The human startle response is a sensitive, noninvasive measure of central nervous system activity that is currently used in a wide variety of research and clinical settings. In this article, we raise methodological issues and present recommendations for optimal methods of startle blink electromyographic (EMG) response elicitation, recording, quantification, and reporting. It is hoped that this report will foster more methodological validity and reliability in research using the startle response, as well as increase the detail with which relevant methodology is reported in publications using this measure.

/pdf/committee-report-guidelines-for-human-startle-eyeblink-3wopiiqcru.pdf

Committee report: Guidelines for human startle eyeblink electromyographic studies.

The basic principles of using sonographic techniques for imaging the elastic properties of tissues are described, with particular emphasis on elastography. After some preliminaries that describe some basic tissue stiffness measurements and some contrast transfer limitations of strain images are presented, four types of elastograms are described, which include axial strain, lateral strain, modulus and Poisson's ratio elastograms. The strain filter formalism and its utility in understanding the noise performance of the elastographic process is then given, as well as its use for various image improvements. After discussing some main classes of elastographic artefacts, the paper concludes with recent results of tissue elastography in vitro and in vivo.

Elastography: ultrasonic estimation and imaging of the elastic properties of tissues.

Alternatives to conventional wet electrode types are keenly sought for biomedical use and physiological research, especially when prolonged recording of biosignals is demanded. This paper describes a quantitative comparison of three types of bioelectrode (wet, dry and insulating) based on tests involving electrode impedance, static interference and motion artefact induced by various means. Data were collected simultaneously, and in the same physical environment for all electrode types. Results indicate that in many situations the performance of dry and insulating electrodes compares favourably with wet electrodes. The influence of non-stationary electric fields on shielded dry and insulating electrode types was compared to wet types. It was observed that interference experienced by dry and insulating electrode types was 40 dB and 34 dB less than that experienced by wet electrode types. Similarly, the effect of motion artefact on dry and insulating electrodes was compared to wet types. Artefact levels for dry and insulating electrodes were significantly higher than those for wet types at the beginning of trials conducted. By the end of the trial periods artefact levels for dry and insulating types were lower than wet electrodes by an average of 8.2 dB and 6.8 dB respectively. The reservations expressed in other studies regarding the viability of dry and insulating electrodes for reliable sensing of biosignals are not supported by the work described here.

https://iopscience.iop.org/article/10.1088/0967-3334/21/2/307/pdf

A direct comparison of wet, dry and insulating bioelectric recording electrodes.

A major disadvantage of the current practice of elastography is that only the axial component of the strain is estimated. The lateral and elevational components are basically disregarded, yet they corrupt the axial strain estimation by inducing decorrelation noise. In this paper, we describe a new weighted interpolation method operating between neighboring RF A-lines for high precision tracking of the lateral displacement. Due to this high lateral-tracking precision, quality lateral elastograms are generated that display the lateral component of the strain tensor. These precision lateral-displacement estimates allow a fine correction for the lateral decorrelation that corrupts the axial estimation. Finally, by dividing the lateral elastogram by the axial elastogram, we are able to produce a new image that displays the distribution of Poisson's ratios in the tissue. Results are presented from finite-element simulations and phantoms as well as in vitro and in vivo experiments.

A new elastographic method for estimation and imaging of lateral displacements, lateral strains, corrected axial strains and Poisson's ratios in tissues.

A novel noncontact indentation system with the combination of an air jet and optical coherence tomography (OCT) was presented in this paper for the quantitative measurement of the mechanical properties of soft tissues. The key idea of this method is to use a pressure-controlled air jet as an indenter to compress the soft tissue in a noncontact way and utilize the OCT signals to extract the deformation induced. This indentation system provides measurement and mapping of tissue elasticity for small specimens with high scanning speed. Experiments were performed on 27 silicone tissue-mimicking phantoms with different Young's moduli, which were also measured by uniaxial compression tests. The regression coefficient of the indentation force to the indentation depth (N mm(-1)) was used as an indicator of the stiffness of tissue under air jet indentation. Results showed that the stiffness coefficients measured by the current system correlated well with the corresponding Young's moduli obtained by conventional mechanical testing (r = 0.89, p < 0.001). Preliminary in vivo tests also showed that the change of soft tissue stiffness with and without the contraction of the underlying muscles in the hand could be differentiated by the current measurement. This system may have broad applications in tissue assessment and characterization where alterations of mechanical properties are involved, in particular with the potential of noncontact micro-indentation for tissues.

/pdf/an-optical-coherence-tomography-oct-based-air-jet-3furfc1mpk.pdf

An optical coherence tomography (OCT)-based air jet indentation system for measuring the mechanical properties of soft tissues.

Movement-induced potentials of streaming potential type were studied in various electrode configurations. The geometric design of the electrode was important for the reduction of noise generated by the movements of gel. Potential and impedance variations were measured for electrode movements in electrolytes. The impedance variations were small and the streaming potentials were electrolyte-concentration dependent and in the order of 10μV. The same type of study was carried out for electrodes applied to the skin. The conclusion from this experiment is that skin deformation potentials dominate the disturbance pattern in this type of recordings.

Movement-induced potentials in surface electrodes

A well defined step compression was applied over an area of the skin and maintained for a fixed time. The resistive force of the tissue, which was continuously recorded, decreased with time as a function of the translocation of fluid volume to the surrounding areas. The rate of decrease was proportional to the fluid mobility. Measurements on ten normal subjects and 14 oedematous patients showed marked differences in the pattern of fluid translocation. Flow rate and total volume flow under compression were calculated and found to vary with the degree of oedema. This noninvasive technique can measure the degree of oedema, which provides important information for diagnosis and treatment.

Noninvasive method for the assessment of subcutaneous oedema.

Potential and impedance variations were studied with varying mechanical stress upon the skin. The size of the potential variations in the skin and the mechanical stress possess a nonlinear relationship which varies between individuals. The impedance variations did not bring about the potential variations. The time sequences for impedance and potential variations do not have the same form when the skin is stressed as when it is relaxed. The rapid initial potential variation upon stressing had a calculated rise time of 30 ms. The rise time during relaxation was 40s. The difference in rise time gives the relationship between potential and deformation a nonlinear character.

Potential and impedance variations following skin deformation.

Since it was first understood1 that it was possible to interfere with the development of an acute myocardial infarction, that it was indeed possible to reduce the amount of tissue damaged because of ischemia 2,3, a lot of scientific interest has been focused on this field. It became even more important when it was shown that there was clinically a good correlation between myocardial infarct size and both morbidity and mortality 4,5,6. Most of this work was, and is, experimental using different animal models where dog is the most commonly used species. Several clinical studies have been made, some indicating infarct size reduction7. The major drawback of clinical studies is the difficulty concerning infarct size estimation which is why the experimental approach is still valid.

Myocardial oxygen pressure across the lateral border zone after acute coronary occlusion in the pig heart.

Changes in skin potentials are known to occur upon stretching and compressing the skin. In this work the relationship between compressional force and changes was studied for forces up to 13·7 N. For a given force, a flatter compressing surface gave lower potential changes than a more curved surface. When temperature increased both changes in potential and current decreased.

S. Ödman

Papers

Movement-induced potentials in surface electrodes

Noninvasive method for the assessment of subcutaneous oedema.

Potential and impedance variations following skin deformation.

Myocardial oxygen pressure across the lateral border zone after acute coronary occlusion in the pig heart.

Changes in skin potentials induced by skin compression.