THE GRADIENT OF PERMEABILITY OF THE SKIN VESSELS AS INFLUENCED BY HEAT, COLD, AND LIGHT

Oesophageal heat exchangers with a diameter of 11mm or 14.7mm are equally effective and safe for targeted temperature management

BACKGROUND

Targeted temperature management (TTM) is widely used in critical care settings for conditions including hepatic encephalopathy, hypoxic ischemic encephalopathy, meningitis, myocardial infarction, paediatric cardiac arrest, spinal cord injury, traumatic brain injury, ischemic stroke and sepsis. Furthermore, TTM is a key treatment for patients after out-of-hospital cardiac-arrest (OHCA). However, the optimal cooling method, which is quick, safe and cost-effective still remains controversial. Since the oesophagus is adjacent to heart and aorta, fast heat-convection to the central blood-stream could be achieved with a minimally invasive oesophageal heat exchanger (OHE). To date, the optimal diameter of an OHE is still unknown. While larger diameters may cause thermal- or pressure-related tissue damage after long-term exposure to the oesophageal wall, smaller diameter (e.g., gastric tubes, up to 11mm) may not provide effective cooling rates. Thus, the objective of the study was to compare OHE-diameters of 11mm (OHE11) and 14.7mm (OHE14.7) and their effects on tissue and cooling capability.

METHODS

Pigs were randomized to OHE11 (N = 8) or OHE14.7 (N = 8). After cooling, pigs were maintained at 33°C for 1 hour. After 10h rewarming, oesophagi were analyzed by means of histopathology. The oesophagus of four animals from a separate study that underwent exactly the identical preparation and cooling protocol described above but received a maintenance period of 24h were used as histopathological controls.

RESULTS

Mean cooling rates were 2.8±0.4°C°C/h (OHE11) and 3.0±0.3°C °C/h (OHE14.7; p = 0.20). Occasional mild acute inflammatory transepithelial infiltrates were found in the cranial segment of the oesophagus in all groups including controls. Deviations from target temperature were 0.1±0.4°C (OHE11) and 0±0.1°C (OHE14.7; p = 0.91). Rewarming rates were 0.19±0.07°C °C/h (OHE11) and 0.20±0.05°C °C/h (OHE14.7; p = 0.75).

CONCLUSIONS

OHE with diameters of 11 mm and 14.7 mm achieve effective cooling rates for TTM and did not cause any relevant oesophageal tissue damage. Both OHE demonstrated acceptable deviations from target temperature and allowed for an intended rewarming rate (0.25°C/h).

TEMPERATURE DISTRIBUTION AND THERMAL DAMAGE OF PERIPHERAL TISSUE IN HUMAN LIMBS DURING HEAT STRESS: A MATHEMATICAL MODEL

The physiological processes taking place in human body are disturbed by the abnormal changes in climate. The changes in environmental temperature are not effective only to compete with thermal stability of the system but also in the development of thermal injuries at the skin surfaces. Therefore, it is of great importance to estimate the temperature distribution and thermal damage in human peripherals at extreme temperatures. In this paper, the epidermis, dermis and subcutaneous tissue were modeled as uniform elements with distinct thermal properties. The bioheat equation with appropriate boundary conditions has been used to estimate the temperature profiles at the nodal points of the skin and subcutaneous tissue with variable ambient heat and metabolic activities. The model has been solved by variational finite element method and the results of the changes in temperature distribution of the body and the damage to the exposed living tissues has been interpreted graphically in relation with various atmospheric temperatures and rate of metabolic heat generation. By involving the metabolic heat generation term in bioheat equation and using the finite element approach the results obtained in this paper are more reasonable and appropriate than the results developed by Moritz and Henriques, Diller and Hayes, and Jiang et al.

THE PARTICIPATION OF SKIN LYMPHATICS IN REPAIR OF THE LESIONS DUE TO INCISIONS AND BURNS

With the aid of solutions of vital dyes the lymphatic capillaries in the ear of the mouse have been studied during the period of immediate reaction to injuries of various sorts and during the period of repair. The behavior of lymphatics severed by incision differs greatly from that of the small blood vessels. Instead of closing they sometimes remain open for as long as 48 hours. Materials introduced into the wound pass directly into the lymphatics through their gaping ends, a fact which will explain why infection from incisions is predominantly along the lymphatics. All around an injury the lymphatics are rendered abnormally permeable. So, too, are the blood vessels, a fact well recognized in the past. Twenty-four to 48 hours later, at a time when the blood vessels in the edematous tissue surrounding the injured area are still much more permeable than normal, the draining lymphatics allow far less to escape than usual. The possible reasons for this have been discussed. The lymphatics participate in the removal of fluid from the edematous tissue. As repair after injury takes place severed lymphatics may reunite when as yet there are no functioning blood vessels. Later an active hyperplasia of the lymphatic channels occurs, an extraordinarily abundant plexus of minute lymph capillaries budding into the area under repair.

THE PHENOMENON OF LOCAL SKIN REACTIVITY TO BACTERIAL FILTRATES: ELICITATION OF LOCAL REACTIVITY BY WAY OF THE VASCULAR SYSTEM

The skin of the rabbit's ear is considerably more resistant than the abdominal skin to the phenomenon of local skin reactivity to bacterial filtrates. Ten times the provocative dose is required if it is given into the vein of the prepared ear and thirty times the provocative dose if it is given into the vein of the non-prepared ear. The state of reactivity cannot be elicited by a preparatory intravenous injection of bacterial filtrates alone into clamped and non-clamped ears. The state also fails to appear in combination with cold, xylol, ethyl urethane, pilocarpine hydrochloride, atropine, calcium gluconate, guinea pig liver extract, histamine dihydrochloride, adrenalin chloride, and pituitrin. Preparatory intravenous injections of toxins are capable of eliciting the state of reactivity in the rabbit's ear when they are accompanied by thermal hyperemia (i.e., exposure to 45°, 50°, and 55°C.). It is also possible to induce the state of reactivity when a mixture of the preparatory factors with testicular extract is given into the veins of clamped ears. The incubation period required may be less than 2 hours. In the light of the above experiments, there are discussed various observations concerning the elicitation of the phenomena of organ reactivity by means of live bacterial cultures and the filtrates thereof.

CHANGES IN THE CUTANEOUS LYMPHATICS OF HUMAN BEINGS AND IN THE LYMPH FLOW UNDER NORMAL AND PATHOLOGICAL CONDITIONS

Vital dyes injected intradermally enter lymphatic capillaries directly, rendering them visible, and appear later in the draining lymphatic trunks as colored streamers. The method enables one to perceive the state of the lymphatic channels and the rate of lymph flow within them. It yields consistent results when tested under physiological conditions known to increase or decrease lymph flow. In the horizontally placed normal limb at rest there is slight lymph flow. In a normal leg or arm hanging downward lymph flow ceases although fluid in the limb increases. When a previously dependent arm is raised above the head, or when the foot of a seated subject is propped on a table, lymph flow in the raised limb becomes active. It ceases in the skin of an arm subjected to partial obstruction of the veins by pressure from without, but very active lymph flow appears during the reactive hyperemia which follows upon the release of venous obstruction. It is still greater following release of total circulatory obstruction, and seems to be the same whether or not the limb has previously been engorged with blood. In the ischemic patches which appear in the skin of a limb during total circulatory obstruction (Bier's spots) the lymphatic capillaries are definitely and considerably constricted, whereas they are slightly dilated in the purple, congested regions of the skin round about. On release of obstruction there occurs a strikingly rapid, equal lymphatic drainage from both regions. The significance of all the findings is discussed. When dye is injected intradermally and the skin sucked, much of the foreign material is driven into the lymphatics draining the injected area.

THE VESSELS INVOLVED IN HYDROSTATIC TRANSUDATION

The gradient of permeability which exists along the cutaneous capillaries and venules is accentuated and broadened in scope by increasing the venous pressure moderately. Under such circumstances transudation leading to edema takes place most abundantly from the venules. The permeability of the portion of the capillary web that is near the arterioles increases only when the venous pressure rises so high as to approximate that in the arteries. Under such circumstances the gradient of permeability along the small vessels disappears, the capillaries and venules everywhere leaking fluid. The character of the vital staining developing under such circumstances indicates, like the evidence of previous work, that the cause for the gradient is to be sought in a structural differentiation.

INTERMITTENT TAKE-UP OF FLUID FROM THE CUTANEOUS TISSUE

Methods have been devised to bring microscopic amounts of fluid into contact with cutaneous connective tissue, under pressure or without pressure, in such a manner that it enters neither blood capillaries nor lymphatics directly. The take-up of fluid brought into contact with the tissues in this way has been measured and its characteristics studied. Elaborate control tests, here described and discussed, have indicated the possible errors in the employment of these methods. Locke's or Tyrode's solutions brought into contact with the cutaneous tissues, by the method described and at atmospheric pressure, pass into the tissue intermittently. Forced into the skin by pressures of 1.0 to 2.0 cm. of water the take-up is still intermittent in character. From this it follows that either the absorption of interstitial fluid from localized regions is periodic or the movements of interstitial fluid are influenced by intermittent physiological changes.

A METHOD TO DETERMINE THE PERIPHERAL ARTERIAL BLOOD PRESSURE IN THE MOUSE

Advantage has been taken of the relative transparency of the claw of the mouse to devise a method, here described, to measure the blood pressure in the animal's leg. Direct measurements of the systolic blood pressure from the carotid arteries of anesthetized mice have also been made. Simultaneous blood pressure readings by both these methods applied to the same animal showed close agreement. The systolic pressure ranged from 60 to 126 mm. Hg, according to the conditions.

II. INDUCED ALTERATIONS IN THE PERMEABILITY OF THE LYMPHATIC CAPILLARY

A standardized solution of a vital dye which escapes with some difficulty from the lymphatics of the ear of the mouse has been utilized in tests of the permeability of the lymphatic wall under various conditions. It has been found that this permeability is subject to great change. The slight pressure that suffices to prevent lymph flow from the ear,—an organ in which such flow goes on normally,—soon results in increased permeability of the obstructed lymphatics without as yet any perceptible dilatation of these vessels. Mechanical stimulation as for example a stroke with a blunt wire, or scratching so light as not to break the epidermis, results in a practically immediate, great increase in lymphatic permeability, which is sharply localized to the region pressed upon. This increase in permeability, though so great that even hemoglobin is let pass by the lymphatics, endures but a few hours. Warming the ear to 43°C. or exposure to mild sunlight increases permeability considerably. Slight chemical irritation increases it greatly, though not so much that particulate matter is let pass. The edema developing as result of lymphatic obstruction or mechanical, thermal, or chemical stimulation is preceded by and associated with a large increase in lymphatic permeability. The facts are discussed in relation to their bearing upon fluid accumulation within the tissue. It is plain that influences within the realm of the normal suffice to increase lymphatic permeability and that those which lead to edema cause a very great increase in it. In proportion as this increase occurs the lymphatics cease to be channels demarcated by a semipermeable membrane. It seems certain that the changes must be in some part responsible for the local accumulation of fluid. There exist possibilities, on the other hand, of a correlation between the functionings of the blood and lymph vessels under certain pathological conditions, as during the resorption of edema.

I. THE PERMEABILITY OF THE WALL OF THE LYMPHATIC CAPILLARY

A technique has been developed for the demonstration of lymphatic capillaries in the ear of the mouse by means of vital dyes and for tests of their permeability under normal and pathological conditions. The lymphatics become visible as closed channels from which the dyes escape secondarily into the tissue. Some of them, cross-connections, with extremely narrow lumen, would seem ordinarily not to be utilized. There is active flow along the lymphatics of the mouse ear under ordinary circumstances. The movement of dye was always toward the main collecting system. The valves of the lymphatics as well as fluid flow prevented distal spread. There was in addition slow migration, apparently interstitial in character, but in the same general direction, of dots of color produced by the local injection of dye. The normal permeability of the lymphatics was studied with dyes of graded diffusibility. Their walls proved readily permeable for those highly diffusible pigments that the blood capillaries let through easily, but retained those that the latter retained. Finely particulate matter (India ink, "Hydrokollag"), they did not let pass. No gradient of permeability was observed to exist along them such as exists along the blood capillaries of certain organs. The observed phenomena of lymphatic permeability, like those of the permeability of the blood capillaries, can be explained on the assumption that the lymphatic wall behaves like a semipermeable membrane.

FACTORS INFLUENCING THE INTERMITTENT PASSAGE OF LOCKE'S SOLUTION INTO LIVING SKIN

Minute amounts of Locke's or Tyrode's solution have been brought into contact with the interstitial connective tissue of the skin of the living mouse, at atmospheric pressure, in such a manner that the blood or lymphatic vessels are not entered directly. Under such circumstances these absorbable fluids enter the tissue spontaneously. Entrance is strikingly intermittent, not continuous, and so too when very slight pressures are brought to bear on the fluids (1). Hyperemia of the tissues, with accompanying dilatation of the blood vessels, increases the entrance of fluids at atmospheric pressure but it is still intermittent. By contrast, venous obstruction leads to intermittent backflow into the apparatus, but reflex hyperemia, following release of the obstruction, is attended by an increase of flow into the tissues in spite of the great reactive dilatation of vessels. The inflow is also intermittent. If the skin is deprived of circulation, fluid does not enter it at all at atmospheric pressure, though it moves in regularly and continuously if slight pressure is put upon it. Edema-forming fluids, described in the text, also enter in a continuous manner when forced into the skin of either living or dead animals. So too do serum and sperm oil. The findings indicate that the passage of interstitial fluid into the blood vessels may be intermittent under normal circumstances and its escape from them as well. The observed occurrence of intermittent flow in the blood vessels of several tissues (9, 15–25) will go far to account for the intermittent entrance of fluid into the skin.

The non-homologous end-joining pathway is not involved in the radiosensitization of mammalian cells by heat shock

A synergistic increase in cell killing is observed when a heat-shock is administered prior to, during, or immediately after exposure to ionizing radiation (IR). This phenomenon, known as heat-radiosensitization, is believed to be mediated by inhibition of repair of radiation-induced double strand breaks (DSB) when cells are exposed to temperatures above 42 degrees C. However, the mechanism by which heat inhibits DSB repair is unclear. The bulk of radiation-induced DSBs are repaired via the non-homologous end-joining pathway (NHEJ). Several reports indicate that the Ku70 and Ku80 subunits of the mammalian DNA-dependent protein kinase (DNA-PK), a complex involved in NHEJ, appear to be susceptible to a heat-induced loss of DNA-binding activity, with Ku80 representing the heat-sensitive component. Since the heat-induced loss and subsequent recovery of Ku-DNA binding activity correlates well with heat-radiosensitization, a role for Ku80 and NHEJ in heat-radiosensitization has been proposed. However, direct evidence implicating Ku80 (and NHEJ) in heat-radiosensitization has been indeterminate. In this study, we demonstrate that equitoxic heat treatments at 42.5-45.5 degrees C induce a similar amount of aggregation of Ku80 in human U-1 melanoma cells. These data suggest that the time-temperature-dependent relationship between heat lethality and Ku80 aggregation are similar. However, the aggregation/disaggregation of Ku80 and its transient or permanent inactivation is unrelated to heat-radiosensitization. When survival curves were obtained for irradiated or irradiated and heated Ku80(-/-) mouse embryo fibroblasts (MEFs) and compared with survival curves obtained for wild-type (WT) cells, we found that heat-radiosensitization was not reduced in the Ku80(-/-) cells, but actually increased. Thus, our findings indicate that Ku80 is not essential for heat-radiosensitization. Non-involvement of Ku-dependent or Ku-independent NHEJ pathways in heat-radiosensitization was confirmed by comparing clonogenic survival between DNA ligase IV-defective and WT human cells. Our data therefore implicate homologous recombination in inhibition of repair of radiation-induced DSBs and as a target for heat-radiosensitization.

Tissue temperatures during ultrasound-assisted lipoplasty

Removing excess subcutaneous fat with the assistance of ultrasonic energy has recently become a technique of interest in the United States after nearly a decade of use in Europe. There are a number of reported advantages of ultrasound-assisted lipoplasty over traditional liposuction, and there are also some theoretical concerns. Ultrasound-assisted lipoplasty involves the conversion of electrical energy to mechanical energy and transfer to the tissues through acoustic pressure waves, with the formation of heat as a by-product. Heat generated in this process dissipates through the body's own cooling mechanisms and conduction to the surrounding tissues, and it does not contribute to the clinical treatment of the adipose tissue. Reports of "burns" and ischemic skin injuries in the literature, and concerns for potential heat-related problems, prompted us to investigate whether significant temperature elevations occur in the clinical setting. Subcutaneous tissue temperature determinations during ultrasound-assisted lipoplasty were begun in February of 1996, and data were collected from 55 patients who had the procedure performed during a 6-month period. Intraoperatively, temperature measurements were made with a data-logging instrument and a needle microprobe inserted into the subcutaneous tissues. Temperatures were taken in the area of liposuction before the infusion of tumescent fluid, after tumescent fluid infusion, and at 5-minute intervals until the end of the procedure. The patient's core body temperature remained stable during the procedure within a narrow range (35.7 degrees C to 36.3 degrees C). There was a gradual increase in the temperature of the subcutaneous tissues over time during the application of ultrasonic energy; however, average subcutaneous temperatures remained below the core temperature (p < 0.05) at all time intervals. Room-temperature tumescent fluid further enhanced the thermal safety zone without lowering core body temperature. There were no temperature related complications in our study population and no untoward effects of performing temperature measurements. We conclude that there is no clinically significant elevation of subcutaneous temperatures during ultrasound-assisted lipoplasty. Reported ischemic skin complications are more likely the result of injury to the subdermal plexus rather than a temperature-induced thermal injury. Although heat is a natural by-product of the energy transfer involved in ultrasound-assisted lipoplasty, the risk of thermal injury is negligible when the procedure is performed by experienced operators. Complete understanding of the technique along with strict adherence to basic principles of flap vascularity will ensure safe and effective performance of ultrasound-assisted lipoplasty.

Experimental studies of moderate temperature burns

The pathology and characteristics of moderate temperature burns have been investigated in rats with a heating apparatus capable of applying thermal doses varying in temperature and exposure time, to which the responses have been observed both macroscopically and microscopically. The macroscopic examination showed only erythema and greyish necrosis. The microscopic changes were divided into six grades of severity from 0 to 5. From the time-temperature threshold curves made by microscopic observations, the critical temperatures for superficial and deep dermal burns, and full skin thickness burns were 37.8 degrees C, 41.9 degrees C and 47.9 degrees C, respectively. According to the data, almost all commercially available topical heaters are considered hazardous. Susceptibility to thermal injury was markedly increased by compression and ischaemia, the effects of which are thought to be due mainly to rapid heat accumulation (heat damage) and hypoxaemia (hypoxic damage).

Reversible injury after mild hyperthermia

Skin contraction and leg contracture resulted from immersion of mice legs in a water bath at temperatures of 42.5 degrees to 43.7 degrees C for 45 to 90 minutes. The maximum contracture was observed between 5 and 15 days after treatment, but little damage remained after about 30 days. After healing of the early tissue damage, there was no progression of residual damage in skin up to 490 days after treatment. In contrast, radiation-induced contracture develops rapidly after 14 days, and may continue to progress for 100 days or more. In the present studies, leg contracture could be attributed primarily to injury in the skin, because skinning the legs before measuring eliminated most of the contracture. Temperature differences between subcutaneous tissue and deep muscle were not consistently observed or statistically significant, and probably made little or no contribution to the difference in thermal response of these tissues.

Permeability of thermally damaged skin: I. Immediate influences of 60 degrees C scalding on hairless mouse skin

Freshly sacrificed hairless mice were burned dorsally by direct contact with 60 degrees C water for periods ranging from 15 seconds to 8 min. Wounds ranging in degree from superficial epidermis damage to injury penetrating well into subcutaneous musculature were inflicted. Burned skin sections and reference abdominal skin sections were excised, placed in diffusion cells and investigated with regards to their permeabilities to water, methanol, ethanol, n-butanol and n-octanol. The data were couched in terms of ratios of permeability coefficients of burned skin to normal skin (scalding coefficients) for the same animal. Scalding increased permeability of skin to all compounds studied but the effects leveled out by 60 seconds. Protracted scalding was without great effect despite progressively increased depth of damage to the tissue as noted in histological sections. The degree of lost barrier competency attributable to 60 degrees C scalding was not marked for any compound but was definitely different for different alkanols. An approximately 3-fold permeability increase was noted with n-butanol, the most affected compound. The data demonstrate that near instantaneous alterations in permeability of skin accompany scalding, that decreased barrier competency does not correlate with the severity of a burn as measured in depth of the burn, and that thermal alteration of permeabilities is dependent on the physicochemical characteristics of the permeants.