Quantifying the effectiveness of ultraviolet-C light at inactivating airborne Mycobacterium abscessus

BACKGROUND

Mycobacterium abscessus (MABS) group are environmental organisms that can cause infection in people with cystic fibrosis (CF) and other suppurative lung diseases. There is potential for person-to-person airborne transmission of MABS among people with CF attending the same care centre. Ultraviolet light (band C, UV-C) is used for Mycobacterium tuberculosis control indoors; however, no studies have assessed UV-C for airborne MABS.

AIM

To determine whether a range of UV-C doses increased the inactivation of airborne MABS, compared with no-UVC conditions.

METHODS

MABS was generated by a vibrating mesh nebulizer located within a 400 L rotating drum sampler, and then exposed to an array of 265 nm UV-C light-emitting diodes (LED). A six-stage Andersen Cascade Impactor was used to collect aerosols. Standard microbiological protocols were used for enumerating MABS, and these quantified the effectiveness of UV-C doses (in triplicate). UV-C effectiveness was estimated using the difference between inactivation with and without UV-C.

FINDINGS

Sixteen tests were performed, with UV-C doses ranging from 276 to 1104 μW s/cm². Mean (±SD) UV-C effectiveness ranged from 47.1% (±13.4) to 83.6% (±3.3). UV-C led to significantly greater inactivation of MABS (all P-values ≤0.045) than natural decay at all doses assessed. Using an indoor model of the hospital environment, it was estimated that UV-C doses in the range studied here could be safely delivered in clinical settings where patients and staff are present.

CONCLUSION

This study provides empirical in-vitro evidence that nebulized MABS are susceptible to UV-C inactivation.

How much of the unemployment effect on mental health is due to income? Mediation analysis in UK data

Background

Employment and income are important determinants of mental health (MH), but the extent to which unemployment effects are mediated by reduced income is unclear. We estimated the total effect (TE) of unemployment on MH and the controlled direct effect (CDE) not acting via income.

Methods

We studied adults 25-64y from nine waves of the representative UK Household Longitudinal Study (n = 45,497/obs=202,297). Unemployment was defined as not being in paid employment; common mental disorder (CMD) was defined as a General Health Questionnaire-12 score ≥4. We conducted causal mediation analysis using inverse probability of treatment weights to estimate odds ratios (OR) and absolute differences for the effects of unemployment on CMD as measured in the same sweep, before (TE) and after (CDE) blocking the income pathway. The percentage mediated by income was 100*(TE-CDE)/TE, with standard errors calculated via bootstrapping. Multiple imputation addressed missingness.

Results

The TE of unemployment on short-term CMD risk was OR: 1.66 (95% CI 1.57-1.76), with 7.09% (6.21-7.97) absolute difference in prevalence; equivalent CDEs were OR 1.55 (1.46-1.66) and 6.08% (5.13-7.03). Income mediated 14.22% (8.04-20.40) of the TE. Percentage mediation was higher for job losses (15.10% [6.81-23.39]) than job gains (8.77% [0.36-17.19]). Mediation by income was lowest for those aged 25-40y (7.99% [-2.57, 18.51]) and those in poverty (2.63% [-2.22, 7.49]).

Conclusions

In the UK, a high proportion of the short-term effect of unemployment on MH is not explained by income, particularly for those who are younger or already living in poverty. Population attributable fractions suggested 16.5% of CMD burden was due to unemployment, with 13.9% directly attributable to job loss rather than resultant income changes. Further research is needed across different European countries to determine how different welfare regimes might moderate these effects, and to investigate longer-term effects.

Key messages

• Unemployment has a clear detrimental effect on MH in the short-term.

• Only a small proportion of this effect appears to be mediated by income.

Nasolabial appearance of bilateral cleft lip repair at five years of age. Comparing techniques of modified advancement-rotation (Delaire) with Manchester repair: a retrospective cohort study

The techniques used to repair bilateral cleft lip have evolved over time, yet little data exist to compare outcomes using the various techniques. The aim of this study was to retrospectively evaluate and compare the aesthetic outcomes of two types of complete bilateral cleft repair: advancement rotation and a historic cohort repaired with the Manchester technique. A total of 32 consecutive patients who had complete repair of bilateral cleft lips were identified retrospectively from our centre using inpatient records. The first 16 (born between 1994 and 2005) underwent the Manchester repair, the second 16 (born between 2006 and 2010) a Delaire modified advancement rotation technique. Standardised photographs were taken at five years post repair and cropped to isolate the nasolabial component. Appearance outcomes were assessed by 20 members of the cleft and plastic surgery team, who were each asked to rate all 32 images using the Asher-McDade five-point scale. A chi squared test was used to determine whether there was a statistically significant difference in cleft scores between the two approaches. There was a mean (SD) of 2.8 (1.02) in the advancement rotation group and a mean (SD) of 3.1 (1.07) in the Manchester group. There was a statistically significant difference in the distribution of scores in the advancement rotation group compared with the Manchester group, with lower scores (better results) in the advancement rotation group (p=0.003). This study demonstrates that the advancement rotation technique for the repair of bilateral cleft lip defects resulted in a superior nasolabial appearance when directly compared with the Manchester repair at 5 years of age.

Validating the Asher-McDade score to assess facial aesthetic outcomes in 22 consecutive complete bilateral cleft lip repairs

Most scoring systems used to assess facial aesthetics in cleft patients tend to lack consistency, and the absence of an internationally agreed system makes comparison challenging. The most widely used and validated tool is the five-point Asher-McDade index. We note that there are currently no reports (to our knowledge) of its use for scoring outcomes after bilateral cleft lip repair. To validate it for this use, the aim was to describe the outcomes of 22 consecutive bilateral cleft lip repairs assessed using this scale. A retrospective review was undertaken of 22 consecutive patients with bilateral cleft lip repairs performed at our centre. Each patient underwent bilateral advancement rotation repair with a vomer flap on one side at three months followed by repair of the remaining hard palate and an intravelar veloplasty three months later. Standardised photographs were taken five years after repair and were cropped to isolate the nasolabial component. Eleven members of the cleft multidisciplinary team were asked to rate each image on a five-point Likert scale. Statistical analysis was performed using a two-way ANOVA test and intraclass correlation coefficient to interrogate intraobserver and interobserver variance. A total of 22 consecutive patients with complete bilateral cleft lips were photographed. The overall mean (range) score for the repairs was 3.2 (4.3 - 1.8). Two-way ANOVA demonstrated that inter-rater variability accounted for just over 10% (11.23% of the total variance, p < 0.0001). As predicted, the single biggest factor affecting score variability was the patient's appearance, which accounted for 44.51% of the total variance between scores (p < 0.0001). Intraobserver variance was not found to be significant, accounting for 0.33% of the total variance (p = 0.0006). We demonstrate that the Asher-McDade scoring system is a valid tool to use when assessing bilateral cleft lip repairs. Variance in the patient's score was significantly related to a true difference in appearance, with only a small percentage of differences being due to intraobserver and interobserver variation.

The causal effects of transition into poverty on mental health in the UK working-age population

Background

Addressing the impact of poverty through income and welfare policies is likely important for public mental health; however, few studies assess potential effect size using causally-informed methodologies. To provide meaningful information for policymakers, we aimed to estimate the average treatment effect of transitioning into poverty on mental health.

Methods

We used data for working-age adults (aged 25-64) from nine waves of the nationally representative UK Household Longitudinal Survey (2009-2019, n = 39,553 obs=155,963). Exposure was transition into poverty (household equiv. income &lt;60% median). Outcome was score ≥4 on General Health Questionnaire-12, indicating likely common mental disorder (CMD). To minimise the influence of reverse causation and time-varying confounders we used a marginal structural modelling (MSM) approach to create inverse probability of treatment weights. We performed secondary analysis stratifying by sex, and calculated population attributable fractions for each model.

Results

Good balance of confounders was achieved between exposure groups. Experiencing new poverty was associated with increased odds of CMD (adjusted OR 1.33, 95% CI 1.24-1.42, p &lt; 0.001) with a 4.8% (3.6-6.0) absolute difference in prevalence: 24.0% vs 19.2%. There was a difference in relative effect by sex, with OR 1.40 (1.25-1.56, p &lt; 0.001) for men vs OR 1.28 (1.18-1.38, p &lt; 0.001) for women. However, there was no marked difference in absolute effect by sex: 4.9% (3.1-6.8) for men vs 4.5% (3.0-6.1) for women. For all analyses traditional logistic regression using the same confounders underestimated the effect in comparison with MSM.

Conclusions

Moving below the poverty line increased odds of CMD by 32.7% after accounting for confounding and reverse causality, with a greater relative impact on men. Our causal estimates suggest transition into poverty currently accounts for 10.7% of the burden of CMD in the UK working-age population - 8.9% for women and 13.1% for men.

Key messages

Reductions in household income worsen mental health, and traditional analytical approaches may be underestimating this causal relationship. Applying causal methodologies to observational data can provide exposure-outcome estimates less susceptible to common biases, which may be of more use to policymakers.

Exploring immunomodulation by endocrine changes in Lady Windermere syndrome

Lung disease due to nontuberculous mycobacteria (NTM) occurs with disproportionate frequency in postmenopausal women with a unique phenotype and without clinically apparent predisposing factors. Dubbed 'Lady Windermere syndrome', the phenotype includes low body mass index (BMI), tall stature and higher than normal prevalence of scoliosis, pectus excavatum and mitral valve prolapse. Although the pathomechanism for susceptibility to NTM lung disease in these patients remains uncertain, it is likely to be multi-factorial. A role for the immunomodulatory consequences of oestrogen deficiency and altered adipokine production has been postulated. Altered levels of adipokines and dehydroepiandrosterone have been demonstrated in patients with NTM lung disease. Case reports of NTM lung disease in patients with hypopituitarism support the possibility that altered endocrine function influences disease susceptibility. This paper catalogues the evidence for immunomodulatory consequences of predicted endocrine changes in Lady Windermere syndrome, with emphasis on the immune response to NTM. Collectively, the data warrant further exploration of an endocrine link to disease susceptibility in Lady Windermere syndrome.

Patient-specific Monte Carlo dose calculations for (103)Pd breast brachytherapy

This work retrospectively investigates patient-specific Monte Carlo (MC) dose calculations for (103)Pd permanent implant breast brachytherapy, exploring various necessary assumptions for deriving virtual patient models: post-implant CT image metallic artifact reduction (MAR), tissue assignment schemes (TAS), and elemental tissue compositions. Three MAR methods (thresholding, 3D median filter, virtual sinogram) are applied to CT images; resulting images are compared to each other and to uncorrected images. Virtual patient models are then derived by application of different TAS ranging from TG-186 basic recommendations (mixed adipose and gland tissue at uniform literature-derived density) to detailed schemes (segmented adipose and gland with CT-derived densities). For detailed schemes, alternate mass density segmentation thresholds between adipose and gland are considered. Several literature-derived elemental compositions for adipose, gland and skin are compared. MC models derived from uncorrected CT images can yield large errors in dose calculations especially when used with detailed TAS. Differences in MAR method result in large differences in local doses when variations in CT number cause differences in tissue assignment. Between different MAR models (same TAS), PTV [Formula: see text] and skin [Formula: see text] each vary by up to 6%. Basic TAS (mixed adipose/gland tissue) generally yield higher dose metrics than detailed segmented schemes: PTV [Formula: see text] and skin [Formula: see text] are higher by up to 13% and 9% respectively. Employing alternate adipose, gland and skin elemental compositions can cause variations in PTV [Formula: see text] of up to 11% and skin [Formula: see text] of up to 30%. Overall, AAPM TG-43 overestimates dose to the PTV ([Formula: see text] on average 10% and up to 27%) and underestimates dose to the skin ([Formula: see text] on average 29% and up to 48%) compared to the various MC models derived using the post-MAR CT images studied herein. The considerable differences between TG-43 and MC models underline the importance of patient-specific MC dose calculations for permanent implant breast brachytherapy. Further, the sensitivity of these MC dose calculations due to necessary assumptions illustrates the importance of developing a consensus modelling approach.

Development of virtual patient models for permanent implant brachytherapy Monte Carlo dose calculations: interdependence of CT image artifact mitigation and tissue assignment

This work investigates and compares CT image metallic artifact reduction (MAR) methods and tissue assignment schemes (TAS) for the development of virtual patient models for permanent implant brachytherapy Monte Carlo (MC) dose calculations. Four MAR techniques are investigated to mitigate seed artifacts from post-implant CT images of a homogeneous phantom and eight prostate patients: a raw sinogram approach using the original CT scanner data and three methods (simple threshold replacement (STR), 3D median filter, and virtual sinogram) requiring only the reconstructed CT image. Virtual patient models are developed using six TAS ranging from the AAPM-ESTRO-ABG TG-186 basic approach of assigning uniform density tissues (resulting in a model not dependent on MAR) to more complex models assigning prostate, calcification, and mixtures of prostate and calcification using CT-derived densities. The EGSnrc user-code BrachyDose is employed to calculate dose distributions. All four MAR methods eliminate bright seed spot artifacts, and the image-based methods provide comparable mitigation of artifacts compared with the raw sinogram approach. However, each MAR technique has limitations: STR is unable to mitigate low CT number artifacts, the median filter blurs the image which challenges the preservation of tissue heterogeneities, and both sinogram approaches introduce new streaks. Large local dose differences are generally due to differences in voxel tissue-type rather than mass density. The largest differences in target dose metrics (D90, V100, V150), over 50% lower compared to the other models, are when uncorrected CT images are used with TAS that consider calcifications. Metrics found using models which include calcifications are generally a few percent lower than prostate-only models. Generally, metrics from any MAR method and any TAS which considers calcifications agree within 6%. Overall, the studied MAR methods and TAS show promise for further retrospective MC dose calculation studies for various permanent implant brachytherapy treatments.

Monte Carlo dosimetry for 103Pd, 125I, and 131Cs ocular brachytherapy with various plaque models using an eye phantom

PURPOSE

To investigate dosimetry for ocular brachytherapy for a range of eye plaque models containing(103)Pd, (125)I, or (131)Cs seeds with model-based dose calculations.

METHODS

Five representative plaque models are developed based on a literature review and are compared to the standardized COMS plaque, including plaques consisting of a stainless steel backing and acrylic insert, and gold alloy backings with: short collimating lips and acrylic insert, no lips and silicone polymer insert, no lips and a thin acrylic layer, and individual collimating slots for each seed within the backing and no insert. Monte Carlo simulations are performed using the EGSnrc user-code BrachyDose for single and multiple seed configurations for the plaques in water and within an eye model (including nonwater media). Simulations under TG-43 assumptions are also performed, i.e., with the same seed configurations in water, neglecting interseed and plaque effects. Maximum and average doses to ocular structures as well as isodose contours are compared for simulations of each radionuclide within the plaque models.

RESULTS

The presence of the plaque affects the dose distribution substantially along the plaque axis for both single seed and multiseed simulations of each plaque design in water. Of all the plaque models, the COMS plaque generally has the largest effect on the dose distribution in water along the plaque axis. Differences between doses for single and multiple seed configurations vary between plaque models and radionuclides. Collimation is most substantial for the plaque with individual collimating slots. For plaques in the full eye model, average dose in the tumor region differs from those for the TG-43 simulations by up to 10% for(125)I and (131)Cs, and up to 17% for (103)Pd, and in the lens region by up to 29% for (125)I, 34% for (103)Pd, and 28% for (131)Cs. For the same prescription dose to the tumor apex, the lowest doses to critical ocular structures are generally delivered with plaques containing (103)Pd seeds.

CONCLUSIONS

The combined effects of ocular and plaque media on dose are significant and vary with plaque model and radionuclide, suggesting the importance of model-based dose calculations employing accurate ocular and plaque media and geometries for eye plaque brachytherapy.

Model-based dose calculations for COMS eye plaque brachytherapy using an anatomically realistic eye phantom

PURPOSE

To investigate the effects of the composition and geometry of ocular media and tissues surrounding the eye on dose distributions for COMS eye plaque brachytherapy with(125)I, (103)Pd, or (131)Cs seeds, and to investigate doses to ocular structures.

METHODS

An anatomically and compositionally realistic voxelized eye model with a medial tumor is developed based on a literature review. Mass energy absorption and attenuation coefficients for ocular media are calculated. Radiation transport and dose deposition are simulated using the EGSnrc Monte Carlo user-code BrachyDose for a fully loaded COMS eye plaque within a water phantom and our full eye model for the three radionuclides. A TG-43 simulation with the same seed configuration in a water phantom neglecting the plaque and interseed effects is also performed. The impact on dose distributions of varying tumor position, as well as tumor and surrounding tissue media is investigated. Each simulation and radionuclide is compared using isodose contours, dose volume histograms for the lens and tumor, maximum, minimum, and average doses to structures of interest, and doses to voxels of interest within the eye.

RESULTS

Mass energy absorption and attenuation coefficients of the ocular media differ from those of water by as much as 12% within the 20-30 keV photon energy range. For all radionuclides studied, average doses to the tumor and lens regions in the full eye model differ from those for the plaque in water by 8%-10% and 13%-14%, respectively; the average doses to the tumor and lens regions differ between the full eye model and the TG-43 simulation by 2%-17% and 29%-34%, respectively. Replacing the surrounding tissues in the eye model with water increases the maximum and average doses to the lens by 2% and 3%, respectively. Substituting the tumor medium in the eye model for water, soft tissue, or an alternate melanoma composition affects tumor dose compared to the default eye model simulation by up to 16%. In the full eye model simulations, the average dose to the lens is larger by 7%-9% than the dose to the center of the lens, and the maximum dose to the optic nerve is 17%-22% higher than the dose to the optic disk for all radionuclides. In general, when normalized to the same prescription dose at the tumor apex, doses delivered to all structures of interest in the full eye model are lowest for(103)Pd and highest for (131)Cs, except for the tumor where the average dose is highest for (103)Pd and lowest for (131)Cs.

CONCLUSIONS

The eye is not radiologically water-equivalent, as doses from simulations of the plaque in the full eye model differ considerably from doses for the plaque in a water phantom and from simulated TG-43 calculated doses. This demonstrates the importance of model-based dose calculations for eye plaque brachytherapy, for which accurate elemental compositions of ocular media are necessary.

Monte Carlo calculated doses to treatment volumes and organs at risk for permanent implant lung brachytherapy

Iodine-125 ((125)I) and Caesium-131 ((131)Cs) brachytherapy have been used with sublobar resection to treat stage I non-small cell lung cancer and other radionuclides, (169)Yb and (103)Pd, are considered for these treatments. This work investigates the dosimetry of permanent implant lung brachytherapy for a range of source energies and various implant sites in the lung. Monte Carlo calculated doses are calculated in a patient CT-derived computational phantom using the EGsnrc user-code BrachyDose. Calculations are performed for (103)Pd, (125)I, (131)Cs seeds and 50 and 100 keV point sources for 17 implant positions. Doses to treatment volumes, ipsilateral lung, aorta, and heart are determined and compared to those determined using the TG-43 approach. Considerable variation with source energy and differences between model-based and TG-43 doses are found for both treatment volumes and organs. Doses to the heart and aorta generally increase with increasing source energy. TG-43 underestimates the dose to the heart and aorta for all implants except those nearest to these organs where the dose is overestimated. Results suggest that model-based dose calculations are crucial for selecting prescription doses, comparing clinical endpoints, and studying radiobiological effects for permanent implant lung brachytherapy.

Sci-Sat AM: Brachy - 11: Improving treatment planning for I-125 lung brachytherapy using Monte Carlo methods

¹²⁵ I brachytherapy used in conjunction with sublobar resection to treat stage I non-small cell lung cancer has been reported to improve disease-free and overall survival rates compared with resection alone. Treatments are planned intra-operatively using seed spacing nomograms or tables to achieve a prescription dose defined 5 mm above the implant plane. Dose distributions for patients treated with this technique at the Mayo Clinic Rochester were reanalyzed using a Monte Carlo (MC) calculation; significant differences were observed between the standard TG-43 dose calculations and the actual dose delivered as determined by MC. This work investigates differences between TG-43 calculated prescription doses and those calculated in more accurate models. Monte Carlo calculations are performed using the EGSnrc user-code BrachyDose with a number of lung tissue phantom models including patient CT-derived phantoms. Seed spacing nomograms using these models are recalculated by determining the dose to the prescription point using the activities per seed required to produce a prescription dose of 100 Gy with the TG-43 point source formalism. Models using nominal density lung or CT-derived density lung tissue result in a significant increase in dose to the prescription point (up to approximately 25%) compared to TG-43 calculated doses. The differences observed suggest that patients routinely receive significantly higher doses than planned using TG-43 derived nomograms. Additionally, deviation from TG-43 increases as seed spacing increases. Media heterogeneities significantly affect dose distributions and prescription doses for ¹²⁵ I lung brachytherapy, underlining the importance of using model-based dose calculation algorithms to plan and analyze these treatments.

A cross sectional study of the prevalence and risk factors for owner misperception of canine body shape in first opinion practice in Glasgow

The objectives of the study were to investigate whether owners were able to assign the correct body shape to their dog and to assess the dog and owner level factors associated with incorrect owner assessment of dog body shape. Six hundred and eighty questionnaires were administered to dog owners in 5 first opinion practices around Glasgow during July 2007. At the same time, the interviewer and owner assessed the body shape of each dog. The interviewer assessment of body shape was taken as the gold standard. Incorrect owner assessment of dog body shape (misperception) was divided into two groups: underestimation and overestimation. Multinomial logistic regression and classification and regression trees (CART) were used to assess risk factors associated with each type of misperception. Misperception of dog body shape was present in 44.1% of owners with underestimation (i.e. the owner considered the animal to have a leaner body shape from the gold standard assessment) being the most common form of misperception. Risk factors identified by both multinomial logistic regression and CART were gender of owner, age of the dog and dog body shape. The classification tree appeared to have improved predictive ability when compared to the multinomial model.

BODILY CHANGES AND DEVELOPMENT OF PULMONARY RESISTANCE IN RATS LIVING UNDER COMPRESSED AIR CONDITIONS

1. 244 albino rats from standard Wistar Institute stock have been kept for periods up to 72 days under the following conditions. (a) Barometric pressure: 3040 mm. Hg. This means a partial pressure of oxygen of 635 mm. Hg and is equivalent to an 83.6 per cent oxygen mixture at normal barometric pressure. (b) Temperature: 28°C. (c) Humidity: 50 per cent relative. (d) Rate of ventilation: 2660 liters per minute for all animals. (e) Food and daily care were provided which induced normal growth in rats in the usual laboratory quarters. 2. The harmful factor in this environment was the increased oxygen tension. In our experiments the acute effects were active hyperemia and edema of the lungs, just as have been described by many investigators. 3. Only a small percentage of rats die from acute oxygen poisoning at the pressure employed. The majority return to good health objectively and survive several months of exposure. 4. Rats under 1 month of age display no clinical signs of acute oxygen poisoning, while in older animals the severity of the reaction and the mortality is directly proportional to the advance in age. 5. The symptoms of acute oxygen poisoning appear on the 3rd day of exposure in adults and reach maximum intensity during the 4th day, all deaths occurring at this time. 6. A continued weight loss is found in old rats, while the young gain weight, but not with normal vigor. 7. Adaptation to this toxic oxygen tension occurs in the albino rat during the first exposure, so that on reexposure acute oxygen poisoning does not develop. 8. Respiratory infection occurred sporadically in roughly 20 per cent of the normal adult rats in our laboratory colony. About the same incidence was found in the experimental rats during exposure; in most of these, chronic bronchiectasis and bronchopneumonia followed and proved fatal, indicating a lowered resistance in exposed animals. 9. Most rats exposed to an 80 per cent oxygen tension late in pregnancy have premature litters and die of acute oxygen poisoning, but if exposed early in pregnancy the majority survive. 10. Litters born during the first exposure of the mother are approximately 50 per cent underweight and die during the first 24 hours after birth. 11. A female, rendered resistant by a first exposure, produced a healthy litter during second exposure. 12. The continuous failure of adults to gain in weight and the fact that young animals grow slowly, together with the slowly progressing pulmonary pathology (11), indicate that high oxygen tensions not only produce acute changes in the lungs but also some alteration in the normal physiological processes, which may be termed "chronic oxygen poisoning."

MORPHOLOGICAL CHANGES IN THE LUNGS OF RATS LIVING UNDER COMPRESSED AIR CONDITIONS

1. The alveolar cells in the lungs of young rats are greater in number and size than in old rats, a gradual transition to the state in the latter occurring from about the 4th to the 6th months of life. 2. On prolonged exposure to an environment having an 83.6 per cent oxygen tension, the cellularity of the alveoli is increased in both young and old animals, so that after 2 to 3 weeks it is impossible to distinguish them by morphological differences. Numerous mitotic figures are present in the alveolar cells. This hyperplasia and hypertrophy is a change which persists for months after the rats return to normal air. 3. Young rats do not develop the symptoms of acute oxygen poisoning, although some perivascular edema and dilatation of the lymphatics results on the 4th day of exposure, when intense acute pulmonary edema is present in old rats. 4. The mortality of acute oxygen poisoning is directly proportional to the age of the animals, although the majority of rats under 6 months of age survive this state and continue in apparent good health for as long as 72 days. All deaths during the acute stage in an 83.6 per cent oxygen tension occur on the 4th day of exposure. 5. After 1 month of exposure lesions are to be seen in the small arterioles of the lungs, consisting of a thickening and hyalinization of the walls with ultimate thrombosis of many. These vascular changes are identical with those seen in the arterioles of the kidney in chronic vascular nephritis. 6. Around the 45th day of exposure the large pulmonary arteries contain lesions in the media. The walls become loose meshed, thickened, and hyalinized, and hyaline cartilage formation is associated with these changes. 7. Reexposure of animals following an interval of 40 days in normal air subsequent to the first exposure of 72 days, does not produce any clinical or pathological changes. An adaptation to this toxic oxygen tension is produced during the first exposure, so that oxygen poisoning does not occur on second exposure. The increased cellularity of the alveolar walls persists. 8. The similarity in the morphological structure of the alveoli in young rats and in previously exposed old rats has a definite relationship to the adaptation that occurs to an oxygen tension of 83.6 per cent, preventing the development of acute oxygen poisoning on reexposure.

Cytomegalovirus retinitis, human immunodeficiency virus antibody positivity and normal T helper cell numbers

We describe a 46-year-old man in whom retinitis was diagnosed as his initial HIV and AIDS defining illness. A diagnosis of CMV infection was made based on the clinical appearance of the fundus and confirmed by DNA polymerase chain reaction (PCR) on his vitreous biopsy. His CD4+ T lymphocyte count at the time was 580 x 10(6)/l (16%) with a CD4:CD8 ration of 0.28. He had a splenectomy following trauma more than 20 years earlier. He responded very well to intravenous and oral ganciclovir and remains recurrence-free almost 2 years later. This case and others highlight two issues: (i) CMV retinitis in HIV positive is not confined to those with very low CD4+ T lymphocyte counts; (ii) previous splenectomy may have an impact on CD4+ cell numbers and function.

Lysosomal thyroid hormone 5'-deiodinase

Lysosomes prepared from rat liver and kidney after loading with the detergent Triton WR-1339 show membrane-bound 5'-deiodinase activity with marked specificity for 3,3',5'-triiodothyronine (reverse T3), lesser activity with respect to thyroxine (T4) and almost none towards 3,3',5'-triiodothyronine (T3). The enzyme is thiol dependent and shows maximal catalysis at pH 7.2. As many of the states known to alter thyroid hormone levels also affect lysosomal function, inhibition of the lysosomal 5'-deiodinase leading to an increase in intracellular reverse T3 may be an initiating mechanism for thyroid hormone change.

Repeated failure of nickel-containing prosthetic heart valves in a patient allergic to nickel

Life-threatening peri-prosthetic incompetence developed with two successive nickel-containing mitral-valve prostheses in a patient allergic to nickel. Neither prosthesis had been incorporated satisfactorily. Her present nickel-free prosthesis seems to be satisfactory 22 months after insertion. Since allergy to nickel may have been involved in the failure of these prostheses, it is recommended that nickel-sensitive patients should be given nickel-free prostheses.

Hypernatraemic dehydration following tricuspid valve replacement

The development of abnormally high plasma sodium and plasma osmolality levels is described in 5 patients following open-heart surgery involving prosthetic replacement of the tricuspid valve. These biochemical abnormalities developed in the early post-operative period and were associated with an excessive diuresis during the first 3 to 4 days after operation. Biochemical correction required a prolonged, high volume intravenous water load, and was paralleled by progressive clinical improvement, notably in peripheral circulation, tissue turgor and cerebral function. Plasma sodium and osmolality levels and observed fluid balance in 20 patients undergoing similar surgical procedures for tricuspid valve lesions fail to show this hypernatraemic, hyperosmolar state, and indicate that the majority of such patients have a markedly positive observed fluid balance in the early post-operative period. These differences are statistically highly significant (p less than 0.001). Consideration of urine/plasma osmolality levels reveals a transient but highly significant impairment of renal concentration in the hypernatraemic patients (p less than 0.001).

Sinoatrial disorders, the "sick sinus" syndrome. Experience with implanted cardiac pacemakers

The long term results of permanent pacemaker implantation in patients with disorders of the sinoatrial node and atrial conduction pathways were studied. In a consecutive series of 300 patients treated by pacemaker implantation, 68 ((22.3%) had sinoatrial disorders. Mean age of the group was 54 years (33-82 years); 37 were male, 31 female. Diagnosis was confirmed by serial electrocardiography with overdrive suppression of sinoatrial node function as indicated. Twenty-two patients presented with sinus bradycardia alone (Type I disorder) and 46 with bradycardia-tachycardia syndrome (Type II disorder) were completely controlled. of the 46 Type II patients, in 30 (65.2%) tachyarrhythmias were controlled by pacing alone and in 14 (30.4%) by pacing and antiarrhythmic drug therapy. Congestive cardiac failure was relieved in 80% and anginal pain in 70% of patients with rate control alone. Systemic embolisation did not recur after pacemaker implantation. The average duration of pacemaker therapy was 52 months (12-96 months). In this series, long term ventricular demand pacing proved beneficial in both types of sinoatrial disorders.

The renal handling of insulin and thyroid hormones in normal man

1. The renal extraction of insulin and thyroid hormones T3 and T4 was studied in man by right renal vein catheterization. 2. The mean renal extraction of insulin was 0-46, suggesting that the right renal vein should be utilized in comparable studies. 3. No renal extraction of thyroid hormones was detected.

Mitral valve replacement in the presence of severe pulmonary hypertension

Thirty patients with severe preoperative pulmonary hypertension (pulmonary artery pressure range 90-165 mmHg, mean 118 mmHg) were reviewed following single mitral valve replacement, with prosthetic valves, within the last 10 years (1964-74). The early and late mortality for this group was no different from that of the total series of mitral valve replacements performed over the same period. Marked postoperative clinical improvement was accompanied by corresponding radiological and electrocardiographic changes. In addition there was a statistically highly significant haemodynamic improvement in the 21 survivors (mean survival time 5 1/2 years). At recatheterization the mean pulmonary artery pressure was 41-5%, the mean wedge pressure 46-3%, and the transpulmonary gradient (PAm-LAm) 36-1% of the preoperative values. It is concluded that gross pulmonary hypertension is not per se a contraindication to mitral valve replacement surgery.

Tricuspid valve replacement: a five-year appraisal

Organic disease of the tricuspid valve required surgery in 18% of all patients undergoing valve replacement over a five-year period. Differentiation of organic from functional disease is difficult and may be made only at open-heart surgery. The results of a series of 56 patients who underwent tricuspid valve replacement are presented; of these, 53 had organic disease. Operative mortality at the end of five years had fallen to 7% with significant clinical improvement in 79% of patients, a reduction in cardiothoracic ratio in 81%, and a low incidence of postoperative tricuspid incompetence.

Early systemic hypertension after surgical closure of atrial septal defect

The systemic haemodynamic changes occurring in the immediate post-operative period were examined in a series of patients undergoing closure of atrial septal defect (A.S.D.) and in a consecutive series of all patients undergoing open-heart surgery in this Unit. Significant systemic hypertension was observed in 47.5% of patients in the A.S.D. series. In an attempt to explain this finding, several other haemodynamic variables were examined in relation to the systemic blood pressure. There was no correlation between central venous pressure or blood loss and systemic blood pressure. However, there was an inverse correlation between blood balance and systolic and diastolic blood pressure at 4 hours after operation. The explantation of this finding is unclear but it may be due to the effects on atrial receptors of lower right atrial and pulmonary artery pressures following closure of the A.S.D. Although the post-operative systemic hypertension was transient in most cases, it may produce adverse effects in the early post-operative period and therefore treatment with hypotensive agents should be considered in severe cases.

Early results of heart valve replacement with the Björk-Shiley prosthesis

The operation on and subsequent course of 88 patients with valve replacements using Björk-Shiley tilting disc prostheses has been reviewed in terms of mortality, clinical results, and valve function. The follow-up period varied between 6 months and 2 years. The hospital mortality was 17% and late mortality 8%. Of those who left hospital, 75% returned to full normal activity and required less (or no) drug therapy other than maintenance anticoagulation. There was one transient embolic episode. Significant intravascular haemolysis does not occur with this prosthesis.

1-Thioisoflavanones and related compounds

Several 1-thioisoflavanones and 1-thioisoflavones have been synthesized. Addition of a thiophenol to atropic acid and cyclization of the resultant thio acids is shown to give rise to a 1-thioisoflavanone. Some reactions of these compounds are described.

Multiple smooth muscle hypertrophies in a newborn infant

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