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Biomedical subjects

A A Pavlov

Publications and source records attributed to A A Pavlov.

At least 19 recordsLinked to original sources
PubMed2002

Mass-independent fractionation of sulfur isotopes in Archean sediments: strong evidence for an anoxic Archean atmosphere.

Mass-independent fractionation (MIF) of sulfur isotopes has been reported in sediments of Archean and Early Proterozoic Age (> 2.3 Ga) but not in younger rocks. The only fractionation mechanism that is consistent with the data on all four sulfur isotopes involves atmospheric photochemical reactions such as SO2 photolysis. We have used a one-dimensional photochemical model to investigate how the isotopic fractionation produced during SO2 photolysis would have been transferred to other gaseous and particulate sulfur-bearing species in both low-O2 and high-O2 atmospheres. We show that in atmospheres with O2 concentrations < 10(-5) times the present atmospheric level (PAL), sulfur would have been removed from the atmosphere in a variety of different oxidation states, each of which would have had its own distinct isotopic signature. By contrast, in atmospheres with O2 concentrations > or = 10(-5) PAL, all sulfur-bearing species would have passed through the oceanic sulfate reservoir before being incorporated into sediments, so any signature of MIF would have been lost. We conclude that the atmospheric O2 concentration must have been < 10(-5) PAL prior to 2.3 Ga.

Archaea↗
PubMed2001

A coupled ecosystem-climate model for predicting the methane concentration in the Archean atmosphere.

A simple coupled ecosystem-climate model is described that can predict levels of atmospheric CH4, CO2, and H2 during the Late Archean, given observed constraints on Earth's surface temperature. We find that methanogenic bacteria should have converted most of the available atmospheric H2 into CH4, and that CH4 may have been equal in importance to CO2 as a greenhouse gas. Photolysis of this CH4 may have produced a hydrocarbon smog layer that would have shielded the surface from solar UV radiation. Methanotrophic bacteria would have consumed some of the atmospheric CH4, but they would have been incapable of reducing CH4 to modern levels. The rise of O2 around 2.3 Ga would have drastically reduced the atmospheric CH4 concentration and may thereby have triggered the Huronian glaciation.

Aerobiosis↗
PubMed2000

Greenhouse warming by CH4 in the atmosphere of early Earth.

Earth appears to have been warm during its early history despite the faintness of the young Sun. Greenhouse warming by gaseous CO2 and H2O by itself is in conflict with constraints on atmospheric CO2 levels derived from paleosols for early Earth. Here we explore whether greenhouse warming by methane could have been important. We find that a CH4 mixing ratio of 10(-4) (100 ppmv) or more in Earth's early atmosphere would provide agreement with the paleosol data from 2.8 Ga. Such a CH4 concentration could have been readily maintained by methanogenic bacteria, which are thought to have been an important component of the biota at that time. Elimination of the methane component of the greenhouse by oxidation of the atmosphere at about 2.3-2.4 Ga could have triggered the Earth's first widespread glaciation.

Atmosphere↗
PubMed1999

Irradiated interplanetary dust particles as a possible solution for the deuterium/hydrogen paradox of Earth's oceans.

Determining the source of Earth's oceans is a longstanding problem in planetary science. Possible sources of water include water ice or water of hydration of silicate minerals in the original material from which the bulk Earth accreted and water brought in by late-arriving planetesimals during the heavy bombardment period (4.5-3.8 Gyr ago) [Chyba, 1989, 1991]. Comets are an attractive source of water because their origin in the outer solar system is consistent with the long timescale for heavy bombardment. However, the high deuterium/hydrogen (D/H) ratio of the three comets that have been studied, Halley, Hyakutake, and Hale-Bopp, indicates that Earth must have had a source with a low-D/H ratio as well. Here we suggest that solar wind-implanted hydrogen on interplanetary dust particles (IDPs) provided the necessary low-D/H component of Earth's water inventory.

Cosmic Dust↗
PubMed1992

[Cardioneurosis (its clinical picture, diagnosis and treatment)].

As a result of clinico-psychopathological and prospective studies (throughout 20 years) of 119 patients diagnosed earlier to have cardioneuroses (neurocirculatory dystonia), it has been established that cardioneuroses cannot be regarded as an independent disease entity since they represent chronic and latent forms of multifactorial mental diseases developing on the basis of affective pathology. Cardioneuroses do not transform to organic lesions of the cardiovascular system and cannot thus be viewed as initial stages of this system diseases including essential hypertension and coronary heart disease. To raise the quality of medical assistance rendered to patients suffering from cardioneuroses, it is advisable that psychosomatic rooms may be set up at the territorial polyclinics.

Chronic Disease↗
PubMed1991

[Side effects of long-term drug therapy of patients with uncomplicated arterial hypertension in a polyclinic].

Pronounced side effects develop in 20% of outpatients receiving chemotherapy for arterial hypertension. Complications arise more often upon administration of clophelin, reserpine, dopegyt and combined regimens. It is established that long-term outpatient treatment of hypertension stage II with clophelin and drug combinations in fixed doses of the components is not beneficial and is inferior to propranolol administration which can be used for many years without any damage to cholesterol and beta-lipoproteins serum levels.

Adolescent↗
PubMed1991

[Secondary medicinal prevention of uncomplicated hypertension in an outpatient clinic].

Drug treatment is indicated for all patients aged under 60 years with stage II essential hypertension and the level of diastolic arterial pressure equal to 100 mm Hg. One should not try to normalize arterial blood pressure in all the cases. The purpose of hypertensive therapy of stage II essential hypertension, grave and of medium gravity, is to reduce diastolic arterial pressure to the magnitude lower than 105 mm Hg and systolic arterial pressure to the magnitude lower than 160 mm Hg. Long-term pharmacotherapy of stage II essential hypertension of mild gravity retards the disease progress, the development of cardiovascular complications and steady loss of work fitness.

Adult↗
PubMed1990

[Tissue oxygen metabolism, hemodynamics and microcirculation in vasorenal hypertension in patients with different types of blood circulation].

The authors examined 68 patients with vasorenal hypertension (VRH). In hyperkinetic type of VRH, the tissue hypoxia is caused by the increase in the cardiac index and rate of blood flow, changes in the microcirculation; in hypokinetic type--by decrease in the cardiac index, sharp increase in the specific peripheral vascular resistance and pronounced changes in all the links of microcirculatory channel as well is observed. Timely correction of the hyperkinetic type of VRH in patients leads to normalization of hemodynamics and elimination of tissue hypoxia. After correction of the hypokinetic type of VRH in patients, neither hemodynamics, nor impairment in the oxygen regimen of the tissues normalizes, even if the positive effect of treatment is noted.

Adult↗
PubMed1990

[Non-invasive diagnosis of the degree of aortic coarctation].

Examined were 42 patients with aortal coarctation at the age of from 6 to 35 years. The differences in hemodynamics, microcirculation and oxygen regimen of tissues depending on the degree of aortal coarctation were revealed. To diagnose the degree of aortostenosis, it is suggested to use the transcutaneous monitoring of PO2 distally to the site of coarctation.

Adolescent↗
PubMed1986

[Analysis of the effectiveness of the dispensary care of patients with internal diseases in a city polyclinic].

Ample untapped reserves of the improvement of dispensarization of the population lie in the strengthening of cooperation between High Medical Schools and medical institutions. Organization of chairs and independent courses of outpatient therapy, daily regular activities of professors, teachers and senior students in outpatient clinics introduce new opportunities for setting up outpatient rehabilitation centers in cities where there are High Medical Schools. The development of new organizational forms, adequate medical recording and the improvement of criteria for the evaluation of dispensarization will contribute to raising the quality of health care of the population in a city outpatient clinic.

Ambulatory Care↗