Moving beyond threshold-based dichotomous classification to improve the accuracy in classifying non-responders

We examined maximal oxygen consumption responses following exercise training to demonstrate the limitations associated with threshold‐based dichotomous classification of responders and non‐responders and proposed alternative methods for classification. Specifically, we: 1) calculated individual probabilities of response, and 2) classified individuals using response confidence intervals (CI) and reference points of zero and a smallest worthwhile change of 0.5 METs. Our findings support the use of individual probabilities and individual CIs to improve the accuracy in non‐response classification.

Does blood lactate predict the chronic adaptive response to training: A comparison of traditional and talk test prescription methods

The purpose of this study was to test the hypotheses (i) that interindividual variability in acute blood lactate responses during exercise at 65% of peak work rate (WR_peak; relative WR_peak protocol (REL)) will predict variability in the chronic responses to exercise training and (ii) that exercising at an intensity that causes uncomfortable speech production (negative talk test (TT) stage (NEG)) elicits high acute blood lactate responses and large adaptations to training. Twenty-eight participants completed 4 weeks of exercise training consisting of REL (n = 14) or NEG (TT, n = 14). Fifteen additional participants were assigned to a no-exercise control group (n = 15). In REL, acute blood lactate responses during the first training session significantly predicted changes in peak oxygen consumption (r = 0.69) after training. TT resulted in consistently high acute blood lactate responses. REL and TT improved (p < 0.05) peak oxygen consumption, WR_peak, and work rate at the onset of blood lactate accumulation (WR_OBLA). Despite nonsignificance, small to medium between-group effect sizes for changes in peak oxygen consumption, WR_peak, and WR_OBLA and a higher work rate, heart rate, rating of perceived exertion, and blood lactate during training at NEG support the potential superiority of TT over REL. When exercise is prescribed using a traditional method (a fixed percentage of WR_peak; REL), acute metabolic stress may partly explain the variance in the adaptations to training. In addition, TT elicited significant increases in peak oxygen consumption, WR_peak, and WR_OBLA, and although our small sample size limits our ability to confidently compare training adaptations between groups, our preliminary results suggest that future investigations with larger sample sizes should assess the potential superiority of TT over REL.

The internet as a source of support for youth with chronic conditions: A qualitative study

BACKGROUND

Adolescents living with chronic conditions often portray themselves as "healthy" online, yet use the Internet as one of their top sources of health information and social communication. There is a need to develop online support programs specific to adolescents with chronic conditions in order to provide a private space to discuss concerns. This paper endeavors to increase our understanding of the online support needs and wants of these adolescents and their interest in and preferences for an online support program.

METHODS

A qualitative descriptive study using semistructured interviews was completed. Stratified purposive sampling was utilized to ensure a representative sample based on age and diagnosis. English speaking adolescents (aged 12-18 years) diagnosed with a chronic condition were recruited from clinic and inpatient areas across 3 paediatric hospitals in Canada.

RESULTS

Thirty-three participants aged 15.3 ± 1.8 years (64% female) completed the study. The main topics identified were (a) the purpose of current online activity, (b) the benefits and challenges of existing online supports, and (c) a description of ideal online resources. The purpose of online activity was social networking, information, online gaming, and social support. When accessing health information online, participants prioritized websites that were easy to access and understand despite the trustworthiness of the site. The reported benefits and challenges varied across participants with many areas perceived as both a benefit and a challenge. The majority of participants were interested in participating in an online support program that included both accurate disease-related information and a community of other adolescents to provide social support.

CONCLUSIONS

Adolescents with chronic conditions are interested in online support that encompasses health information and social support that is flexible and easy to navigate. Findings can be used to develop or adapt existing online support programs for adolescents with chronic conditions to help increase engagement and utilization.

The development of bone mineral lateralization in the arms

Bone mineral content (BMC) is known to be greater in the dominant arm after the age of 8 years. We studied a group of children and found that BMC sidedness gradually increased up to the age of 6 years and then remained stable into late adolescence.

INTRODUCTION

Bone mineral content (BMC) exhibits sidedness in the arms after the age of 8 years, but it is not known whether BMC is greater in the dominant arm from birth or whether lateralization develops in early childhood. To address this, we examined bone mineral status in relation to handedness and age.

METHODS

Subjects (N = 158) were children recently initiating glucocorticoids for underlying disease (leukemia 43 %, rheumatic conditions 39 %, nephrotic syndrome 18 %). Handedness was determined by questionnaire and BMC by dual-energy X-ray absorptiometry.

RESULTS

Median age was 7.2 years (range, 1.5 to 17.0 years), 49 % was male, and the spine BMD Z-score was -0.9 (SD, 1.3). By linear regression, BMC sidedness in the arms was significantly related to age (r = 0.294, p = 0.0005). Breakpoint analysis revealed two lines with a knot at 6.0 years (95 % CI, 4.5-7.5 years). The formula for the first line was: dominant:nondominant arm BMC ratio = 0.029 × age [in years] + 0.850 (r = 0.323, p = 0.017). The slope of the second line was not different from 0 (p = 0.332), while the slopes for the two lines were significantly different (p = 0.027).

CONCLUSIONS

These results show that arm BMC sidedness in this patient group develops up to age 6 years and then remains stable into late adolescence. This temporal profile is consistent with mechanical stimulation of the skeleton in response to asymmetrical muscle use as handedness becomes manifest.

Permeation properties of the hair cell mechanotransducer channel provide insight into its molecular structure

Mechanoelectric transducer (MET) channels, located near stereocilia tips, are opened by deflecting the hair bundle of sensory hair cells. Defects in this process result in deafness. Despite this critical function, the molecular identity of MET channels remains a mystery. Inherent channel properties, particularly those associated with permeation, provide the backbone for the molecular identification of ion channels. Here, a novel channel rectification mechanism is identified, resulting in a reduced pore size at positive potentials. The apparent difference in pore dimensions results from Ca(2+) binding within the pore, occluding permeation. Driving force for permeation at hyperpolarized potentials is increased because Ca(2+) can more easily be removed from binding within the pore due to the presence of an electronegative external vestibule that dehydrates and concentrates permeating ions. Alterations in Ca(2+) binding may underlie tonotopic and Ca(2+)-dependent variations in channel conductance. This Ca(2+)-dependent rectification provides targets for identifying the molecular components of the MET channel.

Prevalent vertebral fractures among children initiating glucocorticoid therapy for the treatment of rheumatic disorders

OBJECTIVE

Vertebral fractures are an under-recognized problem in children with inflammatory disorders. We studied spine health among 134 children (87 girls) with rheumatic conditions (median age 10 years) within 30 days of initiating glucocorticoid therapy.

METHODS

Children were categorized as follows: juvenile dermatomyositis (n = 30), juvenile idiopathic arthritis (n = 28), systemic lupus erythematosus and related conditions (n = 26), systemic arthritis (n = 22), systemic vasculitis (n = 16), and other conditions (n = 12). Thoracolumbar spine radiograph and dual x-ray absorptiometry for lumbar spine (L-spine) areal bone mineral density (BMD) were performed within 30 days of glucocorticoid initiation. Genant semiquantitative grading was used for vertebral morphometry. Second metacarpal morphometry was carried out on a hand radiograph. Clinical factors including disease and physical activity, calcium and vitamin D intake, cumulative glucocorticoid dose, underlying diagnosis, L-spine BMD Z score, and back pain were analyzed for association with vertebral fracture.

RESULTS

Thirteen vertebral fractures were noted in 9 children (7%). Of these, 6 patients had a single vertebral fracture and 3 had 2-3 fractures. Fractures were clustered in the mid-thoracic region (69%). Three vertebral fractures (23%) were moderate (grade 2); the others were mild (grade 1). For the entire cohort, mean +/- SD L-spine BMD Z score was significantly different from zero (-0.55 +/- 1.2, P < 0.001) despite a mean height Z score that was similar to the healthy average (0.02 +/- 1.0, P = 0.825). Back pain was highly associated with increased odds for fracture (odds ratio 10.6 [95% confidence interval 2.1-53.8], P = 0.004).

CONCLUSION

In pediatric rheumatic conditions, vertebral fractures can be present prior to prolonged glucocorticoid exposure.

Strength training by children and adolescents

Pediatricians are often asked to give advice on the safety and efficacy of strength training programs for children and adolescents. This review, a revision of a previous American Academy of Pediatrics policy statement, defines relevant terminology and provides current information on risks and benefits of strength training for children and adolescents.

Organized sports for children and preadolescents

Participation in organized sports provides an opportunity for young people to increase their physical activity and develop physical and social skills. However, when the demands and expectations of organized sports exceed the maturation and readiness of the participant, the positive aspects of participation can be negated. The nature of parental or adult involvement can also influence the degree to which participation in organized sports is a positive experience for preadolescents. This updates a previous policy statement on athletics for preadolescents and incorporates guidelines for sports participation for preschool children. Recommendations are offered on how pediatricians can help determine a child's readiness to participate, how risks can be minimized, and how child-oriented goals can be maximized.

An interaction between PPADS, an ATP antagonist, and a moderately intense sound in the cochlea

In the organ of Corti ionotropic receptors for ATP (ATPRs) on cells that are bathed by perilymph have been suggested to modulate cochlear mechanics. The purpose of the present study was to test the hypothesis that endogenous extracellular ATP acting through ATPRs is involved in modulating cochlear mechanics during moderately intense sound exposure. Guinea pigs were exposed to either: (1) a perilymphatic administration of pyridoxal-phosphate-6-azophenyl-2', 4'-disulfonic acid (PPADS, 1 mM), an ATP antagonist; (2) a moderately intense sound (6.7 kHz tone, 95 dB SPL, 15 min); or (3) a combination of both the PPADS and the sound. The effects on cochlear potentials (cochlear microphonic, CM; negative summating potential, SP; compound action potential of the auditory nerve, CAP; and N(1) latency) evoked by a 10 kHz tone pip were monitored. PPADS alone reduced the CAP and the SP and increased N(1) latency. The intense sound alone reduced the CAP and SP. The combination of PPADS with the intense tone induced reversible effects on cochlear potentials that were greater than induced by either treatment alone. The effect on N(1) latency and low intensity CM was a potentiation since the effect was greater than a simple addition of the effect of either treatment alone. The effects of the combination treatment on CAP, SP and high intensity CM were not different from additive. Results are consistent with the hypothesis that ATPRs in the organ of Corti are involved in modulating cochlear mechanics during moderately intense sound exposure.

Pig fetal septal neurons implanted into the hippocampus of aged or cholinergic deafferented rats grow axons and form cross-species synapses in appropriate target regions

The anatomical specificity of axon growth from fetal pig septal xenografts was studied by transplanting septal cells from E30-35 pig fetuses into cholinergic deafferented (192-IgG-saporin-infused) rats or into aged rats (> 18 months). Cell suspensions (100,000 cells/microl) were injected bilaterally into the dorsal and ventral hippocampus of immunosuppressed rats (10 mg/kg/day cyclosporine A). To assess axonal growth and synapse formation, acetylcholinesterase histochemistry, an antibody to choline acetyltransferase (ChAT), and three pig-positive/rat-negative antibodies: bovine 70kD neurofilament (NF70), human low-affinity NGF receptor (hNGFr), and human synaptobrevin (hSB) were used. In rats with surviving grafts at 6 months, NF70 axonal labeling was more extensive than either ChAT or hNGFr labeling. All three markers demonstrated graft axons extending selectively through the hippocampal CA fields and the molecular layer of the dentate gyrus. Graft axons did not extend into adjacent entorhinal cortex or neocortex. The distribution of pig hSB-positive synapses correlated with AChE-positive fiber outgrowth in to the host. Electron microscopic analysis of hSB-immunostained hippocampal sections revealed pig presynaptic terminals in contact with normal rat postsynaptic structures in the CA fields and the dentate gyrus. These data demonstrate target-appropriate growth of pig cholinergic axons and the formation of cross-species synapses in the deafferented or aged rat hippocampus.

Differences in the distribution of responses to ATP and acetylcholine between outer hair cells of rat and guinea pig

Adenosine 5' triphosphate (ATP) and acetylcholine (ACh) are neurotransmitters (ACh) and/or modulators (ATP) in the mammalian cochlea. In guinea pig, it appears that both neurotransmitters have a similar response distribution, with larger responses being evoked by the ligands in short hair cells compared to long hair cells (e.g., Chen et al., 1995b. Noise exposure alters the response of outer hair cells to ATP. Hear. Res. 88, 215-221.; Erostegui et al., 1994. In vitro pharmacologic characterization of a cholinergic receptor on outer hair cells. Hear. Res. 74, 135 147). The purpose of the present study was to test whether the distribution of responses to ACh and ATP in the OHCs of rat is the same as guinea pig. The ligand-induced current was monitored using the whole-cell configuration of the patch-clamp technique. Results show that in guinea pig OHCs, extracellular application of 100 microM ATP induced a current response in a majority of the same cells that responded to the application of 100 microM ACh. In contrast in rat OHCs, 100 microM ATP did not induce a current in the majority of cells that responded to the application of 100 microM ACh. N-methyl-glucamine (NMG+) substituted for K+ in the pipette solution failed to unmask an ATP-evoked inward current in rat OHCs. In addition, no response was produced in rat or guinea pig OHCs by adenosine, adenosine 5'-monophosphate (AMP) or adenosine 5'-diphosphate (ADP) at 100 microM. Results suggest that in guinea pig ACh-gated channels are present on most of the same OHCs that have ATP-gated ion channels, whereas in rat ACh-gated ion channels are present without ATP-gated channels on some OHCs.

Differences in cholinergic responses from outer hair cells of rat and guinea pig

A cholinergic receptor on outer hair cells (OHC) in guinea pig cochlea induces a K+ current when it is activated by acetylcholine and suberyldicholine but not by nicotine or muscarine (Bobbin, 1995). This unusual receptor may contain an alpha 9-subunit. However, the pharmacology of the alpha 9-subunit cloned from rat and expressed in Xenopus oocytes does not completely match that obtained for the ACh receptor in guinea pig OHCs. The response to 1,1-dimethyl-4-phenylpiperazinium (DMPP) is large in guinea pig OHCs and small in oocytes containing receptors of the alpha 9-subunit. Therefore, we compared the effects of cholinergic receptor agonists in rat and guinea pig OHCs using the whole-cell variant of the patch-clamp technique. ACh caused the largest outward K+ current in OHCs from both rat and guinea pig. Carbachol- and suberyldicholine-induced responses were similar in magnitude in OHCs of rat and guinea pig. However, DMPP produced a small response in OHCs from rat and a large response in OHCs from guinea pig. At a concentration of 100 microM, muscarine, oxotremorine M, nicotine and cytisine induced little response in guinea pig OHCs and none in rat OHCs. Results suggest that the ACh receptor on rat OHCs is similar to the alpha 9-subunit-containing receptor expressed in oocytes but different from the ACh receptor on guinea pig OHCs.

Evidence that glutathione is the unidentified amine (Unk 2.5) released by high potassium into cochlear fluids

An unidentified substance, Unk 2.5, may be important in the function of the cochlea. The efflux of Unk 2.5 into cochlear fluids is increased by intense sound (Bobbin and Fallon, 1992) and by exposure of the cochlear tissue to high concentrations of K+ (Bobbin et al., 1990,1991; Bobbin and Fallon, 1992). The unidentified chemical eluted at 2.5 min in chromatograms obtained by HPLC utilizing fluorescence detection and precolumn o-phthalaldehyde (OPA) derivatization of samples of effluent from the cochlea (e.g., Bobbin et al., 1990). The purpose of this investigation was to provide evidence as to the identity of this unidentified chemical we call Unk 2.5. Therefore, we carried out additional HPLC assays on samples obtained during perfusion of the cochlear perilymph compartment. Glutathione (GSH) was found to elute at the same time (@ 2.5 min) as Unk 2.5 in HPLC chromatograms utilizing precolumn derivatization with OPA and mercaptoethanol. In addition, both Unk 2.5 and GSH reacted with OPA without mercaptoethanol present in the reaction mixture to give a peak at 2.5 min in the chromatogram, but failed to show this peak if stored in solutions with a pH > 7 for several days before the reaction. Results indicate that Unk 2.5 is GSH or a closely related compound. Given this probable identification GSH, aka Unk 2.5, has been demonstrated to be released from tissue in the cochlea by high concentrations of K+ (Bobbin et al., 1990,1991) and by intense sound (124 dB SPL; Bobbin and Fallon, 1992).