0000000000335473
AUTHOR
R. Manz
Impact of Localized Microwave Hyperthermia on the Oxygenation Status of Malignant Tumors
Considerable insight into the mechanisms of heat induced cell death in vitro has been gained during recent years (for reviews see 1–3). Besides the direct cell killing effect of heat, many microenvironmental or milieu factors seem to play an important role during heat treatment of solid tumors in vivo, such that a preferential effect of hyperthermia on tumors has been postulated for the in situ conditions. Environmental factors affecting the tumor milieu, such as tissue oxygen partial pressures, pH values, glucose (?) and lactate levels, nutrient supply and drainage of wastes, have thus become a subject of topical interest.
Intracapillary HbO2 Saturation in Tumor Tissue of DS-Carcinosarcoma During Normoxia
Investigations on solid tumor tissue have shown that O2 uptake by cancer cells depends largely on the supply conditions. The absence of sufficient neovascularization and a general rarefaction of the terminal vascular bed during tumor growth as well as reduced and inhcmogeneous blood flew due to vascular stasis in neoplastic tissue prevent normal functions of the terminal vascular bed. In some areas of the tumor circulating blood is not visible despite the intactness of vessels. Stasis occurs since lacuna-like, sinusoidal and cystiform blood vessels cannot be drained completely because ‘tissue-pressure’ due to continuous cell proliferation can prevent efficient circulation. Thrombosis follow…
Respiratory gas exchange in the rat spleen in situ and intrasplenic oxyhemoglobin saturation.
Measurements of splenic respiratory gas exchange and of HbO2 saturations in the red pulp of the rat spleen have shown that there are no indications of a reduced intrasplenic O2 availability during normoxia. The present studies provide evidence that, in the normal spleen, the intrasplenic sequestration of red blood cells cannot be explained by an O2 deficiency in the red pulp since the commonly accepted notion of an intrasplenic hypoxia is not true.
Impact of Various Thermal Doses on the Oxygenation and Blood Flow in Malignant Tumors Upon Localized Hyperthermia
Hyperthermia exhibits various direct cytocidal effects (Dickson, 1977; Overgaard, 1977; Suit, 1977). During heat treatment in vivo, several indirect mechanisms enhance the direct cell-killing capacity of hyperthermia. Therefore, the effective use of hyperthermia can overcome some of the well-known problems involved in modern radiation therapy at least in some malignant tumors.
Effectiveness of Respiratory Hyperoxia, of Normobaric and of Hyperbaric Oxygen Atmospheres in Improving Tumor Oxygenation
A restriction and an inhomogeneous distribution of diffusive and convective oxygen supply is considered the main cause for pronounced radioresistance in solid tumors (Thomlinson and Gray, 1955; Tannock, 1972). One way to alleviate this crucial problem in tumor therapy is the direct enhancement of oxygen delivery to the cancer cells. This can be performed either by the tumor host breathing pure O2 (respiratory hyperoxia, RHO) or by whole body exposure to pure O2 atmospheres at normobaric or hyperbaric pressures (normobaric oxygenation NMO, and hyperbaric oxygenation, HPO, respectively). Numerous investigations have been undertaken both in animals and in man using RHO, NMO, or HPO as an adjuv…
Heterogeneous Oxygenation of Rectal Carcinomas in Humans: A Critical Parameter for Preoperative Irradiation?
The surgical treatment of rectal carcinoma in humans is often combined with irradiation. However, the efficacy of this latter treatment modality is crucially influenced by the oxygenation status of the tumor tissue to be treated. Therefore, the knowledge of the O2 supply to the tumor tissue is a decisive prerequisite for the assessment of the efficiency of radiotherapy.
Relationship Between Size and Oxygenation Status of Malignant Tumors
During advanced phases of malignant growth, there are typical changes in the microvasculature pattern within the tissue of many solid tumors. Partly due to these peculiarities of tumor vascularization, a series of characteristic variations of tumor microcirculation occurs (for a review see 1). These alterations lead not only to marked restrictions and inhomogeneities of both convective and diffusive transport but also to an impairment of the efficiency of antitumor therapies.
Effect of Localized Hyperthermia on Tumor Blood Flow and Oxygenation
Hyperthermia has been shown to have a lethal effect in tumor cell cultures, particularly at temperatures above 42°C.1 Moreover, it has been demonstrated that hyperthermia retards the growth rate of certain types of malignant tumors and can be effective in completely eradicating some tumors without any major damage to normal tissue.2,3,4 The differential response of solid tumors in vivo to heat treatment in comparison to normal tissue probably results from several factors. Among these the in vivo micro-environment seems to play a decisive role. In general, the interstitial milieu of solid tumors is characterized by tissue hypoxia and anoxia5,6 and by severe tissue acidosis.7 These unfavorabl…