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At least 505 records · Page 28Linked to original sources
PubMed2002

Selective non-response to clinical assessment in the longitudinal study of aging: implications for estimating population levels of cognitive function and dementia.

OBJECTIVE: to identify the cognitive outcome of interviewed participants who did not progress to partake in clinical assessments in a longitudinal aging study. DESIGN: a retrospective study was conducted on participants who were interviewed but who did not complete the clinical assessment (including an extended cognitive assessment) at either Wave 1 or both Wave 1 and Wave 3 of the Australian Longitudinal Study of Ageing. A total of 1947 participants aged 70 and older commenced the study, 246 participants without clinical data at either or both Waves 1 and 3 were identified for the sub-sample followed-up retrospectively. The Informant Questionnaire for Cognitive Decline in the Elderly (IQCODE) was administered to informants and medical records were reviewed. RESULTS: participants who did not complete the clinical assessment at Wave 3 reported poorer health and had poorer cognitive function at Wave 1 independent of age and gender. Rates of possible dementia or cognitive decline were higher in the group who did not undertake the clinical assessment compared with both those who did the clinical assessment and with population data. CONCLUSION: selective non-response to clinical assessment in a longitudinal aging study is associated with higher risk of cognitive decline and probable dementia. Longitudinal aging studies may underestimate rates of dementia and population levels of cognitive decline.

Aged↗
PubMed2007

An approach to joint analysis of longitudinal measurements and competing risks failure time data.

Joint analysis of longitudinal measurements and survival data has received much attention in recent years. However, previous work has primarily focused on a single failure type for the event time. In this paper we consider joint modelling of repeated measurements and competing risks failure time data to allow for more than one distinct failure type in the survival endpoint which occurs frequently in clinical trials. Our model uses latent random variables and common covariates to link together the sub-models for the longitudinal measurements and competing risks failure time data, respectively. An EM-based algorithm is derived to obtain the parameter estimates, and a profile likelihood method is proposed to estimate their standard errors. Our method enables one to make joint inference on multiple outcomes which is often necessary in analyses of clinical trials. Furthermore, joint analysis has several advantages compared with separate analysis of either the longitudinal data or competing risks survival data. By modelling the event time, the analysis of longitudinal measurements is adjusted to allow for non-ignorable missing data due to informative dropout, which cannot be appropriately handled by the standard linear mixed effects models alone. In addition, the joint model utilizes information from both outcomes, and could be substantially more efficient than the separate analysis of the competing risk survival data as shown in our simulation study. The performance of our method is evaluated and compared with separate analyses using both simulated data and a clinical trial for the scleroderma lung disease.

Clinical Trials as Topic↗
PubMed1999

1H NMR imaging of residual dipolar couplings in cross-linked elastomers: dipolar-encoded longitudinal magnetization, double-quantum, and triple-quantum filters.

Contrastfilters for NMR imaging of residual 1H dipolar couplings of elastomers are introduced based on dipolar-encoded longitudinal magnetization, as well as double- and triple-quantum coherences. The spin response is discussed in the initial excitation time regime for methylene, methyl, and methine protons applicable to poly(isoprene) and other elastomers, taking into account the hierarchy of dipolar couplings and the associated editing features of multiple-quantum experiments. The efficiency of these filters is investigated for a series of cross-linked poly(isoprene) samples. Spatially resolved dipolar-encoded longitudinal magnetization decays and double-quantum and triple-quantum buildup curves are presented for a phantom made of poly(isoprene) with different cross-link densities. Two-dimensional images representing residual dipolar couplings are presented using dipolar-encoded longitudinal magnetization, double-quantum, and triple-quantum contrast filters. Images from dipolar-encoded longitudinal magnetization and triple-quantum coherences show the highest resolution and contrast, respectively.

Algorithms↗
PubMed1990

Action of FMRFamide on longitudinal muscle of the leech, Hirudo medicinalis.

1. Nerve terminals associated with longitudinal muscle in the leech show FMRFamide-like immunoreactivity. 2. Structure-activity studies using FMRFamide analogs show that the C-terminal RFamide portion of the molecule is crucial for biological activity on leech longitudinal muscle. 3. The putative protease inhibitor FA (Phe-Ala) increases the peak tension produced by longitudinal muscle in response to superfused FMRFamide and the majority of its analogs, suggesting the presence of peripheral proteases capable of degrading RFamide peptides. 4. FMRFamide decreases the relaxation rate of neurally evoked contractions of longitudinal muscle. FA also decreases the relaxation rate of neurally evoked contractions. 5. Intact and isolated muscle cells respond to superfused FMRFamide with a conductance increase, that leads to depolarization and often with a delayed conductance decrease as the membrane potential is restored to resting levels. 6. The depolarizing response of isolated muscle cells to FMRFamide is dependent on external calcium.

Animals↗
PubMed1992

Effect of fluoride dosage on bone density, sonic velocity, and longitudinal modulus of rabbit femurs.

Relationships between the fluoride dosage administered to weanling New Zealand white male rabbits and some mechanical properties of the compact bone were investigated for a wide range of dosages. The measured quantities were density, longitudinal sonic velocity in the radial direction, and fluoride ion concentration in compact bone. The longitudinal elastic modulus was estimated from the product of the density and the square of the sonic velocity. The relative static load stress was estimated from the ratio of the final body weight to the cross-sectional area of the femur. These measurements and derived quantities provide quantitative measures of bone quality. A slight peak (2% greater than reference) was determined for the density and a slightly larger peak (5% above reference) for the longitudinal sonic velocity at a dosage of approximately 20 mg/kg/day. The longitudinal elastic modulus exhibited a substantial peak, 14% greater than reference. The relative static load stress showed a very slight peak as a function of dosage and also as a function of fluoride concentration in the bone. When plotted against the elastic modulus, a nonlinear monotonic increase was observed with modulus, showing that the cross-sectional area of the bone is responsive to the stiffness of the tissue. Stiffer tissue produces a smaller cross section, whereas a more compliant tissue requires a marked increase in the area.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1995

Sources of inputs to longitudinal muscle motor neurons and ascending interneurons in the guinea-pig small intestine.

Light- and electron-microscopic studies were used to investigate connections between specific subgroups of neurons in the myenteric plexus of the guinea-pig small intestine. Inputs to two classes of calretinin-immunoreactive (IR) nerve cells, longitudinal muscle motor neurons and ascending interneurons, were examined. Inputs from calbindin-IR primary sensory neurons and from three classes of descending interneurons were studied. Electron-microscopic analysis showed that calbindin-IR axons formed two types of inputs, synapses and close contacts, on calretinin-IR neurons. About 40% of inputs to the longitudinal muscle motor neurons and 70% to ascending interneurons were calbindin-IR. Approximately 50% of longitudinal muscle motor neurons were surrounded by bombesin-IR dense pericellular baskets and 40% by closely apposed varicosities. At the electron-microscope level, the bombesin-IR varicosities were found to form synapses and close contacts with the motor neurons. Dense pericellular baskets with bombesin-IR surrounded 36% of all ascending interneurons, and a further 17% had closely apposed varicosities. Somatostatin- and 5-HT-IR descending interneurons provided no dense pericellular baskets to calretinin-IR nerve cells. Thus, calretinin-IR, longitudinal muscle motor neurons and ascending interneurons receive direct synaptic inputs from intrinsic primary sensory neurons and from non-cholinergic, bombesin-IR, descending interneurons.

Animals↗
PubMed1986

A pharmacological and immunohistochemical study of the splanchnic innervation of ileal longitudinal muscle in the toad Bufo marinus.

A study was made of the innervation of the longitudinal muscle of the toad ileum with particular emphasis on the splanchnic innervation by non-adrenergic, non-cholinergic (NANC) nerves. Nerve fibres containing substance P-like immunoreactivity (SP-LI) were observed in the gut wall and in the ileal wall after degenerative section of the splanchnic nerves. Incubation overnight in a high concentration of capsaicin (3 X 10(-4) M) caused degeneration of SP-LI fibres. No evidence was obtained for enteric neurons containing SP-LI. Substance P caused a contraction of the longitudinal muscle similar to that produced by nerve stimulation. The response to nerve stimulation was decreased by about 60% by treatment with alpha-chymotrypsin. Capsaicin normally evoked a contraction of the longitudinal muscle, but did not do so after degenerative section of the splanchnic nerves. Prolonged treatments with high concentrations of capsaicin (5 X 10(-5) M) abolished the excitatory response to nerve stimulation. The results suggest that substance P is the transmitter mediating the NANC contraction. The fibres releasing the transmitter are possibly antidromically activated, sensory afferents. Both transmural stimulation and capsaicin caused a NANC inhibition of longitudinal muscle. Stimulation of perivascular nerves after splanchnic nerve section caused a NANC excitation, as did transmural stimulation even after nerve section or capsaicin treatment.

Animals↗
PubMed1987

Effects of unilateral arterial infusion of GH and IGF-I on tibial longitudinal bone growth in hypophysectomized rats.

We have studied the effect of local arterial infusion of bacterially produced human growth hormone (hGH), insulinlike growth factor I (IGF-I), or pituitary-derived ovine prolactin (oPRL) on longitudinal bone growth of hypophysectomized rats. The substances were infused during a 14-day period by osmotic mini-pumps through a catheter which was implanted into the femoral artery of one hindlimb. Longitudinal bone growth was measured by the intravital marker tetracycline. Infusion of 1 microgram hGH per day stimulated bone growth only of the treated limb and not of the uninfused contralateral limb. Infusion of 10 micrograms hGH per day also stimulated unilateral longitudinal bone growth, but the uninfused contralateral limb also showed a significant growth response, probably because local administration of GH at this dose caused a significant elevation of GH in the systemic circulation. As a result, the differential growth response between the GH-treated and untreated limbs decreased compared to rats that were infused with 1 microgram hGH per day. Unilateral arterial infusion of 5 micrograms human IGF-I or 10 micrograms oPRL per day did not produce a significant growth response. The results of the present study confirm the observation by Schlechter and co-workers, who demonstrated that unilateral arterial infusion of GH maintained tibial cartilage width following hypophysectomy in the rat. The results of Schlechter and coworkers and the results of the present study show that GH in vivo stimulates epiphyseal cartilage growth directly. However, an increased local production of insulinlike growth factors is probably of importance for the expression of the direct effect of GH on longitudinal bone growth.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1999

Ontogeny of adenosine receptors in the longitudinal muscle and muscularis mucosae of the rat distal colon.

The development of adenosine A1 and A2B receptors on the longitudinal muscle and muscularis mucosae of the neonatal rat distal colon has been investigated using homogenate binding, quantitative autoradiography and functional studies. In homogenate binding studies 1,3-[3H]-dipropyl-8-cyclopentylxanthine ([3H]DPCPX) bound with high affinity to A1 receptors in the muscularis mucosae and intact colon from rats aged 10, 15, 20, 25 and 30 days. The affinity of [3H]DPCPX was similar to that in the adult at all ages, but the density of binding sites was higher in the neonatal tissues. Quantitative autoradiography showed a higher density of [3H]DPCPX binding sites in the longitudinal muscle than in the muscularis mucosae at all ages studied (day 10 to adult), and this binding was concentration-dependently displaced by N6-cyclopentyladenosine (CPA). In functional studies the longitudinal muscle relaxed in response to 5'-N-ethylcarboxamidoadenosine (NECA) and CPA at all ages studied (15-30 days), NECA being more potent than CPA. The potency of NECA remained constant and it was antagonised by 1 microM DPCPX at all ages with pA2-values consistent with activation of A2 receptors. The inactivity of 2-[p-(carboxyethyl)-phenylethylamino]-5'-N-ethylcarboxamidoadenosi ne (CGS 21680) indicated that the A2 receptors were of the A2B subtype. The muscularis mucosae contracted in response to CPA at all ages studied (day 15 to adult) and the antagonism by DPCPX (10 nM) were consistent with activation of A1 receptors. In conclusion, binding, autoradiographic and functional studies identified A1 receptors on the rat colon muscularis mucosae at all ages studied. However, while binding and autoradiographic localisation showed the presence of A1 receptors in the longitudinal muscle at all ages studied, functional data only revealed the presence of A2B receptors.

Adenosine↗
PubMed1996

Longitudinal stress fractures of the tibia: diagnosis by magnetic resonance imaging.

OBJECTIVE: Previous works describe magnetic resonance (MR) imaging characteristics of stress fractures. Diagnosis of the atypical, longitudinal type of stress fracture has been reported using computed tomography (CT). This report focuses on MR imaging of longitudinal stress fractures of the tibia. MATERIALS AND METHODS: Six cases are presented in which a longitudinal linear abnormal marrow signal was detected in the middle and distal parts of the tibial shaft. Five patients were imaged using a 1.5 Tesla MR unit. Axial, sagittal and coronal T1 and T2-weighted or fat suppressed proton density fast spin echo images were obtained in all but one patient. One patient was imaged using a 0.5 Tesla MR unit with axial and coronal T1- and T2-weighted sequences. Initial conventional radiographs seen at clinical presentation were interpreted as normal in all cases. Two patients underwent radionuclide bone scan. and one patient was imaged with CT prior to MR imaging. RESULTS: In each instance, MR imaging demonstrated linear marrow signal abnormalities orientated along the long axis of the tibial shaft. Endosteal and periosteal callus was identified on axial images. In all cases, MR imaging clearly demonstrated a fracture extending through one cortex with abnormal signal in both the marrow cavity as well as adjacent soft tissues indicating edema. CONCLUSION: MR imaging was shown to be excellent for demonstration of fracture lines, callus, and marrow and soft tissue abnormalities seen in association with longitudinal stress fractures.

Adolescent↗
PubMed2006

Longitudinal growth in children following kidney transplantation: from conservative to pharmacological strategies.

Impairment of longitudinal growth in children with chronic renal failure (CRF) is multifactorial. It is mainly due to disturbances in the growth hormone (GH)/insulin-like growth factor (IGF)/IGF-binding protein axis. Growth failure can be managed by optimizing nutrition and fluid/electrolyte homeostasis, and overcoming the growth-inhibiting effects of uremia by high-dose recombinant human (rh) GH treatment. A sufficient catch-up growth is one of the determining issues for the overall success of pediatric kidney transplantation (Tx). However, despite satisfactory renal function, spontaneous catch-up growth is often insufficient as glucocorticoid treatment is the main inhibiting factor for longitudinal growth after Tx. In addition, longitudinal growth may be jeopardized by low glomerular filtration rate (GFR) and African American or Hispanic background. Supraphysiological doses of GH and/or IGF-I in vitro and in vivo can partially overcome the growth-inhibiting effects of glucocorticoid treatment. GH-associated increase of leukocyte proliferation and cytotoxicity with stimulated interferon synthesis have been demonstrated. However, it is not clear whether such stimulatory effects on leukocyte function are a transitory or a constant risk factor after organ Tx. Clinical trials of GH in children after renal Tx have suggested a rather moderate or transient effect of rhGH on the immune system, and corticosteroids induce a hyporesponsiveness to the action of GH. As long as corticosteroids are believed to be essential after renal Tx, rhGH should be considered to optimize longitudinal growth in children.

Child↗
PubMed2001

Longitudinal coupling in the basilar membrane.

A systematic and detailed study of the longitudinal coupling exhibited by the basilar membrane (BM) was performed in the excised gerbil cochlea. Contrary to the notion that the adjacent regions of the BM are decoupled from each other, the data indicate that: (a) the BM exhibits longitudinal coupling; (b) the length of the coupled region increases from base to apex of the cochlea; and (c) the cells of the organ of Corti (OC) increase the overall coupling exhibited by the BM. Modeling results show that, at a given location, longitudinal coupling increases the effective stiffness of the OC near the characteristic frequency. Therefore, the effect of longitudinal coupling cannot be neglected in the region of the peak of the traveling wave.

Acoustic Stimulation↗
PubMed2006

Evaluation of cross-sectional and longitudinal construct validity of two vision-related quality of life questionnaires: the LVQOL and VCM1.

The Low Vision Quality of Life (LVQOL) questionnaire and the Vision-related Quality of Life Core Measure (VCM1) are two of the many vision-related quality of life (QOL) questionnaires that have been developed in recent years. Although psychometric properties of the LVQOL and VCM1 compare well with other vision-related QOL questionnaires, construct and longitudinal validity have not been assessed (adequately). The purpose of this study was to examine the cross-sectional and longitudinal construct validity of these questionnaires by testing specific pre-specified hypotheses about the relations of these questionnaires with other measures. The percentage of hypotheses regarding the cross-sectional construct validity that were refuted for the LVQOL was 22% for the basic aspects of vision subscale, 50% for the mobility subscale, 39% for the adjustment subscale and 17% for the reading and fine work subscale. For the VCM1 this percentage was 57%. For the longitudinal construct validity the percentage of hypotheses that were refuted ranged from 33 to 75% for the LVQOL subscales and was 50% for the VCM1. In conclusion, cross-sectional construct validity was satisfactory for the LVQOL subscales, but seemed poor for the VCM1. In addition, the longitudinal validity of these scales was poor to moderate.

Aged↗
PubMed1995

Longitudinal and radial distensibility of the porcine aortic root.

The aortic root has been shown to be a highly distensible structure. The function of the aortic valve is intimately related to the expansion of the aortic root, and current nonexpansible stent designs may affect its performance. We therefore measured the radial and longitudinal expansion of the porcine aortic root as a function of pressure in both a static pressurization model and in an isolated working heart model. The radial and longitudinal expansion of the aortic root was measured using a custom-built digital sonomicrometer. Multiple ultrasonic crystals were sutured exterior to the commissures and along the length of the aortic root, and their separation was tracked at varying aortic pressures. In static testing, we found that commissural separation at zero pressure was 26% +/- 7% (mean +/- standard deviation) less than at 120 mm Hg, whereas the longitudinal distance between the base of the valve and the commissures decreased by 11% +/- 9%. Approximately one quarter of the total dimensional change occurred over the physiologic range of 80 to 120 mm Hg. In the isolated porcine heart model, we measured a greater distensibility than in the static tests. For example, at aortic pressures of 120/80 mm Hg (systolic/diastolic), the diameter of the aortic root would be 22% +/- 6% less at 80 mm Hg than at 120 mm Hg. The longitudinal dimensions would be 15% +/- 8% less at 80 mm Hg than at 120 mm Hg. We conclude that the aortic root contracts significantly when depressurized, as during valve replacement surgery, and that the in vivo distensibility of the aortic root is much greater that what is generally measured in vitro. These results suggest that dimensional changes in the implanted prosthetic valve and the recipient aortic root must be considered to achieve both optimal valve orifice and, in the case of distensible valves such as allografts, a proper valve cusp geometry.

Animals↗
PubMed1988

Immunoreactivity for laminin in the developing ventral longitudinal pathway of the brain.

The first long tract to form in the brain of a vertebrate embryo is the ventral longitudinal pathway. In order to investigate what chemical cues may guide nerve growth cones along this pathway, affinity-purified antibodies to laminin and collagen type IV were used to stain sections of mouse embryos from Embryonic Days 8 through 17. A monoclonal anti-neurofilament antibody was used to show the development of the ventral longitudinal pathway in relationship to immunoreactivity for laminin and collagen type IV. At Day 8 fluorescent immunoreactivity for laminin is bright in the external limiting membrane of the neural tube, but the neuroepithelium does not show bright laminin or neurofilament immunoreactivity. At E9 the ventral longitudinal pathway is forming and punctate immunoreactivity for laminin is present on the surfaces of neuroepithelial cells in the marginal zone, through which axons of the ventral pathway extend. Punctate immunofluorescence for laminin remains concentrated in the marginal zone on Days E10 through E14, but on E16 punctate immunofluorescence was much reduced, although immunoreactivity for laminin remained bright in the maturing pial and arachnoid membranes and on blood vessels in the brain. Immunoreactivity for collagen type IV was strong in the external limiting membrane and on blood vessels, but never showed concentrated punctate immunofluorescence in the marginal zone. These results indicate that laminin may be available on cell surfaces and in extracellular spaces as an adhesive ligand for growth cones during the formation of the ventral longitudinal pathway.

Animals↗
PubMed1991

Radial and longitudinal asymmetry of human pharyngeal pressures during swallowing.

Radial asymmetry of upper esophageal sphincter resting pressure has been previously described; however, neither radial nor longitudinal asymmetry of pharyngeal pressures has been demonstrated. The authors used a specially designed intraluminal transducer catheter (Konigsberg; Konigsberg Instruments, Pasadena, CA) with four solid-state transducers separated by 3 cm and oriented circumferentially at 90 degrees intervals to measure pharyngeal pressures. Two wet swallows at each 1-cm interval along the length of the pharynx were measured in 12 normal volunteers (10 male, 2 female; mean age, 38 years). Pressure data were collected on-line by an Apple IIe microcomputer (Apple Computer Inc., Cupertino, CA) at 100 Hz and analyzed for both radial and longitudinal asymmetry. Significant (P less than 0.05) longitudinal asymmetry was shown in all positions except right lateral. Radial asymmetry was present for the first 4 cm only, with anterior and posterior pressures significantly (P less than 0.05) higher than lateral pressures. It was concluded that pharyngeal pressure responses show both axial and longitudinal asymmetry in the distal pharynx. Awareness of transducer position and orientation is essential in the evaluation of pharyngeal pressures.

Adult↗
PubMed1990

Longitudinal retractive force in pressurized dog and human arteries.

Experiments were performed to examine longitudinal retractive force in pressurized arteries in vitro. This force opposes vessel elongation and prevents the development of tortuosity. Common carotid arteries were excised from six adult dogs and external iliac arteries were excised from six elderly male humans at autopsy. Each vessel was mounted in a tissue bath at in situ length and was pressurized. Longitudinal retractive force was measured under control conditions and after treatment with elastase or collagenase. Results showed that, in the dog vessels, elastin provides all of the longitudinal retractive force. In the aged human vessels, both elastin and collagen provide longitudinal retractive force, with elastin contributing the much greater part.

Age Factors↗
PubMed1991

Ossification of posterior longitudinal ligament of the cervical spine in non-Japanese Asians.

"The Japanese disease," ossification of the posterior longitudinal ligament, is not confined to the Japanese only. A similar incidence of 0.8% was found in this study among non-Japanese Asians. Of 5167 patients who attended the Mount Elizabeth Hospital in Singapore for cervical spine complaints, 43 patients were found to have ossification of the posterior longitudinal ligament, forming the largest non-Japanese series. All but one patient were of Mongolian origin, and males were affected four times more commonly than females. Diabetes mellitus was present in 16%. There was a significant association between ossification of the posterior longitudinal ligament and calcification of other cervical paraspinal ligaments. It is suggested that a generalized tendency to calcification may be an important etiological factor in ossification of the posterior longitudinal ligament. Four of the patients required surgery, and in our experience, anterior spinal fusion with removal of the ossified ligament or multilevel laminoplasty gives satisfactory results.

Adult↗