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Biomedical subjects

I Korhonen

Publications and source records attributed to I Korhonen.

14 recordsLinked to original sources
PubMed1998

Heart rate and blood pressure responses to isometric exercise in young and older men.

The aim of this study was to examine the isometric endurance response and the heart rate and blood pressure responses to isometric exercise in two muscle groups in ten young (age 23-29 years) and seven older (age 54-59 years) physically active men with similar estimated forearm and thigh muscle masses. Isometric contractions were held until fatigue using the finger flexor muscles (handgrip) and with the quadriceps muscle (one-legged knee extension) at 20%, 40%, and 60% of the maximal voluntary contraction (MVC). Heart rate and arterial pressure were related to the the individual's contraction times. The isometric endurance response was longer with handgrip than with one-legged knee extension, but no significant difference was observed between the age groups. The isometric endurance response averaged 542 (SEM 57), 153 (SEM 14), and 59 (SEM 5) s for the handgrip, and 276 (SEM 35), 94 (SEM 10) and 48 (SEM 5) s for the knee extension at the three MVC levels, respectively. Heart rate and blood pressure became higher during one-legged knee extension than during handgrip, and with increasing level of contraction. The older subjects had a lower heart rate and a higher blood pressure response than their younger counterparts, and the differences were more apparent at a higher force level. The results would indicate that increasing age is associated with an altered heart rate and blood pressure response to isometric exercise although it does not affect isometric endurance.

Adult↗
PubMed1997

Frequency shift in baroregulatory oscillation in borderline hypertensive subjects.

The aim of this study was to quantify the frequency shift in vasomotor oscillations in blood pressure we observed in borderline hypertensive individuals in our previous study. Electrocardiogram and intraarterial blood pressure were recorded in 33 normotensive, 29 borderline hypertensive, and 33 mildly hypertensive men (aged 35 to 45 years). Five-minute stationary periods in supine, sitting, and standing positions, and during sleep were extracted from the recordings for autoregressive frequency domain analysis. In borderline hypertensive subjects vasomotor oscillations in the range of 0.05 to 0.12 Hz in blood pressure and heart rate, assumed to be associated with baroreceptor activity, were shifted to lower values as compared with the other two groups. The frequency shift was assessed by median frequency of the oscillations. Significant between-group differences were observed in the supine and sitting positions. No significant between-group differences were seen in normalized spectral power estimates. Further studies are required to determine whether the frequency shift provides prognostic information on cardiovascular morbidity.

Adult↗
PubMed1997

Multivariate closed-loop model for analysis of cardiovascular dynamics.

This paper introduces a closed-loop model for the analysis of interactions between heart rate and blood pressure variability, and respiration. The respiratory influence is modeled with an anti-causal structure to control the possible phase lead of heart rate to instantaneous lung volume. The closed-loop structure between heart rate and blood pressure allows the analysis of inter-relationships between the signals. Simulations and results on experimental data show the identifiability of the model and the robustness of the noise source contribution analysis over a wide range of model orders.

Blood Pressure↗
PubMed1997

Framework for biosignal interpretation in intensive care and anesthesia.

Improved monitoring improves outcomes of care. As critical care is "critical", everything that can be done to detect and prevent complications as early as possible benefits the patients. In spite of major efforts by the research community to develop and apply sophisticated biosignal interpretation methods (BSI), the uptake of the results by industry has been poor. Consequently, the BSI methods used in clinical routine are fairly simple. This paper postulates that the main reason for the poor uptake is the insufficient bridging between the actors (i.e., clinicians, industry and research). This makes it difficult for the BSI developers to understand what can be implemented into commercial systems and what will be accepted by clinicians as routine tools. A framework is suggested that enables improved interaction and cooperation between the actors. This framework is based on the emerging commercial patient monitoring and data management platforms which can be shared and utilized by all concerned, from research to development and finally to clinical evaluation.

Anesthesia↗
PubMed1996

Multivariate autoregressive model with immediate transfer paths for assessment of interactions between cardiopulmonary variability signals.

Multivariate autoregressive modelling provides a method to analyse the dynamic interactions between heart rate (HR), blood pressure (BP) and respiration (RESP) by means of noise source contributions (NSCs). The conventional approach presumes the modelled noise sources are mutually independent. This presumption is, in general, not satisfied and causes an error in the results. In the present study, the effect of this error is analysed. A method is presented to remove the error by making the noise sources independent. The method is based on the inclusion of immediate transfer paths in the model. To quantify the strength of the interactions, a measure called NSC ratio (NSCR); is calculated; this states the amount of variability of the signal arising from other signals. The method is demonstrated by studying the inter-relationships between HR, BP and RESP in a healthy male subject in supine and standing positions. It is found that the error is marked and that the presented method provides corrected estimates for spectral decomposition and NSC analysis. The results show it is necessary to include the immediate transfer mechanisms in the model, while analysing the cardiopulmonary dynamics by means of HR and BP variability.

Blood Pressure↗
PubMed1996

Linear multivariate models for physiological signal analysis: theory.

The general linear parametric multivariate modelling concept is presented. This model combines a variety of different kinds of multivariate linear models. The concept of partial spectral analysis is derived from the general model. Some emphasis is laid on the causality demands of the model, and it is shown that the classic strictly-causal structure must be abandoned in order to utilise the modelling in many practical situations. Two special sub-class models are described in detail: the multivariate autoregressive model and the multivariate dynamic adjustment model. Furthermore, time-varying modelling is considered. The modelling of the real system is presented on a general level as a system identification cycle. The application of the methods to real physiological data is presented in the companion paper.

Data Collection↗
PubMed1996

Linear multivariate models for physiological signal analysis: applications.

Some applications of linear multivariate modelling methods in the analysis of physiological signals are presented. These applications illustrate the methods in the analysis of cardiovascular dynamics, which has been one of the main application fields of the multivariate modelling during the last ten years. It is demonstrated that physiologically meaningful information about the causal interactions in the cardiovascular system can be drawn from the routinely available clinical signals. Both static and dynamic conditions are considered.

Humans↗
PubMed1995

Multivariate autoregressive modelling combined with transcephalic electrical impedance: method to relate neonatal systemic circulation and respiration to cerebral circulation.

We studied the pulsatile component of cerebral circulation with transcephalic electrical impedance (delta Z) in six preterm newborns, three of whom had severe cerebral bleeding, peri-intraventricular haemorrhage (PIVH). The transcephalic electrical impedance delta Z signal, ECG, arterial blood pressure, (aBP) and respirogram were recorded on analogue magnetic tape for 30 min. Artefact-free stationary segments (lasting for 2 min) of the four signals were digitised. A digital multivariate autoregressive (MAR) model was used to study frequency-specific variability in the signals and to quantify interrelations between the variabilities of delta Z, HR, aBP and respiratory signals. MAR modelling describes a system where all the signals simultaneously explain each other. The inherent variability of delta Z was lower and the influences of respiration and aBP on delta Z significantly greater in infants with severe PIVH than in controls. These changes were observed at high frequencies corresponding to respiration and heart rate. This may be interpreted as a marker of pressure passivism in the cerebral circulation following PIVH. We conclude that in preterm babies the application of MAR modelling, together with transcephalic impedance, may be a new, helpful and quantitative method for the study of simultaneous interrelations between variables of cerebral and systemic circulations and respiration.

Cerebral Hemorrhage↗
PubMed1994

Short-term variability of blood pressure and heart rate in borderline and mildly hypertensive subjects.

Electrocardiogram and intra-arterial blood pressure were recorded in 96 men (aged 35 to 45 years) by the Oxford method over a 30-hour period. The study involved 33 normotensive, 29 borderline hypertensive, and 34 mildly hypertensive individuals, as assessed by the cuff method. Five-minute periods during sleep and with subjects in supine, sitting, and standing positions were extracted from the recordings for frequency domain analysis. Power spectrum density estimates of systolic blood pressure, diastolic blood pressure, and heart rate were calculated by an autoregressive method over the bandwidths of 0.02 to 0.075 (low-frequency), 0.075 to 0.15 (midfrequency), and 0.15 to 0.35 Hz (high-frequency), attributable to thermoregulatory, baroreceptor, and respiratory activity. No significant intergroup differences were observed at nighttime, but in different body positions the borderline hypertensive subjects frequently had either greater low-frequency variability or smaller midfrequency variability than the other groups. In this respect, the power spectra for systolic and diastolic blood pressures provided better statistical differentiation between the groups than those for heart rate. Furthermore, the borderline hypertensive subjects exhibited attenuated night-day changes in the low-frequency band for all time series. The results suggest that in borderline hypertension the baroreceptor oscillations are shifted to lower frequencies, presumably reflecting altered function of the sympathetic nervous system. In conclusion, spectral analysis of blood pressure variability for controlled test situations made it possible to detect differences in the cardiovascular regulatory systems between normotensive, borderline hypertensive, and mildly hypertensive individuals.

Adult↗
PubMed1988

Serum levels of thyroid and adrenal hormones, testosterone, TSH, LH, GH and prolactin in men after a 2-h stay in a cold room.

Twenty healthy male volunteers, dressed in shorts, stayed for 30 min in a room with an ambient temperature of 28 degrees C followed by a stay in a room with a temperature of 10 degrees C for 120 min. The mean skin temperature fell rapidly during the first minutes in the cold but the rectal temperature began to fall as late as at 60 min (0.1 degree C) and was 0.4 degrees C lower at the end of the cold exposure than before it. The metabolic rate, and the systolic and diastolic blood pressures, increased, and the pulse rate fell, in the cold. Serum samples were taken before moving to the cold (10 degrees C) room and after the 2-h stay and assayed for 11 hormones. There were no significant changes in the serum concentration of adrenalin, T3, T4, testosterone, TSH or LH. The serum level of noradrenaline increased from 4.5 to 6.3 nmol l-1 (P less than 0.01) and those of cortisol, GH and prolactin fell by 20, 87 and 48% (all P less than 0.01). The total serum proteins increased by 11% and free fatty acids by 28% (P less than 0.01). Our results show that the short-term exposure of adult man to low ambient temperature does not have any effect on the pituitary-thyroid and pituitary-testis axes and adrenal medulla. The increase of noradrenaline is probably due to general activation of the sympathetic nerves at low temperatures. The decreases in the serum levels of GH and prolactin reflect a true decrease in their secretions and may be mediated by inhibitory hypothalamic mechanisms.

Adult↗
PubMed1982

Effects of pH on the gill ATPase activity and blood composition of whitefish (Coregonus peled) and trout (Salmo trutta fario).

1. The effects of pH on blood composition and gill (Na+ + Mg2+) ATPase activity were studied in 142 whitefish and trout kept for 3 to 17 hr in tanks at pH 3.0-9.5 in Northern Finland. 2. pH clearly influenced all blood values, except plasma alanine and aspartate aminotransferases. Blood haemoglobin and packed cell volume of whitefish and trout were lower at pH 9.5 but higher at pH 3.0 than those of controls at pH 6.5. 3. Both fishes had lowest plasma sodium and chloride values in groups kept for 9 to 17 hr in tanks with water acidified to pH 3.0 to 3.5. Changes in the plasma chloride concentration were associated with plasma sodium (r = 0.92, n = 102, P less than 0.001). 4. The gill (Na+ + K+ + Mg2+) ATPase of trout showed high activity over wide ranges of pH (6.0-7.5) at 13 degrees C having a distinct optimum at pH 7.0. 5. Blood glucose and lactate concentrations of whitefish and trout increased after exposure to acid and base. High values at pH 3.0 to 3.5 suggested hypoxic stress due to acidaemia.

Adenosine Triphosphatases↗