The effect of catalytic converter legislation on suicide rates in Grampian and Scotland 1980-2003

OBJECTIVE

To examine the effect of catalytic converter legislation on suicide rates in Grampian and Scotland since its implementation in 1993.

METHODS

(1) Population study in Grampian and Scotland using national population and mortality statistics for 1980 to 2003. (2) Retrospective, controlled cohort study of individualswho had unsuccessfully attempted suicide by motor had unsuccessfully attempted suicide by motor vehicle exhaust gassing to examine the theory of method substitution. method substitution.

RESULTS

There was a significant fall in suicides by motor vehicle exhaust gas inhalation in Scotland and Grampian following the introduction of compulsory catalytic converter legislation. However, in the same time period, there was a significant increase in numbers of suicides by hanging and total suicide rates in Scotland. There was a non-significant trend in a small sample of patients from a local hyperbaric unit for an increased rate of subsequent completed suicide between those who had previously attempted suicide by motor vehicle exhaust gas inhalation and controls.

CONCLUSIONS

Catalytic converter legislation has resulted in a decrease in the number of suicides by motor vehicle exhaust gas inhalation. Overall suicide rates have not decreased. There is evidence to suggest that those who would have previously committed suicide by motor vehicle exhaust gas inhalation find alternative methods of suicide, so called 'method substitution'. Initiatives to reduce suicide rates should be directed at those means that are used by impulsive suicide attempters, as other, determined individuals, will commit suicide by another method.

The stereoscopic anisotropy affects manual pointing

Although binocular disparity can in principle provide absolute depth information, perceived stereoscopic depth depends on the relative disparities between points and their spatial arrangement. An example of this is the stereoscopic anisotropy--observers typically perceive less depth for stereoscopic surfaces when depth varies in the horizontal direction than in the vertical direction. We investigated whether this anisotropy also affects manual pointing. Participants were presented with stereograms depicting surfaces that were slanted in depth about either a horizontal axis (inclination) or a vertical axis (slant), and were asked either to point to the edge of a surface, or to estimate its inclination or slant. For both tasks, a clear anisotropy was observed, with participants perceiving greater depth, and also pointing out steeper surfaces, for inclined surfaces than for slanted surfaces. We conclude that both perception and the control of action are subject to a similar stereoscopic anisotropy, and that performance on the two tasks relies on similar depth processing mechanisms.

Increased resting bronchial tone in normal subjects acclimatised to altitude

BACKGROUND

Normal subjects frequently experience troublesome respiratory symptoms when acclimatised to altitude. Bronchial hyperresponsiveness (BHR) and full and partial flow-volume loops were measured before and after ascent to 5000 m altitude to determine if there are changes in resting bronchial tone and BHR that might explain the symptoms.

METHODS

BHR to histamine was measured using a turbine spirometer to record partial and full flow-volume curves and expressed as log dose slopes. Twenty one subjects were tested at sea level and after acclimatisation at 5000 m altitude.

RESULTS

No significant change in log dose slope measurements of forced expiratory volume in 1 second occurred after acclimatisation, and the maximal expiratory flow with 30% of forced vital capacity remaining (MEF(30%)) rose on the full loop and fell on the partial loop. Their ratio (full divided by partial) rose on average by 0.28 (95% confidence limits 0.14 to 0.42) from the mean (SD) sea level value of 0.87 (0.20).

CONCLUSIONS

There is no increase in BHR in normal subjects acclimatised to altitude but an increase in resting bronchial tone occurs that could be released by deep inspiration. This may be the result of increased cholinergic tone.

Diving accidents in sports divers in Orkney waters

Scapa Flow in Orkney is one of the major world centres for wreck diving. Because of the geography of Orkney and the nature of the diving, it is possible to make relatively accurate estimates of the number of dives taking place. The denominator of dive activity allows the unusual opportunity of precise calculation of accident rates. In 1999, one in every 178 sports divers visiting Orkney was involved in a significant accident, in 2000 the figure was one in 102. Some of these accidents appear to have been predictable and could be avoided by better education and preparation of visiting divers.

Binocular cues are important in controlling the grasp but not the reach in natural prehension movements

Binocular cues are typically considered to be pre-eminent in the control of reaching and grasping behaviour. However, in the absence of such information prehension movements can still be accurate and reliable. The present study therefore was designed to assess further the contribution of binocular information in the control of human reaching and grasping movements. Participants reached for and picked up objects under binocular and monocular viewing, both in the absence of a visible scene around the target objects (complete darkness with 'self-illuminated' objects and hand), and under normal (fully illuminated) viewing. Analysis of kinematic parameters indicated that the removal of binocular information did not significantly affect the major indices of the transport component, although it did affect the grasp component. In contrast, the kinematic parameters in the unlit conditions revealed that both the transport component and the grasp component of the reach were severely disrupted whether binocular cues were available or not. Our results suggest that binocular information may be more important for the control of grasp formation than for the control of the transport component. Elimination of the surrounding scene and normal visual feedback affects both the transport and the grasp. It is concluded that in normal viewing conditions, reaching and grasping movements are less dependent on binocular information than has previously been thought.

Field of view affects reaching, not grasping

It has been observed that wearing goggles that restrict the field of view (FOV) causes familiar objects to appear both smaller and nearer. To investigate this further, we examined the effect of a range of field sizes (4 degrees, 8 degrees, 16 degrees, 32 degrees and 64 degrees) on estimates of object distance and object size used to control reaching and grasping movements of binocular observers. No visual or haptic feedback was available during the experiment. It was found that, as the FOV was decreased, the distance reached by subjects also decreased, whereas the size of their grasp was unaffected. In a second experiment, we compared reaching and grasping responses under binocular and monocular conditions for 8 degrees and 64 degrees field sizes and show that the effects of FOV do not result from the progressive loss of binocular information. We conclude that reducing the FOV produces substantial and dissociable effects on reaching and grasping behaviour and that field size must be taken into account in any context where visuo-motor performance is important.

A jittered squares illusion and a proposed mechanism

A new visual illusion is reported in which randomly positioned squares that are perfectly aligned with the horizontal and vertical appear slightly rotated about their midpoints ('jittered') relative to each other. Possible mechanisms for the illusion have been explored in a series of three experiments. Experiment 1 showed that, unlike the Münsterberg illusion, the Jittered Squares illusion persists at isoluminance. Experiment 2 indicated that the degree of rotation from vertical and horizontal, of rows and columns of squares in which the edges of individual squares remain perfectly aligned with vertical and horizontal, changes the perceived strength of the illusion such that the strongest effect is found at rotations of +/- 10 degrees to +/- 15 degrees. Experiment 3 revealed that the illusion is dependent upon the spatial extent of the gaps between the squares, such that it becomes weaker as the separation increases. On the basis of the findings it is suggested that the jittering results from the extraction of obliquely oriented contours by an integrator mechanism when the difference in orientation, between the edges of the individual squares and the global orientation of a contour made up of a number of edges of individual squares, is not too dissimilar. It is proposed that a mechanism such as simultaneous orientation contrast between these global contours and the vertical and horizontal edges of the individual squares causes the squares to appear rotated away from the orientation of the extracted contours, leading to the perceived jittering.

Far Distance Perception

Determining how people perceive distance is a central issue in the study of visual perception. Whilst near-distance perception has been extensively researched, far-distance perception has received little attention. We review the literature and illustrate key points with new data, focusing on analysis of available information/cues, degree of accuracy, measurement procedures, perceptual/cognitive influences, and geometry of perceived space. Analysis of available cues suggests that under natural viewing there is sufficient information for veridical distance perception. However, distance judgements are inaccurate and vary with mode of measurement (eg absolute vs relative judgements). Inaccuracy includes compression of distance. This has been modelled with the use of different geometries—most commonly power functions. Exponents often average 1.0 but this conceals considerable individual variation (in our data individual exponents ranged from 0.5 to over 1.0). Further, even for averaged exponents values vary between 0.8 and 1.25, as a function of viewing conditions, experimental method, and of the relative contribution of cognitive and perceptual factors. Evidence suggests that distance is encoded at an ordinal level, but for many practical tasks the final judgement must be metric (eg range finding) and this transformation is error-prone (in our data numerical estimates could be a factor of 10 out). Further, many natural judgements require perception of the full layout of the scene (including exocentric distances) rather than the more commonly investigated perception of egocentric distance. Evidence suggests that training based on practice with feedback produces some improvement in accuracy, but this is highly context-specific.

Episode of toxic gas exposure in sewer workers

OBJECTIVES

Sewer workers are used to unpleasant smells, but may be required to investigate unusual ones. Twenty six men were involved in investigation of episodes of such a smell after neighbourhood complaints over several weeks.

METHODS

Workers exposed to the smell were investigated by clinical follow up, lung function tests, and measurement of pituitary function.

RESULTS

14 of the 26 developed subacute symptoms including sore throat, cough, chest tightness, breathlessness, thirst, sweating, irritability, and loss of libido. Severity of symptoms seemed to be dose related. Minor symptoms resolved over several weeks but those more seriously affected have shown deteriorating respiratory symptoms and lung function and remain unable to work a year after the incident. In one, evidence of mild cranial diabetes insipidus was found. Analysis of gas from the sewer showed the presence of a mixture of thiols and sulphides, known to be highly odorous and not normally found in sewers. The source remains unknown.

CONCLUSIONS

Several of these men seem to have developed delayed airways disease and disturbances of hypothalamic function. Such an outcome has not to our knowledge been described before. Despite the presence of the smell, standard safety gas detection equipment used to ensure the sewer was safe to enter failed to indicate the presence of a hazard. Protection against such incidents can only be provided by the use of positive pressure breathing apparatus.

Measurement of oxygen concentration in delivery systems used for hyperbaric oxygen therapy

Efficient delivery of oxygen is important during hyperbaric oxygen therapy. We compared two systems in common use, and developed a method to ensure that O2 delivery was adequate during treatment. The systems were a demand valve system with an oral-nasal mask, and a continuously ventilated hood. Five groups were studied over two different time periods, and a further trial was undertaken to examine exhaled O2 levels. The results showed that an acceptable Fio2 could be reliably achieved only with the continuously ventilated hood system or when trained staff supervised their colleagues using the demand system. Inasmuch as the oral-nasal mask system is the standard equipment for the North Sea diving industry, this work shows the importance of ensuring that the correct dose of O2 is delivered. The study indicates, however, that identification of the problem does not always allow a complete solution, and that a hood-based system is more reliable.

The relationship between anaesthetic uptake and cardiac output

The hypothesis that anaesthetic uptake during maintenance of anaesthesia is related to cardiac output was tested on 21 patients undergoing cardiac surgery. Using a computer-controlled closed breathing system, enflurane was administered to maintain an end-expired concentration of 1%. Cardiac output was measured by thermodilution using a pulmonary artery catheter. A clear qualitative but not quantitative relationship was demonstrated. Changes in anaesthetic requirements at a constant end-expired concentration are a better guide to changes in cardiac output than changes in end-expired carbon dioxide with constant ventilation in patients undergoing cardiac surgery.

Penetration of amoxycillin/clavulanic acid into bronchial mucosa with different dosing regimens

BACKGROUND

The efficacy of an antibiotic is related to its concentration at the site of infection. Previous studies of the concentrations of amoxycillin and clavulanic acid (co-amoxiclav) in respiratory secretions or whole lung tissue have suffered from methodological problems. The concentration of amoxycillin and clavulanic acid was determined in bronchial mucosal biopsy samples obtained at bronchoscopy following five different dosing regimens.

METHODS

Bronchial biopsy and serum samples were obtained from 50 patients undergoing diagnostic bronchoscopy. Ten patients each received 375 mg, 625 mg, 750 mg, and 3.25 g oral, and 1.2 g intravenous co-amoxiclav 1-3 hours before bronchoscopy. The concentrations of clavulanic acid and amoxycillin were determined by high performance liquid chromatography using a microbore column, solid phase extraction, and preconcentration to improve sensitivity tenfold over previous methods.

RESULTS

Concentrations of both clavulanic acid and amoxycillin in bronchial mucosa were dose related and were well above the MIC90 of co-amoxiclav for the common bacterial respiratory pathogens including Haemophilus influenzae, Micrococcus catarrhalis and Streptococcus pneumoniae for all dosing regimens. Mean mucosal levels were 200% and 118% of the corresponding serum levels for amoxycillin and clavulanic acid respectively.

CONCLUSIONS

Amoxycillin and clavulanic acid are concentrated in bronchial mucosa and, even at the lowest dose of 375 mg orally, are likely to produce tissue levels in the lung sufficient to inhibit all the common community acquired respiratory pathogens.

Effect of hyperbaric and normobaric oxygen on pulmonary endothelial cell function

The effect of prior exposure to raised partial pressures of oxygen on pulmonary endothelial cell function was assessed in the isolated perfused rat lung preparation. Prolonged exposure to both 1 bar (48 h) and 2.5 bar (11 h) of oxygen caused pulmonary edema and dyspnea. Exposure to 1 bar oxygen for 48 h (approximately 0.66 lethal duration) caused a decrease in pulmonary 5-hydroxytryptamine (5-HT) clearance, suggesting compromised endothelial cell integrity. No change in 5-hydroxy-indole acetic acid (5-HIAA) efflux was noted. However, exposure to 2.5 bar of oxygen for up to 11 h (approximately 0.85 lethal duration) did not decrease pulmonary 5-HT clearance, implying that endothelial cell integrity was not compromised after this oxygen exposure. Exposure to 2.5 bar oxygen resulted in a reduction in 5-HIAA efflux, possibly indicating a decrease in metabolism of cleared 5-HT. The absence of a demonstrable impairment of 5-HT clearance during the development of pulmonary toxicity on exposure to 2.5 bar of oxygen suggests that there may be important differences in pathologic mechanisms in response to oxygen exposure at partial pressures 1 and 2.5 bar.

Wheezing in a commercial diver due to disinfectant

A case is described of a saturation diver with no previous history of asthma who repeatedly developed work-related symptoms of asthma at pressure, which appear to be causally related to the use of dichlorophen as a disinfectant agent. Although challenge tests were negative, suggesting that dichlorophen may have been acting as an irritant rather than as a sensitizer, the symptoms were abolished by the use of an alternative disinfectant agent. The potential importance of this effect in a diver is discussed, and the case highlights the importance of the use of nontoxic agents in the diving environment.

Iron lung: bronchoscopic and pathological consequences of aspiration of ferrous sulphate

Acute bronchial damage was caused by aspiration of a ferrous sulphate tablet, early histological changes (unlike in the few previously reported cases) being observed in the biopsy specimens.

Effect of commercial diving on ventilatory function

A retrospective analysis of spirometric data from divers attending for annual medical examination at intervals from three to nine years was carried out to examine the long term effect of diving on lung volumes. Those divers with records over a three or four year interval (group 1, n = 224) showed a mean reduction of forced vital capacity (FVC) of 240 ml; those with records over a five or more years interval (group 2, n = 123) showed a reduction of FVC of 400 ml. These reductions remained significant when expressed as a percentage of predicted normal values. The reduction of FVC between records did not correlate with the diver's age, maximum operating depth, duration of diving career, or weight change but was positively correlated with the initial FVC. The reductions in FVC were similar in smokers and non-smokers. The change in forced expiratory volume in one second (FEV1) followed a similar pattern but was less pronounced than the effect on FVC. The decline in FVC associated with diving occurs from values of FVC that are above the predicted normal; few values below predicted normal were observed. The effect may represent either a gradual return towards the predicted normal or a pathological reduction in lung volume.

The circulatory response to lifting and carrying and its modification by beta-adrenoceptor blockade

The circulatory effects of lifting and holding weighted suitcases of 5, 10 and 15 kg, and carrying the same suitcases at two different walking speeds were evaluated in 6 normal subjects before and after beta-adrenoceptor blockade with 160 mg oxprenolol. Lifting and holding induced significant weight-induced increments in systolic and diastolic blood pressure which were not attenuated by beta-blockade. There was a significant increase in heart rate only on lifting the 15 kg weight which was attenuated by oxprenolol. Dynamic exercise (walking) with the same weighted suitcases resulted in rate and speed related increase in systolic pressure and heart rate, the magnitude of which was greater than that of lifting alone. The isometric pressor response was attenuated when walking and carrying at 2 mph, but completely abolished by the metabolic and heat induced vasodilatation when walking at 4 mph. Following beta-blockade both the absolute blood pressure and the systolic pressor and heart rate responses to combined lifting and carrying were attenuated. The diastolic pressor response induced by lifting, which was offset in the control period by the vasodilation induced by dynamic exercise was progressively attenuated proportionate to the load carried following beta-blockade; presumably this reflected systemic vasoconstriction to maintain mean perfusion pressure in the presence of central beta-blockade. These observations suggest that the isometric component which predominates at slow walking speeds when carrying weights between 5 and 15 kg is completely suppressed by the vasodilatation at fast walking speeds. Beta-blockade, while reducing heart rate and systolic pressor response to the same stimuli, leads to an augmented systemic vascular resistance which is particularly evident at high metabolic workloads.

Influence of sympatholytic drugs on the cardiovascular response to isometric exercise

1. The effects of single oral doses of various sympatholytic drugs on the heart rate and blood pressure increases during isometric handgrip contraction were studied in six healthy subjects. 2. Bethanidine reduced both the systolic and diastolic increases in pressure. Clonidine reduced the systolic but not the diastolic increase. Oxprenolol alone or in combination with phentolamine or phenyoxybenzamine failed to influence the pressor response. 3. The increase in systemic blood pressure associated with sustained contraction of voluntary muscle appears to be relatively resistant to acute sympathetic adrenoreceptor blockade in man.