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Biomedical subjects

J Schaeffer

Publications and source records attributed to J Schaeffer.

12 recordsLinked to original sources
PubMed1992

Colour Doppler ultrasound assessment of arteriovenous haemodialysis fistulas.

Satisfactory function of the arteriovenous fistula (AVF) is essential for adequate haemodialysis in patients with chronic renal failure. Existing methods to assess AVF function are imprecise (eg, clinical examination) or invasive (eg, angiography). We assessed the value of colour flow-doppler ultrasound (CFDU) in the investigation of clinically suspected AVF dysfunction. 51 patients with suspected impairment of AVF function were studied by CFDU, and 28 also underwent angiography. The findings were compared with the reference standard of the findings at reoperation. CFDU showed AVF stenoses in 18 patients, which were all confirmed at reoperation; the results of angiography in 13 of these 18 patients showed complete agreement with the findings of CFDU and surgery. CFDU showed partial or complete AVF thrombosis in 33 patients, confirmed in all patients at reoperation; 15 patients also underwent angiography, and thrombi were not found in 6 (in 4 because of technical failure). 7 patients had aneurysms on CFDU that were confirmed by surgery in all patients and by angiography in 2 of the 3 patients studied. CFDU enables reliable non-invasive assessment of AVF morphology and function and may become the procedure of choice for AVF assessment in patients with suspected AVF abnormalities.

Adult↗
PubMed1992

Inpatient group processes parallel unit dynamics.

The authors conducted a quantitative examination of parallels between milieu and therapy group dynamics on a short-term inpatient unit. The Ward Atmosphere Scale was used to assess the milieu, and the Group Climate Questionnaire-S to measure processes in key groups. Assessments were made by patients and staff once each week for 10 months. The authors found clear parallels between ward and therapy group processes. The parallels reflected the impact of patterns utilization of the unit, its treatment philosophy, and the emotional dynamics of its constituents. Examination of these associations also revealed limitations of the treatment setting, clarified the potential impact of particular staff interventions, and demonstrated biases in the rating methods. Study of parallel process on the psychiatric unit is a rich source of information on the nature of inpatient treatment.

Adolescent↗
PubMed1990

Hypocalcemia and hypercalcitoninemia in critically ill children.

To study Ca metabolism in critically ill children, we measured ionized Ca (Ca2+), parathyroid hormone (PTH), calcitonin, 25 hydroxycholecalciferol (25[OH] D3), 1-25 dihydroxycholecalciferol (1-25[OH]2D3, and gastrin levels in critically ill children and in healthy controls. Patients were considered hypocalcemic if Ca2+ was less than 1.1 mmol/L. Six (14%) of 45 patients were hypocalcemic. Five hypocalcemic patients were studied and were found to have higher calcitonin levels than normocalcemic patients and healthy controls and higher PTH levels than healthy controls. 25(OH)D3 and 1-25(OH)2D3 were not significantly different in the three groups of patients. Gastrin levels were low in critically ill patients, whether or not they were hypocalcemic. We conclude that hypocalcemia occurs frequently in critically ill children. It is associated with raised levels of calcitonin and PTH. The mechanism for the increase in calcitonin is unknown.

Acute Disease↗
PubMed1989

The influence of the transmembrane sodium gradient on the responses of pulmonary arteries to decreases in oxygen tension.

A Na/Ca exchange system has been demonstrated in systemic vascular smooth muscle and has been suggested as a mechanism for the entry and extrusion of Ca2+. Using isolated rings of bovine intrapulmonary arteries, we sought to determine whether a Na/Ca exchange mechanism is present in pulmonary vascular smooth muscle, and if so, whether it contributes to the modulation of vascular tone during hypoxia. Under both normoxic (PO2 greater than or equal to 120 mm Hg) and hypoxic (PO2 less than or equal to 40 mm Hg) conditions, the amplitude of the 40 mM K+ contraction was significantly (p less than 0.005) enhanced when most of the external Na+ was replaced with N-methylglucamine (NMG) (Na+ = 1.2 mM). The rate of contraction was also increased by replacing Na+ with NMG during normoxia (1.02 +/- 0.24 to 2.52 +/- 0.57 mg/mg weight/s, p less than 0.005) and hypoxia (1.72 +/- 0.74 to 4.08 +/- 1.63 mg/mg weight/s, p less than 0.05). Although the relaxation rate was slowed in the low Na+ media during normoxia (3.48 +/- 1.07 with Na+ versus 2.58 +/- 0.81 mg/mg weight/s with NMG, p less than 0.02), it was unaltered during hypoxia (3.15 +/- 0.90 with Na+ versus 2.95 +/- 0.83 mg/mg weight/s with NMG, p = 0.3). The ratio of relaxation rates in the normal and low Na+ media correlated with the perfusate PO2 (r = 0.76, p less than 0.001). During normoxia and hypoxia, inhibition of the Na+,K+ pump by strophanthidin, which increases intracellular [Na+], reversibly enhanced the amplitude of the K+ contraction, even when the voltage-gated channels were blocked with verapamil.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1988

Relationship of dialysis modality and other factors to cognitive function in chronic dialysis patients.

To determine if dialysis modality may be an independent factor in the level of cognitive function in chronic dialysis patients, cognitive function was studied in 17 pairs of continuous ambulatory peritoneal dialysis (CAPD) and center hemodialysis (CHD) subjects matched for sex, age, diabetic status, and interval since dialysis onset. Data on current metabolic, medical, psychological, and vocational function status were obtained. Neuropsychological (NP) measures included the Number Cancellation Protocol (NCP), Trailmaking test forms A and B (TMT A, TMT B), Symbol Digit Modalities (SDM), and the Rey Auditory Verbal Learning Test (RAVLT). The CAPD subject group had consistently more efficient cognitive function than the CHD subject group. Regardless of modality, the groups of subjects under age 51 and those who were vocationally active had significantly better NP performance. No cognitive function differences were found in groups categorized by sex or duration of dialysis. Creatinine levels were more highly correlated with NP scores than were BUN levels, with higher creatinine levels associated with better cognitive function. Serum calcium, CO2, total protein, albumin, and SGOT levels also were correlated with NP scores. CAPD may be more effective than HD in reversing uremic encephalopathy by mechanisms mostly unrelated to serum creatinine and BUN levels. Longitudinal studies will be needed to determine if dialysis modality is an independent factor in the degree of reversal of uremic encephalopathy.

Adult↗
PubMed1988

Role of sarcoplasmic reticulum in arterial contraction: comparison of ryanodines's effect in a conduit and a muscular artery.

Ryanodine interferes with sarcoplasmic reticulum function in various types of muscle; in vascular smooth muscle, it can inhibit contractions that depend on sarcoplasmic reticulum calcium release, probably by depleting the sarcoplasmic reticulum calcium store. We tested ryanodine and calcium channel blockers (verapamil, diltiazem, and nitrendipine) on small rings of rat thoracic aorta (RA) and bovine tail artery (BTA) to determine the relative contributions of sarcoplasmic reticulum calcium release and gated calcium entry to contractions induced by norepinephrine, caffeine, and 100 mM K depolarization. Ryanodine blocked caffeine contractions in both tissues and attenuated norepinephrine responses (by 52% in RA, 14% in BTA) but minimally altered potassium contractions. Calcium channel blockers almost completely abolished potassium contractions and reduced norepinephrine contractions (by 45% in RA, 82% in BTA) but hardly affected caffeine responses. The blocking effects of ryanodine and calcium channel antagonists on the norepinephrine responses were additive. Ryanodine had no effect on baseline tension in the standard media; however, when calcium extrusion via Na-Ca exchange was inhibited by low external sodium (0-calcium, low-sodium solution), tension increased progressively after introduction of ryanodine. This indicates that the sarcoplasmic reticulum calcium released by ryanodine then accumulated in the cytosol and activated contraction; restoration of external sodium caused prompt relaxation. The smaller effects of caffeine and ryanodine in BTA indicate that sarcoplasmic reticulum plays a less important role in calcium control in this tissue, with gated calcium entry dominating. These functional findings are correlated with electron-microscopic evidence that BTA has about 60% less sarcoplasmic reticulum than does RA. Ryanodine appears to be a useful tool for determining the functional relevance of sarcoplasmic reticulum for contraction in different arterial smooth muscles.

Alkaloids↗
PubMed1987

Differences in matrix vesicle concentration among growth plate zones.

We studied the proximal tibial growth plates of 15-day-old mice to determine if matrix vesicle concentration varies among growth plate zones or between the pericellular and territorial matrix compartment and the interterritorial matrix compartment. Growth plates were examined by electron microscopy and divided into five zones: reserve zone (RZ), upper proliferative zone (UPZ), lower proliferative zone (LPZ), upper hypertrophic zone (UHZ), and lower hypertrophic zone (LHZ) which included the calcifying zone. We measured the diameter and volume fraction of matrix vesicles and calculated their numerical density and volume per cell and number per cell in the pericellular and territorial matrix and in the interterritorial matrix of each zone. In the pericellular and territorial matrix compartment, the matrix vesicle concentration progressively decreased from the RZ to the LHZ. Changes in matrix vesicle concentration in the interterritorial matrix followed a different pattern. Between the RZ and the UPZ, matrix vesicle numerical density declined slightly and then increased to peak values in the LPZ and UHZ, followed by a decline between the UHZ and the LHZ. These changes in matrix vesicle concentration paralleled previously reported changes in intramitochondrial calcium content, suggesting that matrix vesicle production in growth plate may be related to intracellular calcium concentration. The existence of the maximum concentration of matrix vesicles in the LPZ and UHZ longitudinal septa which do not mineralize followed by a decline in matrix vesicle concentration in the LHZ longitudinal septa which mineralize suggests that a high concentration of matrix vesicles may be needed to prepare the matrix for mineralization or to initiate mineralization and that matrix vesicles are depleted during mineralization.

Animals↗
PubMed1986

Morphometric analysis of chondrocyte hypertrophy.

In the hypertrophic zone of the cartilaginous growth plate, chondrocytes enlarge, assume a more spherical shape, and form a population of cells called the hypertrophic chondrocytes. The mechanisms that are involved in the formation of hypertrophic chondrocytes are poorly understood. Cell hypertrophy usually refers to an increase in cell size and volume associated with an increase in organelles. In this study, we sought to determine whether the formation of hypertrophic chondrocytes represents true cell hypertrophy associated with an increase in organelles or whether it is due to swelling and fluid accumulation. Morphometric analyses of electron micrographs were carried out to determine changes in cell number, cell volume, cell organelle volumes, and matrix volumes in the reserve zone, upper proliferative zone, lower proliferative zone, upper hypertrophic zone, and lower hypertrophic zone. Between the upper proliferative zone and the lower hypertrophic zone, the cells increased their mean volume more than 500 per cent. As they enlarged, their matrices altered; territorial matrix volume increased as its collagen content decreased, and interterritorial matrix volume decreased as its collagen content increased between the lower proliferative zone and the lower hypertrophic zone. Between the upper proliferative zone and the lower hypertrophic zone, the absolute volume per cell of endoplasmic reticulum, Golgi membranes, and mitochondria increased 126 per cent, while the volume of cytoplasm and nucleoplasm increased 779 per cent, apparently by accumulation of water. Cell organelles of the lower hypertrophic zone did not show the changes that are associated with cell injury or death. Thus, the synthesis of organelles contributed to chondrocyte enlargement, but the primary mechanism of cell enlargement was cytoplasmic and nuclear swelling.

Animals↗
PubMedDate not supplied

Platelet free calcium concentrations measured with fura-2 are influenced by the transmembrane sodium gradient.

The influence of the transmembrane Na+ gradient on the intracellular free calcium concentration, [Ca2+]i, was studied in Sepharose gel-filtered platelets from healthy human subjects, using the Ca-sensitive fluorescent dye, fura-2. Raising the internal Na+ concentration, [Na+]i, by Na+ pump inhibition with 0.05 mM ouabain, without changing external Na+ did not cause a significant increase in [Ca2+]i. Substitution of extracellular Na+ by iso-osmolar sucrose induced a rapid (half-time about 2 min) and significant rise in [Ca2+]i; this effect was amplified in Na-loaded platelets. Partial restitution of external Na+ in these cells with increased [Ca2+]i promoted a significant and rapid Na+ concentration-dependent fall in [Ca2+]i; little decline in [Ca2+]i was observed if K+ was used instead of Na+. These observations represent in vitro evidence for the existence of a Na/Ca exchange mechanism in human platelets that may, in vivo, participate in the control of [Ca2+]i.

Benzofurans↗