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Biomedical subjects

D Postma

Publications and source records attributed to D Postma.

9 recordsLinked to original sources
PubMed2001

Pyrite oxidation in unsaturated aquifer sediments. Reaction stoichiometry and rate of oxidation.

The oxidation of pyrite (FeS2) contained in unsaturated aquifer sediment was studied by sediment incubation in gas impermeable polymer laminate bags. Reaction progress was followed over a period of nearly 2 months by monitoring the gas composition within the laminate bag. The gas phase in the incubation bags became depleted in O2 and enriched in CO2 and N2 and was interpreted as due to pyrite oxidation in combination with calcite dissolution. Sediment incubation provides a new method to estimate low rates of pyrite oxidation in unsaturated zone aquifer sediments. Oxidation rates of up to 9.4 x 10(-10) mol FeS2/g x s are measured, and the rates are only weakly correlated with the sediment pyrite content. The reactivity of pyrite, including the inhibition by FeOOH layers formed on its surface, apparently has a major effect on the rate of oxidation. The code PHREEQC 2.0 was used to calculate the reaction stoichiometry and partitioning of gases between the solution and the gas phase. Pyrite oxidation with concurrent calcite dissolution was found to be consistent with the experimental data while organic carbon oxidation was not. The reaction involves changes in the total volume of the gas phase. The reaction scheme predicts the volume of O2 gas consumed to be larger than of CO2 produced. In addition the solubility of CO2 in water is about 30 times larger than of O2 causing a further decrease in total gas volume. The change in total gas volume therefore also depends on the gas/water volume ratio and the lower the ratio the more pronounced the loss of volume will be. Under field conditions the change in total volume may amount up to 20% in the absence of calcite and over 10% in the presence of calcite. Such changes in gas volume during the oxidation of pyrite are expected to result in pressure gradients causing advective transport of gaseous oxygen.

Carbon Dioxide↗
PubMed1998

Peak expiratory flow variability, bronchial responsiveness, and susceptibility to ambient air pollution in adults.

Bronchial hyperresponsiveness (BHR) and peak expiratory flow (PEF) variability are associated expressions of airway lability, yet probably reflect different underlying pathophysiologic mechanisms. We investigated whether both measures can be used interchangeably to identify subjects who are susceptible to ambient air pollution. Data on BHR (>= 20% fall in FEV1), PEF variability (ampl%mean PEF > 5% on any day during an 8-d period with low air pollution levels) and diary data on upper and lower respiratory symptoms, cough, and phlegm were collected in 189 subjects (48-73 yr). The acute effects (lag0) of particulate matter with a diameter less than 10 micrometers (PM10), black smoke, SO2 and NO2 on the prevalence of symptoms were estimated with logistic regression. In subjects with airway lability, both when expressed as PEF variability (69%) and BHR (28%), the prevalence of symptoms increased significantly with increasing levels of air pollution, especially in those with the greater PEF variability (n = 55, 29%). We found no such consistent positive associations in adults without airway lability. PEF variability, and to a smaller extent BHR, can be used to identify adults who are susceptible to air pollution. Though odds ratios were rather low (ranging from 1.13 to 1.41), the impact on public health can be substantial because it applies to large populations.

Acute Disease↗
PubMed1988

Endoscopy of the airway in infants and children.

We believe that many of our readers will appreciate having some familiarity with the procedures described in this manuscript. For those who have had difficulty in deciding whether the need for diagnosis justifies the risk of a procedure, this perspective will shed new light on the problem. It is appropriate to warn our readers that complete unanimity on several points is not yet evident. For example, the indications for flexible bronchoscopy, by whom the procedure should be done, and even more specific technical aspects are questions not completely resolved. However, this article is not an effort to instruct anyone in how to do the procedure. Rather, it is an effort to acquaint our readers with progress in the field. With that in mind, we are confident that the remaining questions will be answered on the basis of the training, experience, and, ultimately, the good judgment of all the physicians involved.

Bronchoscopes↗
PubMed1984

The nose, minor salivary glands, and sarcoidosis.

Fifty-nine patients referred to the ear, nose, and throat clinic for random minor salivary gland (MSG) biopsy were studied. After a careful head and neck examination, a random MSG biopsy and a random inferior turbinate or specific nasal lesion biopsy was done. Of 30 patients with bilateral hilar lymphadenopathy (BHL), 12 of 26 who were thought to have sarcoidosis had abnormal findings on MSG biopsy. Of 29 patients without BHL, none of the six who were later believed to have sarcoidosis had abnormal findings on MSG biopsy. The other 23 patients without BHL and who later were believed findings on MSG biopsy. A careful history, physical examination, and chest roentgenogram should precede referral for random MSG biopsy. Patients without BHL and without other evidence for systemic sarcoidosis do not benefit from random MSG biopsies. This is especially true because of the relative nonspecificity of the finding of a noncaseating granuloma.

Biopsy↗
PubMed1984

Pyogenic otorhinologic infections in acquired immune deficiency syndrome.

A 25-year-old homosexual man with acquired immune deficiency syndrome had CNS toxoplasmosis, mucosal candidiasis, acute otitis media, and sinusitis. These problems persisted despite multiple courses of antibiotic therapy. Surgical drainage proved to be the only effective means of controlling his otorhinologic infections. We recommend early surgical intervention for this type of patient when standard antibiotic therapy for sinusitis and otitis media proves ineffective.

Acquired Immunodeficiency Syndrome↗
PubMed1982

Polyethylene sponge total ossicular replacement prosthesis. A histopathologic study.

The histopathologic findings of a functioning high-density polyethylene sponge (Plastipore) total ossicular replacement prosthesis in a patient who died of unrelated causes are reported herein. The lack of inflammatory cell infiltration of foreign-body giant cells within, or adjacent to, the prosthesis helps substantiate the safety and efficacy of Plastipore in the reconstruction of the ossicular chain.

Adult↗