Viasys Healthcare, Inc.

Nicolet Instrument Corporation

William J Lutz

Daniel J Lombardi

The present invention provides a system and method for establishing a synchronized time frame for signals in a medical monitoring system. In particular, the present invention provides a system and method for synchronizing the time frame of stimulation signals provided by a stimulator to a subject and response signals received by an amplifier device from the subject in response thereto. Thus, the present invention allows accurate display and analysis of the relationship between stimulation and response signals by a monitoring device. Time frame synchronization of stimulus and response signals is achieved using a periodic bus cycle clock signal which is provided by a bus, i.e., an IEEE 1394 bus, connecting together each of the devices in the monitoring system. For example, a time frame synchronized stimulation trigger signal may be generated by a stimulus synchronization circuit including a phase-locked loop for providing a local clock signal synchronized to the periodic bus cycle clock signal, and employing the local clock signal to provide a multi-bit signal indicating a segment during a bus cycle during which the stimulation signal is provided by the stimulator to the subject.

Time frame synchronization of medical monitoring signals

A combination referential and differential amplifier circuit for a medical signal monitoring system includes a plurality of electrode inputs, including at least one reference electrode input, a plurality of medical signal amplifiers, and switching means for selectively coupling each of the plurality of electrode inputs to each of the inputs of the plurality of medical signal amplifiers. Each electrode input may be selectively coupled to several amplifier inputs. The output of a medical signal amplifier with the amplifier inputs thereof coupled to electrode inputs, neither of which is a reference electrode input, produces a differential amplifier signal output. A medical signal amplifier with the inputs thereof coupled to electrode inputs, one of which is the reference electrode input, produces a referential signal output. Thus, a combination of differential and referential electrophysiologic signal channels may be provided.

Combination referential and differential amplifier for medical signal monitoring

An audiometer is provided with attenuators which have two successive stages, a main attenuator providing a large range of attenuation and a second stage which is capable of providing silent switching and finely adjustable attenuation. The signal from the main attenuator in the first stage is provided through two signal paths in the second stage to two input terminals of the earphone, with the sound output from the earphone determined by the voltage across the two input terminals. The first of the signal paths includes a pad having fixed attenuation which provides a low level voltage output signal to the one input terminal, and the other signal path includes an adjustable attenuator which provides fine adjustment of the magnitude of the output signal across the earphones. The adjustable attenuator may include multiplying digital to analog converters which have an attenuation determined by their digital input word with the signal from the main attenuator provided as the voltage reference signal to the digital to analog converters. The attenuation may be controlled utilizing a microprocessor to provide the data words to the multiplying digital to analog converters. A switching circuit is provided on the output of the adjustable attenuator to disconnect the adjustable attenuator from the earphone when that attenuator's output is not required. This disconnection improves the signal to noise ratio for low level signal because the noise at the output of the adjustable attenuator does not contribute to the earphone signal. As a result, the available dynamic range is increased by the attenuation of the fixed attenuator. No clicks are produced when the adjustable attenuator is switched in or out.

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Middleton, WI, United States of America

William J Lutz