Effect of ventilation on cerebral oxygenation in patients undergoing surgery in the beach chair position: a randomized controlled trial.

BACKGROUND: Surgery in the beach chair position (BCP) may reduce cerebral blood flow and oxygenation, resulting in neurological injuries. The authors tested the hypothesis that a ventilation strategy designed to achieve end-tidal carbon dioxide (E'(CO2)) values of 40-42 mm Hg would increase cerebral oxygenation (Sct(O2)) during BCP shoulder surgery compared with a ventilation strategy designed to achieve E'(CO2) values of 30-32 mm Hg. METHODS: Seventy patients undergoing shoulder surgery in the BCP with general anaesthesia were enrolled in this randomized controlled trial. Mechanical ventilation was adjusted to maintain an E'(CO2) of 30-32 mm Hg in the control group and an E'(CO2) of 40-42 mm Hg in the study group. Cerebral oxygenation was monitored continuously in the operating theatre using near-infrared spectroscopy. Baseline haemodynamics and Sct(O2) were obtained before induction of anaesthesia, and these values were then measured and recorded continuously from induction of anaesthesia until tracheal extubation. The number of cerebral desaturation events (CDEs) (defined as a ≥20% reduction in Sct(O2) from baseline values) was recorded. RESULTS: No significant differences between the groups were observed in haemodynamic variables or phenylephrine interventions during the surgical procedure. Sct(O2) values were significantly higher in the study 40-42 group throughout the intraoperative period (P<0.01). In addition, the incidence of CDEs was lower in the study 40-42 group (8.8%) compared with the control 30-32 group (55.6%, P<0.0001). CONCLUSIONS: Cerebral oxygenation is significantly improved during BCP surgery when ventilation is adjusted to maintain E'(CO2) at 40-42 mm Hg compared with 30-32 mm Hg. CLINICAL TRIAL REGISTRATION: ClinicalTrials.gov NCT01546636.

Delayed thymocyte development induced by augmented expression of p56lck.

Accumulating evidence supports the contention that CD4 and CD8 receptor molecules play a critical signaling role during thymocyte development. The lymphocyte-specific protein tyrosine kinase (p56lck), by virtue of its physical association with these surface components, provides a likely candidate for the biochemical signal transducing element required for these effects. To investigate the function of p56lck in T lymphocytes, transgenic mice were produced that carry either the wild-type lck gene or a mutated lck gene encoding a constitutively activated form of p56lck (p56lckF505). Both transgenes were expressed in thymocytes under the control of the lck proximal promoter element. A large set of founder animals was obtained in which steady-state accumulation of lck transgene mRNA directly correlated with transgene copy number, suggesting that this transgene contains a dominant control region. Progeny of these founders exhibited a transgene-dependent dose-related decrease in the production of thymocytes bearing functional antigen receptors. This effect was strictly dependent on p56lck activity, in that both wild-type and mutated versions of the genes induced similar effects with differing efficiencies. Remarkably, even a twofold increase in p56lck abundance was sufficient to substantially disrupt the appearance of functional thymocytes. These results indicate that thymocyte maturation is regulated in part by signals derived from p56lck.

The protein tyrosine kinase p56lck regulates thymocyte development independently of its interaction with CD4 and CD8 coreceptors [corrected].

The lck gene encodes a lymphocyte-specific protein tyrosine kinase of the nonreceptor type that is implicated in signal transduction pathways emanating from the CD4 and CD8 coreceptors. Previous studies also support a role for p56lck in regulating T cell receptor beta gene rearrangements and, more generally, thymocyte development. Here we report that a mutant form of p56lck, which is incapable of interacting with CD4 or CD8, behaves indistinguishably from association-competent p56lck with respect to its ability to affect thymocyte maturation. The effects of p56lck remained specific in that the closely related src-family kinase p59hck was incapable of substituting for p56lck in arresting beta locus gene rearrangements. These data support the view that src-family kinases perform highly specialized and often nonoverlapping functions in hematopoietic cells, and that p56lck acts independently of its association with CD4 and CD8 to regulate thymocyte development.

Requirement for p56lck tyrosine kinase activation in T cell receptor-mediated thymic selection.

The nonreceptor protein tyrosine kinase p56lck (Lck) serves as a fundamental regulator of thymocyte development by delivering signals from the pre-T cell receptor (pre-TCR) that permit subsequent maturation. However, considerable evidence supports the view that Lck also participates in signal transduction from the mature TCR. We have tested this conjecture by expressing a dominant-negative form of Lck under the control of a promoter element (the distal lck promoter) that directs high expression in CD4+CD8+ thymocytes, mature thymocytes, and peripheral T cells, thereby avoiding, complications that result from the well-documented ability of dominant-negative Lck to block very early events in thymocyte maturation. Here we report that expression of the catalytically inactive Lck protein at twice normal concentrations inhibits thymocyte positive selection by as much as 80%, while leaving other aspects of cell maturation intact. This effect was studied in more detail in mice simultaneously bearing the male-specific H-Y alpha/beta TCR transgene and ovalbumin-specific DO10 alpha/beta TCR transgene, where even equimolar expression of the dominant-negative Lck protein substantially vitiated the positive selection process. Although deletion of H-Y alpha/beta thymocytes proceeded normally in male mice despite the presence of catalytically inactive Lck, modest inhibition of superantigen-mediated deletion was in some cases observed. These data further implicate Lck in the propagation of all TCR-derived signals, and indicate that even very modest deficiencies in the representation of functional Lck molecules could in humans, profoundly alter the character of the peripheral TCR repertoire.

Proline residues in CD28 and the Src homology (SH)3 domain of Lck are required for T cell costimulation.

The Src family tyrosine kinases Lck and Fyn are critical for signaling via the T cell receptor. However, the exact mechanism of their activation is unknown. Recent crystal structures of Src kinases suggest that an important mechanism of kinase activation is via engagement of the Src homology (SH)3 domain by proline-containing sequences. To test this hypothesis, we identified several T cell membrane proteins that contain potential SH3 ligands. Here we demonstrate that Lck and Fyn can be activated by proline motifs in the CD28 and CD2 proteins, respectively. Supporting a role for Lck in CD28 signaling, we demonstrate that CD28 signaling in both transformed and primary T cells requires Lck as well as proline residues in CD28. These data suggest that Lck plays an essential role in CD28 costimulation.

Interaction of the IL-2 receptor with the src-family kinase p56lck: identification of novel intermolecular association.

In the interleukin-2 (IL-2) system, intracellular signal transduction is triggered by the beta chain of the IL-2 receptor (IL-2R beta); however, the responsible signaling mechanism remains unidentified. Evidence for the formation of a stable complex of IL-2R beta and the lymphocyte-specific protein tyrosine kinase p56lck is presented. Specific association sites were identified in the tyrosine kinase catalytic domain of p56lck and in the cytoplasmic domain of IL-2R beta. As a result of interaction, IL-2R beta became phosphorylated in vitro by p56lck. Treatment of T lymphocytes with IL-2 promotes p56lck kinase activity. These data suggest the participation of p56lck as a critical signaling molecule downstream of IL-2R via a novel interaction.

Transformation of NIH 3T3 fibroblasts by an activated form of p59hck.

Phosphorylation of a tyrosine residue near the carboxy terminus of src-family protein tyrosine kinases is believed to regulate the biological activity of these gene products. Conversion of this tyrosine in p59hck (Tyr-501) to a phenylalanine residue by using oligonucleotide-directed mutagenesis yielded a product (p59hckF501) with very potent transforming activity. Quantitative analysis by a soft-agar cloning assay revealed that p59hckF501 was more than 100-fold more effective than a closely related transforming element, p56lckF505, in colony formation. Cells bearing p59hckF501 had increased levels of protein phosphotyrosine. The ability of p59hckF501 to transform NIH 3T3 cells was abolished by a second mutation believed to destroy the ATP-binding domain.

Portal vein thrombosis causing neonatal cerebral infarction.

Neonatal cerebral infarction often occurs in the absence of known risk factors. Two such cases are described in which portal vein thrombosis was documented during two dimensional echocardiography. In both cases, infarcts were consistent with embolic events. A novel mechanism is proposed, which may explain some cases of "idiopathic" neonatal cerebral infarction.

Immunosuppressive measles encephalitis.

A case of immunosuppressive measles (rubeola) encephalitis in a 12-year-old boy in remission from acute lymphoblastic leukemia is described. The patient presented with focal seizures which led to epilepsia partialis continua and then progressive obtundation. Magnetic resonance imaging revealed focal abnormalities, predominantly in the cortex, that on light and electron microscopic examination were demonstrated to be highly localized areas of neuronal loss, gliosis, and secondary Wallerian degeneration with paramyxovirus inclusions in the oligodendrocytes and surviving neurons.

Lck plays a critical role in Ca(2+) mobilization and CD28 costimulation in mature primary T cells.

To investigate the signaling function of the Src-family protein tyrosine kinase Lck in mature T cells, we generated transgenic mice that expressed Lck in thymocytes but not in peripheral lymphocytes. We compared the phenotype and signaling capacity of Lck-deficient T cells with T cells from mice expressing a dominant inhibitory form of Lck and found that both mouse strains have diminished numbers of mature CD8(+) T cells and respond poorly to CD28 costimulation. However, while T cells that lack Lck fail to mobilize Ca(2+) after stimulation, those expressing the dominant negative protein do so normally. Our data demonstrate that Lck plays several unique roles in mature lymphocyte signaling.

Positive and negative selection of thymocytes depends on Lck interaction with the CD4 and CD8 coreceptors.

Considerable evidence supports a role for the Src family protein tyrosine kinase Lck in regulating multiple aspects of thymocyte development. In this report, we establish that early events in T lymphopoiesis are restored to Lck-deficient mice by provision of a transgene encoding a version of Lck that cannot interact with the coreceptors CD4 and CD8. In addition, we demonstrate that later events in thymocyte development, specifically, the processes of positive and negative selection, are compromised in mice where the only Lck available cannot associate with either CD4 or CD8. We conclude that not only is Lck activity required for positive and negative selection, but that that activity must be coupled to the CD4 and CD8 coreceptors.

Cerebrospinal fluid hypoxanthine and xanthine concentrations as indicators of metabolic damage due to raised intracranial pressure in hydrocephalic children.

Intracranial pressure and cerebrospinal fluid hypoxanthine and xanthine concentrations were measured in hydrocephalic children with suspected raised intracranial pressure. There was a highly significant correlation between intracranial pressure and cerebrospinal fluid hypoxanthine and xanthine levels.

Childhood moyamoya presenting as dementia: report of a case.

A case is presented of moyamoya disease in an Anglo-Saxon child whose principal clinical feature, uniquely, was dementia. CT findings were unexplainable so angiography was performed. Moyamoya is an angiographic entity which has been associated with a wide variety of conditions. No satisfactory hypothesis has yet emerged to link these conditions or to explain the predilection of the Japanese for this disease.

Protein tyrosine kinase p56lck controls allelic exclusion of T-cell receptor beta-chain genes.

During T-cell development, site-specific DNA rearrangements mediating assembly of beta- and alpha-chain genes of the T-cell receptor (TCR) are developmentally ordered. In particular, assembly and expression of a complete beta-chain gene blocks further rearrangements at the beta-locus (a process referred to as allelic exclusion) and drives the generation and expansion of CD4+8+ cells. Although the mechanism used by TCR beta chains to deliver such signals is unknown, studies in transgenic animals have suggested that the lymphocyte-specific protein tyrosine kinase p56lck may impinge on a similar signalling pathway. The hypothesis that TCR beta chains deliver intracellular signals via p56lck makes an explicit prediction: that interference with p56lck function will mitigate the effects of a simultaneously expressed TCR beta chain. Here we confirm this prediction through examination of allelic exclusion in mice expressing both a functional TCR beta chain transgene and a catalytically inactive form of p56lck.

A dominant-negative transgene defines a role for p56lck in thymopoiesis.

The lymphocyte-specific protein tyrosine kinase p56lck participates in T cell signaling through functional interactions with components of the T cell antigen receptor complex and the interleukin-2 receptor. Additional insight into the function of p56lck has now been obtained through the generation of transgenic animals expressing high levels of a catalytically inactive form of this kinase (p56lckR273). Mice bearing the lckR273 transgene manifested a severe defect in the production of virtually all T lymphocytes. Those exceptional CD3+ cells that escaped the effects of the lckR273 transgene were confined primarily to the T cell subset that expresses gamma/delta T cell receptors. Remarkably, construction of a dose-response curve for the effects of the lckR273 transgene revealed that developmental arrest of thymocytes occurred at a discrete stage in the normal T cell maturation pathway, corresponding to a point at which thymoblasts ordinarily begin a series of mitotic divisions that result in expansion and maturation. These results suggest that p56lck normally regulates T cell production by metering the replicative potential of immature thymoblasts.

Cerebrospinal fluid myelin basic protein immunoreactivity as an indicator of brain damage in children.

Cerebrospinal fluid (CSF) myelin basic protein (MBP) was measured blind by double antibody competitive inhibition radioimmunoassay (RIA) in 20 children who had seizures and 17 children with hydrocephalus. MBP values correlated with clinical outcome and mean maximum intracranial pressure (ICP) in the hydrocephalic group, and with type of convulsion in the epileptic group. A value of 20ng/ml or more was regarded as significantly raised. A significant rise in MBP levels could be demonstrated in those with ICP alone and in patients with additional problems, whose levels tended to be even higher. Hydrocephalic children with normal ICP and children with seizures had similar normal MBP levels, and in the latter group clinical outcome was not related to MBP levels. For individual patients CSF MBP is of little value as a prognostic indicator, or as a method of quantifying cerebral damage.

Referral patterns of family physicians may allow population-based incidence studies of childhood epilepsy.

PURPOSE: To evaluate the burden of illness of childhood epilepsy on patient, care giver, and society, representative incidence cohorts must be followed longitudinally. Case ascertainment through pediatricians and neurologists would be a valid method if family physicians refered all new cases of childhood epilepsy. The study objective was to determine whether family physicians' referral patterns in Southwestern Ontario make it possible to conduct a population-based incidence study of childhood epilepsy by sampling only from specialists' practices. METHODS: Of the 1,718 family physicians practicing in Southwestern Ontario, a systematic sample participated in a mailed survey. Case simulations describing seven types of childhood seizures were presented to physicians with instructions to respond as to whether they would investigate/manage without referral; refer to a specialist only if problems occurred; or refer to a specialist always. RESULTS: Of 214 family physicians, 185 (86.4%) returned completed surveys; 86% would not refer a child with a febrile seizure. Referral to a specialist would be made always by 93% of family physicians for patients with status epilepticus, 95% for worsening partial epilepsy, 82% for a first, brief, generalized clonic seizure, 80% for absence epilepsy, and 99% for neonatal seizures. Only 50% of family physicians would always refer a neurodevelopmentally abnormal child with generalized clonic epilepsy, but a further 37% would refer if problems occurred. CONCLUSIONS: It is feasible to recruit a representative population-based cohort of recently diagnosed patients for epidemiologic studies of childhood epilepsy by surveying pediatricians and neurologists. These survey results could be used to adjust estimates of incidence obtained through specialists' practices for the bias in case ascertainment that may result from this practical method.

Thymic tumorigenesis induced by overexpression of p56lck.

The lck gene encodes a membrane-associated protein tyrosine kinase (p56lck) that is believed to participate in lymphocyte-specific signal transduction pathways. To investigate the function of this molecule, transgenic mice were generated carrying the wild-type lck gene or a mutated lck gene encoding a constitutively activated form of p56lck (p56lckF505). Transgene expression in thymocytes was achieved in each case using the lck proximal promoter element. Mice expressing high levels of either p56lckF505 or p56lckY505 reproducibly developed thymic tumors. The sensitivity of thymocytes to p56lck-induced transformation suggests that disturbances in lck expression may contribute to the pathogenesis of some human neoplastic diseases.

Anatomical validation of middle cerebral artery position as identified by transcranial pulsed Doppler ultrasound.

The basal cerebral arteries were insonated using transcranial pulsed Doppler ultrasound (TPDU) at 2 MHz. The Doppler sample volume (SV) depths at which signals were obtained which could be attributed to the middle, anterior and posterior cerebral arteries (MCA, ACA and PCA) were compared with measurements in adult cadavers and with B-scan ultrasound studies in infants. The depth of the internal carotid artery (ICA) terminal division into ACA and MCA was closely correlated for both groups. In adults, it was found at 5.6 +/- 1.0 cm using TPDU while in cadavers it was found at 5.3 +/- 0.5 cm from the temporal bone. In infants, it was found at 3.2 +/- 0.3 cm for the right side, and 3.2 +/- 0.2 cm for the left side using TPDU, and at 3.4 +/- 0.4 cm and 3.4 +/- 0.5 cm for right and left sides respectively using B-scan ultrasound. The mean depth of the MCA mid-point in infants as defined by TPDU and B-scan was also closely correlated, with values of 2.8 +/- 0.3 cm and 2.7 +/- 0.3 cm for right and left sides respectively using TPDU and of 2.8 +/- 0.4 cm and 2.7 +/- 0.4 cm for right and left sides respectively using B-scan ultrasound. Values for the most lateral part of the MCA did not correlate. In adults, signals from the ACA and PCA were obtained at greater SV depth than the MCA, thus preventing confusion.