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Biomedical subjects

A Spitzer

Publications and source records attributed to A Spitzer.

At least 19 recordsLinked to original sources
PubMed1992

Illness and treatment appraisal processes of healthy and hemophilic boys.

The purposes of this study was to describe patterns characterizing appraisal processes of chronically ill and healthy school-age boys regarding illness and treatment situations. The specific aims were to describe (a) the domains representing the process of appraisal, (b) the relationships among the domains, and (c) the patterns of appraisal based on the interplay among the various domains. The sample included 18 healthy boys and 18 hemophilic boys. The two groups were matched on the basis of child's age and family socioeconomic level. A qualitative methodology was used to understand the ways in which boys appraise illness- and treatment-related stimuli. Findings showed that appraisal processes of school-age boys were comprised of four interacting domains: delineation of the context, fears related to the stimuli, the emotional response to the stimuli, and the final decision. The characteristics of these domains and the relationships among them resulted in two patterns of appraisal: amplification and minimization.

Adaptation, Psychological↗
PubMed1992

The influence of the shape of mechanical stimuli on muscle stretch reflexes and SEP.

Stretching of human thenar muscle was carried out using mechanical stimuli of different amplitudes and velocities in 50 normal subjects. Amplitudes of early M1 and late M2 reflex responses as well as cortical evoked potentials were recorded. M1 and M2 increased with a larger mechanical stimulus. Steeper mechanical stimuli generated larger M1 amplitudes, whereas M2 remained unaffected. Amplitudes of early cortical evoked potentials increased with increase of both rise-time and amplitude of muscle stretch. The shape of the mechanical stimulus is critical for the resulting reflex response. The different behaviours of M1 and M2 with increasing stimulus velocity are in favour of their different origins. Our results support a participation of slowly conducting muscle spindle afferents in the generation of the late M2 response in distal human hand muscles.

Adult↗
PubMed1992

Results of a randomized clinical trial of medical versus surgical management of infants and children with grades III and IV primary vesicoureteral reflux (United States). The International Reflux Study in Children.

A total of 132 infants and children with grades III and IV primary vesicoureteral reflux was entered into a prospective trial comparing medical to surgical management. Inclusion criteria were an age not exceeding 10 years and a glomerular filtration rate of at least 70 ml. per minute per 1.73 m.2. Children with significant urinary tract malformations and clinical signs/symptoms of dysfunctional voiding were not accepted into the trial. Medical therapy consisted of continuous low dose antibiotic prophylaxis until vesicoureteral reflux resolved. The type of surgical procedure used for the correction of reflux was left to the discretion of the surgeon. Outcome variables included the appearance or progression of renal lesions, rate of renal growth, recurrence rate of urinary tract infection or pyelonephritis, changes in total kidney glomerular filtration rate, development of hypertension and resolution rate of vesicoureteral reflux. Followup at 6, 18, 36 and 54 months after entry included, in addition to history and physical examination, voiding cystourethrography, excretory urography and a urine culture. Of the patients 68 were allocated to the medical group and 64 to the surgical group. They were stratified for age, sex and preexisting renal scarring. Of the patients 10% were boys, 47% were between 2 and 6 years old at entry, 93% had a history of pyelonephritis, 67% had either scarring or thinning of the parenchyma at entry, 87% had grade IV vesicoureteral reflux in at least 1 unit and 56% had bilateral reflux. There were no significant differences in the frequency distribution of entry characteristics between the patients allocated to either group. New renal scarring developed in 22% of medical and 31% of surgical patients (p < 0.4). Growth of kidneys with grade IV vesicoureteral reflux was slightly less than normal in the medical (-0.67 +/- 0.15 standard deviation) and surgical (-0.42 +/- 0.11 standard deviation) groups (p < 0.7). Pyelonephritis occurred in 15 medical patients versus 5 surgical patients (p < 0.05). There was no significant change in glomerular filtration rate within each treatment group and no difference in glomerular filtration rate between groups. No patient had hypertension during the followup period. The disappearance rate of vesicoureteral reflux in patients with grade IV reflux was approximately 8% per year. Of the medical patients 75% still had vesicoureteral reflux after 3 years of observation.(ABSTRACT TRUNCATED AT 400 WORDS)

Child↗
PubMed1992

Children's knowledge of illness and treatment experiences in hemophilia.

The purpose of this study was to describe what children with hemophilia understand about their unique illness and treatment experiences. Subjects included 20 children with hemophilia between the ages of 6 years and 13 years who had no evidence of cognitive problems. Following the principles of grounded theory, data about children's experiences of hemophilia and their understanding of these experiences were obtained through a semistructured interview using five pictorial stimuli representing illness and treatment domains. Data analysis was conducted using the constant comparative method. Children's knowledge was described in regard to (a) the nature of hemophilia and its origin, (b) the major illness experience: bleeding, (c) the nature of treatment and its purpose, and (d) the major treatment experience: poking. Findings indicated that although school-aged children with hemophilia were engaged actively in gaining knowledge about their disease and treatment, the overall level of understanding of children aged 6 years to 13 years did not follow a distinct path of development. Major areas of knowledge deficiency included knowledge about how one contracts hemophilia and the purpose of treatment.

Adolescent↗
PubMed1991

Motor potentials evoked in tibialis anterior by single and paired cervical stimuli in man.

Latencies of compound muscle action potentials evoked in lower limb muscles after transcranial stimulation shorten and amplitudes enlarge when the target muscle is contracted. After transcutaneous stimulation of the cervical cord with single electrical stimuli, the latency is not affected by muscle contraction. This is thought to be due to a lack of temporal summation at the spinal motoneurones. Results are different when paired stimuli are used. With contraction most motoneurones respond to the first cervical stimulus while in a relaxed condition they respond to the second. Temporal summation brings motoneurones to their firing threshold. Therefore, cervical double stimulation is more effective than single stimuli. It is however less powerful than cortical stimulation. Paired stimuli are most powerful at an interval of 2 ms similar to the D I-wave interval after cortical stimulation.

Action Potentials↗
PubMed1991

Renal protein synthesis in diabetes mellitus: effects of insulin and insulin-like growth factor I.

Is increased synthesis of proteins responsible for the hypertrophy of kidney cells in diabetes mellitus? Does the lack of insulin, and/or the effect of insulin-like growth factor I (IGFI) on renal tubule protein synthesis play a role in diabetic renal hypertrophy? To answer these questions, we determined the rates of 3H-valine incorporation into tubule proteins and the valine-tRNA specific activity, in the presence or absence of insulin and/or IGFI, in proximal tubule suspension isolated from kidneys of streptozotocin diabetic and control rats. The rate of protein synthesis increased, while the stimulatory effects of insulin and IGFI on tubule protein synthesis were reduced, early (96 hours) after induction of experimental diabetes. Thus, hypertrophy of the kidneys in experimental diabetes mellitus is associated with increases in protein synthesis, rather than with decreases in protein degradation. Factor(s) other than the lack of insulin, or the effects of IGFI, must be responsible for the high rate of protein synthesis present in the hypertrophying tubules of diabetic rats.

Animals↗
PubMed1991

Changes in NMR-visible kidney cell phosphate with age and diet: relationship to phosphate transport.

To test the hypothesis that growth and dietary Pi affect the intracellular concentration of Pi ([Pi]i) as well as its renal reabsorption, we measured nuclear magnetic resonance (NMR)-visible [Pi]i in isolated perfused kidneys of less than 1- and greater than 4-wk-old guinea pigs fed various amounts of Pi. Changes in [Pi]i were correlated with those in fractional Pi reabsorption (FRPi) in vivo and in capacity (Vmax) for Na(+)-Pi cotransport in microvilli derived from animals of similar age and fed the same diets. In animals fed normal (0.76% Pi) diet, [Pi]i was lower (0.91 +/- 0.14 vs. 1.85 +/- 0.23 mM, P less than 0.05), whereas FRPi was higher (0.90 +/- 0.02 vs. 0.70 +/- 0.03, P less than 0.01) in less than 1- than in greater than 4-wk-old guinea pigs. Pi deprivation decreased [Pi]i in mature animals to 0.74 +/- 0.29 mM, P less than 0.05, and increased FRPi to 0.99 +/- 0.01. Excess dietary Pi increased [Pi]i in immature animals to 1.67 +/- 0.56 mM, P less than 0.05, and decreased FRPi to 0.55 +/- 0.03. Diet-induced changes in [Pi]i were associated with reciprocal changes in Vmax of similar absolute magnitude in immature and mature animals. However, diets that resulted in comparable [Pi]i at the two ages were associated with higher (P less than 0.05) Vmax in less than 1- than in greater than 4-wk-old animals. The reciprocal nature of the relationship between [Pi]i and renal Pi transport indicates that [Pi]i is primarily determined by Pi efflux from the cells or Pi organification rather than Pi influx through Na(+)-Pi cotransport. Findings indicate that changes in [Pi]i with growth or diet may be a cause but cannot be the consequence of changes in abundance or maximal mobility of Na(+)-Pi cotransporters. Data also indicate that factors in addition to low [Pi]i contribute to the high Na(+)-Pi cotransport capacity observed in renal microvilli of growing animals.

Aging↗
PubMed1991

[Magnetic stimulation using double coils--methodology and normal findings].

Magnetic stimulation of the motor cortex and spinal nerve roots was investigated in a group of 45 normal subjects using double coils. Figure of eight coils allows for an isolated excitation of the motor cortex of one hemisphere which cannot be achieved with circular coils. To evoke compound responses in hand muscles the optimal position of the figure of eight coil is with its centre about 5 cm lateral of the vertex and contralateral to the target muscle. The coil handle is in frontal position (occipito-frontal direction of the stimulation current in the coil; physical current definition is used resembling the electron flow from - to +). For the excitation to leg muscles the double coil centre is over the vertex with the handle contralateral to the target muscle (frontal current direction). Cervical roots can easily be stimulated using figure of eight coils with the handle contralateral to the target muscle and the coil centre over the root segment.

Adult↗
PubMed1990

NMR studies of phosphate metabolism in the isolated perfused kidney of developing rats.

During growth, the capacity for renal phosphate (Pi) reabsorption varies as a function of Pi demand. These changes occur in the absence of changes in extracellular concentration of Pi and are also observed in renal cells cultured in defined media. These findings suggest a direct regulatory effect of intracellular Pi on its transport systems. We postulate that a low intracellular Pi concentration [( Pi]i) occurs in the developing kidney as a consequence of differences in Pi metabolism between growing and mature cells and that a low [Pi]i, in turn, leads to adaptive changes in renal Pi transport. In order to assess this hypothesis, we used 31P-nuclear magnetic resonance (NMR) to measure the intracellular concentrations of NMR-visible Pi and phospho-metabolites and the rates of Pi turnover due to adenosine triphosphate (ATP) synthesis, in isolated perfused kidneys of 3- to 4-week-old and 12- to 13-week-old rats. The [Pi]i was lower (1.7 +/- 0.1 vs 2.7 +/- 0.1 mM, P less than 0.05) in kidneys of growing than of adult rats, while the ATP (2.9 +/- 0.3 vs 2.8 +/- 0.5 mM) and adenosine diphosphate (ADP) (-0.2 mM) concentrations were similar at the two ages, consistent with a high phosphorylation potential in the kidneys of the younger animals. Radiofrequency irradiation of the gamma-P of ATP resulted in reduction in the intensity of the Pi resonance of 62 +/- 5% in the newborn and 38 +/- 3% in the adult (P less than 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)

Adenosine Triphosphate↗
PubMed1990

The influence of stimulus type on the magnetic excitation of nerve structures.

The voltage measured was that induced in a measuring coil from 3 different commercially available magnetic stimulators. The strongest stimulus was from the Cadwell, followed by Novametrix and then Digitimer. The Digitimer and Novametrix produced a monophasic pulse, whilst the Cadwell stimulator produced a polyphasic pulse, all measured by an induction coil. This is thought to be the reason why reversed coil polarity does not influence the position of peripheral nerve excitation with a Cadwell stimulator; this is, however, the case with the two other magnetic stimulators. Nevertheless, electrical stimulation was found to be the most useful method for exciting peripheral nerves. The lack of influence of Cadwell coil polarity on the excitation of spinal roots and motor cortex is also thought to be due to the bipolar stimulus effect mentioned above. The stimuli induced by Digitimer and Novametrix are monophasic, exciting one hemisphere first, depending on the direction of the current impulse. The stimulus generated by Cadwell excites both hemispheres by reversal of current direction.

Electric Stimulation↗
PubMed1990

Measurement of stress in clinical nursing.

The Nurse Stress Checklist was developed to measure stress in clinical nursing as a multidimensional construct. The instrument was formulated within a transactional model of stress. The items were derived from five domains thought to contribute to nurse stress in clinical settings and were organized into a questionnaire. Holmes Schedule of Recent Events was included as a validity measure. The instrument was tested on 104 staff nurses working in three institutions in an urban community. Exploratory factor analysis was applied to the 74 items presented to subjects in Likert-type format. Five factors were derived and subjected to psychometric evaluation. Internal consistency reliability for the five factors was good, ranging from 0.80 to 0.91. Means and measures of dispersion supported the potential of the five subscales to discriminate among respondents on the attributes being measured. Intercorrelations of the factors provided evidence of the distinctiveness of the five components of stress, although factor loadings showed some overlap between Personal Reactions and Work Concerns and Work Concerns and Work Completion Concerns. Validity of the factors also was supported by correlations with Holmes' Schedule of Recent Events. Content validity was supported by comparison of these results with findings of other investigators. Limitations of the results are discussed, and recommendations for future work on the instrument are offered.

Adult↗
PubMed1989

Correlation of structure and function in developing proximal tubule of guinea pig.

Unlike the case in rat, rabbit, and other species in which nephron formation continues into the newborn period, nephrogenesis in the guinea pig is completed well before the time of birth. Therefore, the marked increase in proximal tubule reabsorption that occurs during the postnatal period in that species can be attributed entirely to an increase in the absorptive capacity of existing nephron units. The purpose of the present morphometric studies was to correlate that change in proximal tubule function with changes in the apical and basolateral cell membrane surface areas. The apical and basolateral membrane surface densities were found to be approximately equal to each other and to remain constant throughout development. Because of increasing tubule volume, however, both membranes doubled in size between 1 and 3 wk of age and eventually increased by a factor of 3.5 in the adult. At the same time, there was little change in the length of tight function complexes measured in the plane of the luminal surface. Using previously published functional data and tubule length data, a good correlation was found between absolute absorption and total basolateral membrane surface area throughout the entire period of development in proximal tubules. Absorption per unit area of basolateral membrane was approximately 0.55, 0.41, 0.56, and 0.42 X 10(-6) nl.min-1.micron-2 in the 1st, 2nd, and 3rd wk, and in adult animals, respectively, and thus was similar to that reported for proximal tubule segments of adult rabbit and juvenile to adult rat.

Absorption↗
PubMed1989

Renal reabsorption of phosphate during development: transport kinetics in BBMV.

The mechanism responsible for enhanced reabsorption of phosphate (Pi) in growing animals was assessed in renal brush-border membrane vesicles (BBMV) prepared from 3- to 14-day-old and greater than 57-day-old guinea pigs. On standard diet, Vmax (pmol.mg-1.s-1) of Na+-Pi cotransport was higher (P less than 0.001) in newborn (650 +/- 77) than in adult (144 +/- 17) but Vmax of Na+-glucose cotransport did not differ with age. Low dietary Pi did not affect significantly Vmax of Na+-Pi cotransport in the newborn (P greater than 0.8) but increased it in the adult (to 318 +/- 32, P less than 0.05). A high Pi intake resulted in a smaller relative decrease in Vmax in the newborn than in the adult (27 vs. 44%, P less than 0.05). In the newborn, the serum Pi (mM) decreased on a low-Pi diet (from 1.8 +/- 0.1 to 0.8 +/- 0.1, P less than 0.001) and rose by twofold on the high-Pi diet (to 3.5 +/- 0.2, P less than 0.001). In the adult, there were no significant changes in serum Pi with changes in Pi intake (P greater than 0.5). Thus in the newborn the Na+-Pi cotransport system is characterized by high transport capacity but low adaptability to changes in dietary Pi.

Aging↗
PubMed1988

NMR measurements of intra- and extravesicular sodium in renal microvilli.

Previous attempts to separate the nuclear magnetic resonances of intra- and extravesicular Na+ in brush-border membrane vesicles (BBMV) were unsuccessful and led to the proposal of rapid exchange of Na+ via sodium channels in BBMV. However, passive conductance of Na+ in this membrane has been found to be relatively small. This inconsistency prompted us to use a different shift reagent to reassess the issue. In guinea pig renal BBMV (15-30 mg protein/ml) equilibrated with Na+ (130 mequiv. 1), using the impermeant Na+ shift reagent dysprosium tripolyphosphate (3 mM), the resonances of intra- (3.3%) and extravesicular (96.7%) Na+ were resolved by 6 ppm. Increases in Na+ conductance induced by gramicidin D did not alter the characteristics of intra- and extravesicular Na+ resonances. By contrast, addition of glucose caused a transient increase in the area of the intravesicular Na+ resonance. The clear separation between the intra- and the extravesicular Na+ resonances allowed us to measure the relaxation times of Na+, which depend on its interactions with its immediate environment. The longitudinal relaxation time of intravesicular Na+ (13 +/- 1 ms) was much shorter than that of the extravesicular Na+ (44.0 +/- 0.4 ms). Thus, in intact renal BBMV, as well as in membranes treated with the cationophore gramicidin D, the exchange of Na+ between the intra- and the extravesicular compartments is slow on the NMR time scale, consistent with the low Na+ channel density of this membrane. In contrast, the increase in intravesicular Na+ induced by glucose, is consistent with a significant contribution of the glucose cotransport pathway to Na+ flux across these membranes. The short longitudinal relaxation time of Na+ in the intravesicular space indicates interaction of Na+ with BBMV binding sites or ordering of these ions in the intravesicular compartment.

Alkaline Phosphatase↗
PubMed1988

The relationship between renal metabolism and proximal tubule transport during ontogeny.

The proximal tubules of newborn and adult animals reabsorb a similar fraction of the filtered load of Na+ and H2O (65%-70%). In tubules from adult animals, transcellular, active Na+ reabsorption accounts for one-third of the total, while two-thirds occur passively through the paracellular pathway, driven by hydrostatic and oncotic forces (one-third) and by cell-generated effective osmotic and ionic gradients (one-third). Since two-thirds of the Na+ is reabsorbed passively and does not require energy, the mature proximal tubule has a high Na+/O2 molar ratio (48 Eq of Na+/mol of O2). Measurements of ouabain-sensitive oxygen consumption in suspensions of proximal tubules indicate that in newborn, aerobic metabolism can support about 50% of the net Na+ transport rate compared with the 33% in tubules from adult animals. Independent confirmation of the direct and proportional relationship between active Na+ transport and ouabain-sensitive O2 consumption exists for the adult but not for the newborn. However, measurements of epithelial conductances and of transepithelial hydrostatic and oncotic pressure differences indicate that passive paracellular fluxes can account for the remaining 50% of the proximal Na+ reabsorption in newborn. The high permeability of the proximal tubules of newborn animals to small molecular weight solutes suggests that cell-generated osmotic and ionic transepithelial gradients are minimal in the tubules of newborn animals. Yet in the newborn, the osmolality of the end proximal tubule fluid was found to exceed that in plasma. This indicates that osmotic gradients due to differences in reflection coefficients for preferentially reabsorbed solutes and Cl- do exist across the proximal tubules of the newborn and suggests that these gradients may contribute to Na+ and H2O reabsorption. If this is indeed the case, then the contribution of active and of hydrostatic and oncotic pressure-driven flows to the overall reabsorption of Na+ and fluid has been overestimated. Resolution of this discrepancy requires measurements of the reflection coefficients for HCO3- and Cl- in the proximal tubule of the newborn. The metabolic processes by which energy is supplied to renal proximal cells during development are also incompletely characterized. There is evidence that maturation of aerobic metabolism, Krebs cycle enzymes activity, and of the mitochondrial membrane surface area precede the development of net reabsorptive transport (Na+, H2O, HCO3, glucose). By contrast, maturation of Na(+)-K(+)-ATPase activity at the basolateral cell membrane follows that in reabsorptive transport and does not limit its development.(ABSTRACT TRUNCATED AT 400 WORDS)

Adult↗
PubMed1988

Renal reabsorption of phosphate during development: tubular events.

Studies performed in our laboratory on the isolated perfused kidney of the guinea pig have demonstrated that the rate of Pi reabsorption is substantially greater in the newborn than in the adult, when appropriate corrections are being made either for differences in glomerular filtration rate (GFR) or in renal tubular mass. In order to determine the location of this enhanced reabsorption along the nephron, micropuncture experiments were performed on euvolemic, non-fasted guinea pigs 5-14 and 42-49 days of age, maintained on standard guinea-pig chow diet (0.76% Pi). Concomitant measurements of overall kidney function were also obtained. The results confirmed that fractional reabsorption of Pi (TRPi%) across the entire kidney was significantly higher (P less than 0.01) in the newborn (89.93 +/- 2.55%) than in the adult (78.25 +/- 2.89%) animals. The difference was also significant (P less than 0.05) when TRPi was expressed in mol/ml GFR (1.87 +/- 0.14 vs 1.53 +/- 0.12, respectively). At comparable locations along the proximal tubule (TF/Pin of 1.90 +/- 0.16 in the newborn, and 1.79 +/- 0.15 in the adult, P greater than 0.70), the fraction of the filtered load of Pi reabsorbed was significantly higher (P less than 0.001) in the immature (76.66 +/- 2.74%) than in the mature (67.21 +/- 2.74%) guinea pigs. Estimates based on the differences between proximal Pi reabsorption and the urinary excretion of Pi indicate that the reabsorption of Pi in tubular segments located beyond the proximal tubule is also enhanced in the newborn when compared with the adult (15.62 +/- 2.11% vs 10.51 +/- 1.83%, respectively, P less than 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗