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Biomedical subjects

D M Chapman

Publications and source records attributed to D M Chapman.

At least 19 recordsLinked to original sources
PubMed2001

Dispersion of interface waves in sediments with power-law shear speed profiles. II. Experimental observations and seismo-acoustic inversions.

The propagation of seismic interface waves is investigated in soft marine sediments in which the density is constant, the shear modulus is small, and the profile of shear speed c(s) versus depth z is of the power-law form c(s) (z) = c0z(v), in which c0 and v are constants (0< v < 1). Both the phase speed V and the group speed U of interface waves scale with frequency as f(v/(v -1)) and they obey the simple relation U= (1 - v) V. These relations are derived in a simple way using ray theory and the WKB method; a companion paper [O. A. Godin and D. M. F. Chapman, J. Acoust. Soc. Am. 110, 1890 (2001)] rigorously derives the same result from the solutions to the equations of motion. The frequency scaling is shown to exist in experimental data sets of interface wave phase speed and group speed. Approximate analytical formulas for the dispersion relations (phase and group speed versus frequency) enable direct inversion of the profile parameters c0 and v from the experimental data. In cases for which there is multi-mode dispersion data, the water-sediment density ratio can be determined as well. The theory applies to vertically polarized (P-SV) modes as well as to horizontally polarized (SH) modes (that is, Love waves).

Journal Article↗
PubMed2001

Dispersion of interface waves in sediments with power-law shear speed profiles. I. Exact and approximate analytical results.

In the upper tens of meters of ocean bottom, unconsolidated marine sediments consisting of clay, silt, or fine sand with high porosity are "almost incompressible" in the sense that the shear wave velocity is much smaller than the compressional wave velocity. The shear velocity has very large gradients close to the ocean floor leading to strong coupling of compressional and shear waves in such "soft" sediments. The weak compressibility opens an avenue for developing a theory of elastic wave propagation in continuously stratified soft sediments that fully accounts for the coupling. Elastic waves in soft sediments consist of "fast" waves propagating with velocities close to the compressional velocity and "slow" waves propagating with velocities on the order of the shear velocity. For the slow waves, the theory predicts the existence of surface waves at the ocean-sediment boundary. In the important special case of the power-law depth-dependence of shear rigidity, phase and group velocities of the interface waves are shown to scale as a certain power of frequency. An explicit, exact solution was obtained for the surface waves in sediments characterized by constant density and a linear increase of shear rigidity with depth, that is, for the case of shear speed proportional to the square root of the depth below the sediment-water interface. Asymptotic and perturbation techniques were used to extend the result to more general environments. Theoretical dispersion relations agreed well with numerical simulations and available experimental data and, as demonstrated in a companion paper [D. M. F. Chapman and O. A. Godin, J. Acoust. Soc. Am 110, 1908 (2001)] led to a simple and robust inversion of interface wave travel times for shear velocity profiles in the sediment.

Journal Article↗
PubMed1997

Case management by physician assistants and primary care physicians vs emergency physicians.

OBJECTIVES: To determine whether physician assistants' (PAs') and primary care physicians' (PCPs') case management for 5 common primary care medical problems is similar to that of emergency physicians (EPs). METHODS: An anonymous survey was used to compare PAs, PCPs, and EPs regarding intended diagnostic and treatment options for hypothetical cases of asthma, pharyngitis, cystitis, back strain, and febrile child. Published national practice guidelines were used as a comparison criterion standard where available. The participants stated that they treated all of the patients and responded to all of the cases to be included in the survey. The responses of the PA and PCP groups were compared with those of the EP group, and financial charges for care by each group were analyzed. RESULTS: The EPs tended to follow treatment guidelines closer than did other primary care specialists. The management of PCPs and PAs differed from that of EPs, as follows: [table: see text] CONCLUSION: The EPs more closely followed clinical guidelines than did the PAs and PCPs for these standardized clinical scenarios. Although the relationship of such theoretical practice to actual practice remains unknown, use of these clinical scenarios may identify intended practice patterns warranting attention.

Adult↗
PubMed1997

Workforce projections for emergency medicine: how many emergency physicians does the United States need?

OBJECTIVE: To mathematically model the supply of and demand for emergency physicians (EPs) under different workforce conditions. METHODS: A computer spreadsheet model was used to project annual EP workforce supply and demand through the year 2035. The mathematical equations used were: supply = number of EPs at the beginning of the year plus annual residency graduates minus annual attrition; demand = 5 full-time equivalent positions/ED x the number of hospital EDs. The demand was empirically varied to account for ED census variation, administrative and teaching responsibilities, and the availability of physician extenders. A variety of possible scenarios were tested. These projections make the assumption that emergency medicine (EM) residency graduates will preferentially fill clinical positions currently filled by EPs without EM board certification. RESULTS: Under most of the scenarios tested, there will be a large deficit of EM board-certified EPs well into the next century. Even in scenarios involving a decreasing "demand" for EPs (e.g., in the setting of hospital closures or the training of physician extenders), a significant deficit will remain for at least several decades. CONCLUSIONS: The number of EM residency positions should not be decreased during any restructuring of the U.S. health care system. EM is likely to remain a specialty in which the supply of board-certified EPs will not meet the demand, even at present levels of EM residency output, for the next several decades.

Computer Simulation↗
PubMed1997

The nature of cuticular "ruffles" on slowly plucked anagen hair roots.

When an anagen hair is slowly plucked, the root's surface near the distal end of the keratogenous zone shows rings of 'ruffles' which are cuticular scales rolled back towards the root tip in a tight curl. During extraction, the rachet-like cuticle of the inner root sheath tears apart the almost differentiated cuticular scales on the root's cortex. Further extraction rolls up the cuticle because of the friction with the inner root sheath cuticle and because the torn intercellular cement reconstitutes so that the ruffle's curl is stabilized by cohesion (self-gluing). No evidence was found for pretensioning in the root's cuticle as an explanation for the curling.

Hair↗
PubMed1996

Open thoracotomy procedural competency: validity study of teaching and assessment modalities.

STUDY OBJECTIVES: To determine (1) reliability and validity estimates of three modalities used to assess open thoracotomy procedural competency and (2) the effect of computer practice on procedural performance as measured by the three assessment modalities. METHODS: An experimental, sequential assessment design with volunteer examinees completing all three assessment modalities (paper, computer, pig model) was implemented at the animal support facilities of a university medical school with an affiliated emergency medicine residency program. Level of physician training (student, resident, faculty) and type of computer practice (thoracotomy, cricothyrotomy) were independent variables. Procedural competency scores were determined for each modality; scores were defined in terms of performance time and performance accuracy for three thoracotomy procedures (opening the chest, pericardiotomy, and aortic cross-clamping). RESULTS: Thoracotomy performance on the pig reliably discriminated among examinees known to differ in level of training. However, computer simulation performance did not significantly differ among examinees with different levels of training. Computer simulation practice significantly improved later performance on the computer assessment (P < .05) but not on the pig assessment. The greatest predictor of procedural competency (time and accuracy) on the pig assessment was the ability to sequentially order procedural steps. CONCLUSION: This study establishes the pig model as superior to the paper and computer models as the criterion standard for open thoracotomy assessment. Psychometric properties support the pig model as the most reliable and valid model yet described for assessing thoracotomy procedural competency. Computer simulation practice using visual images (complex anatomy) and the sequential ordering of procedural steps through paper modeling show promise for teaching and assessment of prerequisite skills required to develop psychomotor procedural competency.

Animals↗
PubMed1996

An objective measurement of the anchoring strength of anagen hair in an adult with the loose anagen hair syndrome.

A 21-year-old male presented with the life-long symptom of slowly growing, easily extractable hair lacking sheath remnants. The distribution and density of all his hair regions appeared normal and there was no alopecia. A hair-pull test was painless and resulted in all hairs being removed, all in keeping with a diagnosis of loose anagen hair syndrome (LAHS). The trichogram was normal. Electronically measured epilation revealed values which were significantly lower than controls. His hair follicles were remarkable for this syndrome in that they looked perfectly normal with light microscopy; however, the segment of the follicle with the keratogenous zone was significantly shorter than normal. It is postulated that a subtle intercellular defect must reside in the line of shear proximal to the level of cuticular differentiation to account for the weak anchoring of the root in the follicle. A consequence of a genetic error probably causes both the weak anchoring and the slow hair growth.

Adult↗
PubMed1995

Subcutaneous microvascular (capillary) calcification. Another basis for livedo-like skin changes?

A morbidly obese woman with acute renal failure, high serum phosphorus and slightly depressed serum calcium levels, developed areas of induration in the subcutis with associated livedo reticularis. Later, the subcutis became necrotic and the skin ulcerated. The arterioles, and notably widened occluded capillaries, were found to contain calcium and phosphorus as determined by energy dispersive spectrometry. X-ray diffraction of the subcutis in an early stage of this lesion showed that the mineral was most likely a poorly crystalline hydroxyapatite.

Adult↗
PubMed1995

Qualitative research methodologies in emergency medicine.

Qualitative research methodologies, though often used in other fields and in medical educational investigations. have not been used to study problems in emergency medicine (EM). These methodologies address qualitative data and provide a process of describing, interpreting, and explaining the dynamics of a population or phenomenon. The stages of a qualitative investigation include initial narrative description, interpretation, theory development, assessment of generalization, and evaluation. Important differences between this framework and those of quantitative research methods are described. These methods may be applied to systematic investigation of virtually any observable phenomenon or process in EM in which a better understanding of process would be valuable, such as patient flow, patient satisfaction issues, patient turnover and sign-out processes, bedside teaching, EM teamwork dynamics, and development of the career interests of students and residents. As with quantitative research, EM academicians should seek collaboration and appropriate training with guidance by established qualitative investigators when applying these methods.

Emergency Medicine↗
PubMed1992

The bare:ensheathed anagen root ratio as a function of the speed of epilation.

Small tufts of chest hair were epilated at different rates and the roots classified as to growth phase, presence or absence of root sheaths and whether the shafts were fractured. With respect to anagen roots, a slow epilation gives bare roots whereas an increase in the rate of epilation increases the proportion of ensheathed roots. As the rate of epilation increases, the proportion of fractured hair shafts increases. These findings are relevant to epilation used as a diagnostic procedure because it is not possible to have both a high proportion of well-formed ensheathed anagen roots without some breakages.

Hair↗
PubMed1992

The anchoring strengths of various chest hair root types.

The force required to epilate single chest hairs was measured electronically during a slow (0.09 m/s) machine-driven extraction. Telogen hairs showed a mean anchoring strength of 70 g (s.d. = 16). Anagen hairs, with variable amounts of surrounding root sheaths, had a mean of 71 g (s.d. = 10) whereas bare anagen hairs had a mean of 66 g (s.d. = 13). The catagen phase had a mean of 62 g (s.d. = 8). It is highly likely that the anchoring mechanisms of anagen and telogen roots are as different physiologically as these roots are different anatomically yet both are sufficiently strong to resist the ordinary tractions and pullings to which hair is subject.

Biomechanical Phenomena↗
PubMed1991

An experimental induction of the dysplastic-dystrophic anagen-hair-root condition.

When ensheathed or experimentally desheathed well-formed anagen chest hairs are carefully pulled through a constriction, a range of deformations of the soft bulbar and suprabulbar regions can give rise to so-called dysplastic and dystrophic roots. It is claimed that these deformations arise in a similar manner during extraction of hair from the skin and that these deformations usually represent artefacts; furthermore, it is concluded that only by viewing thick sections of skin can one circumvent these artefacts.

Hair↗
PubMed1988

Objective measurement of three epidermal parameters in psoriasis vulgaris and in dermatopathology in general.

Three objective parameters which characterize the main features of the epidermis are described. One parameter relates to the mean thickness of the epidermis determined by a simple method. The second descriptive number is the ratio of the thickness of the strata corneum, lucidum and granulosum to the stratum malpighii. The third number relates to the degree of folding of the dermo-epidermal junction. The ratio of the mean thickness of abnormal to normal stratum corneum (for the same skin region) is suggested as an objective measure of hyperkeratosis; likewise, the ratio of abnormal to normal stratum malpighii is an objective measure of acanthosis. A single parameter can be measured against time to follow changes during the pathogenesis, treatment or remission of epidermal disease. As psoriasis undergoes progressive acanthosis, the geometry of the folding of the dermo-epidermal junction is such that cells of the stratum malpighii retain their close association with the cylindrical dermal papillae.

Adult↗