High-quality recording of bioelectric events

A multichannel instrumentation amplifier, developed to be used in a miniature universal eight-channel amplifier module, is described. After discussing the specific properties of a bioelectric recording, the difficulties of meeting the demanded specifications with a design based on operational amplifiers are reviewed. Because it proved impossible to achieve the demanded combination of low noise and low power consumption using commercially available operational amplifiers, an amplifier equipped with an input stage with discrete transistors was developed. A new design concept was used to expand the design to a multichannel version with an equivalent input noise voltage of 0·35 μV RMS in a bandwidth of 0·1–100 Hz and a power consumption of 0·6 mW per channel. The results of this study are applied to miniature, universal, eight-channel amplifier modules, manufactured with thick-film production techniques. The modules can be coupled to satisfy the demand for a multiple of eight channels. The low power consumption enables the modules to be used in all kinds of portable and telemetry measurement systems and simplifies the power supply in stationary measurement systems.     

Remarks on the structure-activity relationship of some antibacterial silver non-sulfanilamide compounds

In this study some physical parameters of a number of silver non-sulfanilamide compounds (acetate, 4-nitrobenzoate, nitrate, salicylate and 2-thiosalicylate) and silver sulfadiazine are related to the antibacterialin vivo activity of these compounds. The stability constant and solubility are important factors in the development of the biological activity and the mechanism of action (active as silver ion or the whole molecule).     

High-quality recording of bioelectric events

In the first part of the review the various mechanisms that could be the cause of interference in bioelectric recordings are considered. It is demonstrated that the performance of a good amplifier can be seriously degraded in its functioning if the whole measurement situation is not taken into account. Several techniques used to reduce interference, of which guarding and driven right leg circuits are the most important, are analysed. In the second part of the review some examples of the application of the theory in practical situations are presented. The instrumentation amplifier circuit normally used in bioelectric recordings is improved for measurements under difficult circumstances. Another application is a low-cost 64-channel amplifier for multichannel ECG recordings. The third application is a device that can be added to bioelectric measurement systems and will provide a major reduction in interference.     

Understanding the meaning of the shunt fraction calculation

The pulmonary shunt fraction ( \({{\dot Qs} \mathord{\left/ {\vphantom {{\dot Qs} {\dot Qt}}} \right. \kern-0em} {\dot Qt}}\) ) is frequently calculated in critically ill patients to monitor the effectiveness of pulmonary oxygenation. The breathing of pure oxygen often results in higher calculated \({{\dot Qs} \mathord{\left/ {\vphantom {{\dot Qs} {\dot Qt}}} \right. \kern-0em} {\dot Qt}}\) values that have been attributed to the development of atelectasis, ventilation-perfusion imbalance, or both. To interpret properly the changes in calculated \({{\dot Qs} \mathord{\left/ {\vphantom {{\dot Qs} {\dot Qt}}} \right. \kern-0em} {\dot Qt}}\) that occur when the inspired oxygen fraction is altered, the changes produced in all the variables affecting \({{\dot Qs} \mathord{\left/ {\vphantom {{\dot Qs} {\dot Qt}}} \right. \kern-0em} {\dot Qt}}\) must be known. This tutorial presents an in-depth analysis of the four variables affecting the calculation of \({{\dot Qs} \mathord{\left/ {\vphantom {{\dot Qs} {\dot Qt}}} \right. \kern-0em} {\dot Qt}}\) \(\dot Vo_2 \) (oxygen uptake), \(\dot Qt\) (cardiac output), Cc'O₂(oxygen content in pulmonary end capillaries), and \(C\bar vO_2 \) (oxygen content in mixed venous blood). These variables are related according to the following equation, which derived by combining the Fick and the classic shunt equations: \({{\dot Qs} \mathord{\left/ {\vphantom {{\dot Qs} {\dot Qt}}} \right. \kern-0em} {\dot Qt}} = 1 - [({{{{\dot Vo_2 } \mathord{\left/ {\vphantom {{\dot Vo_2 } {\dot Qt}}} \right. \kern-0em} {\dot Qt}})} \mathord{\left/ {\vphantom {{{{\dot Vo_2 } \mathord{\left/ {\vphantom {{\dot Vo_2 } {\dot Qt}}} \right. \kern-0em} {\dot Qt}})} {(Cc'O_2 }}} \right. \kern-0em} {(Cc'O_2 }} - C\bar vO_2 )]\) . Three-dimensional surface representations relating these variables are also presented to help the reader understand the effects of these variables on the calculated \({{\dot Qs} \mathord{\left/ {\vphantom {{\dot Qs} {\dot Qt}}} \right. \kern-0em} {\dot Qt}}\) .     

Delayed coma in head injury: Consider cerebral fat embolism

Objective

To describe a case of a young man with delayed coma after mild head injury, suggestive of cerebral fat embolism (CFE). To underline the value of MR imaging in the differential diagnosis of secondary deterioration in mild head injury.

Case report

A 21-year-old man admitted with mild head injury after a fall with facial fractures and long bone fractures. He was admitted to the intensive care unit and was mechanically ventilated. Weaning was not possible because of desaturations and pulmonary congestion. Low platelet count and anaemia developed. On several time points during his admission cerebral imaging data were obtained. Non-contrast CT on admission was normal while follow-up MRI showed extensive white matter abnormalities. These imaging abnormalities combined with the clinical presentation suggests cerebral fat embolism (CFE) as the most likely cause of secondary deterioration in our patient.

Conclusions

In head injured patients with long bone fractures one should consider cerebral fat embolism. When the classical clinical syndrome is not present, MR imaging is warranted for diagnosis and to exclude other causes of secondary deterioration.     

The juvenile head trauma syndrome – Deterioration after mild TBI: Diagnosis and clinical presentation at the Emergency Department

Background

Annually 14.000 children with traumatic brain injury (TBI) are admitted to the Emergency Department (ED) in the Netherlands. Presentation varies and a specific entity comprises the juvenile head trauma syndrome (JHTS) with secondary deterioration after a mild trauma. As outcome of JHTS can be fatal, early recognition is essential.