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H G Goovaerts

Publications and source records attributed to H G Goovaerts.

15 recordsLinked to original sources
PubMed1991

Recording fetal breathing movements with a passive transducer based on an inductive principle.

A new transducer has been developed, based on an inductive principle, for recording fetal movements and sounds. The compliance of this transducer, the INductive PHOno-sensor (INPHO), can be matched to that of the maternal abdomen to provide an optimal transfer of displacement between maternal abdomen and transducer. In this manner, it is possible to detect fetal breathing movements by digital filtering of the INPHO signal in a frequency band between 0.5 and 2.0 Hz. Singular breathing movements can be detected and this was verified by real time ultrasound imaging. The INPHO transducer shows a flat (+/- 1.5 dB) frequency response between 0.2 and 200 Hz. The signal-to-noise ratio of the transducer system is better than 95 dB, and enables very weak movements and sounds to be detected. Spectral analysis of the processed signal shows that modulation of fetal breathing by maternal breathing takes place. The measuring setup allows for the quantitative assessment of fetal respiratory sinus arrhythmia.

Fetal Heart↗
PubMed1991

Recording and processing of fetal movements and sounds obtained with the Inpho inductive transducer.

A recently developed transducer based on an inductive principle allows recording of fetal displacement signals on the maternal abdominal wall. The transducer is a relatively passive device, in contrast to commonly applied ultrasound transducers. This permits long-term observation of fetal movements and sounds. The bandwidth of the system is DC-200 Hz (+/- 3 dB), and signal-to-noise ratios of more than 96 dB have been measured in a laboratory setup, whereas in the practical situation a signal-to-noise ratio of 78 dB has been established. The transducer has been applied to study fetal respiratory sinus arrhythmia, which means that fetal breathing movements have to be extracted from the transducer's output. This proved possible by digital filtering of the displacement signal as detected by the transducer. The transducer has also been applied in a study where the signal-to-noise ratio of fetal heart sounds as a function of location of the fetus and position of the transducer on the maternal abdominal wall has been studied. It proved possible to adequately record fetal heart sounds for measurement of fetal heart rate. Also uterine activity could be recorded using the sensor's DC output.

Female↗
PubMed1991

A comparative clinical study of fetal phono- and movement-sensors from Amsterdam, Cambridge and Edinburgh.

In a European collaboration, a joint project to conduct an experimental and clinical investigation of recently developed sensors from three centres (Amsterdam, Cambridge and Edinburgh) has been carried out. The Amsterdam sensor was based on an inductive principle whereas the Cambridge and Edinburgh transducers used a piezo-electric material (PVDF) as transducing element. Nine patients with varying gestational age (29-38 weeks) were measured in a clinical investigation. Recordings of fetal heart sounds (FHS) and fetal breathing movements (FBM) were made using three sensors; one from each centre. These recordings were digitized directly into a computer using a purpose-built data acquisition system. For each patient 3 min of FBM data, and 1 min of FHS data were recorded by each sensor. The FBM recordings were carried out simultaneously with ultrasound, so as to enable a correlation to be made between both recordings. The FHS recordings were carried out simultaneously with the maternal heart pulse, to discount any maternal heart influences on the resulting signals. Of the nine patients analysed, FHS were recorded in seven patients. On the other hand, it appeared difficult to identify fetal breathing movements in the FBM recordings due to the dominance of the maternal breathing component. The analysis of the FBM signals and its correlation with ultrasound could not be carried out due to the relatively poor quality of the signals detected by the sensors, given the present techniques of analysis. The evaluation of the FHS recordings showed that although there is relatively little difference between the sensors, the inductive sensor performed best.

Cardiotocography↗
PubMed1991

Coherent average technique--a tutorial review.

This paper highlights the effects of digitization in relation to the effective numberical range over which the signal to be averaged has to be resolved. The effect of quantization noise on the number of averaging cycles is assessed and it is shown that for averaging weak signals such as the HIS bundle electrogram, high resolution analogue-to-digital (A/D) conversion is required so as to prevent a substantial increase in the number of averaging cycles. Also the requirement for adequate low-pass filtering is discussed and relationships between the numerical range of the A/D conversion process, the order of the low-pass filter, its cut-off frequency and sampling frequency are formulated.

Analog-Digital Conversion↗
PubMed1991

A comparative experimental study of fetal phono- and movement-sensors from Amsterdam, Cambridge and Edinburgh.

This paper describes the experimental studies and results of a collaborative investigation between three European institutes: Amsterdam, Cambridge and Edinburgh. The object of this investigation and the collaborative exchanges was to evaluate and compare different sensors for recording fetal sounds and movements from each centre. This would be carried out in a series of experimental and clinical tests involving researchers from each of the European institutes, and using three sensors: one from each centre. Experimental measurements have been performed regarding the conversion gain, frequency response, equivalent input noise and dynamic range of the transducers. The measurements were carried out using a vibration-free table testing rig to evaluate these characteristics of each of the sensors. The equivalent input noise ranged from 50 nm to 1600 nm for the transducers studied.

England↗
PubMed1989

Method for the measurement of susceptibility to decubitus ulcer formation.

A method for measuring the susceptibility of a patient to develop decubitus ulcers is described and initially evaluated. It is based on an indirect, noninvasive measurement of the transient regional blood flow response after a test pressure load which simulates the external stimulus for pressure-sore formation. This method was developed to determine the individual risk of a patient and to study the subfactors which contribute to the susceptibility. This would also offer the possibility of evaluating the effect of preventive treatment aimed at reducing the susceptibility. The method was found to discriminate between preselected elderly patients at risk on the one hand, and non-risk patients and healthy young adults on the other hand. No differences in blood flow responses were found between the non-risk elderly patients and the healthy young adults. This suggests that age per se is not a factor in the formation of pressure sores. In the risk group the recovery time after pressure relief was found to be three times as long as the duration of the pressure exercise. This indicates that the recovery time after pressure exercise may be as important as the period of pressure exercise in deducing the risk of developing decubitus ulcers.

Adult↗
PubMed1989

Measurement of transcellular fluid shift during haemodialysis. Part 1. Method.

A method is presented to measure transcellular fluid shifts during haemodialysis based on a simplified model of the electrical admittance of biological tissues. It allows for the measurement of intracellular and extracellular conductivities and their ratios. The method is noninvasive, clean and harmless, and can be easily computerised in order to be performed continuously. A typical example is given of a recording during haemodialysis.

Body Fluids↗
PubMed1989

A transducer for recording fetal movements and sounds based on an inductive principle.

Recording fetal breathing movements requires a transducer with a large dynamic range. The compliance of the transducer should be matched to the compliance of the maternal abdominal wall in order to pass the very weak acoustic signal caused by heart sounds and fetal breathing movements on to the transducer. The output signal is stored on the hard disc of a personal computer (PC) simultaneously with a control signal indicating the presence of breathing movements. Ultrasound imaging is exclusively used for verification of breathing movements. The images are stored on videotape simultaneously with control signals from the PC for synchronisation of data and image. Substantial digital filtering is necessary to discriminate between actual breathing movements and other fetal activities. It is shown that by optimal adjustment of the transducer's compliance to that of the maternal abdominal wall individual breathing movements can indeed be measured.

Female↗
PubMed1989

A transducer for detection of fetal breathing movements.

The paper describes a new transducer for detection of fetal movements and sounds from the maternal abdominal wall. This transducer is based on an inductive principle. The compliance of the transducer should match the compliance of the maternal abdominal wall in order to detect the very weak acoustic signal caused by individual fetal breathing movements. The contact area of the transducer is supported on a membrane, the tension of which can be adjusted so as to match the compliances of tissue and transducer. The goal of this paper is to investigate detection of fetal movements in order to monitor fetal condition and motility. The more specialized field of investigating fetal heart rate variability by studying the relationship between fetal breathing movements and fetal heart rate may become of more interest in the future. The inductive phonometer (INPHO) shows a flat (+/- 1.5 dB) frequency response between 0.2 and 200 Hz which is not affected by the compliance adjustment. Some in vivo measurements have been performed. The transducer signal is stored on a 20MB hard disk of an Olivetti M24 Personal Computer (PC) simultaneously with a control signal indicating the presence of breathing movements. Ultrasound imaging is exclusively used for verification of breathing movements. The images are stored on videotape simultaneously with control signals from the PC for synchronization of data and image. Substantial digital filtering is necessary to discriminate between actual breathing movements and other fetal activities. It is shown that optimal adjustment of the transducer's compliance to that of the maternal abdominal wall is possible and that individual breathing movements can indeed be measured.

Female↗
PubMed1987

System for continuous high-resolution measurement of distances in the eye.

We describe a new system for accurate measurement of intraocular distances; it is used in conjunction with standard A-scan ultrasound equipment. A processing unit has been developed which enables selection of time intervals between echoes. Up to four intervals can be chosen and simultaneously measured. The output of the system is derived from a pulse duration-to-voltage converter which presents an output voltage proportional to the selected time interval. In this way variations in intraocular distances larger than about 0.01 mm can be detected.

Biophysical Phenomena↗