Effect of carbogen breathing on tumour microregional blood flow in humans

Abstract

Background and purpose: Carbogen is currently being re-evaluated as a radiosensitiser. It acts primarily by increasing tissue pO 2, although there is evidence to suggest that enhanced tumour blood flow may also be a component of its action. Materials and methods: Ten tumours in eight patients with advanced malignant disease were studied. Up to six microprobes, each with an estimated sampling volume of 10 −2 mm 3, were inserted into the tumours. Ten min of baseline readings were taken prior to a 10 min carbogen ( 95% O 2 5% CO 2 ) breathing period, measurements were continued for a further 10 min. Results: The results show that in 34 microregions analysed no overall change in tumour perfusion was seen with carbogen breathing. Individual tumour analysis demonstrated variation in response between patients to carbogen — after 6 min of carbogen four tumours showed an increase in blood flow by more than 10% of the pre-breathing value, two a decrease and four no change. The magnitude of change was small, with only two tumours fluctuating by more than 25%. Conclusions: These findings confirm the presence of transient fluctuations in microregional blood flow in human tumours but suggest that the radiosensitising action of carbogen lies primarily in its effect on increasing the oxygen capacity of blood. This supports the addition of agents such as nicotinamide with carbogen in order to overcome both diffusion and perfusion limited hypoxia.