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Biomedical subjects

N Tiffin

Publications and source records attributed to N Tiffin.

14 recordsLinked to original sources
PubMed2003

PAX7 expression in embryonal rhabdomyosarcoma suggests an origin in muscle satellite cells.

Rhabdomyosarcoma (RMS) is a common paediatric soft tissue sarcoma that resembles developing foetal skeletal muscle. Tumours of the alveolar subtype frequently harbour one of two characteristic translocations that juxtapose PAX3 or PAX7, and the forkhead-related gene FKHR (FOXO1A). The embryonal subtype of RMS is not generally associated with these fusion genes. Here, we have quantified the relative levels of chimaeric and wild-type PAX transcripts in various subtypes of RMS (n=34) in order to assess the relevance of wild-type PAX3 and PAX7 gene expression in these tumours. We found that upregulation of wild-type PAX3 is independent of the presence of either fusion gene and is unlikely to contribute to tumorigenesis. Most strikingly, upregulated PAX7 expression is almost entirely restricted to cases without PAX3-FKHR or PAX7-FKHR fusion genes and may contribute to tumorigenesis in the absence of chimaeric PAX transcription factors. Furthermore, as myogenic satellite cells are known to express PAX7, this pattern of PAX7 expression suggests this cell type as the origin of these tumours. This is corroborated by the detection of MET (c-met) expression, a marker for the myogenic satellite cell lineage, in all RMS samples expressing wild-type PAX7.

Animals↗
PubMed2001

High levels of the MDM2 oncogene in paediatric rhabdomyosarcoma cell lines may confer multidrug resistance.

The MDM2 protein is known to be overexpressed in some sarcomas including rhabdomyosarcoma. However, the extent to which the MDM2 protein influences sensitivity to chemotherapeutic drugs is unclear. We have analysed this further using stable transfection of the mdm2 gene into 4 well-characterised human paediatric rhabdomyosarcoma cell lines. Transfection with the mdm2 gene resulted in increased levels of the MDM2 protein in all the cell lines. In 2 of the lines, SCMC and RD, the mdm2 gene caused between 2-fold and 61-fold increase in resistance to vincristine, etoposide and doxorubicin but not to cisplatin. In these lines there was an increase in expression of the mdr-1 gene which encodes P-glycoprotein, but not the mrp1 gene which encodes the multidrug resistance protein (MRP). The resistance was reversible using the MDR modulator PSC833, confirming the presence of P-glycoprotein. We conclude that MDM2 overexpression may be a mechanism by which multidrug resistance is regulated in some rhabdomyosarcomas.

ATP Binding Cassette Transporter, Subfamily B, Mem↗
PubMed2001

Comparative expressed sequence hybridization to chromosomes for tumor classification and identification of genomic regions of differential gene expression.

Altered expression of genes can have phenotypic consequences in cancer development and treatment, developmental abnormalities, and differentiation processes. Here we describe a rapid approach, termed comparative expressed sequence hybridization (CESH), which gives a genome-wide view of relative expression patterns within tissues according to chromosomal location. No prior knowledge of genes or cloning is required, and minimal amounts of tissue can be used. Expression profiles are achieved in a manner similar to the identification of chromosomal imbalances by comparative genomic hybridization analysis. The approach is demonstrated to indicate a chromosomal region that harbors overexpressed genes that may be associated with a drug-resistant phenotype. In addition, known and new regions of differential gene expression in both normal tissues and tumor samples from the soft tissue sarcoma group of rhabdomyosarcoma (RMS) are indicated. These regions included 2p24; overexpression of MYCN at 2p24 was confirmed by quantitative reverse transcription-PCR for all of the alveolar RMS cases and did not necessarily correspond to genomic amplification. Evidence including region specific microarray analysis indicated that overexpression of several genes from a region may be required for detection by CESH. This evidence is consistent with clusters of functionally related genes and mechanisms that affect the expression of a number of genes at a particular genomic location. The distinctive CESH profiles demonstrated in different subtypes of RMS show potential for tumor classification.

Chromosomes, Artificial, Yeast↗
PubMed2001

In vitro prevention of the emergence of multidrug resistance in a pediatric rhabdomyosarcoma cell line.

We have established preclinical models for the development of drug resistance to vincristine (a major drug used in the treatment of pediatric rhabdomyosarcoma) using cell lines. The RD cell line has a mutant P53 phenotype and does not have detectable P-glycoprotein (P-gp) or multidrug resistance-related protein (MRP) despite expressing low levels of mdr-1 mRNA, which encodes P-gp and mrp1 mRNA. Resistant variants of RD were derived by exposure to increasing concentrations of vincristine. This was repeated on six occasions, resulting in three cell lines which could tolerate 64 x the IC(50) concentration. Six independent agents were tested for their ability to prevent the development of resistance in this model. Despite at least 10 attempts, resistance did not develop in the presence of the multidrug resistance (MDR) modulators PSC833, VX710, and XR9576. This strongly suggests that these agents may delay or even prevent the development of resistance to vincristine. This was also confirmed in a second rhabdomyosarcoma cell line, Rh30. In contrast, the agents indomethacin (MRP1 modulator), CGP41251 (protein kinase C inhibitor), and dexrazoxane (putative MDR prevention agent) did not affect the development of resistance in the RD model. Characterization of the resistant cell lines indicated the presence of increased mdr-1 and P-gp expression, which resulted in resistance to the agents doxorubicin, etoposide, and vincristine but not cisplatin. The resistance could be modulated using PSC833 or VX710, confirming that functional P-gp is present. No apparent differences were seen between the resistant cell lines derived in the absence and presence of the various agents. These experiments strongly suggest that the development of MDR may be preventable using modulators of MDR and merit clinical studies to test this hypothesis.

ATP Binding Cassette Transporter, Subfamily B, Mem↗
PubMed1993

An evaluation of the physical and functional characteristics of infant resuscitators.

Self-inflating resuscitators (SIRs) are commonly used to assist ventilation in the newborn. Despite their widespread use, there is limited information available on the functional and physical characteristics of SIRs. We studied five new infant bag-valve units to compare their physical characteristics, including reservoir, accumulator, and dead space volumes (VD), pressure relief mechanism (PRM), inspiratory resistance (RI), and functional mechanics including stroke volume (SV), fraction of delivered oxygen (FDO2), and cycle frequency at -5 degrees C, 20 degrees C, and 49 degrees C, using a test lung apparatus and experienced respiratory therapists. In addition, deficiencies and features that may render them less than ideal were sought. All SIRs met minimum standards for reservoir and accumulator volumes, RI (< 20 cmH2O/L/sec), SV (20-70 ml), and FDO2 (> 90%) as determined by the Canadian Standards Association (CSA) and the American Society for Testing of Materials (ASTM). However, the following deficiencies were noted: 1) MPR and Pulmanex had no PRM (ASTM requirement); 2) MPR could not cycle at -5 degrees C; 3) the VDs for Pulmanex (10 ml) and MPR (15 ml) were high; 4) the CPR connector broke during normal use, and the MPR connector frequently disconnected; 5) the Laerdal expiratory valve was incompetent; and 6) the Laerdal and CPR could be misassembled for use. Our study shows that some commercially available SIRs do not meet all CSA and ASTM standards and may not be ideal in specific clinical situations. The choice of a SIR may be dictated by the clinical situation in which its use is intended.

Equipment Design↗
PubMed1992

Relationship of cross-brain oxygen content difference, cerebral blood flow, and metabolic rate to neurologic outcome after near-drowning.

We evaluated the relationship of global cerebral blood flow, cross-brain oxygen content difference, cerebral metabolic rate for oxygen, intracranial pressure, and cerebral perfusion pressure to functional neurologic outcome in 12 comatose children on 2 consecutive days after near-drowning. Five children survived with functional neurologic outcome; five died and two survived with severe neurologic damage. Children who survived with functional neurologic outcome had a significantly higher cross-brain oxygen content difference (7.89 +/- 2.62 vs 3.91 +/- 1.59 ml/dl; p = 0.028) at 24 hours and a higher cerebral metabolic rate for oxygen 48 hours after admission (3.19 +/- 2.86 vs 0.96 +/- 0.45 ml/100 gm per minute; p = 0.030) compared with those who died or survived in a damaged state. There were no significant differences in global cerebral blood flow, intracranial pressure, and cerebral perfusion pressure between groups at either 24 or 48 hours. Our preliminary data suggest that a higher cross-brain content difference value is an important early variable associated with functional neurologic recovery after near-drowning. However, a single cross-brain oxygen content difference value must be interpreted with caution because considerable variability may occur among patient groups.

Adolescent↗
PubMed1992

An evaluation of the physical and functional characteristics of resuscitators for use in pediatrics.

OBJECTIVE: To evaluate the physical and functional characteristics of pediatric self-inflating resuscitators. DESIGN: Tested under simulated clinical conditions. Results were analyzed by descriptive analysis. SETTING: A pulmonary laboratory in a university hospital. METHODS: Eight new pediatric self-inflating resuscitators were obtained from the manufacturers and evaluated for functional characteristics including: a) fraction of delivered oxygen at 10 L/min and a tidal volume of 300 mL; b) maximum stroke volume against no resistance; and c) maximum cycling frequency at -5 degrees C, 20 degrees C, and 48 degrees C. The resuscitators were also evaluated for physical characteristics, including potential for misassembly, pressure relief valves, expiratory valve leak, and inspiratory resistance. RESULTS: All resuscitators met the minimum standards of the Canadian Standards Association and American Standards for Testing of Materials. However, one bag cycled at only 32 breaths/min at -5 degrees C, marginally within accepted standards. Only five self-inflating resuscitators had pop-off valves. These valves malfunctioned, with valve activation occurring well above the accepted standards. Three of the self-inflating resuscitators could be misassembled for use. Four of the resuscitators were unable to deliver tidal volumes required for preoxygenation in a 20-kg child. CONCLUSIONS: While these self-inflating resuscitators met the minimum standards, they are all unable to deliver 100% oxygen. One unit is probably not appropriate in the out-of-hospital setting when ambient temperatures are less than 0 degrees C. Those resuscitators that can be misassembled are dangerous in unskilled hands. In addition, reliance on pop-off valve activation to limit airway pressure is dangerous.

Child↗
PubMed1991

Evaluation of performance characteristics of disposable bag-valve resuscitators.

OBJECTIVE: To evaluate the performance characteristics of disposable bag-valve resuscitators. DESIGN: Single and multitrial tests under simulated clinical conditions. Results of multitrial tests were analyzed by multivariate analysis of variance. SETTING: A pulmonary laboratory in a university hospital. METHODS: We evaluated eight DRs to determine: a) physical characteristics, including the potential for misassembly; b) FIO2 of 1.0 and flow rates of 10 L; c) tidal volume (VT) (male and female operators) using one and two hands; and d) cycling rates at 5 degrees, 20 degrees, and 48 degrees C. RESULTS: All resuscitators met the minimum requirements of the Canadian Standards Association and the American Society for Testing and Materials. However, the CPR and LSP could be assembled incorrectly for use. Three units (B Sav, Pulm, and MPR) delivered significantly less than 80% oxygen (overall p less than .05). Significant increases were seen in VT using two hands vs. one hand (1176 vs. 960 mL, p less than .001) and males vs. females using two hands (1284 vs. 1102 mL, p less than .02). One unit (B Sav) could only be used with two hands. The maximum cycling rates for all units increased significantly (p less than .05) with an increase in temperature from -5 degrees to 20 degrees to 40 degrees C. However, two units (Bag E and MPR) failed to deliver 20 breaths/min at -5 degrees C, while the B Sav and Pulm valves became dysfunctional at 48 degrees C. CONCLUSIONS: While these DRs meet the minimum standards, they should be chosen carefully and evaluated before application in the clinical environment.

Disposable Equipment↗
PubMed1991

Physiological responses to endotracheal and oral suctioning in paediatric patients: the influence of endotracheal tube sizes and suction pressures.

OBJECTIVE: To study the influence of varying outer suction catheter (SC) diameter (OD) to inner endotracheal tube (ETT) diameter (ID) and suction pressures (SP) on heart rate (HR), respiratory rate (RR), mean arterial pressure (MAP), arterial oxygen saturation (SaO 2) and intracranial pressure (ICP) during ETT and oral suctioning. An additional aim was to define an optimal suction catheter size that would prove easy to introduce and be rapidly effective in clearing secretions with the least physiological alteration. DESIGN: Prospective study. SETTING: Paediatric intensive care unit. PATIENTS: Ventilated paediatric patients. INTERVENTION: Patients had ETT suctioning performed in a random fashion using suction catheters with SC outer diameter to inner ETT diameter of approximately 0.4, 0.7 and 0.9 using varying pressures (80, 100, 120 mmHg). Using the medium size suction catheter (OD/ID = 0.7) at 100 mmHg of suction pressure, oral suctioning was compared to ETT suctioning. MEASUREMENTS AND MAIN RESULTS: Seventeen patients were studied (age 6.5 + 5 months). All suction catheters at varying pressures resulted in similar transient alterations in HR, RR, MAP, SaO 2 and ICP following ETT suctioning. Significant changes were seen in SaO 2, HR and ICP, irrespective of the catheter diameter or suction pressure. Oral suctioning resulted in similar trends and magnitude of changes as for ETT suctioning in MAP, RR, HR, and ICP, but less change occurred in the SaO 2 (p less than 0.05). The catheters with OD/ID of 0.7 were easiest to introduce and most effective in clearing secretions. CONCLUSION: Our study suggests that: 1. Tracheal toilet using variations in OD/ID ratios and SP within limits tested resulted in similar significant adverse changes in HR, ICP and SaO 2 and similar trends in RR and MAP. 2. Based on the ease of introduction and the effectiveness of clearing secretions, a medium SC (OD/ID = 0.7) is most appropriate for infants and children. 3. Oral suctioning also results in adverse physiological changes, therefore similar precautions to those taken during tracheal suctioning should be followed for oral suctioning.

Blood Pressure↗
PubMed1990

Prototype volume-controlled resuscitator for neonates and infants.

Twenty-five infants receiving assisted ventilation in an ICU were manually ventilated for 5-min periods using either a new prototype volume-controlled resuscitator (VCR) or a standard self-inflating resuscitator (SIR). Variables monitored during these 5-min periods included heart rate, respiratory rate, mean arterial pressure, mean airway pressure (Paw), end-tidal CO2 (PetCO2), pulse oximetry oxygen saturation, PaO2, and PaCO2. Significant differences in posttrial values for the following variables were: a) PetCO2 (31.2 +/- 9.1 vs. 25.6 +/- 8.2 torr, p less than .001); b) PaCO2 (38.0 +/- 4.9 vs. 33.2 +/- 6.7 torr, p less than .01); and c) pH (7.4 +/- 0.6 vs. 7.5 +/- 0.1, p less than .04) at comparable Paw (9.5 +/- 7.6 vs. 8.0 +/- 6.0, NS). Eighty-four percent (21/25) of infants in the VCR group had normal PaCO2 values (35 to 45 torr) while only 44% (11/25) in the SIR group achieved normocarbia (p less than .001). Measurements of the highest (Pmax) and lowest (Pmin) inspiratory pressure (cm H2O) in 15 patients demonstrated marked variation in Pmax with the SIR. Differences in Pmax (SIR minus VCR) were significant (10.8 +/- 3.7, p less than .02) but not in Pmin (0.5 +/- 3.5, NS). Our study demonstrates that ventilation with the VCR resulted in less hyperventilation with minimal pressure variability as compared with the SIR. Further studies in the neonate are warranted.

Equipment Design↗
PubMed1989

Jugular venous bulb catheterization in infants and children.

Cross-brain oxygen extraction may be altered by coma, hyperventilation, hypothermia, or barbiturates, and has been demonstrated in adults and more recently in children to be related to functional neurologic recovery after a variety of brain injuries. However, measurement of cross-brain oxygen extraction in children is currently not a part of routine clinical care, partly because there have been no published attempts relating the technique of jugular venous bulb (JVB) catheterization and its complication in children. We catheterized the JVB to measure cerebral venous oxygen content and calculate cross-brain oxygen extraction in 26 deeply comatose neonates and children ranging in age from a few hours to 14 yr. Bedside catheterization using the Seldinger technique was successful in 25 children, with standard venous cutdown necessary in the remaining child. All JVB catheterizations were performed with parental consent and during continuous monitoring of the intracranial (ICP) or fontanelle, as well as arterial, pressure. ICP was not significantly altered by the cannulation procedure in any of the children studied, although the cannulation occurred early in the child's course when ICP was well controlled. Inadvertent carotid artery puncture with bleeding controlled by local pressure occurred in four children, and catheter malposition was confirmed on lateral skull xray in two others. Jugular venous bulb catheters remained in place for 2 to 7 days (average 3) and malfunction or obstruction of the catheter did not occur. Organisms were grown from three of 26 catheter tips submitted for culture, with peripheral blood cultures also positive for the same organisms in two of these.(ABSTRACT TRUNCATED AT 250 WORDS)

Adolescent↗
PubMed1989

Effects of hyperventilation, hypothermia, and altered blood viscosity on cerebral blood flow, cross-brain oxygen extraction, and cerebral metabolic rate for oxygen in cats.

Therapies including hyperventilation (HV) and hypothermia (HT) are currently simultaneously used in brain-injured children at risk for cerebral swelling to reduce cerebral blood flow (CBF) and alter cerebral metabolic rate for oxygen (CMRO2). Since HV and HT may contribute to significant patient morbidity, we evaluated the effects of these treatments in combination on CBF, CMRO2, and cross-brain oxygen extraction (CBO2) using the Kety-Schmidt technique before controlled bleeding to alter blood viscosity in 20 lightly anesthetized, paralyzed cats, and after bleeding in another 17 cats. The degree of HV (PaCO2 24 to 26 torr) and HT (32 degrees and 30 degrees C) used were representative of that employed in pediatric neurointensive care. HV at normothermia resulted in a significant decline in CBF (P less than .05) and an unchanged CMRO2. HV and HT together to 32 degrees C resulted in a further significant fall in CBF and CMRO2 (p less than .05), but an unchanged CBO2. Further cooling of the animal to 30 degrees C during HV, both before and after controlled bleeding, resulted in no further significant fall in CBF, CBO2, or CMRO2. This relationship was found despite a significant fall in Hgb (p less than .001), suggesting that blood viscosity did not significantly influence CBF at this temperature. Our data suggest that HT to 32 degrees C during HV may have therapeutic benefit by decreasing CBF and CMRO2, but further cooling to 30 degrees C may not result in further cerebral protective effects.

Animals↗
PubMed1988

Prototype volume-controlled neonatal/infant resuscitator.

Face mask or bag endotracheal tube manual ventilation of neonates and infants has relied primarily on the use of self-inflating resuscitation devices (SIRs). While SIRs have the advantage of being simple to use and, therefore, require minimal training, recent research has demonstrated significant drawbacks to these devices. These drawbacks have included their large physical size, the tendency of such devices to cause significant hyperventilation, and the extreme variability of pressures necessary to activate the pop-off valve safety feature. This latter problem is especially serious in the infant where large pressure variations may increase the potential for pulmonary barotrauma. In an attempt to minimize the disadvantages of SIRs, we developed a prototype volume-controlled resuscitation device (VCD). We then compared the VCD to the SIRs in a cat model using blinded volunteer health care personnel previously familiar with SIRs only. Ventilation of the cat with the VCD yielded arterial and end-tidal CO2 values more closely resembling the physiologic state at a lower mean airway pressure. The data suggest that a human trial of manual ventilation with the prototype VCD is warranted.

Animals↗