Oligohydramnios

OLIGOHYDRAMNION, oligohydramnios (from Greek oligos-small, hydor-water and amnion-inner fetal membrane), malawiodye, abnormal development of the egg, in which the amount of amniotic fluid is less than 500 cm³, and in the most severe degrees can amount to several tablespoons. The causes of O. are not yet sufficiently clarified. O. is most often observed in monozygotic twin pregnancies; the main cause of O. is impaired intrauterine blood circulation. The next variety of O. are cases in which the amniotic fluid gradually leaks through rupture of the membranes during pregnancy (hydrorrhoea amnialis). Some authors assume the cause of O. in the fact that the amniotic fluid is absorbed through the epithelial layer of the amnion. Extremely rarely O. occurs as a result of absence of kidneys in the fetus or atresia of the urethra (the described case studies, e.g., Bronnikov's, with normal content of amniotic fluid in congenital absence of kidneys may speak against the possibility of O. arising on this basis). O. occurs in approximately 1% of all births, and its moderately expressed forms apparently are not registered. Due to the close adhesion of the fetal membranes to its body, mechanical difficulties arise for its normal development and growth. In addition, partitions (see Amniotic threads, constrictions, adhesions) can form in the cavity of the amniotic sac, which lead to intrauterine amputations and the most diverse malformations of the fetus. Cases of such fetal malformations are described in the literature; of these, particularly indicative is the case of Timofeev with a sharp violation of the body configuration, spina bifida and other deviations. Signs of O. are determined by external and internal obstetric examination. When examining and measuring the pregnant woman, a small volume of the abdomen is noted, the size of the uterus is also small; when palpating, parts of the fetus are sometimes remarkably clearly determined; fetal movement is sometimes noticeable even when examining the abdomen. Fluctuation and ballottement are very weakly expressed or even absent; fetal heartbeat is clearly heard in various points of the abdomen (conducted heartbeat). Fetal movement can be perceived by the pregnant woman as pain. The course of labor in O. due to violation of hydrodynamic conditions in the uterine cavity is significantly slowed down. The physiological role of the fetal sac in the opening of the cervix is lost, the advancement of the presenting part is delayed, contractions are painful and unproductive. Insufficient amount of posterior waters slows down the period of expulsion. On internal examination, a small opening of the cervix and a 'flat' sac (see Births) are determined, the membranes as if envelop the presenting part. All this bears the clinical name 'dry' labor. There are no remedies for O. during pregnancy. During labor, treatment consists in rupture of the sac if there are corresponding conditions from the cervix and pelvis. This small intervention eliminates all the above-mentioned symptoms, the opening of the cervix progresses, the period of expulsion of the fetus begins, labor is accelerated.

[A. Aleksandrov. OLIGODACTYLIA, malformation of development, in which the total number of fingers on the hand or foot is less than five. OLIGODYNAMIC ACTION (from Greek oligos-small and dynamis-force), action of small force, a name given by Nägeli (Nageli) to the toxic action on cells (algae Spirogyra) of pieces of copper and silver metals, which were immersed in a vessel where the algae were located. In this case, the microscopic picture differed from that which Nägeli observed when the algae were exposed to large concentrations of salts of the same metals. He explained the action of the latter by chemical processes and contrasted it with the action of small concentrations, which cannot be detected by chemical reactions and which, in his opinion, are too small to produce a chemical effect. Regardless of the view of its nature, O. d. is now commonly called the action on protoplasm of heavy metals and their salts in quantities that are impossible or very difficult to detect in the acting medium by chemical means. Following Nägeli, most work on O. d. of metals was done on bacterial cultures. Most observations were made by placing a piece of metal wire on an agar plate sown with bacterial culture. During the growth of the culture, a sterile belt remains around the wire. O. d. of metals is manifested on bacteria and in aqueous cultures when pieces of metal are immersed in water, which thus, in the authors' expression, 'activates' and acquires disinfectant properties. In this case, the walls of the vessel in which the water is located also acquire disinfectant properties ('activation' of glass). O. d. of metals was also observed on protozoa, on tissue cultures, as well as on isolated organs of warm-blooded animals (heart block when touching the His bundle area with a metal stick). O. d. can include the observations of Zakusov in Kravkov's laboratory on the action of heavy metals on vessels of the isolated ear. According to these experiments, when pieces of copper, silver, mercury, nickel, rhodium, gold and platinum metals are immersed in Ringer-Locke solution, it acquires active properties with respect to the vessels of the ear, causing a constricting, and sometimes dilating effect on them. In experiments on O. d., copper and silver were mainly used, but according to most authors, other heavy metals are also capable of producing this action to some degree. From the very beginning of experiments on O. d., it was assumed that it depends on the transition into solution of some amount of metal in ionized form. Nägeli managed to obtain a similar action on algae by applying weak concentrations of soluble copper salts. However, authors who saw in O. d. a special phenomenon pointed out the possibility of obtaining O. d. when using practically insoluble salts (e.g. AgCl) and asserted that it, in contrast to experiments with soluble salts, is obtained also when it is impossible by ordinary chemical reactions to quantitatively determine the metal in the solution. To solve the question of the nature of O. d., attempts were made to use indirect paths, studying the conditions in which it is enhanced or weakened, in particular when adding to water activated by metal one or another salts. The results were contradictory and allowing different interpretations (Saxl). At present, with the availability of more sensitive methods for determining ion concentration, it has become possible to approach the question directly. Using the electrometric method, Leitner determined the concentration of silver ions in the phenomenon of O. d., caused by metallic silver, AgCl, and compared it with the concentration of ions in a solution of AgNO₃ of minimum strength giving the same effect. The experiments were conducted with Bacterium coli. It turned out that in all these cases the concentration of silver ions in the 'activated' water is practically the same (of the order of 10⁻⁸ g/l). Other researchers who used other sufficiently accurate determination methods came to similar results (H. Freundlich, K. Sollner). Thus, it can be considered proven that O. d. is the usual action of small concentrations of ions of heavy metals and does not require for its explanation the assumption of some special unknown process. 'Activation' of the vessel walls is explained by adsorption of metal ions on them. O. d. is now finding practical application in hygiene for disinfection of drinking water in the form of silvering sand in water filters.