electrode, where E, I, A and sigma dz respectively represent the electric field, the externally imposed peak current, the cross sectional area of the stimulating electrode and the perpendicular conductivity of the skin. Pulses were 30 mA, 140 microseconds and 128 pulses per second (pps). These parameters were previously used in our laboratory to enhance cutaneous regeneration, in vivo, with RPECS.

A novel electric design for electromagnetic stimulation--the Slinky coil.

A novel coil design for inductive electromagnetic stimulation of neural cells has been simulated and experimentally tested. This coil improves the focal effect of a magnetic stimulator, and it reduces its inductance, hence the efficiency of the system is improved. The basic structure of the device is derived from the popular "Slinky" toy. The actual device is formed by winding different numbers of loops forming a helical coil on a half torus. The loops are bunched at the axis of the torus. The coil, due to its geometry, generates a unique distribution of eddy currents in nearby tissues which is favorable compared to a solenoid type stimulator. This renders the Slinky coil more selective than conventional coils used for magnetic stimulation. The distribution of eddy currents was analyzed using Matlab, following Faraday's Law of Induction. Improved focality permits the current through the coil to be reduced for the same effect. In addition, the reduced inductance of the Slinky coil decreases the power requirement; thus, the improved efficiency of the system may allow the generation of bursts of pulses, and expand the utilization of the system to possible functional activation of certain neuro-muscular structures when peripheral nerves are stimulated.

Theoretical study of rectangular pulse electrical stimulation (RPES) onskin cells (in vivo) under conforming electrodes.

Our previous in vivo experimental results have shown RPES can enhance skin wound healing by using conforming electrodes. Based on an equation of polarization transmembrane voltage [Cole, K. S. 1972], two equations were derived to describe the peak RPES intensity on skin cells in vivo: (1) U = 1.5 a J/sigma, (2) Jm = 1.5 a (J/sigma) (Cm/tau). Where U: polarization transmembrane voltage. a: radius (R) for spherical cells or semi-length (L) for long fibers parallel to the electrical field. J: external imposed pulse current density under the electrode. sigma: average conductivity of skin tissue. Jm: transmembrane displacement current density. Cm: membrane capacitance per unit area and tau: time constant. Calculations indicated that the sensory fibers (SF) would receive the strongest stimulation compared to other cells in skin since generally LSF > or = 100 R. The sensitivity of SF to the stimulation could enhance skin wound healing as well as protect normal skin cells from harmful electroporation. From these theoretical calculations. We proposed a theoretical range of the pulse current density as: U1 sigma/(1.5 L) < or = J < or = U2 sigma/(1.5 L), where U1 and U2 are the excitation threshold voltage (about 0.01 V) and polarization electroporation voltage (about 0.1 V) for a SF respectively, for RPES to enhance skin wound healing.

Schrodinger equation, Maxwell-Bolzmann distribution and a single channel current.

The dual nature, wave and particle, of ions in the biological system was considered. A theoretical model, based on the steady state Schrodinger equation and Maxwell-Bolzmann distribution of energy, is proposed to describe passive transport of ions through a biological membrane channel in a time independent field. Constant height (V2) and length(L) of the potential energy barrier and effective mass of ions are used in the model. This model shows that an ion may go through or be reflected from a channel whether its energy is lower or higher than the barrier. This is a departure from classical theory. Based on a published I-Vm (channel current-transmembrane voltage) curve from an activated K+ channel in a human erythrocyte membrane [Palle Christophersen, 1991], calculations with our model show that more than 99% of the channel current is contributed by ions with higher energy than the potential barrier. The current can be amplified 10,000 times while V2 is reduced from 0.45 eV (channel closed) to 0.20 eV (channel opened) at Vm = 0.07 V. In contrast, the current changes only 1.5% while L is narrowed from 90 A to 30 A at Vm = 0.07 V, V2 = 0.20 eV. The energy barrier: V2 = 0.16 + 0.43 Vm (eV), at r = 0.99, for 0.02 V < or = Vm < or = 0.12 V.

Low-energy transvenous ablation of the canine atrioventricular conduction system with a suction electrode catheter.

A single suction electrode catheter was used for His bundle electrogram recording. His bundle pacing, and low-energy (20 or 30 J) His bundle ablation in seven dogs. The suction electrode catheter was actively fixed to the atrial endocardium at the His bundle level. Electrophysiologic studies were performed in the control state, immediately after, and late (greater than 40 days) after His bundle ablation and results were correlated with histologic findings in the conduction system. Unipolar His bundle recording and pacing were successfully performed in all dogs with the suction electrode catheter before and after ablation. Complete heart block developed after a single 20 J shock delivered via the suction electrode catheter in all dogs immediately, but reverted to 1:1 atrioventricular conduction with first-degree atrioventricular block in two dogs in which one or two additional shocks (20 or 30 J) produced complete heart block. Mean ablation energy per shock was 22 +/- 4 J. The mean total delivered energy per dog was 31 +/- 20 J. Late electrophysiologic study in all dogs showed persistent complete heart block in five dogs and paroxysmal second-degree or third-degree atrioventricular block in two dogs. Gross examination of the ablation site showed a white plaque above the medial tricuspid leaflet (1.4 to 2.0 cm long and 0.4 to 0.6 cm wide). Microscopically, fibrosis of the penetrating and branching His bundle was seen in all dogs, with minimal atrioventricular node and atrial involvement. Significant proximal right bundle branch fibrosis was observed in the two dogs receiving one or two additional shocks. We conclude that the suction electrode catheter permits repeated His bundle recording, pacing, and ablation with a single catheter. Permanent and safe low-energy ablation of the canine His bundle is feasible. Focal injury localized to the target area in the conduction system can be obtained.

Laser catheter-induced atrioventricular nodal delays and atrioventricular block in dogs: acute and chronic observations.

Selective modification of atrioventricular (AV) nodal conduction, that is, induction of varying degrees of AV nodal delays or block (second or third degree), or both, was achieved with a pervenous laser catheter technique. In six adult mongrel dogs anesthetized with pentobarbital (Nembutal), 5F leads were placed through femoral and external jugular veins and placed into the right atrium and His bundle region. Through another femoral vein, a 200 micron optical fiber was inserted by way of a 7F catheter with a preformed curved tip. Guided by fluoroscopy and His bundle electrograms, the fiber's tip was positioned in the AV nodal region. After autonomic blockade was achieved with intravenous propranolol (5 mg) and atropine (1 mg), AV conduction was analyzed. An argon laser delivered 3 to 4 watts into the fiber in bursts of 10 seconds' duration until the desired degree of AV nodal delay or block (second or third degree) was manifested. Monitoring of His bundle electrograms was continued for 2 hours. Four weekly serial electrocardiograms were recorded, after which electrophysiologic studies were repeated. Acute post-lasing studies showed that: in all six dogs, the mean PR interval was prolonged from 116 ms (range 100 to 135) to 153 ms (range 120 to 185), with the prolongation being caused exclusively by AH lengthening from 68 ms (range 50 to 90) to 105 ms (range 65 to 140); the mean effective refractory period of the AV node increased from less than 185 ms (range less than 150 to less than 200) to 215 ms (range 190 to 280); and the mean atrial pacing cycle length, at which second degree AV nodal block was manifested, increased from 210 ms (range 160 to 260) to 261 ms (range 205 to 320).(ABSTRACT TRUNCATED AT 250 WORDS)

Principles of multimode pacing.

Although physiologic pacing systems have multiplied recently, their functional evaluation by ECG analysis remains an area of relative complexity. More thorough and detailed specifications of operation are necessary to aid the clinician in his effort to understand and assess the function of a DDD pacer. Elimination of cross-talk via various available methods should simplify interpretation. Awareness by physicians will provide the necessary feedback to the designers to create more physiologic systems in the future.

Use of a double atrial-triggered standby pacemaker system for a patient with a biventricular bypass heterotopic cardiac homograft.

In a patient who had a biventricular bypass heterotopic cardiac homograft a double atrial-triggered standby pacemaker system was implanted to allow sequential atrial pacing of both hearts. The system design permitted either the recipient or the donor heart to dictate the rate of its fellow, depending on which heart had the faster spontaneous sinus rate at any time. Alternative methods for achieving sequential pacing are discussed.

The significance of electrode surface area and stimulating thresholds in permanent cardiac pacing.

This paper reports a long-term clinical study of evolving chronic thresholds of cardiac stimulation in patients with implanted pacemakers and two types of permanent prevenous unipolar pacing leads. A comprehensive collection of threshold measurements is presented and analyzed. These data were accumulated over a period of more than 4 years by measuring stimulation thresholds at each of five stimulus pulse durations ranging from 0.5 to 2.5 msec. Measurements were made at initial implantation and at first (21 month) and second (42 month) reimplantations.