Critical appraisal and further development of the methodology for open circuit calorimetry in neonates.

A non-invasive technique for open circuit calorimetry based on a Vickers 79 incubator as the gas collection chamber was developed and evaluated. The technique, which involved drawing air from the incubator hood at 11 1/min for gas analysis, did not have a significant cooling effect on the infant and the noise levels within the incubator did not exceed current safety standards. A new technique for checking the calibration of the whole system was developed as the traditional alcohol burn method proved unsatisfactory. Either pure oxygen or carbon dioxide were fed into the incubator hood at controlled physiological rates using a calibrated throttling valve. Over a number of calibration checks the mean error of the system proved to be +/- 4.3% for oxygen and +/- 4.45% for carbon dioxide. Less than a fifth of this error was attributable to the pump and flow meter. When oxygen is introduced to the system at a constant physiological rate it takes 30 min for a plateau to be reached. Therefore it is recommended that this system is used when readings are to be taken in a steady state situation or data is to be cumulated over a long period of time such as in an energy balance study. A run in period of 30 min before collecting data is essential. It is recommended that a calibration check is performed before each study.     

Long-term acceptance of continuous positive airway pressure in obstructive sleep apnea

We studied the long-term acceptability of nasal continuous positive airway pressure (CPAP) treatment in 168 consecutive patients, 147 with obstructive sleep apnea (OSA) and 21 with snoring. Follow-up was between 1.5 and 78 months. At latest follow-up 107 of 168 (64%) were still using CPAP. Acceptance of CPAP was least for patients with snoring alone (6 of 21 persisted) and best for patients with both excessive daytime somnolence and severe hypoxemia (minimum SaO2 less than 75%), of whom 40 of 45 (89%) persisted with treatment. Patients with excessive daytime somnolence but without severe hypoxemia were less tolerant of CPAP (39 of 71, 55%, persisted) than patients with no symptoms of excessive somnolence but with severe hypoxemia (21 of 30, 70%, persisted). The most common reasons for discontinuing CPAP were intolerance of the mask (26 of 61), the inconvenience of treatment (16 of 61), and the lack of symptomatic benefit from treatment (10 of 61). We concluded that long-term acceptance of CPAP was difficult to predict in advance but that it was most likely in patients with the most severe sleep apnea. Because intolerance of the mask and inconvenience were the most common reasons for ceasing treatment, improvements in the design of CPAP systems and careful patient training may improve the acceptability of CPAP substantially.     

Regulation of human alveolar macrophage- and blood monocyte-derived interleukin-8 by prostaglandin E2 and dexamethasone.

Mononuclear phagocytes are important immune effector cells that play a fundamental role in cellular immunity. In addition to their antigen-presenting and phagocytic activities, monocytes/macrophages produce a vast array of regulatory and chemotactic cytokines. Interleukin-8 (IL-8), a potent neutrophil-activating and chemotactic peptide, is produced in large quantities by mononuclear phagocytes and may be an important mediator of local and systemic inflammatory events. In this investigation, we describe the effects of prostaglandin E2 (PGE2) and dexamethasone (Dex) on IL-8 mRNA and protein expression from lipopolysaccharide (LPS)-treated human peripheral blood monocytes (PBM) and alveolar macrophages (AM). We demonstrate the dose-dependent suppression of IL-8 from LPS-stimulated PBM by PGE2. Treatment of stimulated PBM with 10(-6) M PGE2 resulted in maximal inhibition, causing 60% suppression of both IL-8 mRNA and extracellular protein levels. In contrast, PGE2 (10(-6) to 10(-8) M) did not significantly alter IL-8 mRNA or protein expression from LPS-treated AM. Treatment of LPS-stimulated PBM and AM with Dex (10(-6) to 10(-8) M) resulted in 75% decline in IL-8 mRNA and extracellular protein from either cell population. Pretreatment of PBM with PGE2 or Dex 1 or 2 h before LPS stimulation caused a significant suppression of steady-state IL-8 mRNA levels; however, administration of either of these modulators 1 or 2 h after LPS stimulation failed to have an inhibitory effect.(ABSTRACT TRUNCATED AT 250 WORDS)     

Detection of chromosomes and estimation of aneuploidy in human spermatozoa using fluorescence in-situ hybridization

The development and application of fluorescence in-situ hybridization (FISH) has opened the way for comprehensive studies on numerical chromosome abnormalities in human spermatozoa. FISH can be rapidly applied to large numbers of spermatozoa and thus overcomes the major limitation of karyotyping spermatozoa after penetration of zona-free hamster oocytes. The simultaneous hybridization of two or more chromosome-specific probes to spermatozoa and subsequent detection of the bound probes using different fluorescent detection systems enables two or more chromosomes to be localized simultaneously in the same spermatozoon and provides a technique for undertaking reasonable estimates of aneuploidy. The most commonly used probes are those which bind to the centromeric region of specific chromosomes. Most studies to date have concentrated on estimating aneuploidy in spermatozoa from normospermic men, although reports are beginning to appear on aneuploidy in spermatozoa from subfertile and infertile men. Multi- probe FISH studies have generally reported disomy (hyperhaploidy) estimates of 0.05-0.2% per chromosome. There is preliminary evidence that some chromosomes such as X, Y and 21 are predisposed towards higher rates of non-disjunction during spermatogenesis. There are also suggestions of inter-donor variability in aneuploidy frequencies for specific chromosomes, although this requires confirmation in larger studies. While FISH is clearly a powerful technique that has many applications in reproductive medicine, it must also be realized that it does have limitations and the technology itself is still evolving and has yet to be fully validated on spermatozoa.      

Improved performance of intravascular pO2 sensor incorporating poly(MPC-co-BMA) membrane

The first in vivo evaluation of a pO₂ sensor constructed with a novel copolymer is described. The performance of the sensor is assessed under dynamic conditions in vitro and in vivo. This sensor is more stable and reliable than the control sensor with a heparintreated polyethylene membrane.     

Immunization of adult hamsters against Clostridium difficile-associated ileocecitis and transfer of protection to infant hamsters.

In this investigation, the role of antibodies against Clostridium difficile toxins A and B in protecting hamsters against C. difficile-associated ileocecitis was examined. We also studied the transfer of protection against C. difficile-associated intestinal disease from immunized female hamsters to their infants. Adult female hamsters immunized parenterally with toxoid A or a mixture containing both toxoids A and B were protected against clindamycin-induced C. difficile-associated fatal ileocecitis. On the other hand, hamsters immunized with toxoid B or a broth filtrate from a nontoxigenic strain of C. difficile were not protected against C. difficile-induced ileocecitis. Antibody against the immunizing toxoid could be demonstrated in both the serum and the cecal contents of hamsters. Some infant hamsters from mothers immunized with toxoid A or AB were protected against C. difficile-associated ileocecitis, while infant hamsters from mothers immunized with toxoid B or a nontoxigenic broth filtrate were not protected against disease. Neutralizing antibodies to toxins A and B could be demonstrated in both maternal milk and serum, as well as in infant serum and intestinal contents. Foster-mothering experiments demonstrated that maternal protection of infants against C. difficile-associated ileocecitis was transferred to infant hamsters through breast milk. These results suggest that toxin A may play a more important role in the pathogenesis of C. difficile-associated ileocecitis in hamsters than toxin B. Furthermore, variations in the severity of C. difficile-associated illness in infants and adults may reflect the lack or presence of passively or actively acquired immunity against C. difficile toxins.