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Biomedical subjects

D K Martin

Publications and source records attributed to D K Martin.

At least 73 records · Page 4Linked to original sources
PubMed1990

A direct-reading device for measurement of patch-clamp micropipette tip diameters.

This paper describes an electronic device for the measurement of the diameter of the tip opening of micropipettes. The device measures the threshold pressure required to produce bubbles from the micropipette submerged in a liquid and displays the tip inner diameter in micrometres. We demonstrate that this technique can be used effectively in a range of liquids of different density, surface tension and viscosity and that the thickness of the glass from which the micropipettes are made does not influence the measurements.

Electronics↗
PubMed1989

A unifying parameter to describe the clinical mechanics of hydrogel contact lenses.

We studied the relation of postlens squeeze pressure to the clinical fit of hydrogel contact lenses. This relation was statistically significant (p less than 0.01) for a variety of contact lenses currently prescribed over a range of thickness, water content, back central optic radius, diameter, and back vertex power. The squeeze pressure provided a useful parameter to describe and compare the clinical fit of hydrogel contact lenses and a model with which the fit of a lens to an eye could be predicted. There was virtually no movement of the contact lenses across the eye when the squeeze pressure was more than -14 mm H2O (-1370 dynes/cm2). However, the mechanics of the lens motion when the squeeze pressure was less than this critical pressure appeared to be related to a more complicated combination of the squeeze pressure and the other forces in the eye-lens system.

Contact Lenses, Hydrophilic↗
PubMed1988

Computer predictions of abnormal test results. Effects on outpatient testing.

We developed statistical equations to predict abnormalities on eight commonly ordered diagnostic tests and we gave the predictions to 112 physicians practicing in an academic internal medicine practice. Half of each physician's patients were randomized to intervention status. All diagnostic tests were ordered by microcomputer, and when a physician ordered one of the eight study tests for an intervention patient, the computer displayed the probability (0% to 100%) that the test would be positive for the main abnormality being tested for. The physician could then cancel the test if desired. During a six-month controlled trial, when there were more than 15,000 scheduled patient visits, patient charges for the eight study tests were 8.8% less for the intervention patients. The largest reductions (greater than 10%) were for serum electrolyte level tests and complete blood cell counts, the two most commonly ordered tests. Physicians ordered fewer low-probability tests for intervention patients than for controls, suggesting that with timely predictive information, physicians can target tests to higher-risk patients.

Clinical Laboratory Techniques↗
PubMed1988

Postural modifications of VDU operators wearing bifocal spectacles.

This paper describes the postural changes experienced by presbyopic operators of VDU workstations while wearing a pair of bifocal spectacles. All operators reported in this paper had suffered neck and back aches, in addition to generalised problems of asthenopia, while using the VDU workstation. The ages of the operators ranged between 47 and 58 years. The operators' head movements, in looking from the keyboard to the screen, were two to three times greater when bifocal spectacles were worn compared with specially prescribed single-vision occupational spectacles. There were also greater movements in the flexion of the wrist and elbow while using bifocal spectacles and looking from the keyboard to the screen. There was no relationship between the amount of head movement and the position of the bifocal reading segment with respect to the operators' pupil. It was concluded that the symptoms reported by these presbyopic operators were due to static loading of the muscles in the neck and back, induced by the use of bifocal spectacles.

Journal Article↗
PubMed1987

Osmolality of the tear fluid in the contralateral eye during monocular contact lens wear.

The effect of monocular hydrogel contact lens wear on the osmolality of the tear fluid in the ipsilateral and contralateral eyes was measured. The hydrogel contact lenses were of similar diameter and either 38% or 70% water content with thicknesses of 0.07 mm, 0.15 mm or 0.30 mm. The ipsilateral eye showed an initial 2 m.osm/kg decrease (hypo-osmotic) in tear fluid osmolality from baseline after lens insertion. After 5 min the osmolality increased (hyperosmotic) to 15 m.osm/kg greater than baseline, remaining around this level for the 60 min of lens wear. This hyperosmotic change was attributed to an increase in water evaporation due to disruption of the tear film by the contact lens. There was a similar pattern of change in the contralateral eye, but of smaller magnitude. All contact lenses produced a similar effect on tear fluid osmolality, except the combination of a 0.30 mm thick lens of 70% water content fitted with a flat bearing relationship which induced a greater hyperosmotic change after 5 min wear.

Adolescent↗
PubMed1987

Computerized display of past test results. Effect on outpatient testing.

STUDY OBJECTIVE: To determine the effect of displaying previous results of diagnostic tests on the ordering of selected outpatient tests. DESIGN: Sixteen-week controlled trial with a 13-week pre-intervention and 8-week post-intervention observation periods. Patients were randomly assigned to intervention or control groups so that each physician was his or her own control. Only scheduled visits were included. Randomization occurred before the pre-intervention observation period. SETTING: Academic primary care general medicine clinic affiliated with an urban general hospital. SUBJECTS: Pre-intervention period: 111 physicians (97 internal medicine residents, 14 faculty internists), 4683 patients, 5942 scheduled visits. INTERVENTION period: same 111 physicians, 5946 patients, 8148 visits. Post-intervention period: 76 physicians (62 residents, 14 faculty), 2571 patients, 2858 scheduled visits. INTERVENTION: With an order for one of eight selected diagnostic tests through microcomputer workstations, a window was opened on the screen and previous test results were displayed along with the time interval between the first and last result. Tests were ordered for control patients into the same workstations without previous results displayed. MEASUREMENTS AND MAIN RESULTS: Previous results of one or more study tests were available for display for 96% of scheduled patients. Significantly lower results (p less than 0.05 by paired t-test) for the selected tests were found for intervention patient visits than for control visits: charges per visit (mean +/- SE) for intervention patients $12.17 +/- 0.62, compared with $13.99 +/- 0.77 for controls, a 13.0% difference; tests per visit were 0.51 +/- 0.03, compared with 0.56 +/- 0.03, an 8.5% difference. The number of study tests ordered decreased significantly for intervention patients (16.8%) and for controls (10.9%). During the post-intervention period, ordering of study tests increased for both groups, but the increase from the intervention period was not significant. CONCLUSIONS: Presenting physicians with previous test results reduced the ordering of those tests. The actual effect may have been greater than 13%, because there were reductions in study tests ordered for both intervention and control patients during the intervention period when compared with the pre-intervention period, and both tended to rise after the intervention, or display, was turned off.

Data Display↗
PubMed1986

Forces developed beneath hydrogel contact lenses due to squeeze pressure.

The hydrodynamic squeeze pressure in the fluid thin film beneath hydrogel contact lenses fitted onto an axisymmetric model eye were measured. These pressures were due to the contact lens relaxing after deformation by an applied force of similar magnitude to the human eyelid force. The distribution of pressure for contact lenses typically fitted to human eyes was negative with respect to atmospheric pressure at the corneal apex and became less negative at the corneo-scleral limbus. The force that the contact lens applied to the cornea was determined by integrating the pressure distribution from the corneal apex to the limbus. This force varied from 6.0 X 10(-4) N to -7.8 X 10(-1) N depending on the thickness, elastic modulus and bearing relationship of the contact lens. An expression was derived to determine the pressure developed beneath the annulus of the hydrogel contact lens overlapping the cornea, in terms of the measured force over the cornea beneath the contact lens and the chord diameters of the contact lens and cornea. It was found that the deformation of hydrogel contact lenses on the model eye did not follow a linear elastic shell theory.

Biophysical Phenomena↗
PubMed1986

The presence of a contact lens induces a very small increase in the anterior corneal surface temperature.

The anterior corneal surface temperature beneath a contact lens covering the cornea was determined from measurements of the average heat flow from the cornea to the atmosphere (efflux) in a group of 13 healthy young subjects. The average heat efflux was 1.1 X 10(-2) cal X cm-1 X sec-1. The mean corneal surface temperature of the same group was 34.5 degrees C for the open eye and 36.2 degrees C for the closed eye conditions. The anterior corneal surface temperature beneath a 0.07 mm thick hydrogel contact lens (40% water content) was found to be 34.6 degrees C (rise of 0.1 degree C) and 34.9 degrees C (rise of 0.4 degree C) beneath a 0.3 mm thick hydrogel contact lens (40% water content), using the measurement of corneal heat efflux and taking the contact lens to have a slight insulating effect. Contact lenses of higher water content caused a smaller rise in anterior corneal surface temperature than lenses of lower water content.

Body Temperature↗
PubMed1984

Physiological response of the contralateral cornea to monocular hydrogel contact lens wear.

Previous authors have suggested that monocular contact lens wear can induce changes in the contralateral eye. However, most of these contralateral responses have yet to be substantiated or satisfactorily explained. This paper reports a randomized, controlled, single-masked experiment in which corneal thickness, corneal oxygen consumption, and the endothelial bleb response were monitored for 3 hr in both eyes of eight unadapted subjects who wore thick hydrogel lenses on one eye only. No significant contralateral effect was observed in any of the parameters examined. These findings reaffirm the validity of using the contralateral eye as a control in experiments with hydrogel contact lenses.

Adult↗
PubMed1983

Tubal microsurgery with the carbon dioxide laser.

Thirty New Zealand White female rabbits underwent tubal resection and reanastomosis for comparison of conventional microsurgery and laser microsurgical techniques. The rabbits were divided into three groups. The first group of 10 rabbits had 3 cm of tissue resected by knife from each uterine horn; the cut ends were then reanastomosed in one layer with 8-0 Vicryl sutures with the use of the operating microscope. The second group of 10 rabbits had 3 cm of tissue resected by laser from each uterine horn; the cut ends were then reanastomosed in one layer with 8-0 Vicryl. The third group of 10 rabbits had 3 cm of tissue resected by laser from each uterine horn; the cut ends were then reanastomosed by "welding" the tissues with the laser. All rabbits in the first group became pregnant. Only four in the second group became pregnant, but none in the third group became pregnant. It is concluded that the carbon dioxide laser beam as used in this study has no place in tubal resection and reconstruction.

Animals↗
PubMed1982

A new method for measuring the diameter of the in vivo human cornea.

An in vivo method of measuring the size of the human cornea by using catoptric imagery as devised for both closed-circuit television and 35-mm camera systems. The system was validated by using precision reticules and casts of eyes. The reproducibility of the closed-circuit television system was +/- 0.11 mm. The mean horizontal corneal diameter (HCD) for a sample of the right eyes of 50 subjects was 12.89 +/- 0.60 mm. The system was also used to measure horizontal visible iris diameter (HVID). The mean HVID for the same sample was 11.64 +/- 0.49 mm. Although there was a good general correlation between HCD and HVID, the HVID was found to be a poor predictor of HCD for the individual eye.

Adult↗
PubMedDate not supplied

The value of serum iron studies as a test for iron-deficiency anemia in a county hospital.

To evaluate the performance of serum iron studies as a diagnostic test for iron-deficiency anemia in a county hospital, the authors identified retrospectively all general medicine patients who had had bone-marrow aspirates for the work-up of non-macrocytic anemias from 1978 through 1983. Re-reading a sample of aspirates from the 254 study patients (42 with iron deficiency) verified the presence or absence of iron. Analysis with logistic regression, likelihood ratios, and receiver operating characteristic curves demonstrated that the total iron-binding capacity (TIBC) performed markedly better as a diagnostic test than did the transferrin saturation test. While no single TIBC level was diagnostic, the TIBC provided a good estimate of the probability of iron-deficiency anemia.

Anemia, Hypochromic↗
PubMedDate not supplied

The prognosis of hyponatremia at hospital admission.

To assess the risk of mortality in patients with hyponatremia at the time of hospital admission, the authors studied data for 13,979 patients admitted over a 46-month period. Of the 763 (4%) admitted with hyponatremia, 757 (99%) were matched by age, gender, and admitting date with normonatremic control patients. Hyponatremic patients were more than seven times as likely to die in the hospital than the control patients, and they were more than twice as likely to die after discharge (p less than 0.0001 for both). This relationship with in- and outpatient mortality held when controlling for the diagnoses found more often in the hyponatremic patients. Hyponatremia appears to be an indicator of increased risk of death regardless of the disease with which it is associated.

Adult↗