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Biomedical subjects

A Koski

Publications and source records attributed to A Koski.

9 recordsLinked to original sources
PubMed1997

Lossless ECG encoding.

We have studied the lossless encoding of ECG signals. With suitable code we aim to reduce the storage space needed by ECG signals. Several methods designed for ECG compression use lossy, i.e. irreversible techniques, in which the original signal is lost, but the restored approximation is almost equal to the original. We aimed, however, to use reversible methods which are able to restore the original signal exactly. We have examined various methods and developed a new approach based on structural recognition and extraction of ECG complexes. Comparative conclusions are drawn from the compression efficiency of lossless and lossy methods. In this study, the effect of sampling frequency, resolution and filtering is also examined.

Algorithms↗
PubMed1996

Modelling ECG signals with hidden Markov models.

In this paper, we have studied the use of continuous probability density function hidden Markov models for the ECG signal analysis problem. Our previous work has focused on syntactic pattern recognition methods in signal processing. Hidden Markov model is basically a non-deterministic probabilistic finite state machine, which can be constructed inductively. It has been widely used in speech recognition and DNA modelling. We have found that hidden Markov models are very suitable for ECG recognition and analysis problems and that they are able to model accurately segmented ECG signals.

Artificial Intelligence↗
PubMed1996

Segmentation of digital signals based on estimated compression ratio.

We have studied the problem of approximating a digital signal with a suitable continuous broken line. We use the approximative broken line for further analysis of the signal as detection of peaks, waves, and other structural features. We can also save considerable amount of storage space with an approximation that does not lose too much significant information about the original signal. Our work is based on examining different distance metrics and different segmentation methods with respect to the remaining residual error in the resulting approximation. The aim of the work has been to develop a method that can perform segmentation with an acceptable amount of residual error without a need to define a large set of parameters that control the segmentation process. Our contribution is to examine the effect of the estimated compression ratio of the resulting approximation and finding an estimate of this compression ratio. We first define a target in the form of a compression ratio of the resulting approximation and then by applying our method, try to find a suitable threshold parameter to achieve this target. We have tested our method with electrocardiogram (ECG) signals and the compression ratio of the approximation has been found to be a suitable target to control the segmentation process.

Algorithms↗
PubMed1988

Fifteen-year interval spirometric evaluation of the Oregon predictive equations.

The 1969 Oregon spirometric predictive equations were evaluated by retesting 199 of the 988 original sample population after 15 years. The 1969 data were used to test for sample bias between the retested and not-retested groups. There was no significant difference in mean values for age, height, or test results except for a five-year age difference in men. Regression analysis of residuals and the differences between calculated and predicted values of annual decrements of FVC, FEV1, and FEF25-75% on age revealed no statistically significant age trend. Although residual means were statistically significant for FVC and FEV1 for men and FVC and FEF25-75% for women, the differences between calculated and predicted annual decrements were significant only for women in FEF25-75%. Although group performance was accurately predicted for most tests, test SDs and SEMs demonstrated considerable individual variation. Lower limits of normality are suggested to assist in evaluating previously-tested patients.

Adult↗
PubMed1988

Prediction of normal spirometric values for adults incapable of standing.

A significant problem exists in predicting normal values for pulmonary function in subjects unable to stand for measurement of height. We studied 196 normal men and women to determine the relationship between sitting and standing height. Two predictors of standing height are recommended: (1) standing-to-sitting height ratio; and (2) multiple regression equations using sitting height and age. Either of these relationships can be selected as a predictor of height for substitution into any standard spirometric prediction equations. Spirometric prediction equations using age and sitting height are also presented.

Body Height↗
PubMed1975

Normal values and evaluation of forced end-expiratory flow.

A new spirometric measurement was performed with 803 healthy, nonsmoking men and women. Using the forced vital capacity curves, the forced end-expiratory flow (FEF75-85%) had a negative correlation with age and a positive correlation with height. Prediction formulas and nomograms were constructed. Comparison with the forced mid-expiratory flow (FEF25-75%) showed generally larger correlation coefficients for physical characteristics and coefficients of variation for the FEF75-85%. Expressing both the FEF75-85% and FEF25-75% as ratios of forced vital capacity did not improve the coefficients. The mean flow rates of 75 male smokers were compared with 213 non-smokers 30 to 49 years of age. The FEF75-85% significantly distinguished between a group of smokers and a group of nonsmokers, but the FEF25-75% showed no significant difference. In 9 patients with presumed peripheral airways disease, FEF25-75% ranged from 70 to 110 per cent of predicted normal but FEF75-85% was 30 to 72 per cent of predicted. An extensively studied control group of 22 healthy, asymptomatic, nonsmoking subjects had FEF75-85% values of 80 to 163 per cent of predicted. Both small groups of 9 patients and 22 control subjects had FEF75-85% values within 1.65 standard error of estimate. In subgroups of 319 persons, use of 75 per cent of predicted mean for FEF75-85% was of greater value in attempting to screen normal from abnormal population than using 1.65 standard error of estimate. The FEF75-85% is suggested as a useful simple ventilatory test to detect early obstructive pulmonary disease.

Adult↗