Irreversible damage

The tenn tribology translates literally into the study of nibbing . In modem parlance this field is held to include four phenomena adhesion, friction, lubrication and wear. For the most part these are phenomena that occur between pairs of solid surfaces in contact with one another or separated by a thin fluid film. Adhesion describes the resistance to separation of two surfaces in contact to while friction describes their tendency to resist shearing. Lubrication is the phenomenon of friction reduction by the presence of a fluid (or solid) film between two surfaces. Finally, w>ear describes the irreversible damage or defonnation that occurs as a result of shearing or separation. 

Materials that have been buried underwater cause a special problem. Waterlogged woods and leathers (139), although quite stable under such burial conditions, are ia danger of irreversible damage through drying out upon recovery. Indeed, after excavations from bogs or upon recovery from underwater sites, these items need to be stored underwater until laboratory treatment. 

Despite all these safeguards to extend the service life of the antifreeze, fluid replacement is requited periodically. Typically, fluids are replaced because of irreversible damage caused by one of four conditions contamination, gel formation because of glycol/siUcate reaction, extensive glycol degradation caused by overheating or excessive oxygen exposure, or inhibitor depletion. 

Besides short-term impacts, the potential for irreversible damage to the lungs from... 

There is another type of condition that results from exposure to high humidity. The alteration in electrical properties caused by moisture absorption in nylon and phenolics is reversible. When the moisture content is decreased, the properties of the materials recover to close to the original values. In some instances the exposure to moisture and electrical fields can cause irreversible damage that can lead to failure. 

It is recommended that women of childbearing age take 400 pg/d synthetic folic acid as a supplement in order to reduce the risk of neural tube defects of the embryo when they later become pregnant (periconcep-tional folic acid supplementation) [2]. When supplementing folic acid, it should be considered that this vitamin can mask the simultaneous presence of vitamin B12 deficiency. The typical symptom of vitamin B12 deficiency, megaloblastic (= macrocytic) anemia, will be reduced by high doses of folic acid, yet the nervous system will - in the long run - be irreversibly damaged (= funicular myelitis) when vitamin B12 is not provided as well. 

A notable property of liposomes, which has not been appreciated enough, is the presence of water inside liposomes. This makes them an excellent delivery system for biotechnologically engineered proteins with tertiary and quanternary structures which are sensitive to irreversible damage induced by dehydration, as often occurs with alternative, particulate carrier systems. 

With modest impairment of blood flow, this mechanism allows for preservation of oxidative metabolism without alteration in electrical function. However, when CPP and therefore CBF are sufficiently low, OEF reaches a maximum and cannot increase further. Brain tissue ceases to function electrically, resulting in a neurologic deficit. Microvascular collapse occurs, and CBV falls. If the oxygen supply falls low enough, the tissue dies. Of critical clinical importance is the observation that the amount of time it takes for tissue to suffer irreversible damage is inversely related to the severity of the ischemic insult. Tissue that is completely deprived of blood will die within a few minutes, but less severely hypoperfused tissue may survive for many hours, and may be saved by timely thrombolysis that restores perfusion, or perhaps by another therapeutic intervention. 

In most cases, the ultimate volume of an infarct is larger than that seen in initial DWI images,encompassing both initially DWI-abnormal tissue and other tissue into which the infarct extends. The ultimate volume of an infarct also is usually larger than that seen in early CBV maps. However, DWI images rather than CBV maps are usually used to identify the infarct core, both because infarcts are usually far more conspicuous in DWI images than in CBV maps, and because the DWI detects lesions that have been irreversibly damaged despite... 

If the injected acid itself contains iron (III), a precipitation of the asphaltic products can occur when it comes in contact with certain crude oils. This leads to practically irreversible damage of the zone treated. The amount of precipitate generally increases with the strength and concentration of the acid. Certain organic sulfur compounds, such as ammonium thioglycolate, mercaptoethanol, cysteamine, thioglycerol, cysteine, and thiolactic acid [581], can reduce the iron (HI). 

Proximal tubule cells are exquisitely sensitive to vasculat disturbances and acute tubular necrosis (ATN) can occur naturally in areas of poor perfusion resulting from falling blood pressure, or vasospasm of renal vessels or arterioles. In other words hypoxia associated with partial ischaemia can cause severe damage. It is not then surprising that anoxia associated with iatrogenic, surgically induced total ischaemia produces irreversible damage within a short time unless steps are taken to prevent it. 

Reduction in temperature to above 0°C is the common denominator to all techniques for inhibiting warm ischaemic damage. However, hypothermia alone can only delay the onset of irreversible damage and not prevent it. Furthermore, cold can itself be damaging. Kidneys for transplantation are in clinical practice cooled to 0°-10°C either after they have been removed from... 

The well-known fact that in irreversibly damaged cells, respiratory control is lost and is accompanied by oxidation of cytochromes a and as, as well as NADH (Taegtmeyer et al., 1985), was originally thoug it to be due to substrate deficiency (Chance and Williams, 1955) but may be due to an enzymatic defect resulting in an inability to metabolize NADH-linked substrates (Pelican etal., 1987). It seems likely therefore that return of function is dependent on preservation of mitochondrial membrane integrity, and the structure and activities of respiratory chain (R.C) complexes I-IV (Chance and Williams, 1955). 

A number of factors can cause initial damage to the kidney. The resulting sequelae, however, follow a common pathway that promotes progression of CKD and results in irreversible damage leading to ESRD (Fig. 23-1). 

Cellular changes may result in cell death, which if extensive, may produce irreversible damage to an organ or tissue or may result in the death of the individual. If the cell recovers, altered metabolism and function may still occur, which may be repaired or may result in the manifestation of clinical symptoms. These changes may also be expressed at a later time as tumors or cellular mutations, which may result in abnormal tissue. 

Each breakdown is accompanied by some sound effect and is followed by a steady degradation of properties.284 It can also lead to a complete destruction of the oxide with visible fissures and cracks.286 The particular behavior observed depends on a large number of factors (electrolyte concentration,287 defect concentration in the oxide,288 etc.). The breakdown of thin-film systems (M-O-M and M-O-S structures) as a rule leads to irreversible damage of oxide dielectric properties.289... 

Autoxidation occurs in the body which may cause irreversible damage. 

In order to protect the environment, the precautionary approach shall be widely applied by the States according to their capabilities. Where there are threats of serious or irreversible damage, lack of full scientific certainty shall not be used as a reason for postponing cost-effective measures to prevent environmental degradation. ... 

---