Biomedical subjects

P Dolan

Publications and source records attributed to P Dolan.

At least 73 records · Page 4Linked to original sources

PubMed1996

Psychological questionnaires: do "abnormal" scores precede or follow first-time low back pain?

STUDY DESIGN: A prospective study of psychological risk factors for first-time low back pain with repeated use of psychological questionnaires. OBJECTIVES: To measure the reproducibility of scores from psychological questionnaires, and to compare this with changes that follow an individual's first attack of back pain. Secondly, to determine which scores predict first-time back pain. SUMMARY OF BACKGROUND DATA: "Abnormal" psychometric scores are associated with several aspects of back pain behavior. Little is known, however, about their reproducibility or long-term stability, and there has been no definitive answer to the question: which comes first, "abnormal" scores or low back pain? METHODS: 403 volunteers with no history of "serious" low back pain (defined as pain requiring medical attention or absence from work) participated in a functional spinal assessment. At the time of initial assessment and at 6-month intervals thereafter, the volunteers completed the following questionnaires: the Health Locus of Control, which was subdivided into three sections labelled "Internal," "Powerful others," and "Chance"; the Modified Somatic Perception Questionnaire; and the Zung depression scale. Scores from the Modified Somatic Perception Questionnaire and from the Zung depression scale were added to form a measure of psychological distress. Additional questionnaires inquired about any back pain experienced in the previous 6 months. Only three volunteers had left the study at the 18-month follow-up. At that time 162 participants had reported "any" low back pain, of which 79 were "serious." RESULTS: Intraclass correlation coefficients for scores repeated after 6 months ranged from 0.67-0.80, and reproducibility of scores was equally high between the 0-, 6-, 12- and 18-month assessments. None of the scores were affected by "any" low back pain, and only the Modified Somatic Perception Questionnaire scores changed after "serious" back pain was reported. In a multivariate analysis, the most significant predictor of first time "serious" or "any" back pain was a history of non-"serious" back pain (P < 0.001). Of the psychological factors, the sum of Modified Somatic Perception Questionnaire scores and Zung questionnaire scores was the best predictor of "serious" back pain (P = 0.037), and the Modified Somatic Perception Questionnaire score was the best predictor of "any" back pain (P = 0.002). The 25% of participants with the highest sum of scores from the Modified Somatic Perception Questionnaire and Zung questionnaire was 2.7 times more likely to develop "serious" back pain than the 25% with the lowest sum of these scores. Nevertheless, after accounting for the affects of a history of non-"serious" back pain, psychometric scores predicted less than an additional 3% of reported back pain. CONCLUSIONS: The scores from the Modified Somatic Perception Questionnaire and Zung questionnaire were reproducible over 18 months and were affected little by first episodes of back pain; yet these scores were significant predictors of it. "Abnormal" scores from these questionnaires precede back pain in a small number of people.

Adolescent↗

PubMed1996

Sustained loading generates stress concentrations in lumbar intervertebral discs.

STUDY DESIGN: Cadaveric motion segment experiment. Measurements on each specimen were compared before and after creep loading. OBJECTIVES: To show how sustained "creep" loading affects stress distributions inside intervertebral discs. SUMMARY OF BACKGROUND DATA: The central region of an intervertebral disc acts like a hydrostatic "cushion" between adjacent vertebrae. However, this property depends on the water content of the tissues and may be lost or diminished after creep. METHODS: Twenty-seven lumbar motion segments consisting of two vertebrae and the intervening disc and ligaments were loaded to simulate erect standing postures in life. The distribution of compressive stress in the disc matrix was measured by pulling a miniature pressure transducer through the disc in the midsagittal plane. Profiles of vertical and horizontal compressive stress were repeated after each specimen had been creep loaded in compression for 2-6 hours. RESULTS: Creep reduced the hydrostatic pressure in the nucleus by 13-36%. Compressive stresses in the anulus were little affected when the profiles were measured at 1 kN, but at 2 kN, localized peaks of compressive stress appeared (or grew in size) in the posterior anulus after creep. CONCLUSIONS: Increased loading of the apophysial joints causes an overall reduction in intradiscal stresses after creep. In addition, water loss from the nucleus causes a transfer of load from nucleus to anulus. Stress concentrations may lead to pain, structural disruption, and alterations in chondrocyte metabolism. Disc mechanics depend on loading history as well as applied load.

Adult↗

PubMed1996

Health state valuations from the general public using the visual analogue scale.

In the clinical and economic evaluation of health care, the value of benefit gained should be determined from a public perspective. The objective of this study was to establish relative valuations attached to different health states to form the basis for a 'social tariff' for use in quantifying patient benefit from health care. Three thousand three hundred and ninety-five interviews were conducted with a representative sample of the adult British population. Using the EuroQol health state classification and a visual analogue scale (VAS), each respondent valued 15 health states producing, in total, direct valuations for 45 states. Two hundred and twenty-one re-interviews were conducted approximately 10 weeks later. A near complete, and logically consistent, VAS data set was generated with good test-retest reliability (mean ICC = 0.78). Both social class and education had a significant effect, where higher median valuations were given by respondents in social classes III-V and by those with intermediate or no educational qualifications. These effects were particularly noticeable for more severe states. The use of such valuations in a social tariff raises important issues regarding the use of the VAS method itself to elicit valuations for hypothetical health states, the production of separate tariffs according to social class and/or education and the appropriate measure of central tendency.

Activities of Daily Living↗

PubMed1996

Relationship between myoelectric and mechanical manifestations of fatigue in the quadriceps femoris muscle group.

Fatigue is commonly defined as "the failure to maintain the required force". As such, it may be argued that the use of electromyographic (EMG) power spectral statistics to monitor muscle fatigue is inappropriate, because, during the maintenance of a submaximal force of contraction, EMG changes are readily observable in the absence of any decline in the muscle's mechanical output. However, it is possible that the EMG changes reflect the changing metabolic status of the muscle and hence its inability to generate its normal maximal force. The present study sought to examine whether the decline in EMG median frequency, which occurs during the maintenance of a submaximal force, is correlated with a reduction in the muscle's maximum force-generating capacity. The maximum voluntary contraction (MVC) of the knee extensors in ten young, healthy subjects was determined. On five separate occasions, randomly assigned forces of 20,30,40, 50 and 60% MVC were held to the limit of endurance. At intervals throughout the sustained contractions, subjects were required to rapidly generate an MVC for 1-2 s, then return to the fixed submaxial target force. Surface EMG signals were recorded throughout the contractions from the rectus femoris and vastus lateralis muscles, from which the power spectrum median frequency was calculated. Regression analysis revealed highly significant relationships between the rate of decline in MF and the rate of decline in MVC, and between each of these parameters and endurance time to fatigue (P = 0.0001, in each case). It is concluded that the decline in MF can be used to monitor fatigue, where fatigue is defined as the inability to generate the maximum force that can be produced by the muscle in its fresh state.

Adult↗

PubMed1996

Valuing health states: a comparison of methods.

In eliciting health state valuations, two widely used methods are the standard gamble (SG) and the time trade off (TTO). Both methods make assumptions about individual preferences that are too restrictive to allow them to act as perfect proxies for utility. Therefore, a choice between them might instead be made on empirical grounds. This paper reports on a study which compared a "props" (using specifically-designed boards) and a "no props" (using self-completion booklets) variant of each method. The results suggested that both non props variants might be susceptable to framing effects and that TTP props outperformed SG props.

Adolescent↗

PubMed1996

Modelling valuations for health states: the effect of duration.

An important issue which has been raised in the measurement of health status is the effect that the time spent in a health state may have on the way that state is perceived. Recently a set of valuations for health states defined in terms of the EuroQol Descriptive System was generated from a study of over 3000 members of the UK general public. The valuations were elicited using the visual analogue scale (VAS) and time trade-off (TTO) methods and were for states that lasted for 10 years. Using VAS valuations for states lasting 1 month, 1 year and 10 years derived from a subset of respondents to the general population study, this paper presents valuation "tariffs" for all EuroQol states based on the different durations. The results support those of previous studies which suggest that poor states of health become more intolerable the longer they last. Such findings suggest that the results of studies in which the value given to a health state is assumed to be linearly related to the time spent in that health state should be treated with caution and subjected to sensitivity analysis over an appropriate range of values.

Activities of Daily Living↗

PubMed1996

Time-dependent changes in the lumbar spine's resistance to bending.

OBJECTIVE: To show how time-related factors might affect the risk of back injury. DESIGN: Mechanical testing of cadaveric lumbar motion segments. BACKGROUND: High bending stresses acting on the lumbar spine are associated with injuries to the intervertebral discs and ligaments. Since these soft tissues are viscoelastic, the bending stress ('bending moment') must depend on the speed of movement and the duration of loading, but this has not previously been quantified. METHODS: Forty-five cadaveric lumbar segments, consisting of two vertebrae and the intervening disc and ligaments, were loaded in combined bending and compression in order to simulate movements and postures in living people. The relationship between flexion angle and bending moment was determined at different loading rates, and after sustained loading in bending and in compression. RESULTS: Rapid flexion movements increased the peak bending moment by 10-15% compared to slow movements. On average, repeated flexion over a period of 5 min reduced the peak bending moment by 17%, and 5 min of sustained flexion reduced it by 42%. Two hours of compressive creep loading reduced the height of the intervertebral discs by 1.1 mm, increased the range of flexion by 12%, and reduced peak bending moment by 41%. CONCLUSIONS: The scale of these changes suggests that, in life, the risk of bending injury to the lumbar discs and ligaments will depend not only on the loads applied to the spine, but also on loading rate and loading history. RELEVANCE: The results show how time-dependent factors can increase the risk of bending injury to the osteoligamentous lumbar spine.

Journal Article↗

PubMed1996

Inconsistency and health state valuations.

The comparison of scaling methods used to value health states sometimes rests upon an analysis of aggregate scores. This analysis is usually undertaken once 'inconsistent' respondents have been excluded from the data. However, it is important to be able to judge the extent to which respondents as a whole are logically consistent when assigning values to health states. The degree of inconsistency will depend on how the health states are described, how the questionnaire is administered and who the respondents are. This paper analyses the inconsistency rates from two studies in which valuations for EuroQol health states were elicited using the visual analogue scale (VAS) method. The studies differed in design and incorporated several different variants of the standard EuroQol questionnaire, thus providing an opportunity to examine the relative importance of the different factors that were thought to affect inconsistency rates. Our general conclusions are that inconsistency rates are higher for interviewer-based than for postal surveys, possibly due to response bias, and that inconsistency rates are positively related to age and negatively related to educational attainment.

Activities of Daily Living↗

PubMed1996

The effect of experience of illness on health state valuations.

There is increasing interest in health status measurement and the relative weights that patients and the general public attach to different states of health and illness. One important question that has been raised is whether preferences differ according to the characteristics of the respondents, such as their experience of illness. The results presented in this article suggest that current health status has an important effect on the valuations attached to different health states, with those in poorer health generally giving higher valuations. Past experience of illness, on the other hand, appears to have a negligible effect on valuations. These findings pose real problems for policy makers. To the problem of whose values should count can be added the problem of when these values should count, since the results imply that different valuations may be given by the same respondent depending on how recent their experience of illness was.

Adult↗

PubMed1996

'Stress' distributions inside intervertebral discs. The effects of age and degeneration.

We investigated the distribution of compressive 'stress' within cadaver intervertebral discs, using a pressure transducer mounted in a 1.3 mm diameter needle. The needle was pulled along the midsagittal diameter of a lumbar disc with the face of the transducer either vertical or horizontal while the disc was subjected to a constant compressive force. The resulting 'stress profiles' were analysed in order to characterise the distribution of vertical and horizontal compressive stress within each disc. A total of 87 discs from subjects aged between 16 and 87 years was examined. Our results showed that age-related degenerative changes reduced the diameter of the central hydrostatic region of each disc (the 'functional nucleus') by approximately 50%, and the pressure within this region fell by 30%. The width of the functional annulus increased by 80% and the height of compressive 'stress peaks' within it by 160%. The effects of age and degeneration were greater at L4/L5 than at L2/L3, and the posterior annulus was affected more than the anterior. Age and degeneration were themselves closely related, but the stage of degeneration had the greater effect on stress distributions. We suggest that structural changes within the annulus and endplate lead to a transfer of load from the nucleus to the posterior annulus. High 'stress' concentrations within the annulus may cause pain, and lead to further disruption.

Adolescent↗

PubMed1996

Community hospital charges for orthognathic surgery.

Hospital charges for orthognathic surgery with rigid fixation were evaluated for 80 patients from a community surgical practice. Although the surgeon can control to some degree the length of stay and charges for room and board, ancillary services, laboratory, radiology, and medicine by altering practice patterns, these charges together are less than 24% of the hospital bill. Seventy-six percent of the total hospital charges are generated in the operating room (i.e., operating room, anesthesia, recovery, and respiratory apparatus). Surgeons have minimal control over these changes. Further negotiations with private and government third parties about reimbursement for orthognathic surgical procedures require a cooperative effort between the hospital and the surgeons.

Hospital Charges↗

PubMed1995

1 alpha,25-dihydroxyvitamin D3 analogs featuring aromatic and heteroaromatic rings: design, synthesis, and preliminary biological testing.

Aromatic compounds 2a-c, analogs of 1 alpha, 25-dihydroxyvitamin (calcitriol, 1), and heteroaromatic compounds 4a-c and 5a-c, analogs of 19-nor-1 alpha, 25-dihydroxyvitamin D3 (3), were designed to simulate the topology of their biologically potent parent compounds while avoiding previtamin D equilibrium. Convergent and facile total syntheses of the analogs (+)-2b, (+)-2c, (-)-4b, and (-)-5b were achieved via carbonyl addition of regiospecifically formed organolithium nucleophiles to the enantiomerically pure C,D-ring ketone (+)-17, characteristic of natural calcitriol (1). Likewise, hybrid analogs 20a-c were prepared to determine whether incorporation of a known potentiating side chain would lead to increased biological activity. Preliminary in vitro biological testing showed that aromatic analogs (+)-2b, (+)-2c, and 20a-c as well as heteroaromatic analogs (-)-4b and (-)-5b have very low affinities for the calf thymus vitamin D receptor but considerable antiproliferative activities in murine keratinocytes at micromolar concentration. No biological advantage was observed in this keratinocyte assay for the doubly modified hybrid analogs 20a-c over the singly modified parent (+)-2b. Analog (+)-2b, but surprisingly not the corresponding analog 20b differing from (+)-2b only in the side chain, showed considerable activity in nongenomic opening of calcium channels in rat osteosarcoma cells.

Animals↗

PubMed1995

Geographic distribution of co-dominant DNA stemlines in breast carcinoma.

Breast carcinomas often contain multiple DNA stemlines in flow cytometric DNA histograms. However, due to mixing during tissue disaggregation the microanatomical relationship between the cells which comprise distinct stemlines is unclear. We performed image cytophotometric DNA analysis (IA) on two separate areas of intact tissue sections of 19 breast carcinomas which were selected on the basis of flow cytometric (FCM) DNA content heterogeneity (i.e., multiple stemlines). For comparison, similar analyses were performed on seven tumors with unimodal FCM DNA histograms. Six of the 7 tumors (86%) with unimodal FCM histograms were also unimodal in both IA DNA histograms. Among tumors with heterogeneous FCM DNA histograms, the presence of multiple stemlines was confirmed in IA DNA histograms in 16/19. In nine of these 16 cases, multiple DNA stemlines having similar DNA indices were present in both areas of neoplasm examined with IA. The remaining seven cases displayed unimodal IA histograms in both areas, however DNA indices differed between the two histograms. These findings imply that cell populations corresponding to flow cytometrically detected DNA stemlines are often intimately admixed, even within geographically separated portions of breast tumors. This pattern suggests that productive interactions between genetically distinct tumor populations may lead to stable co-dominance of ancestral clones during progression of some breast carcinomas.

Breast Neoplasms↗

PubMed1995

Fatigue of the erector spinae muscles. A quantitative assessment using "frequency banding" of the surface electromyography signal.

STUDY DESIGN: The authors investigated fatigue-induced changes in the frequency content of the surface electromyographic (EMG) signal from the erector spinae muscles. OBJECTIVES: The objective of the study was to understand the EMG changes in fatiguing muscle and to obtain a reliable index of fatigue. SUMMARY OF BACKGROUND DATA: Power spectral analysis has been used increasingly in recent years to monitor muscle fatigue, but parameters other than the mean or median frequency have received little attention. METHODS: Thirty-five healthy volunteers participated. They pulled upward with constant force on a handlebar attached to a floor-mounted load cell while the EMG signal from the erector spinae was recorded at the levels of T10 and L3 at 1024 Hz; 1.0-sec "windows" of the signal were analyzed using fast Fourier transforms, and the resulting power spectra were divided into 10 frequency bands between 5 Hz and 300 Hz. The median frequency, total power, and peak amplitude of the spectra were also calculated. Changes in the frequency content of the EMG signal were examined during submaximal contractions of different intensity and duration. RESULTS: Median frequency decreased steadily during the contractions, whereas total power and peak amplitude increased. The most repeatable and linear index of change was the increase in the EMG signal in the 5-30 Hz frequency band. The middle-to-high frequency component of the EMG signal increased during the early stages of the contractions, but decreased as the endurance limit was approached. CONCLUSIONS: Changes in the 5-30 Hz band of the EMG power spectrum provide a more reliable and linear index of fatigue in the erector spinae muscles than do changes in median frequency. In the erector spinae, the early effects of fatigue appear to be delayed by the recruitment of additional motor units.

Adult↗

PubMed1995

Recent advances in lumbar spinal mechanics and their clinical significance.

Of the many problems associated with low back pain, those which are most amenable to biomechanical investigation are identified. Recent advances in lumbar spinal mechanics are then reviewed in five sections dealing with mechanical function, mechanisms of failure, movements in vivo, loading in vivo, and the biological consequences of mechanical loading. The discussion suggests that mechanical fatigue damage may frequently be the underlying cause of low back pain, even when degenerative changes are evident in the tissues, and the review ends by suggesting some priority areas for future research.

Journal Article↗

PubMed1995

The effect of past and present illness experience on the valuations of health states.

The effects of age, sex, income, and other socioeconomic factors on valuations for health states have been reported in the literature. However, little attention has been paid to the influence of illness experience, either current or past, on valuations for of states. This paper addresses that question using six separate data sets covering some 1,900 subjects. Each data set contains information on self-reported current health status and experience of serious illness in self, family, and others. Past experience of illness has not been found to affect valuations, but there is some evidence to suggest that, compared with those who claim to be in full health, those who describe their current health as dysfunctional give higher valuations (i.e., closer to good health) for all health states, and particularly so for the more severe states. The most striking result, however, concerns the relationship between respondents' valuations of their own health and their subsequent valuations of hypothetical health states. In all studies, it has been observed that a low self-rated health status is associated with significantly lower valuations of less severe states, including full health. The findings of this paper suggest a real dilemma for health services researchers and policy makers. The importance of the choice of valuations used in the evaluation of health care now must be recognized, because different results may be obtained according to the current health status of those respondents from whom valuations are.

Adult↗

PubMed1994

The strength in anterior bending of lumbar intervertebral discs.

STUDY DESIGN: This was a motion segment experiment. OBJECTIVES: To determine the strength in bending of lumbar intervertebral discs. METHODS: Eighteen "motion segments" consisting of two vertebrae and the intervening disc and ligaments were loaded to simulate forward bending movements in life. The range of flexion and the resistance to bending of each specimen was compared before and after removal of the posterior elements. Nine of the discs were tested after the intradiscal pressure had been reduced by damaging the vertebral end plate in compression. RESULTS: The posterior elements restricted the disc to 80% of its full range of flexion. The strength in anterior bending of isolated discs decreased with age and was 33 Nm on average. Reducing intradiscal pressure did not affect the discs' strength in bending. CONCLUSIONS: Disc failure in bending occurs through overstretching of the outer anulus in the vertical direction. In life, the posterior elements may not adequately protect the posterior anulus from fatigue damage.

Adolescent↗

PubMed1994

Electromyographic median frequency changes during isometric contraction of the back extensors to fatigue.

STUDY DESIGN: This was a cross-sectional study involving 229 healthy, back pain-free individuals. OBJECTIVES: To examine the relationship between electromyographic manifestations of fatigue and endurance time during isometric contraction of the back extensors to fatigue. SUMMARY OF BACKGROUND DATA: Despite the wide-spread use of electromyography to monitor muscle fatigue, its relationship with endurance time has not been well investigated. METHODS: Using skin-surface electrodes, electromyographic signals were recorded from thoracic (T10) and lumbar (L3) regions of erector spinae during an isometric endurance test, and the rate of change in median frequency of the electromyographic power spectrum (MFGRAD) was calculated. RESULTS: MFGRAD was significantly higher at L3 than at T10. The best predictor of endurance time was given by the greater MFGRAD observed at either region. MFGRAD calculated over a submaximal time period (50% total time or 60 sec) also correlated significantly with endurance time. Women displayed a significantly longer endurance time and lower MFGRAD than men. CONCLUSIONS: Endurance appears to be limited by the most fatigable region of the muscle group. MFGRAD is a suitable technique for monitoring back muscle fatigue, even when it is determined over a submaximal time period. The back extensors of women are less fatigable than those of men when the same task is performed.

Adult↗