TISSUE DRESSING HAVING GAS
This application claims the benefit of U.S. application Ser. No. 60/479,745, filed on Jun. 18, 2003, which is herein 5 incorporated by reference in its entirety.
FIELD OF THE INVENTION
The present invention relates generally to supplying a gas io to an area.
BACKGROUND OF THE INVENTION
Throughout this application various publications are ref- ^ erenced by arabic numerals within parentheses. Full citations for these publications may be found at the end of the specification immediately preceding the claims. The disclosures of these publications in their entireties are hereby incorporated by reference into this application in order to 2o more fully describe the state of the art to which this invention pertains.
The healing of wounds and the effect of oxygen tension has been intensively studied (1). Among the components important in the healing process are fibroblast proliferation, 25 angiogenesis, collagen synthesis, and reepithelialization.
Soon after injury, whether accidental or surgically induced, undifferentiated mesenchymal cells transform to migratory fibroblasts, which migrate into and across the injured wound. It is known that fibroblasts are aerobic in 30 nature. Fibroblasts are stimulated to produce collagen. While experiments from cultured fibroblasts suggest that high lactate and ascorbic acid concentration typical of hypoxic conditions may activate some of the fibroblast collagen-synthesizing enzymes, animal studies involving 35 low, normal, and high oxygen tensions nevertheless demonstrate increased rates of collagen synthesis under hyperoxic rather than hypoxic conditions.
Angiogenesis, on the other hand, appears to be stimulated by a hypoxic tissue gradient, with new capillaries extending 40 in the direction of lower oxygen concentration. When a hypoxic gradient no longer exists, angiogenesis is minimized or static. Epithelialization is also known to be related to oxygen tension, with higher rates of epithelial proliferation observed under hyperoxic as opposed to hypoxic con- 45 ditions.
The supply of oxygen to healing wound tissue may be derived from three sources: oxygen chemically bound to hemoglobin in whole blood; oxygen dissolved in plasma; and oxygen which diffuses into plasma or tissue from the 50 exterior. In deep wounds, the latter is of little importance. The studies of R. R Gruber et al., for example, indicate that oxygen tension, measured polarographically, increases markedly at 3 bar of 100% 02 in the superficial dermis (0.30-0.34 mm), while the relative oxygen concentration of 55 the deep dermis (1.8-2.2 mm) is unchanged under the same conditions (2).
In surface wounds, all sources of oxygen are important. In wounds of large surface area, however, for example ulcers, only the tissue at the edges of the ulcer or at its base are well 60 supplied with blood, and the growing granulation tissue, in the absence of oxygen diffusing from the exterior, must be supplied by diffusion from blood vessels and plasma, a relatively inefficient process.
It is well established, also, that occlusive coverings that 65 maintain a moist environment promote wound healing (3). Furthermore, it is well known that the changing of wound
dressings may interfere with the healing process by disrupting the healing tissue where granulation and collagen synthesis has not imparted sufficient tensile strength to avoid rupture upon dressing removal. However, due to the inability of the blood and plasma to supply optimal oxygen concentration, and due to the further reduction in oxygen from the exterior brought about by the presence of the occluding dressing, a hypoxic condition may rapidly be reached. Although this condition may encourage angiogenesis, it negatively affects collagen synthesis and epithelialization. Moreover, various Clostridium species, e.g., C. perfringens and C. septicum, are induced to germinate under hypoxic conditions, which can also support other anaerobic flora (4). In addition to minimizing anaerobic flora by discouraging germination, hyperoxic conditions are known to reduce the concentration of other pathogens as well.
Past treatment of chronic ulcers and gangrenous tissue has, in many cases, involved extensive debridement in combination with antibiotics and systemic hyperbaric oxygen. Room size hyperbaric oxygen chambers or chambers sized for the individual patient have employed pure oxygen at pressures of 2 to 3 bar. Treatment time is limited, as oxygen toxicity and central nervous system (CNS) disorders may result from the increased oxygen content of the blood. Such treatments have met with a great deal of success, but the success may not be due to the increased systemic blood and plasma-derived oxygen supply. The blood and plasma already contain sufficient oxygen for the healing process. Rather, it is the diffusion-limited access of oxygen to the wound that limits the oxygen supply required for optimal healing and minimization of infection. The increased oxygen tension in the wound most likely results directly from increased diffusion into the wound surface from the oxygen in the chamber. Gruber, for example, indicates that rate of oxygen absorption from the skin is roughly proportional to oxygen concentration from nearly 0% to 30% (2). Gruber further indicates, however, that oxygen absorption tends to level off at higher oxygen concentrations.
Due to the expense of large hyperbaric chambers and the systemic effects of oxygen toxicity that they may engender, topical hyperbaric chambers have been proposed. Topical chambers operating at "normal" hyperbaric pressures of 2-3 bar are difficult to seal to the body or extremity being treated, however, without interfering with blood supply to the wound locus. Thus, hyperbaric chambers operating at only modestly elevated pressure have been manufactured, such as a device operating at 22 mm Hg pure oxygen (1.03 bar) (5). However, such chambers are expensive and difficult to sterilize (6). Cross-infection is stated to be common.
Heng and others have proposed a simple hyperbaric oxygen treatment chamber consisting of a polyethylene bag that may be secured to the body or extremity with adhesive tape (6), or a transparent nylon bag with straps and VELCRO® closures (7). Pressure is maintained at between 20 mm Hg and 30 mm Hg. However, the leakage associated with the sealing of such bags requires a relatively high rate of oxygen flow. Thus, this method is useful only in facilities with sufficient oxygen supply, or in controlled home environments where a large oxygen tank is permissible. A disposable hyperbaric treatment bag with improved closure is disclosed in U.S. Pat. No. 5,029,579. Another disposable hyperbaric treatment bag is disclosed in U.S. Pat. No. 5,478,310.
In U.S. Pat. No. 4,875,483, a combination layered dressing having an external low oxygen-permeability layer and an abutting internal oxygen permeable layer has been proposed. The relatively low permeability exterior layer is left attached