Biomedical subjects

I Sipinková

Publications and source records attributed to I Sipinková.

8 recordsLinked to original sources

PubMed1997

Effect of respiration and posture on heart rate variability.

The physiological control system of the heart produces a highly complex pattern of cardiac rhythmicity which is reflected in the variability of heart rate. The aim of this study was to analyse the effects of posture and breathing frequency on the cardiac control system by various noninvasive techniques. Seven healthy subjects (24+/-5 years, mean age+/-S.D.) were studied in the supine and sitting positions while breathing spontaneously or at a fixed rate (3, 6, 12, 24, 48, 60 breaths.min(-1)). Time series of instantaneous beat-to-beat heart rates were evaluated by spectral analysis and by the dimensionless approximate entropy parameter. The total spectral power as well as the low (<0.05 Hz) and mid frequency (0.05-0.12 Hz) spectral components were higher in the sitting position. Mean approximate entropy (+/-S.D.) (0.85+/-0.15 in sitting and 0.87+/-0.16 in lying subjects) was unaffected by postural changes or breathing frequencies higher than 6 breaths x min(-1). Analysis in the frequency domain revealed that the activity of the autonomic components controlling heart rate was modified by ventilation and postural changes, whereas approximate entropy, a unique measure of the complexity and integrity of the cardiac control system, was almost unaffected by respiration and posture.

Adult↗

PubMed1995

Changes in the thoracic impedance distribution under different ventilatory conditions.

The present study was performed with the aim of checking the suitability of EIT in imaging regional thoracic impedance variations during lung ventilation under predefined conditions and to compare EIT with established reference techniques. A new technique of functional EIT imaging designed to visualize physiologically relevant information from the sequentially registered series of thoracic distributions was introduced. Experiments were performed on five spontaneously breathing healthy subjects and on 12 anaesthetized supine pigs. 16 electrodes were placed around the thorax and consecutive transthoracic impedance distributions were measured at a rate of 1 Hz (Sheffield APT system mark I, IBEES, Sheffield, UK). Several voluntary breathing manoeuvres were performed in human subjects and the tracings of local impedance were compared with standard spirometry. In animal experiments EIT was applied during artificial ventilation at different ventilation rates and during stepwise passive emptying and filling of either one or both lungs while the respiratory muscles were relaxes. Further, selective blockade of lung regions resulting in regionally reduced ventilation was performed and the capability of EIT to follow and differentiate local ventilatory disturbances was checked by reference techniques (x-ray and staining methods). The experiments revealed an overall agreement between the spirometric and impedance data in all breathing patterns performed. A linear relationship between changes of the air content of the lungs and the regional thoracic impedance was shown (intraindividual correlation coefficient range, 0.986-0.999; n = 12 animals). The functional images of the impedance distribution across the thorax reproduced adequately the typical anatomical characteristics of the pig and the human thorax. The spatial resolution of EIT functional images was sufficient to differentiate lung areas corresponding to approximately 20 ml tissue volume. EIT with the additional evaluation procedure of functional imaging was shown to be a suitable and reliable method of imaging different ventilatory conditions with the potential to become a useful tool for monitoring respiratory function.

Adult↗

PubMed1994

Mechanical respiratory system input impedance during high-frequency oscillatory ventilation in rabbits.

OBJECTIVES: To study the mechanical properties of the rabbit respiratory system during high-frequency oscillatory ventilation by means of mechanical respiratory impedance measurement and to characterize the changes in oscillation mechanics of the respiratory system occurring after bilateral vagotomy. DESIGN: Acute experimental trial. SETTING: Physiology laboratory. SUBJECTS: Ten adult rabbits (mean body weight 3.1 kg). MEASUREMENTS AND MAIN RESULTS: Anesthetized rabbits were exposed to short runs of high-frequency oscillatory ventilation, with stroke volumes of 5.0, 6.6, and 10.0 mL, applied at oscillation frequencies of 10, 15, 20, and 25 Hz before and after vagotomy. Mechanical respiratory input impedance was determined from the pressure and flow signals simultaneously measured at the airway opening and analyzed in terms of its real and imaginary parts. (The real part of respiratory impedance characterizes the resistive property of the lungs and chest wall; the imaginary part of respiratory impedance characterizes the elastic and inertial properties of the lungs and chest wall.) At all stroke volumes and oscillation frequencies studied, vagotomy resulted in a decrease in the real part of respiratory impedance. After vagotomy, the real part of respiratory impedance was stroke volume-independent, and exhibited negative frequency dependency. Vagotomy also led to a decrease in the imaginary part of respiratory impedance, mainly at lower oscillation frequencies, and thus, to a higher resonant frequency of the respiratory system. CONCLUSIONS: Mechanical respiratory impedance measurement proved to be a useful method to study the mechanical properties of the respiratory system during high-frequency oscillatory ventilation. The results suggest that vagally mediated reflex changes in respiratory system mechanics are associated with high-frequency oscillatory ventilation, depending on the ventilatory variables that are used.

Airway Resistance↗

PubMed1994

Dopamine-dependent diastolic dysfunction in moderate hypothermia.

We designed an experimental animal study to study the effects of dopamine (DA) on diastolic function in hypothermia. DA was applied at five incremental infusion rates in 6 sheep during normothermia and moderate hypothermia (29 degrees C). Left ventricular end-diastolic pressure (LVEDP) was increased during hypothermia as compared with normothermia at all doses of DA. Contraction and relaxation velocity were changed only slightly during hypothermia; during normothermia, both velocities were markedly increased. The pronounced hemodynamic effect observed during hypothermia was further intensified by occurrence of aftercontractions, which disappeared at very high DA doses. These paradoxic results were considered the result of hypothermia-induced reduction in active transport mechanisms responsible for regulation of the cytoplasmic CA2+ concentration. The generally reduced inotropic effect of DA, the risk of paradoxic reactions, and the occurrence of aftercontractions must be taken into account when emergency drugs are administered clinically during hypothermia.

Animals↗

PubMed1994

Peripheral and cardiac effects of a new phosphodiesterase inhibitor in comparison with enoximone.

The effect of the new phosphodiesterse inhibitor R80122 (E)-N-cyclohexyl-N-methyl-2-[[[phenyl(1,2,3,5-tetrahydro-2-oxoimidazo [2,1-b]-quinazolin-7-yl)methylene] amino]oxy]acetamide, (CAS 133718-29-3) on haemodynamic parameters and myocardial oxygen consumption were intraindividually compared with those of enoximone, a clinically established phosphodiesterase inhibitor. In 12 anaesthetised sheep the drugs were given in randomized order as i. v. infusions for 6 min at each setting (10, 20 and 30 micrograms.kg-1.min-1 (R80122) and 32, 64 and 96 micrograms.kg-1.min-1 (enoximone)). R 80122 as well as enoximone caused a significant increase in cardiac inotropism with a simultaneous increase of myocardial oxygen consumption. The peripheral resistance was significantly decreased by both drugs. The haemodynamic effects elicited by the application of equieffective doses of R80122 and enoximone did not show any differences.

Animals↗

PubMed1990

Multiple breath washout of He and SF6 in panting dogs.

Pulmonary gas transport mechanisms in panting were studied by multiple breath washout of two poorly soluble inert gases of similar solubility but different diffusivity (He and SF6). The experiments were performed in 6 chronically tracheotomized conscious dogs (mean body weight 31.0 kg) which, upon exposure to elevated room temperature, were enforced to thermal panting (mean breathing frequency 288/min). After equilibration of lung gas with 1% He and 1% SF6 followed by changeover to test gas-free air, end-tidal gas concentrations during multiple breath washout were recorded by mass spectrometry. The washout time course was analyzed into 3 exponential components. The initial fast component was considered to be in part determined by the transient response of the measuring system, whereas the intermediate and the slow component could be attributed to lung washout. The mean He/SF6 ratio of medium and slow rate constants was 1.06 and 1.13, respectively (both values differing from 1.0 at P less than 0.001). It is concluded that gas transport in dog lungs during panting was mainly determined by convection, diffusion-dependent processes being discernible but playing a minor role.

Animals↗

PubMedDate not supplied

Expirograms of O2, CO2 and intravenously infused C2H2 and Freon-22 during panting in dogs.

To study pulmonary gas transport in panting, expirograms of several inert and respiratory gases were simultaneously measured in panting dogs. The experiments were performed on 5 conscious dogs (mean body weight 34.4 kg) provided with a chronic tracheostomy. Panting at a mean frequency of 312/min (5.2 Hz) was induced by elevated room temperature (mean 28.1 degrees C). Isotonic saline equilibrated with 50% acetylene and 50% Freon-22 was infused intravenously at a constant rate (4 ml/min). Fractional concentrations in the tracheostomy tube were measured by a respiratory mass spectrometer, using a special sampling system designed for quasi-continuous analysis of rapidly changing gas concentrations. Air flow was monitored by an ultrasonic transit-time flowmeter. A tracing of expired gas concentrations versus expired volume showed no alveolar plateau, displaying a steep increase of Freon-22, acetylene and CO2 (decrease of O2) up to the onset of inspiration. The small but statistically highly significant differences between the expirograms of CO2 and O2, and of Freon-22 and acetylene, could be qualitatively explained by ventilation-perfusion inequalities with sequential emptying, by Taylor dispersion and by reversible solution in airway mucosa in the course of the respiratory cycle.

Acetylene↗

PubMedDate not supplied

Simulation of arterial drug concentration after intravenous application.

The aim of this study was to develop a widely applicable model for circulatory indicator dispersion which could describe the pharmacokinetics of early drug distribution. The model assumes that the substance is injected into the right atrium and measured in the aorta. The dilution curve results from the dispersion and recirculation of the indicator in the body. The concentration time curve in the aorta, r, can be described as r = c0 + g* r, where g is the transport function of the body and c0 is the concentration time course, which is measured for the first time in the aorta. If the body transport function is known, then the aortic dilution curve of a drug can be predicted for different elimination rates and injection times. The site of interest can be chosen arbitrarily, i.e. the concentration of inflow into the kidney or any other organ can be described.

Animals↗