The microvasculature is a ubiquitous organ system having a major role in the pathogenesis of radiation damage to normal tissues. Although the kinetics of radiation damage to endothelial cells is similar to other tissues (as reflected by Do and Dq) the late effect is a manifestation of injury, not only to the endothelial cell population, but also to the basement membrane. Tissue damage is progressive. The initial expression of radiation injury is an increased permeability leading to changes in the extracellular milieu. There is an irregular proliferation of endothelial cells leading to capillaries of irregular diameter and shape. Fibrous proliferation increases the histohematic barrier and is ultimately reflected in a loss of parenchymal cells. Replacement fibrosis progresses until a steady state is reached where the surviving parenchymal cells can be sustained by the microvasculature. The clinical significance depends on the role of the organ system involved. For patients who have medical conditions which adversely effect the stability of the vascular system (hypertension, diabetes, etc.), the expressions of radiation injury may be more severe and increase the morbidity associated with these diseases. Angiogenesis in granulation tissue is less radiosensitive than in steady-state parenchymal tissues. Wound healing is not significantly affected by commonly used therapeutic doses of irradiation, 40-50 Gy delivered 4-6 weeks preoperatively or postoperatively early in the development of the granulation tissue, but may be complicated where a significant degree of fibrosis has developed. The vascular responses leading to telangiectasia were discussed.

Reicosky, D.C., Winkelman, L.J., Baker, J.M. and Baker, D.G., 1989. Accuracy of hourly air temperatures calculated from daily minima and maxima. Agric. For. Meteorol., Temperature is one of the critical variables that drives biological systems and is of fundamental importance in crop growth models. The objective of this work was to determine the accuracy of several methods for calculating hourly air temperatures from daily maxima and minima. Methods that have as inputs daily minimum and maximum temperature were selected from the literature based on their use in existing growth models and simplicity. Four years of hourly air temperature data collected during the growing season at 2 m over well-watered grass were used to test the various methods. Six days from each growing season were randomly selected for detailed analysis, and an additional 9 days were selected to cover a range of daily maximum temperatures and solar radiation. The absolute mean error within a 24-h period ranged from 0.5 to 9.3 ° C for the 6 randomly selected days for all 4 years of the data. All methods worked reasonably well on clear days but with limited success on overcast days. Daily maximum temperature did not appear to affect the accuracy of any of the methods. If accurate timing of temperature input to models is critical, the results indicate direct measurement of hourly temperature may be necessary.

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