Management of spontaneous pneumothorax: an American College of Chest Physicians Delphi consensus statement

OBJECTIVE

Provide explicit expert-based consensus recommendations for the management of adults with primary and secondary spontaneous pneumothoraces in an emergency department and inpatient hospital setting. The use of opinion was made explicit by employing a structured questionnaire, appropriateness scores, and consensus scores with a Delphi technique. The guideline was designed to be relevant to physicians who make management decisions for the care of patients with pneumothorax.

OPTIONS

Decisions for observation, chest tube placement, surgical interventions, and radiographic imaging.

OUTCOMES

Effectiveness of pneumothorax resolution, duration of and patient tolerance of care, and pneumothorax recurrence.

EVIDENCE

Literature review from 1967 to January 1999 and Delphi questionnaire submitted in three iterations to a multidisciplinary physician panel.

VALUES

The guideline development group determined by consensus the relevant outcomes to be considered in developing the Delphi questionnaire.

BENEFITS, HARMS, AND COSTS

The type and magnitude of benefits, harms, and costs expected for patients from guideline implementation.

RECOMMENDATIONS

Management decisions vary between patients with primary or secondary pneumothoraces, with observation of small pneumothoraces being appropriate only for primary pneumothoraces. The level of consensus varies regarding the specific interventions indicated, but agreement exists for the general principles of care.

VALIDATION

Recommendations were peer reviewed by physician experts and were reviewed by the American College of Chest Physicians (ACCP) Health and Science Policy Committee.

IMPLEMENTATION

The guideline recommendations will be published in printed and electronic form with distribution of synopses for patients and health care providers. Contents of the guideline will be incorporated into continuing medical education programs.

SPONSORS

The ACCP.

On the thymus in the differentiation of "H-2 self-recognition" by T cells: evidence for dual recognition?

In the thymus, precursor T cells differentiate recognition structures for self that are specific for the H-2K, D, and I markers expressed by the thymic epithelium. Thus recognition of self-H-2 differentiates independently of the T cells H-2 type and independently of recognition of nonself antigen X. This is readily compatible with dual recognition by T cells but does not formally exclude a single recognition model. These conclusions derive from experiments with bone marrow and thymic chimeras. Irradiated mice reconstituted with bone marrow to form chimeras of (A X B)F1 leads to A type generate virus-specific cytotoxic T cells for infected targets A only. Therefore, the H-2 type of the host determines the H-2-restricted activity of killer T cells alone. In contrast, chimeras made by reconstituting irradiated A mice with adult spleen cells of (A X B)F1 origin generate virus-specific cytotoxic activity for infected A and B targets, suggesting that mature T cells do not change their self-specificity readily. (A X B)F1 leads to (A X C)F1 and (KAIA/DC) leads to (KAIA/DB) irradiation bone marrow chimeras responded against infected A but not B or C targets. This suggests that cytotoxicity is not generated against DC because it is abscent from the host's thymus epithelium and not against DB because it is not expressed by the reconstituting lymphoreticular system. (KBIB/DA) leads to (KCIC/DA) K, I incompatible, or completely H-2 incompatible A leads to B chimeras fail to generate any measurable virus specific cytotoxicity, indicating the necessity for I-specific helper T cells for the generation of killer T cells. Finally adult thymectomized, irradiated and bone marrow reconstituted (A X B)F1 mice, transplanted with an irradiated thymus of A origin, generate virus-specific cytotoxic T cells specific for infected A targets but not for B targets; this result formally demonstrates the crucial role of thymic epithelial cells in the differentiation of anti-self-H-2 specificities of T cells.

Fluidity of water confined to subnanometre films

The fluidity of water in confined geometries is relevant to processes ranging from tribology to protein folding, and its molecular mobility in pores and slits has been extensively studied using a variety of approaches. Studies in which liquid flow is measured directly suggest that the viscosity of aqueous electrolytes confined to films of thickness greater than about 2-3 nm remains close to that in the bulk; this behaviour is similar to that of non-associative organic liquids confined to films thicker than about 7-8 molecular layers. Here we observe that the effective viscosity of water remains within a factor of three of its bulk value, even when it is confined to films in the thickness range 3.5 +/- 1 to 0.0 +/- 0.4 nm. This contrasts markedly with the behaviour of organic solvents, whose viscosity diverges when confined to films thinner than about 5-8 molecular layers. We attribute this to the fundamentally different mechanisms of solidification in the two cases. For non-associative liquids, confinement promotes solidification by suppressing translational freedom of the molecules; however, in the case of water, confinement seems primarily to suppress the formation of the highly directional hydrogen-bonded networks associated with freezing.

Bracteomania, an inflorescence anomaly, is caused by the loss of function of the MADS-box gene squamosa in Antirrhinum majus

Anomalous flowering of the Antirrhinum majus mutant squamosa (squa) is characterized by excessive formation of bracts and the production of relatively few and often malformed or incomplete flowers. To study the function of squamosa in the commitment of an inflorescence lateral meristem to floral development, the gene was cloned and its genomic structure, a well as that of four mutant alleles, was determined. SQUA is a member of a family of transcription factors which contain the MADS-box, a conserved DNA binding domain. In addition, we analysed the temporal and spatial expression pattern of the squa gene. Low transcriptional activity of squa is detectable in bracts and in the leaves immediately below the inflorescence. High squa transcript levels are seen in the inflorescence lateral meristems as soon as they are formed in the axils of bracts. Squa transcriptional activity persists through later stages of floral morphogenesis, with the exception of stamen differentiation. Although necessary for shaping a normal racemose inflorescence, the squa function is not absolutely essential for flower development. We discuss the function of the gene during flowering, its likely functional redundancy and its possible interaction with other genes participating in the genetic control of flower formation in Antirrhinum.

Confinement-Induced Phase Transitions in Simple Liquids

The liquid-to-solid transition of a simple model liquid confined between two surfaces was studied as a function of surface separation. From large surface separations (more than 1000 angstroms) down to a separation corresponding to seven molecular layers, the confined films displayed a liquid-like shear viscosity. When the surface separation was further decreased by a single molecular spacing, the films underwent an abrupt, reversible transition to a solid. At the transition, the rigidity of the confined films (quantified in terms of an "effective viscosity") increased reversibly by at least seven orders of magnitude.

The major histocompatibility complex of the mouse

Like physicists striving to develop a unified field theory, immunologists are attempting to bring order to the microcosmos of defense reactions. Indications are that one of the most important constants in this microcosmos is the major histocompatibility complex (MHC) of the species. A test of any interpretation of the MHC's role in immunity is how well it explains this system's polymorphism. One of the most crucial questions an MHC hypothesis must answer is: Why are there so many alleles at this complex?

Genetic control of the immune response. Mapping of the Ir-1 locus

Eleven strains of mice bearing recombinant H-2 chromosomes derived from known crossover events between known H-2 types were immunized with a series of branched, multichain, synthetic polypeptide antigens [(T,G)-A--L, (H,G)-A--L, and (Phe,G)-A--L]. Results with nine of the eleven H-2 recombinants indicated that the gene(s) controlling immune response to these synthetic polypeptides (Ir-1) is on the centromeric or H-2K part of the recombinant H-2 chromosome. Results with two of the eleven recombinant H-2 chromosomes indicated that Ir-1 was on the telomeric or H-2D part of the recombinant H-2 chromosome. Both of these recombinants were derived from crossovers between the H-2K locus and the Ss-Slp locus near the center of the H-2 region. One of these recombinants, H-2(y), was derived from a known single crossover event. These results indicate that Ir-1 lies near the center of the H-2 region between the H-2K locus and the Ss-Slp locus. The results of a four-point linkage test were consistent with these results. In 484 offspring of a cross designed to detect recombinants between H-2 and Ir-1, only two putative recombinants were detected. Both of these recombinants were confirmed by progeny testing. Extensive analysis of one of them has shown that the crossover event occurred within the H-2 region. (Testing of the second recombinant is currently under way.) Thus, in the linkage test, recombinants between H-2 and Ir-1 are in fact intra-H-2 crossovers. These results permit assignment of Ir-1 to a position between the H-2K locus and the Ss-Slp locus.

Molecular characterisation of the Arabidopsis SBP-box genes

The Arabidopsis thaliana SPL gene family represents a group of structurally diverse genes encoding putative transcription factors found apparently only in plants. The distinguishing characteristic of the SPL gene family is the SBP-box encoding a conserved protein domain of 76 amino acids in length, the SBP-domain, which is responsible for the interaction with DNA. We present here characterisation of 12 members of the SPL gene family. These genes show highly diverse genomic organisations and are found scattered over the Arabidopsis genome. Some SPL genes are constitutively expressed, while transcriptional activity of others is under developmental control. Based on phylogenetic reconstruction, gene structure and expression patterns, they can be divided into subfamilies. In addition to the Arabidopsis SPL genes, we isolated and determined the sequences of three SBP-box genes from Antirrhinum majus and seven from Zea mays.

The traditional and a new version of the mouse H-2 complex

The H-2 complex has traditionally been interpreted as a maze of regions, subregions and loci coding for different traits. The two main theses presented here are, first, that a single H-2 locus is pleiomorphic in that it controls several functions such as allograft rejection, cell-mediated lymphocytotoxicity, mixed lymphocyte reaction, immune response, immune suppression and restriction of T-cell specificity; and second, that the physiological function of the H-2 complex is to guide T lymphocytes in their function of distinguishing self from non-self, and that all other H-2-controlled traits are artificial derivatives of this basic function. These two theses lead to a new, simplified interpretation of the H-2 complex.

Serologically defined and lymphocyte-defined components of the major histocompatibility complex in the mouse

The mixed leukocyte culture (MLC) test is an in vitro model of the recognition phase of the homograft response. For the most part, activation in MLC is dependent on differences of the major histocompatibility complex (MHC). Our present studies in the mouse suggest that activation is primarily associated with differences of genetic regions of the MHC other than those which control the serologically defined (H-2) antigens. These differences do not lead to cytotoxic or agglutinating antibody formation despite extensive immunization; we have called these differences lymphocyte-defined (LD) differences. The strongest stimulation in MLC is associated with differences of the Ir region. It is possible that the Ir product is the T cell receptor and that it is this same molecule which can act as the stimulatory agent in MLC. Other possibilities are discussed.

Divergence time and population size in the lineage leading to modern humans

We have developed maximum likelihood (ML) methods for comparisons of nucleotide sequences from unlinked genomic regions. In the case of a single species, the ML method primarily estimates the effective population size (Ne) under both constant size and abrupt expansion conditions. In the case of two or three species, the ML method simultaneously estimates the species divergence time and the effective size of ancestral populations. This allows us to trace the evolutionary history of the human population over the past several million years (my). Available sequences at human autosomal loci indicate Ne = 10,000 in the Late Pleistocene, a figure concordant with the results obtained from mitochondrial DNA sequence and allele-frequency data analysis, and there is no indication of population expansion. The ML analysis of two species shows that humans diverged from chimpanzees 4.6 my ago and that the human and chimpanzee clade diverged from the gorilla 7.2 my ago. Furthermore, the effective population size of humans more than 4.6 my ago is nearly 10 times larger than Ne of modern humans. The effective population size in the human lineage does not seem to have remained constant over the past several million years. The ML model for three species predicts slightly different, but consistent results to those obtained by the two-species analysis.

Membrane breakdown in acute and chronic neurodegeneration: focus on choline-containing phospholipids

Breakdown of cellular membranes is a characteristic feature of neuronal degeneration in acute (stroke) and chronic (senile dementia) neurological disorders. The present review summarizes recent experimental and clinical work which concentrated on changes of choline-containing phospholipids as indicators of neuronal membrane breakdown. Experimental studies identified glutamate release, calcium influx, and activation of cellular phospholipase A2 (PLA2) as important steps initiating membrane breakdown in cultured neurons or brain slices under hypoxic or ischemic conditions. Proton NMR studies have shown an elevation of choline-containing compounds in the brain of Alzheimer patients while neurochemical studies in post mortem-brain demonstrated increases of the catabolic metabolite, glycerophosphocholine, an indicator of PLA2 activation. In contrast, studies of cerebrospinal fluid, phosphorus NMR studies, and measurements of phospholipases in post mortem Alzheimer brain gave ambiguous results which may be explained by methodical limitations. The finding that, in experimental studies, choline was a rate-limiting factor for phospholipid biosynthesis has stimulated clinical studies aimed at counteracting phospholipid breakdown, e.g. by combinations of choline and cytidine. Future experimental approaches should clarify whether loss of membrane phospholipids is cause or consequence of the neurodegenerative disease process.

The lymphoreticular system in triggering virus plus self-specific cytotoxic T cells: evidence for T help

The thymus determines the spectrum of the receptor specificities of differentiating T cells for self-H-2; however, the phenotypic expression of T cell's specificity for self plus virus is determined predominantly by the H-2 type of the antigen presenting cells of the peripheral lymphoreticular system. Furthermore, virus specific helper T cells are essential for the generation of virus-specific cytotoxic T cells. For cooperation between mature T cells and other lymphocytes to be functional in chimeras, thymic epithelial cells and lymphohemopoietic stem cells must share the I region; killer T-cell generation also requires in addition compatibility for at least one K or D region. These conclusions derive from the following experiments: A leads to (A X B)F1 chimeric lymphocytes do produce virus-specific cytotoxic T-cell activity for infected A but not for infected B cells; when sensitized in an acutely irradiated and infected recipient (A X B)F1 these chimeric lymphocytes respond to both infected A and B. Therefore the predominantly immunogenically infected cells of chimeras the radiosensitive and by donor stem cells replaced lymphoreticular cells. In this adoptive priming model (KAIA/DB leads to KAIA/DC) chimeric lymphocytes could be sensitized in irradiated and infected F1 against KA and DC but not against infected DB targets. In contrast KBIB/DA leads to KCIC/DA chimeras' lymphocytes could not be sensitized at all in appropriately irradiated and infected F1 recipients. Thus these latter chimeras probably lack functional I-specific T helper cells that are essential for the generation of T killer cells against infected D compatible targets. If T cells learn in the thymus to recognize H-21 or K, D markers that are not at least partially carried themselves in other cells of the lymphoreticular system immunological interactions will be impossible and this paradox situation results in phenotypic immune incompetence in vivo.

The molecular descent of the major histocompatibility complex

In the last few years, more than 500 primate major histocompatibility complex (Mhc) genes or parts thereof have been sequenced. The extraordinary sequence information is used here to draw conclusions about the manner of Mhc evolution. The Mhc genes are found to evolve at a relatively slow rate with the regularity of a clock. It takes from 1 to 6 million years for a new mutation to be incorporated into an Mhc allele, and the mutation rate is comparable to that of most other primate genes. The nonsynonymous sites coding for the peptide-binding region (PBR) are under relatively weak positive selection pressure (selection coefficient of a few percent only); the nonsynonymous non-PBR sites are under moderate negative selection pressure. The positive pressure is probably provided by parasites and is responsible for the trans-species persistence of allelic lineages at functional Mhc loci for more than 40 million years.

Socio-economic disparities in preterm birth: causal pathways and mechanisms

Preterm birth is the leading cause of infant mortality in industrialised societies. Its incidence is greatly increased among the socially disadvantaged, but the reasons for this excess are unclear and have been relatively unexplored. We hypothesise two distinct sets of causal pathways and mechanisms that may explain social disparities in preterm birth. The first set involves chronic and acute psychosocial stressors, psychological distress caused by those stressors, increased secretion of placental corticotropin releasing hormone (CRH), changes in sexual behaviours or enhanced susceptibility to bacterial vaginosis and chorioamnionitis, cigarette smoking or cocaine use, and decidual vasculopathy. The second hypothesised pathway is a gene-environment interaction based on a highly prevalent mutation in the gene for methylenetetrahydrofolate reductase (MTHFR), combined with low folate intake from the diet and from prenatal vitamin supplements, consequent hyperhomocysteinemia, and decidual vasculopathy. We propose to test these hypothesised pathways and mechanisms in a nested case-control study within a prospectively recruited and followed cohort of pregnant women with singleton pregnancies who deliver at one of four Montreal hospitals that serve an ethnically and socio-economically diverse population. Following recruitment during the late first or early second trimester, participating women are seen at 24-26 weeks, when a research nurse obtains a detailed medical and obstetric history; administers several scales to assess chronic and acute stressors and psychological function; obtains blood samples for CRH, red blood cell and plasma folate, homocysteine, and DNA for the MTHFR mutation; and performs a digital and speculum examination to measure cervical length and vaginal pH and to obtain swabs for bacterial vaginosis and fetal fibronectin. After delivery, each case (delivery at < 37 completed weeks following spontaneous onset of labour or prelabour rupture of membranes) and two controls are selected for placental pathological examination, hair analysis of cotinine, cocaine, and benzoylecgonine, and analysis of stored blood and vaginal specimens. Statistical analysis will be based on multiple logistic regression and structural equation modelling, with sequential construction of models of potential aetiological determinants and covariates to test the hypothesised causal pathways and mechanisms. The research we propose should improve understanding of the factors and processes that mediate social disparities in preterm birth. This improved understanding should help not only in developing strategies to reduce the disparities but also in suggesting preventive interventions applicable across the entire socio-economic spectrum.

Effect of topically applied T4 endonuclease V in liposomes on skin cancer in xeroderma pigmentosum: a randomised study. Xeroderma Pigmentosum Study Group

BACKGROUND

In patients with xeroderma pigmentosum the frequency of all forms of skin cancer is higher than in the general population, owing to a genetic defect in DNA repair. The bacterial DNA repair enzyme, T4 endonuclease V, delivered intracellularly, increases the rate of repair of sunlight-induced DNA damage in human cells. We tested the ability of this enzyme in a liposomal delivery vehicle applied topically (T4N5 liposome lotion) to lower the rate of new skin cancers in patients with xeroderma pigmentosum.

METHODS

30 patients were enrolled in this prospective, multicentre, double-blind study. Patients were randomly assigned T4N5 liposome lotion or a placebo liposome lotion, to be applied daily for 1 year. At 3-monthly visits, new actinic keratoses and basal-cell carcinomas were identified and removed. Analyses were by intention to treat.

FINDINGS

20 patients were assigned T4N5 liposome lotion and ten placebo lotion; one placebo-group patient withdrew before treatment and one withdrew with progressive disease at 9 months. The annualised rate of new actinic keratoses was 8.2 among the patients assigned T4N5 liposome lotion and 25.9 among those assigned placebo (difference 17.7 [95% CI 11.8-26.5]; p=0.004 by Poisson modelling). For basal-cell carcinoma, the annualised rates of new lesions were 3.8 in the treatment group and 5.4 in the placebo group (difference 1.6 [0.38-2.82]). No significant adverse effects were found among any of the patients.

INTERPRETATION

DNA damage has an important role in the development of skin cancer and precancerous skin lesions. The topical application of DNA repair enzymes to sun-damaged skin of patients with xeroderma pigmentosum lowered the rate of development of two forms of these lesions during a year of treatment.