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Biomedical subjects

G A Crawford

Publications and source records attributed to G A Crawford.

At least 19 recordsLinked to original sources
PubMed2006

Microstructure and deformation behavior of biocompatible TiO2 nanotubes on titanium substrate.

Titanium oxide coatings have been shown to exhibit desirable properties as biocompatible coatings. We report on the quantitative microstructure characterization and deformation behavior of TiO(2) nanotubes on Ti substrate. Nanotubes were processed using anodic oxidation of Ti in a NaF electrolyte solution. Characterization of the as-processed coatings was conducted using scanning electron microscopy and focused ion beam milling. Increases in anodization time had no significant effect on tube diameter or tube wall thickness. Coating thickness, however, increased with time up to 2h of anodization, at which point an equilibrium thickness was established. Nanoindentation was used to probe the mechanical response in terms of Young's modulus and hardness. Progressively higher values of elastic modulus were obtained for thinner films consistent with increasing effects of the Ti substrate. A possible deformation mechanism of densification of the porous oxide and wear of the dense surface is suggested and discussed.

Biomechanical Phenomena↗
PubMed1994

Arginine vasopressin and osmolality in the elderly.

OBJECTIVES: To evaluate the influence of age on plasma arginine vasopressin (AVP) concentrations and the relationship between plasma AVP and serum osmolality in younger and older subjects, and in the elderly, to assess the effect of gender on plasma AVP concentration and to determine the impact of prostaglandin blockade on renal responsiveness to AVP. DESIGN: Cross-sectional study; randomized, double-blind, crossover, placebo-controlled study. SETTING: The Renal Laboratory, Royal North Shore Hospital (younger adults) and Clinical Room, St Vincents Hospital (elderly subjects). PARTICIPANTS: 45 younger adults (35 +/- 9 years), and 41 elderly subjects (29 males, 12 females; 78 +/- 3 years). All subjects were healthy and non-institutionalized. The elderly subjects were screened to exclude significant pathology (clinical assessment, multiple investigations). INTERVENTION: Blood samples were drawn from all younger and elderly subjects. The elderly subjects were randomly allocated indomethacin or placebo for 1 month. Following a 1 to 2-week washout, the alternative was administered for a further 1 month. MAIN OUTCOME MEASURES: Plasma AVP and serum osmolality and plasma AVP, serum, and urine osmolality at baseline were measured on indomethacin and placebo. RESULTS: In the elderly subjects, baseline plasma AVP concentration was significantly higher than in the younger subjects studied (4.7 +/- 0.7 vs 2.1 +/- 0.2 pg/mL respectively; P = 0.0003). Plasma AVP was strongly correlated with serum osmolality in the younger subjects (r = 0.76, P = 0.0001) but not in the elderly cohort (r = -0.18, P = 0.26). No difference was found between the sexes in plasma AVP (P = 0.89), and indomethacin treatment did not alter the plasma AVP/urine osmolality ratio (P = 0.85) in the elderly subjects. In addition, changes in plasma AVP with indomethacin therapy did not correlate with changes in serum osmolality (r = 0.16, P = 0.09). CONCLUSIONS: Aging is accompanied by an increase in plasma AVP concentrations. In healthy, elderly subjects, plasma AVP is not dependent on serum osmolality and is not influenced by gender. Indomethacin has no effect on the renal responsiveness to plasma AVP.

Adult↗
PubMed1988

Arginine vasopressin in primigravid human pregnancy. A prospective study.

The relationship between plasma osmolality (Posm) and plasma arginine vasopressin (Pavp) was determined in: (1) 62 normal primigravidas (P) at various stages of gestation and 35 nonpregnant, healthy volunteers (NP) under conditions of normal hydration or water deprivation, and (2) a separate group of 29 normotensive primigravidas during both the second and third trimesters under normal hydration. Pavp was similar in the P and NP groups, and Posm and Pavp were correlated significantly in both groups, but the osmotic threshold was lowered by 11 mosm/kg in primigravidas. In the prospective study, Pavp and Posm were correlated significantly at both stages. Pavp rose between trimesters, as did plasma volume and plasma renin activity, but urine volume and osmolality and Posm did not change significantly. These data confirm that resetting of the osmostat is operative in primigravid pregnancy and extend these observations by demonstrating that this phenomenon is established at least as early as mid-pregnancy. Furthermore, the osmoregulatory system does not appear to be altered by changes in plasma volume or plasma renin as pregnancy progresses.

Adult↗
PubMed1983

Careers with heroin.

This report examines heroin use careers within a sample of 147 Black male heroin addicts and their nonaddicted friends. Based on the extent of their heroin use, subjects were classified into the following subgroups: "light" experimenters, "moderate" experimenters, "heavy" experimenters, and addicts. Our findings indicate that no single career line of pattern characterizes all heroin users. While some users quickly progress from initiation to heroin to regular, intermittent use or "chipping" to daily heroin use and physical dependence, others are deflected at various points along the way. In this report we describe some of the sociobehavioral processes or career contingencies associated with movement from one level of heroin use to the next.

Achievement↗
PubMed1981

Impaired lipoprotein lipase activation by uraemic and post-transplant sera.

1. Lipoprotein lipase was separated from normal human post-heparin plasma by affinity chromatography and assayed with a 14C-labelled triolein emulsion. No enzyme activity was detected unless whole serum was included in the assay as a source of cofactor, apolipoprotein C-II. 2. After a 10 h fast, serum obtained from 46 normal subjects, eight patients with hypertriglyceridaemia but normal renal function, patients with chronic renal failure (24 undialysed, 20 haemodialysed) and 14 recipients of renal allografts, was added to incubation medium for the assay of lipoprotein lipase to determine the maximum activation of the enzyme. 3. When serum was obtained from normal subjects, maximum activation of the enzyme correlated positively with the concentration of triacylglycerol in the sample. Neither sex nor age had a significant effect on the maximum activation achieved by serum from control subjects. 4. The maximum lipoprotein lipase-activating capacity of serum from uraemic and transplant patients was significantly reduced when compared with serum from healthy controls or from the non-uraemic hypertriglyceridaemic patients. 5. Maximum enzyme activation correlated positively with high-density lipoprotein cholesterol in serum from undialysed patients, but did not correlate positively with total serum triacylglycerols in any of the patient groups. Only in transplant recipients was there a significant inverse relationship between serum creatinine concentrations and maximum enzyme activation. 6. Although lipoprotein lipase activation was impaired in uraemic subjects and renal transplant recipients, this appeared to be due more to the presence of an inhibitor than to cofactor deficiency.

Apolipoprotein C-II↗
PubMed1980

Socio-familial characteristics of black male heroin addicts and their nonaddicted friends.

To determine whether family, peer, and school variables are associated with divergent heroin-use patterns or career outcomes, we interviewed 183 black male heroin addicts, experimenters, and non-heroin users from Chicago's south side. While subgroup differences on socio-familial variables generally were not statistically significant, we did observe a number of trends in the expected direction. For example, addicts were more likely than experimenters or nonusers to come from broken homes, to have friends who were involved in serious types of drug use and other illegal activities, and to drop out of high school. At the same time, the pervasiveness of some of our measures of "social disharmony" across the sample suggest that, at least in some inner-city black neighborhoods, these patterns are perhaps becoming the norm.

Adolescent↗
PubMed1980

Impaired plasma triglyceride clearance as a feature of both uremic and posttransplant triglyceridemia.

After accurate plasma volume calculation, endogenous plasma very-low-density-lipoprotein (VLDL)-triglyceride turnover rates were measured in 20 undialyzed patients with chronic renal failure (CRF) and in 16 renal transplant recipients with stable graft function. When kinetic criteria were based on a group of healthy subjects (Vmax = 36.7 mumoles/hr/kg), it was clear that, on the whole, CRF patients had a reduced capacity for VLDL-triglyceride removal (Vmax = 14.0 mumoles/hr/kg), as did graft recipients (Vmax = 19.5 mumoles/hr/kg). In transplant recipients with impaired graft function, however, extremes of both under removal and over production of VLDL-triglycerides were observed. In CRF, defective clearance was accompanied by a reduction in postheparin lipoprotein and hepatic lipase activities, although there was no statistical relationship. Enzyme activities were not reduced, however, after transplantation, and the metabolic factors responsible for defective clearance were not clearly identified.

Adolescent↗
PubMed1980

Early life-style differences among black male heroin addicts and their nonaddicted friends.

To determine whether early life-style variables (i.e., involvement in illicit drug use and other illegal activities) might be associated with subsequent patterns of heroin use, we conducted personal history interviews with 186 Black male heroin addicts, experimenters, and nonheroin users. Our findings indicate that patterns of heroin use should be viewed within the broader context of involvement in a deviant life-style. Addicts and heavy experimenters were more likely than moderate experimenters or nonheroin users to have been heavy users of illicit drugs such as marijuana, barbiturates, amphetamines, and codeine cough syrup and to have been involved in illegal activities such as drug dealing, property offenses, and violent crimes during or after leaving high school.

Adult↗
PubMed1978

Precursors to heroin: a pilot study of young heroin addicts and their nonaddicted friends.

To determine whether differences in life styles and patterns of drug use may help to account for willingness to try heroin and/or likelihood of becoming addicted, personal history interviews were conducted with 15 young heroin addict, 15 experimenters who used the drug but did not become addicts, and 15 nonusers who never tried heroin altough they wre exposed to it. The findings suggest that willingness to try heroin can be better understood within the context of a broader involvement in a deviant way of life. Unlike their nonuser peers, addict and experimenter subjects tended to have identified with deviant rather than conventional role models. Prior to first heroin use, most of them were heavily involved in multiple drug use and other illegal activities. Addicts and experimenters knew that one does not become addicted after trying heroin only once, and many believed they had enough "will power" to avoid a heroin habit.

Adolescent↗