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S Kontis

Publications and source records attributed to S Kontis.

7 recordsLinked to original sources
PubMed1990

An online technique for estimating cerebral carbon dioxide reactivity.

A technique for measuring cerebral reactivity using transcranial pulsed Doppler ultrasound is described; the system includes a spectrum analyser and capnometer. Data acquisition and manipulation is under software control. Main stem middle cerebral artery blood velocity is monitored continuously using the transcranial Doppler technique, whilst the operator initiates data collection and controls the inspired gas composition. The calculation of cerebral CO2 reactivity is based upon linear regression analysis of normalized, time-averaged middle cerebral velocity on end-tidal pCO2 and is displayed graphically. Measurement of middle cerebral CO2 reactivities can be completed within 15 min. Results from two subjects, a healthy volunteer and a patient with occlusive disease, are shown to illustrate the technique.

Blood Flow Velocity↗
PubMed1990

Aortic compliance measured by non-invasive Doppler ultrasound: description of a method and its reproducibility.

1. Aortic compliance (expressed as percentage increase in lumen diameter for a pulse pressure of 10 mmHg) was calculated from the characteristic pulse wave velocity deduced from 'foot to foot' transit times of the blood flow pulse over a measured length of aorta. Two continuous wave Doppler ultrasound transducers were used: one insonating the root of the left subclavian artery, the other the abdominal aorta proximal to its bifurcation. Measurements were made after the subject had been supine for 5 min to achieve stable conditions. 2. Transit times were calculated on-line in real-time from the delay between the start of the systolic upstroke in the flow velocity sonograms recorded by the two transducers. 3. Within-visit variation was minimized by measuring over 45 cardiac cycles repeated three separate times and calculating an overall mean value for aortic compliance. A full measurement took 5-10 min. 4. Reproducibility of this overall mean value of aortic compliance was assessed at 1 month in 30 subjects (aged 60 +/- 7 years, mean +/- SD) and at 3 months in 23 different subjects (59 +/- 8 years). Aortic compliance values ranged from 0.1 to 2.0%/10 mmHg. 5. The mean paired difference between aortic compliance values was -0.02 between 0 and 1 months, and 0.03 between 0 and 3 months, with respective 95% confidence limits of -0.06 to 0.03 and -0.03 to 0.09 embracing zero, thus not differing significantly from baseline.(ABSTRACT TRUNCATED AT 250 WORDS)

Aorta↗
PubMed1989

On-line Doppler ultrasound measurement of aortic compliance and its repeatability in normal subjects.

An on-line technique is described for measuring aortic compliance using a two-probe Doppler ultrasound method. It is shown that automatic processing of blood velocity signals obtained simultaneously from the left subclavian artery and abdominal aorta enables real-time computation of the time delay observed between the systolic upstroke (or foot) of sonograms from these arteries during the same heart beat. An average foot-to-foot transit time (obtained from a number of cardiac cycles) and the physical separation between the two ultrasonic transducers is used to calculate aortic compliance. Using the above method, the reproducibility of aortic compliance measurements was studied in 12 healthy volunteers over different time intervals. Four of these subjects were measured 7 times each at 10 min intervals whilst the remaining eight subjects were measured 9 times each at hourly intervals. This reproducibility study indicated a significant variation of aortic compliance (P less than 0.001) in the same person regardless of time period. The coefficient of variation ranged approximately between 5% and 18%.

Aorta, Abdominal↗
PubMed1988

A new method of encoding and displaying audio Doppler-shift signals: the chromagram.

A technique based on chromaticity is described for processing and displaying audio Doppler-shift signals. A chromaticity vector is derived for a fixed time interval (e.g. 5 ms) of the input Doppler signal, which is directly related to the Fourier power spectrum distribution of that signal over that interval. An approximated approach is then described for implementing the above "chromagraphic analysis" in order to meet Doppler ultrasound real-time requirements. A static and dynamic chromagram display format is defined which enables the chromaticity information to be displayed in colour on a digital television monitor.

Color↗
PubMed1988

Chromaticity-coded Doppler blood velocity sonagrams: preliminary observations.

This paper describes the application of chromaticity to spectrally analysed Doppler blood velocity signals. Chromaticity enables a particular colour to be assigned to the power/frequency distribution within each instantaneous spectral sweep of a sonagram. Successive spectral sweeps of a sonagram can then be colour-coded in this fashion to produce a chromaticity-coded sonagram. Two chromaticity-coded sonagrams are presented to illustrate various blood flow features. Standard sonagram display formats are also presented for comparison purposes. It appears that the chromaticity-coded sonagram offers the ability to digitally encode the instantaneous power spectral distribution with a single chromaticity vector.

Blood Flow Velocity↗
PubMedDate not supplied

A computerized method for processing of spectrally analysed Doppler-shifted signals from insonated arteries.

A microcomputer-based technique is described for processing blood-velocity signals after they have been spectrally analysed. The system consists of a real-time dual channel spectrum analyser interfaced to a BBC model B microcomputer. The microcomputer is programmed to store and display in real-time spectral information received from the analyser. Stored sonograms can be readily retrieved from memory on request and displayed on the microcomputer's TV-monitor for viewing and/or subsequent numerate interogation. The proposed system is software controlled and is therefore both versatile and expandable, enabling accommodation of future sonagram processing methods and new diagnostic parameters.

Arteries↗