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Biomedical subjects

R I Kitney

Publications and source records attributed to R I Kitney.

At least 37 records · Page 2Linked to original sources
PubMed1988

Dynamic measurement of human capillary blood pressure.

1. Capillary blood pressure was measured in man using a dynamic servo-nulling system and direct micropuncture. This enabled assessments of the normal variations in pressure which influence fluid filtration and reabsorption. 2. Seventy-eight capillaries in 19 subjects were punctured in one of three positions around the capillary loop with the hand at the level of the sternal angle. Mean pressure around the loop fell from 37.7 +/- 3.7 mmHg (arteriolar limb, mean +/- SEM, n = 12) to 19.4 +/- 1.0 mmHg (apex, n = 25) to 14.6 +/- 0.5 mmHg (venular limb, n = 41) at skin temperatures of 18.7-33.1 degrees C. These values agree closely with Landis' original studies in 1930 [E. Landis (1930) Heart, 15, 209-228]. 3. The mean filtration/reabsorption state of any particular capillary limb was not static because of cardiac, vasomotor and respiratory fluctuations in capillary pressure. From a total of 38 capillaries in which recordings were analysed for 30 s, the fluctuations in pressure were such that 27 capillaries probably had periods of both filtration and reabsorption. 4. Computerized superimposition and coherent averaging of trains of capillary pulses enabled an accurate description of the pulse waveform to be made in three capillaries. This was remarkably similar to waveforms from the radial artery, albeit at reduced amplitude (average 3.6 +/- 3.4 mmHg, mean +/- SD overall). The time for the pulse to travel between the radial artery and the finger capillary was approximately 10 ms, which implies a propagation velocity of several metres per second.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1987

The Zoom Wigner transform and its application to the analysis of blood velocity waveforms.

The analysis of blood velocity using noninvasive Doppler ultrasound is now an important clinical technique. The paper discusses the application of the Wigner transform to the estimation of blood velocity from the Doppler signal. A new type of Wigner transform, the Zoom Wigner Transform or ZWT is developed. The ZWT has certain advantages over the standard Wigner transform, particularly in relation to the frequency resolution of specific components, these are discussed. The final section of the paper considers practical aspects of blood velocity estimation and illustrates the use of the WZT in relation to other methods.

Blood Flow Velocity↗
PubMed1986

The analysis of blood velocity measurements by autoregressive modelling.

Analysis of velocity disturbances arising in poststenotic flow is examined using the technique of autoregressive modeling. The essential elements of this method are described including relevant criteria for selecting the model order. Velocity data employed in the analysis are taken from in vivo measurements in the dog aorta, and the results indicate that the autoregressive method improves the resolution of coherent features in disturbed flow patterns. By applying homomorphic filtering to individual beats, the occurrence of organized structures convected from their origin in the shear layer is readily identified.

Animals↗
PubMed1986

Application of the Pisarenko Harmonic Decomposition method to physiological data.

In this paper the Pisarenko Harmonic Decomposition (PHD) method is presented as a technique for short duration spectral estimation; it has been tested under various conditions to provide guidelines for its implementation. There appears to be a range of frequencies for which the PHD method gives non-biased frequency estimates. A rapid method for obtaining the sampling frequency required for non-biased frequency estimates is also discussed.

Adult↗
PubMed1985

Neonatal heart rate variability and its relation to respiration.

The heart rate and respiration signals from nine healthy full term neonates were studied using autoregressive spectral analysis and cross-correlation techniques. The heart rate spectra could be divided into three regions of activity: a very low frequency (VLF) region from 0-0.04 Hz; a low frequency (LF) band from 0.04-0.20 Hz; and a high frequency (HF) region above 0.20 Hz. The newborns exhibited very little respiratory sinus arrhythmia in their heart rate variability in contrast to the situation for adults and older infants. However, variations in heart rate correlated strongly with changes in the breath amplitude, leading to what may be termed a breath amplitude sinus arrhythmia. The neonatal heart rate behaviour under stable conditions of oscillation could be simulated with a nonlinear control model provided the delay time in the baroreceptor loop of the model was taken to be approximately 2 seconds longer than in adults. This is consistent with the immature neurological status of neonates.

Computers↗
PubMed1985

Transient interactions between blood pressure, respiration and heart rate in man.

Auto regressive spectral estimation techniques have been used to follow transient interactions between mean blood pressure, respiration and heart rate. This demonstrates that these inter-relationships are variable. It is concluded that while central modulation of heart rate is the major factor in the interactions, when the heart rate is fixed, peripheral modulation of the blood pressure by respiration is clearly demonstrated.

Adult↗
PubMed1984

Time series analysis of neuronal signals recorded in the cerebellum of trained monkeys.

Recordings from cerebellar neurones have been made in monkeys trained to track a target moving sinusoidally at 0.33 Hz. The neuronal point even time series was first low pass filtered at 0.33 Hz to compare with the target and monkey movements. Short lengths of data were then subjected to Fourier and autoregressive spectral analysis in order to characterize higher frequencies in the neuronal signal. Stable components were identified at around 0.33 Hz (when the monkey was tracking well), 1.0 Hz and 8.5 Hz. The variation of many of the intermediate frequencies was suggestive of entrainment interactions between the basic components. The power at 1.0 Hz may result from the operation of a visuomoter control loop, whilst 8.5 Hz may characterize proprioceptive control.

Action Potentials↗
PubMed1983

The design of digital filters for biomedical signal processing. Part 3: The design of Butterworth and Chebychev filters.

The first two papers in this series reviewed the basic concepts which apply to digital filter theory and presented design techniques based on the z plane pole-zero plot. In this paper these methods are used to develop digital versions of Butterworth and Chebychev filters. The basic theory of both filter types is reviewed and the bilinear transformation is used to derive the z-transforms of the filters from their s-plane continuous time descriptions. Recurrence relationships which may be used to implement filters of various orders are developed. The impulse and frequency responses of the elements are illustrated and examples are given of their application to ECG data.

Analog-Digital Conversion↗
PubMed1983

The design of digital filters for biomedical signal processing. Part 2: Design techniques using the z-plane.

Design methods for digital filters using z-plane techniques are developed out of the basic concepts described in part 1. The relationship between impulse response shape and side lobe generation in the frequency response is investigated by means of rectangular, triangular and cosine window filters. The limited choice of cut-off frequencies available for simple linear phase digital filters is explained. Design direct from the frequency domain is summarized. z-plane techniques for the design of high- and band-pass digital filters and the digital equivalents of analogue filters are described. s-plane to z-plane mapping by means of the Bilinear transformation is compared to the direct z-transform method of filter design.

Biomedical Engineering↗
PubMed1981

Comparison of methods for obtaining a heart rate variability signal from 60 x real time ECG data.

The analysis of heart rate variability (HRV) has received increasing attention, particularly since the widespread introduction of 24 hour monitoring procedures. This paper compares methods for obtaining the HRV signal in both real time and 60 x real time. Software and hardware methods are compared from a number of points of view including accuracy and suitability for analysing 24 hour recordings. The question of drop-outs resulting from noisy ECG records is discussed and one hardware method for minimizing the problem is described which uses a level restorer in conjunction with the HRV signal generator.

Computers↗
PubMed1979

A nonlinear model for studying oscillations in the blood pressure control system.

The idea that physiological systems sometimes include oscillations as part of their control function is a relatively new idea; the paper discusses the role of such oscillations in the regulation of arterial blood pressure and how they can be studied by modelling techniques. A nonlinear model is proposed which can be related directly to the physiology. This is seen as an important step because mainly previous studies of biological oscillations have used lumped equations, e.g. the Van der Pol equation, which do not possess the property. On the basis of the model, the oscillatory behaviour of the blood pressure control system is analysed by the application of the dual input describing function technique, a powerful analytical method which has wide application to the study of nonlinear oscillatory phenomena in physiology. The final section of the paper considers the digital simulation of the model by Z transform techniques and how the simulation can be used to study the interaction of respiratory and blood pressure control systems.

Blood Pressure↗