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Biomedical subjects

D B Smith

Publications and source records attributed to D B Smith.

At least 55 records · Page 3Linked to original sources
PubMed1998

The effect of leg flexion angle on the mechanomyographic responses to isometric muscle actions.

The purpose of this investigation was to examine the effect of leg flexion angle on the relationship between mechanomyographic (MMG) amplitude and isometric torque production. Adult males (n = 9) performed isometric muscle actions of the leg extensors at 25, 50, 75, and 100 percent maximal voluntary contraction (%MVC) on a calibrated CYBEX 6000 dynamometer at 25, 50, and 75 degrees below full extension. A piezoelectric MMG recording device was placed over the mid-portion of the rectus femoris. At 25 degrees of leg flexion, the MMG amplitude increased to 100%MVC. At 50 and 75 degrees of leg flexion, however, MMG amplitude increased to 75%MVC, and then did not change significantly (P > 0.05) between 75 and 100%MVC. These findings indicate that the MMG amplitude-isometric torque relationship is joint angle specific and may be the result of leg flexion angle differences in: (1) muscle stiffness, or (2) motor unit activation strategies.

Adult↗
PubMed1998

Effects of accelerated testing on porcine bioprosthetic heart valve fiber architecture.

We undertook the following study to quantitatively assess the changes in porcine bioprosthetic heart valve (PBHV) fiber architecture to increasing levels of fatigue damage using an in vitro accelerated test model. PBHVs were subjected to 0-500 million test cycles at 16 Hz, and small-angle light scattering (SALS) was used to quantify the gross fiber structure of the cusps. The degree of gross fiber alignment remained essentially constant from 0 to 500 million cycles over the entire cusp. Increasing fiber orientation randomness, indicative of local damage, was observed only in the vicinity of the nodulus of Arantii after 50 million cycles. The SALS data from the damaged regions suggested shearing between fiber layers, which may be part of the failure process and accelerates valve failure. Histological analysis revealed a relatively intact gross fiber structure with the collagen fiber crimp remaining, although delamination and de-registration of the crimp was also observed. Accelerated tested PBHVs also demonstrated a pronounced 'sagging', which began at the earliest cycle number tested (1.4 million cycles) and whose rate decreased logarithmically with cycle number. Results of this study suggest that PBHV cusps can alter their shape without any visually apparent material yielding or fiber failure under continual cyclic loading. Further, while most of the 4 mmHg pressure fixed PBHV's gross fiber architecture remains unchanged after 500 million cycles of accelerated testing, localized accumulated fiber damage can occur on a sub-visual structural level as early as 50 million cycles.

Animals↗
PubMed1998

Gender comparisons of the mechanomyographic responses to maximal concentric and eccentric isokinetic muscle actions.

PURPOSE: The purpose of this study was to determine whether there is a gender difference in the velocity-related patterns of mechanomyographic (MMG) responses to maximal isokinetic concentric (CON) and eccentric (ECC) muscle actions. METHODS: Adult males (N = 15) and females (N = 16) performed maximal CON and ECC muscle actions of the leg extensors on a calibrated Cybex 6000 dynamometer at velocities of 30, 90, and 150 degrees.s-1. MMG was detected by a piezoelectric crystal contact sensor placed over the vastus lateralis muscle. RESULTS: The results indicated that there were decreases in CON peak torque (PT) across velocities, while ECC PT remained constant with increasing velocity for both genders. MMG amplitude increased significantly (P < 0.05) with velocity in both the males and females for CON and ECC muscle actions. There was a gender difference in the velocity-related patterns of MMG responses to maximal isokinetic CON muscle actions; however, there was no gender difference in the pattern of ECC MMG responses. CONCLUSIONS: The gender difference in CON MMG responses may be attributed to the greater percent decline in CON PT across velocity for the females than the males. In addition, the males displayed greater CON and ECC MMG amplitudes at all muscle action velocities than the females, possibly because of gender differences in muscle mass and/or thickness of the adipose tissue layer.

Acceleration↗
PubMed1998

Detection in chimpanzees of a novel flavivirus related to GB virus-C/hepatitis G virus.

Infection with hepatitis G virus (HGV) or GB virus-C (GBV-C) is widely distributed in human populations. Viruses related to GBV-C/HGV have been recovered from several New World primate species, including tamarins, owl monkeys and marmosets. To understand more about the relationship between GB viruses and their hosts, we used primers from the 5' non-coding (5'NC), non-structural 3 (NS3) and NS5 regions in nested polymerase chain reactions to screen for related viruses infecting non-captive chimpanzees (Pan troglodytes, troglodytes and verus subspecies). Sequences from the 5'NCR and NS5 regions were amplified from samples taken from 3 of 39 chimpanzees, and from one chimpanzee in the NS3 region. Sequence comparisons of each region revealed that the GB virus infecting chimpanzees was distinct from both GBV-C/HGV and from any of the known GBV-A sequences, but was more closely related to human viruses. GB viruses recovered from different chimpanzees were more diverse than variants of GBV-C/HGV found in humans, with 25% sequence divergence in the 5'NCR and 20% (9.5% amino acid) sequence divergence in NS5 between variants recovered from the troglodytes and verus subspecies, compared with 7.4% and 10.4% (1.9% amino acid) divergence amongst GBV-C/HGV variants infecting humans. Finding GBV-C/HGV-related viruses in an Old World monkey species suggests that GB-like viruses may be widely distributed in simians, and suggests a close evolutionary relationship with their natural hosts.

Amino Acid Sequence↗
PubMed1998

Long-term evolution of the hypervariable region of hepatitis C virus in a common-source-infected cohort.

The long-term evolution of the hepatitis C virus hypervariable region (HVR) and flanking regions of the E1 and E2 envelope proteins have been studied in a cohort of women infected from a common source of anti-D immunoglobulin. Whereas virus sequences in the infectious source were relatively homogeneous, distinct HVR variants were observed in each anti-D recipient, indicating that this region can evolve in multiple directions from the same point. Where HVR variants with dissimilar sequences were present in a single individual, the frequency of synonymous substitution in the flanking regions suggested that the lineages diverged more than a decade previously. Even where a single major HVR variant was present in an infected individual, this lineage was usually several years old. Multiple lineages can therefore coexist during long periods of chronic infection without replacement. The characteristics of amino acid substitution in the HVR were not consistent with the random accumulation of mutations and imply that amino acid replacement in the HVR was strongly constrained. Another variable region of E2 centered on codon 60 shows similar constraints, while HVR2 was relatively unconstrained. Several of these features are difficult to explain if a neutralizing immune response against the HVR is the only selective force operating on E2. The impact of PCR artifacts such as nucleotide misincorporation and the shuffling of dissimilar templates is discussed.

Amino Acid Sequence↗
PubMed1998

Addressing racial inequities in health care: civil rights monitoring and report cards.

Large racial inequities in health care use continue to be reported, raising concerns about discrimination. Historically, the health system, with its professionally dominated, autonomous, voluntary organizational structure, has presented special challenges to civil rights efforts. De jure racial segregation in the United States gave way to a period of aggressive litigation and enforcement from 1954 until 1968 and then to the current period of relative inactivity. A combination of factors--declining federal resources and organizational capacity to address more subtle forms of discriminatory practices in health care settings, increasingly restrictive interpretations by the courts, and the lack of any systematic mechanisms for the statistical monitoring of providers--offers little assurance that discrimination does not continue to play a role in accounting for discrepancies in use. The current rapid transformation of health care into integrated delivery systems driven by risk-based financing presents both new opportunities and new threats. Adequate regulation, markets, and management for such systems impose new requirements for comparative systematic statistical assessment of performance. My conclusion illustrates ways that current "report card" approaches to monitoring performance of such systems could be used to monitor, correct, and build trust in equitable treatment.

Adolescent↗
PubMed1998

The racial segregation of hospital care revisited: Medicare discharge patterns and their implications.

OBJECTIVES: This paper measures current patterns of hospital segregation among Medicare beneficiaries. METHODS: Data from the fiscal year 1993 Medicare Provider Analysis and Review (MEDPAR) file, the index of dissimilarity, and a linear regression model are used to test the effects of standard metropolitan area characteristics on hospital segregation. RESULTS: The overall hospital segregation index was 0.529, ranging by state from 0.154 to 0.746. Hospital segregation in 126 standard metropolitan areas was positively related to population size, hospital density, and residential segregation and negatively related to income inequities and location in the South. CONCLUSIONS: Racial segregation remains high and may produce both reporting biases and unequal effects of public policy.

Black or African American↗
PubMed1998

The culture of long-term care: impact on a continence care program.

Continence care in long-term care settings is a major caregiver and economic burden, with incontinence affecting an estimated 50% to 70% of all residents. Traditionally the continence care of residents is assigned to the nursing assistants and continence programs have been on paper only. These programs have had dismal success rates. Factoring in the culture of the long-term care setting can make the continence program more comprehensive and improve success rates.

Aged↗
PubMed1997

Characteristics of nucleotide substitution in the hepatitis C virus genome: constraints on sequence change in coding regions at both ends of the genome.

Comparison of complete genome sequences for different variants of hepatitis C virus (HCV) reveals several different constraints on sequence change. Synonymous changes are suppressed in coding regions at both 5' and 3' ends of the genome. No evidence was found for the existence of alternative reading frames or for a lower mutation frequency in these regions. Instead, suppression may be due to constraints imposed by RNA secondary structures identified within the core and NS5b genes. Nonsynonymous substitutions are less frequent than synonymous ones except in the hypervariable region of E2 and, to a lesser extent, in E1, NS2, and NS5b. Transitions are more frequent than transversions, particularly at the third position of codons where the bias is 16:1. In addition, nucleotide substitutions may not occur symmetrically since there is a bias toward G or C at the third position of codons, while T left and right arrow C transitions were twice as frequent as A left and right arrow G transitions. These different biases do not affect the phylogenetic analysis of HCV variants but need to be taken into account in interpreting sequence change in longitudinal studies.

Base Sequence↗
PubMed1997

Incidence of objectively diagnosed thromboembolic disease in cancer patients undergoing cytotoxic chemotherapy and/or hormonal therapy.

From August 1993 to May 1994 there were 1505 inpatient and 2590 outpatient chemotherapy treatment episodes at the Clatterbridge Centre for Oncology. A total of 21 thromboembolic events, including two arterial events, were recorded among these patients at a median of 8 weeks from the start of treatment (range 0-14 weeks), and 2 episodes occurred at the time of first presentation. The median age of the patients developing thromboembolism was 53 (range 29-75) years, and there were 14 women and 7 men. In all, 13 of the events (62%) occurred in patients receiving inpatient treatment and 8 (38%), in outpatients. The incidence of thrombosis per treatment episode in inpatients was therefore 0.008 as compared with 0.003 in outpatients. The associated malignancies were breast cancer (5), testicular cancer (4), lung cancer (3), ovarian cancer (3) and non-Hodgkin's lymphoma (2), with bladder, colon, anal and brain cancer providing 1 case each. The following bulky pelvic or para-aortic disease was present in 9 patients: testicular cancer (3), ovarian cancer (3), lymphoma (2) and bladder cancer (1). In all, 20 of the 21 thrombotic episodes were successfully treated, with 1 patient dying from the complications of venous gangrene. Thromboembolic disease is a relatively common and important cause of morbidity and mortality in cancer patients that requires early recognition and treatment.

Adult↗
PubMed1997

Mechanomyographic responses to concentric isokinetic muscle contractions.

The purpose of this investigation was to examine the effects of velocity of contraction on the mechanomyographic (MMG) responses to maximal concentric isokinetic leg extension movements. Eight adult males [mean (SD) age, 22.3 (1.3) years] performed maximal leg extensions on a calibrated Cybex 6000 dynamometer at velocities of 60, 120, 180, 240, 300, and 360 degrees x s(-1) x MMG responses were detected by a piezoelectric recording device placed over the vastus lateralis muscle. Intraclass reliability correlations ranged from R = 0.84 to 0.97 and from 0.90 to 0.99 for peak torque and MMG amplitude values, respectively, with no significant differences (P > 0.05) between the mean values for test versus retest at any contraction velocity. There were significant differences (P < 0.05) in peak torque at all velocities except 240 [135 (27) Nm] versus 300 [127 (27) Nm], and 300 versus 360 degrees x s(-1) [115 (37) Nm]. The mean MMG amplitude at 60 degrees x s(-1) [61 (67) mV] was significantly less (P < 0.05) than that at 360 degrees x s(-1) [452 (451) mV]. These results indicate a velocity-related dissociation between MMG amplitude and peak torque. Furthermore, it was hypothesized that the increases in MMG amplitude were due to velocity-related decreases in muscle stiffness which allowed for greater muscle fiber oscillations.

Adult↗
PubMed1997

Mechanomyography and oxygen consumption during incremental cycle ergometry.

The purpose of this investigation was to describe and compare the relationships for mechanomyography (MMG) and oxygen consumption rate (VO2) versus power output during incremental cycle ergometry. Twenty four adult males [mean (SD) age, 22.1 (2.0) years] volunteered to perform an incremental test to exhaustion on a cycle ergometer. A MMG piezoelectric recording device was placed mid-thigh over the vastus lateralis muscle and VO2 was measured using standard open circuit procedures. The r2 values for the MMG and VO2 versus power output relationships ranged from 0.79 to 0.99 and 0.97 to 0.99, respectively. In 20 of the 24 subjects there was no significant (P > 0.10) difference between the slope values for the normalized MMG and VO2 (expressed as a percentage of maximal values) versus power output relationships. The results of this study indicate that MMG procedures can be used to quantify muscular activity and monitor changes in exercise intensity during cycle ergometry. Furthermore, the present findings demonstrated a close association between the mechanical (MMG) and metabolic (VO2) aspects of muscular contraction during incremental cycle ergometry.

Adult↗
PubMed1997

Device choice and experience level in endoscopic foreign object retrieval: an in vivo study.

BACKGROUND: Successful foreign object retrieval may depend on device choice and the experience level of the endoscopist, although these factors have not been systematically evaluated. METHODS: In anesthetized pigs, the ability to retrieve foreign objects (metal tack, button disc battery, wooden toothpick) placed endoscopically into the stomach was assessed. Seven university medical center gastroenterology attending physicians (5 clinical and 2 basic science research [BSR]), and 4 fellows-in-training participated. The devices used were the Roth retrieval net, rat tooth forceps, Dormia basket, polypectomy snare, and radial jaw forceps. The time to retrieve each object into an esophageal overtube within a 5 minute maximum was measured. RESULTS: Only the Roth net and Dormia basket were successful in retrieving the button disc battery, although the Roth net was superior (100% vs 27%, Fisher p < 0.025). All devices were equally successful at retrieving the tack (82% to 100%, p = NS). The snare was significantly faster than the Roth net (p < 0.05). For the tack, there was significantly fewer difficulties encountered with the snare than the Roth net (Fisher p < 0.03). The Roth net was incapable of retrieving the toothpick; the other devices were equally successful (91% to 100%). The clinical attendings had a significantly higher success rate (95%) than the fellows (82%, chi squared p < 0.05) or combined fellows/BSR attendings (80%, p < 0.02), and were significantly faster than the fellows (p < 0.0002) or the fellows/BSR attendings (p < 0.0003). CONCLUSIONS: The Roth net is the best device for retrieving smooth objects such as the button disc battery. For sharp objects, such as the tack and toothpick, best results were achieved with the snare, although the forceps were also effective. More experienced endoscopists had higher success rates and faster retrieval times. Both device choice and the experience level of the endoscopists have an impact on successful foreign object retrieval.

Animals↗
PubMed1997

Brown recluse spider bite: a case study.

The case of a young man with a chronic, resistant, and unpredictable wound is described. The wound is believed to have been caused by the bite of a brown recluse spider. This article presents a brief overview of the potential sequelae of brown recluse spider bite and a pictorial review of this young man's wound during a 22-month period.

Adult↗
PubMed1997

Validity of near-infrared interactance for estimating relative body fat in female high school gymnasts.

The present investigation examined the validity of near-infrared interactance (NIR) estimates of relative body fat (% fat) from the Futrex-5000 (F5000), Futrex-5000A (F5000 A), and Futrex-1000 (F1000) instruments. Ninety-eight female high school gymnasts (X age+/-SD = 15.7+/-1.2 yr) participated in this investigation. Subsamples were used to cross-validate the F5000 (n = 52), F5000A (n = 46), and F1000 (n = 89) instruments. The NIR % fat estimates were validated against criterion % fat from underwater weighing (UWW) using the adult conversion constants of Brozek et al. (6) (UWWB) and the female age-specific constants of Lohman (23) (UWWL). The cross-validation statistical analysis included examination of the constant error (CE), standard error of estimate (SEE), r, and total error (TE). In addition, full-model multiple regression analyses were used to predict UWWB or UWWL from body weight (BW) and height (HT). BW and HT were correlated with % fat at R = 0.65-0.70, while the validity coefficients for the NIR instruments ranged from r = 0.40-0.78. The F5000 resulted in nonsignificant CE values (-0.3 % fat vs UWWB and 1.5 % fat vs UWWL; p > 0.008) as well as the lowest TE values (TE = 3.1 % fat vs UWWB and 4.0 % fat vs UWWL). All other NIR estimates of % fat resulted in TE values > or = 6.3 % fat. In addition, for all NIR instruments there were negative correlations for the plots of the CE versus the mean of predicted and criterion (UWWB and UWWL) % fat. Therefore, the present findings indicated that the F5000 provided more accurate estimates of % fat than the F5000A or F1000 instruments, but may underestimate the desired minimal body weight for female gymnasts at the low end of the % fat distribution.

Adipose Tissue↗
PubMed1997

Validity of bioelectrical impedence equations for estimating fat-free weight in high school female gymnasts.

The present study examined the validity of bioelectrical impedence (BIA) equations for estimating fat-free weight (FFW) in female gymnasts by comparing the values to those obtained from underwater weighing (UWW). Ninety-seven female Caucasian high school gymnasts (mean age +/- SD = 15.7 +/- 1.1 yr) participated in the study. FFW from UWW was calculated from percent fat using the revised formula of Brozek et al. (mean FFW +/- SD = 43.8 +/- 4.5 kg) and the age-specific constants of Lohman (mean FFW +/- SD = 44.8 +/- 4.6 kg). Cross-validation analyses included examination of the constant error (CE), SEE, r, and total error (TE). The results indicated similar trends between equations when based on either the Brozek or Lohman conversions; however, the CE, SEE, and TE values were consistently lower for the majority of the equations using the revised formula of Brozek et al. Based upon the results of the cross-validation analyses, the equation of Houtkooper et al. and the interlaboratory equations of Van Loan et al. and Lohman, which resulted in identical TE values of 2.4 kg are recommended for use with young high school gymnasts.

Adolescent↗
PubMed1997

The origin of hepatitis C virus genotypes.

For many RNA viruses, relatively recent times of origin of extant viruses are implied by the high rate of substitution observed in longitudinal studies. However, extrapolation of short-term rates of substitution can give misleading estimates of times of divergence. We show here that the common ancestor of different types of hepatitis C virus (HCV) is older than previously thought. The rate of HCV sequence change was measured amongst a cohort of individuals infected following administration of anti-D immunoglobulin. Virus sequences were obtained in the E1 and NS5B genes and compared with each other and with sequences from an infective batch. Taking account of the bias towards synonymous transition substitutions, the time of divergence of variants of subtype 1b is estimated to have occurred 70-80 years ago. The numerous subtypes of HCV are proposed to derive from more than 300 years of endemic infection in certain geographical regions, with recent spread of some subtypes to other parts of the world. Estimation of the time of origin of the major HCV genotypes (types 1-6) is problematic, but our data and analogy with other viruses suggest that divergence occurred at least 500-2000 years ago.

Antibodies, Anti-Idiotypic↗