Rewarming

Microwaves have successfully been used for rewarming of blood for medical appHcations (157). Another successful appHcation, not commetciali2ed as of this writing, is the use of microwave heating for rapid tissue fixation (158,159). This procedure appears to reduce the time for tissue sample analysis... 

MPa (44 psi) for vaporizing and rewarming to cool the natural gas feed and high-pressure refrigerant. 

For most tissues, cells and organs, the effects of cold on the cellular membrane are fully reversible. Cells cooled to 1 °C to 4 °C for short periods of time (about four hours) can regain normal cellular functions, including membrane-linked functions, when rewarmed. This seems to suggest that the phase transition in the membrane-bound phospholipids is reversible when the temperature is elevated to normothermia. 

Schwab et al. Stroke 1999 30(5) 1153 Prospective pilot study moderate hypothermia in severe stroke and ICP 25 of 25 tx with hypothermia Hypothermia to 33-34°C with cooling blankets in pts with compete MCA infarct and ICP monitor 44% mortality, all by herniation after secondary rise in ICP after rewarming period. Good control of ICP during hypothermia period. Forty percent rate of pneumonia... 

Steiner T, Eriede T, Aschoff A, Schelhnger PD, Schwab S, Hacke W. Effect and feasibihty of controlled rewarming after moderate hypothermia in stroke patients with malignant infarction of the middle cerebral artery. Stroke 2001 32(12) 2833-5. 

Rewarm passively with a blanket. Active rewarming may cause distributive shock... 

In the processing of mbber compounds (mixing, rewarmings, calendering, extrusion) heat history is a term used to indicate the total heat which has been received by the compound, particularly the temperatures reached by the mbber and the time it has been held at these temperatures. See Scorching. 

The rate of rewarming is especially critical. One has to differentiate between quasistatic situations, which are independent of time and all other dynamic states, in which the history of the present situation and the rate of the further changes play an important role. 

Fig. 1.21. Schematic drawing of an instrument to measure the electrical resistance (ER) of a sample during cooling and rewarming (Fig. 2 from [1.27]).

Fig. 1.22. Resistance as function of the temperature during cooling at 1 °C/min and rewarming at 3 °C/min.

Using DTA and ER measurements of quickly (200 °C/min) frozen sucrose-NaCl solutions, Mac Kenzie presented the different events occurring during slow rewarming. Among others two sucrose-NaCl solutions were studied a 24 % sucrose solution with 6 % NaCl... 

Fig. 1.27.1. DTA measurement of a 24 % sucrose - 6 % NaCl solution during slow rewarming after quick (200 °C/min) freezing.

Fig. 1.31. Behavior of a sucrose - NaCI solution at different sucrose - NaCI concentrations and temperatures after quick freezing (200 °C/min), during slow rewarming (Fig. 8 from [1.25]).

Fig. 1.32. Plot of the DTA measurement of a 50 % glycerine-solution during slow rewarming after quick freezing at 75 to 200 °C/min.

Fig. 1.33. DTA plot of a 50 % glucose solution, frozen at 3 °C/min, during rewarming.

C/min) all freezable water is crystallized, or if the rewarming is interrupted before the melting starts and the product cooled down again to e. g. -150 °C, the rewarming curves resemble that in Fig. 1.33. There is no water left, which can crystallize at Td. There are only two events, which are denoted (as by Mac Kenzie) with antemelting and incipient melting. 

Fig. 1.36.1. Electrical resistance (ER) as function of temperature during cooling and rewarming of a virus suspension. The suspension subcools from -10 °C to approx. -46 °C and freezes at -60 °C to -65 °C. During rewarming the resistance drops clearly at approx. -33 °C. This product should be freeze dried at rice = -40 °C or a little higher (Fig. 7 from [1.27]).

Gatlin [1.30] measured not only Tg. for mannitol and Na-cefazolin by DSC, but also the dependence of the exothermic crystallization energy from the rewarming rate (Fig. 1.47). 

Talsma et al. [1.34] described the freezing behavior of certain liposomes by DSC measurements. Besides the expected influences of freezing and rewarming speeds, and of the CPAs (mannitol and mannitol in Tris-buffer solutions) it was shown, that the heterogeneous and homogeneous crystallization in mannitol solutions exists and the nucleation of ice depends also on the liposome size In small liposomes (e. g. 0.14 pm) mannitol suppressed the heterogeneous crystallization more effectively than in large (0.87 pm) liposomes. If in certain substances no crystallization or eutectic mixtures can be found by DSC (cephalosporin, Williams [1.35]) with the used experimental conditions, one has to seek different conditions [1.32]. 

Curve A After cooling at 30 °C/min down to -100 °C, the DSC plots have been recorded during rewarming with 5 °C/min. Tg approx. -85 °C, respectively -88 °C. At approx. -48 °C, respectively -44 °C, ice crystallization starts clearly, followed by the beginning of the melting of ice. (During freezing only a part of the water has been crystallized.)... 

Curve B After cooling down to -100 °C, the product has been warmed up at 10 °C/min to -48 °C, kept for 15 min at this temperature (thermal treatment), cooled down again at 10 °C/min to -100 °C, and the DSC plot (B) measured during rewarming. During thermal treatment all freezable water is crystallized, and Tg is increased to -58 °C, respectively -57 °C. During rewarming, no crystallization can be detected (Fig. 2 from [1.33]). 

Heat flow as a function of time during rewarming of the samples measured by DSC. 

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