Search PubMed⌕ Search

Biomedical subjects

G Nyman

Publications and source records attributed to G Nyman.

At least 55 records · Page 3Linked to original sources
PubMed1991

The Maryland Plan: the rest of the story.

Since 1976 the Maryland Plan, a statewide initiative sponsored jointly by the University of Maryland and the Maryland Mental Hygiene Administration, has recruited more than 200 university-trained psychiatrists into Maryland's state hospitals and community mental health centers. Although the plan's goals and strategies have been well publicized, no comparable joint state-university recruitment program has been launched outside of Maryland. The authors describe the conditions in Maryland that made successful collaboration possible, including a large and stable university residency program, attractive incentives available for the university from the state, a favorable economic climate, a crusading spirit, and psychiatric authority in the central office of the mental hygiene administration.

Academic Medical Centers↗
PubMed1990

Atelectasis causes gas exchange impairment in the anaesthetised horse.

The anatomical basis of gas exchange impairment in the anaesthetised horse was studied by computerised tomography (CT; three shetland ponies) and morphological analysis (one pony and three horses). By means of CT, densities were seen in dependent lung regions early during anaesthesia, both with spontaneous breathing and with mechanical ventilation. The densities remained for some time where they had initially been created when the animal was turned from dorsal to sternal recumbency. Deep insufflation of the lungs reduced the dense area. Gas exchange was impaired roughly in proportion to the dense area. On histological analysis, the densities were atelectatic and congested with blood. Gravimetry showed no more extravascular water per unit lung tissue in the atelectatic than in the 'normal' regions, and the blood content was increased only slightly. It is concluded that the horse develops atelectasis in dependent lung regions early during anaesthesia in dorsal recumbency, and that atelectasis is the most likely explanation for the large shunt and impaired arterial oxygenation regularly seen during anaesthesia.

Anesthesia↗
PubMed1989

Ventilation-perfusion relationships in the anaesthetised horse.

Ventilation-perfusion relationships were studied by the multiple inert gas elimination technique in seven horses while they were conscious and during inhalation anaesthesia with halothane. A generally good match between ventilation and perfusion was found in the conscious, standing horse. During anaesthesia a huge shunt developed, ie perfusion of completely unventilated lung regions, both in dorsal and left lateral recumbency and whether the horse was breathing spontaneously or mechanically ventilated. The shunt was significantly greater and the arterial oxygen tension (PaO2) significantly lower in dorsal than in left lateral recumbency. Little or no perfusion of low VA/Q regions was observed during anaesthesia, whether ventilation was spontaneous or mechanical. Positive end-expiratory pressure (PEEP) did not significantly improve PaO2 or reduce the shunt. Selective mechanical ventilation of dependent lung regions with PEEP reduced the shunt markedly, an effect that was not achieved by conventional mechanical ventilation with general PEEP. The findings seem compatible with alveolar collapse during anaesthesia, causing shunt, whereas the absence of clearly low VA/Q regions questions the role of airway closure as the major disturbance of gas exchange.

Anesthesia, Inhalation↗
PubMed1988

Sampling irregularity perturbs visual reconstruction.

We explored the human observer's ability to detect and discriminate sine-wave and square-wave gratings that were sampled at intervals varying from 4.7 to 9.4 arcmin. To study the effect of sampling irregularity on visual performance, we varied the position of each line sample on the basis of a Gaussian probability distribution, the standard deviation of which varied from 0 (regular sampling) to 4.7 arcmin (highly irregular sampling). The results indicate that irregular sampling has no systematic effect on the observer's ability merely to detect the presence of a sine- or square-wave grating. In contrast, sampling irregularity strongly impairs the subject's ability to discriminate between these waveforms. A model based on the convolution of difference-of-Gaussians-type weighting profiles predicted that sampling irregularity should have little to no effect on the output of a channel tuned to the third harmonic of the square-wave grating. The findings thus suggest the existence of a sampling scheme in the visual system. This scheme is based on local feature-selective mechanisms, probably edge detectors, that are highly sensitive to the relative position of the sample points in the space domain.

Discrimination, Psychological↗
PubMed1988

Apparent contrast of spatially and temporally sampled gratings.

We have measured the apparent contrast of spatially and temporally sampled gratings having the spatial frequency of 2, 4 and 8 c/deg. A contrast matching task was used in two different sampling conditions which allowed us to stimulate selectively the sustained and transient mechanisms in spatial and temporal vision. The results demonstrate the visual interpolation characteristics in the two domains and suggest a better response linearity for spatial than for temporal interpolation. The strongest nonlinear responses were obtained for temporally sampled medium spatial frequency gratings, suggesting separate temporal processing mechanisms for medium and high spatial frequencies

Humans↗
PubMed1987

Selective mechanical ventilation of dependent lung regions in the anaesthetized horse in dorsal recumbency.

The effect of selective mechanical ventilation of dependent lung regions were studied in anaesthetized horses (mean weight 486 kg) in dorsal recumbency. Blood-gas measurements were performed with the horse in the lateral position during spontaneous breathing (before selective intubation) and in dorsal recumbency during spontaneous breathing, general mechanical ventilation, and spontaneous breathing + selective mechanical ventilation. Arterial oxygen tension (PaO2) was 32.3 kPa in the lateral position during spontaneous breathing with a high inspired oxygen fraction (FlO2 greater than 92%). In dorsal recumbency PaO2 decreased to 10.9 kPa during spontaneous breathing and was not significantly affected by general mechanical ventilation (PaO2 12.6 kPa). The institution of selective mechanical ventilation with a selective positive end-expiratory pressure (PEEP) of 20 cm H2O caused a marked increase in PaO2 to an average of 35.3 kPa. It is concluded that selective intubation of dependent regions in the diaphragmatic lobes is a feasible procedure and that selective mechanical ventilation with PEEP markedly improves arterial oxygenation in the anaesthetized horse in dorsal recumbency.

Anesthesia, General↗
PubMed1987

Systemic and centrally mediated angiotensin II effects in the horse.

The primary aim of the study was to evaluate the potential value of intravenous (i.v.) infusion of angiotensin II (AII) for phonocardiographic differential diagnosis of equine valvular insufficiency. Ten-minute AII infusions at 4.5-33 pmol kg-1 min-1 induced clear-cut dose-dependent rises in systemic arterial blood pressure (aBP), whereas the pulmonary aBP remained largely unaffected. It implies that i.v. infusion of AII at about 10 pmol kg-1 min-1 could be a valuable tool for the acoustic differentiation between mitral and tricuspid valvular dysfunction in the horse. The infusion at, and above 9 pmol kg-1 min-1 caused increased heart rate. This chronotrophic effect was not strictly dose-dependent and exhibited significant tachyphylaxis. Angiotensin II administration at, or above 9 pmol kg-1 min-1 was needed to induce an urge to drink, suggesting that angiotensin-induced thirst does not appear in the euhydrated horse until the octapeptide reaches supraphysiological blood concentration. Determinations of plasma aldosterone concentration (PA) revealed comparatively high morning control values (269 +/- 46 pmol-1). Three consecutive AII infusions with 10-min intervals and at increasing dosages caused a cumulative, almost fourfold elevation of PA. The PA pattern indicated that AII-induced hypersecretion of aldosterone continued for several minutes after the end of the infusions, but also showed that the metabolic clearance of the hormone took precedency of the secretion within 20 min post-infusion. In two of the horses a fall in PA occurred during a fourth, final infusion, indicating that in these instances the previous AII administration had impoverished the store of aldosterone available for release from the adrenal cortex.

Aldosterone↗
PubMed1987

Ventilation-perfusion relationships in the standing horse: an inert gas elimination study.

The multiple inert gas elimination technique was adapted for use in the conscious standing horse. The modifications included increased infusion rate of the inert gases (30 ml/min), extended infusion time (60 mins) in order to reach steady state, and construction of a nose mask mixing box system for collection of expired gas. Eight adult horses with a mean weight of 454 kg and a mean age of 6.1 years were studied while standing under resting conditions. Ventilation was 65.2 liters/min and cardiac output measured by thermodilution 40.2 liters/min. Systemic and pulmonary artery mean pressures were 114 and 26 mmHg, respectively. Three horses showed a unimodal VA/Q distribution centred upon a mean VA/Q of one. Five horses had a bimodal distribution with an additional high VA/Q mode comprising 2 to 18 per cent of ventilation. The mean logarithmic standard deviation of perfusion was 0.41. There was no perfusion of 'low' VA/Q regions, but minor shunting on an average of 1 per cent was noted. Inert gas dead space (minus apparatus dead space) averaged 38 per cent of total ventilation. Arterial oxygen tension varied from 11 to 14 kPa and the mean arterial CO2 tension was 5.7 kPa. It is concluded that the standing horse in general has a good match between ventilation and perfusion but that some individuals display high VA/Q regions, possibly explained by poor perfusion of upper lung regions.

Acetone↗