Patients in the intensive and critical care unit frequently undergo diagnostic radiology procedures such as computed tomography (CT) and X-ray imaging. As these patients often require respiratory assistance and are vulnerable to infection, it is important to understand the potential acute effects of these procedures on the lungs and immune system. The aim of this study was to determine the acute effects of a single clinically relevant low-dose X-ray exposure in order to establish baseline responses in markers of lung injury and immune function in a rodent model.
Male Sprague-Dawley rats (200-250 g) were irradiated with 0, 2, 20 or 200 mGy whole-body X-rays in an XRAD 320 irradiator. Markers of lung injury and immune activation in the lungs and spleen were evaluated 0.5, 4, and 24 h post-irradiation to examine the acute stages of the physiological and immunological response. Intratrachaeal lipopolysaccharide (LPS) exposure was used as a positive control model of acute lung injury. Lung injury endpoints included respiratory mechanics, pulmonary oedema, arterial blood oxygenation, histological analysis, and cellular and proteinaceous infiltrate via bronchoalveolar lavage. Immunological measures in the spleen focused on splenocyte proliferation, using the MTS assay and differential cell counts before and after stimulation with LPS or concanavalin A (Con A), as compared to unstimulated cultures.
Splenocyte proliferation in response to Con A, but not LPS, was significantly decreased after 200 mGy in vivo X-irradiation (repeated measures two-way ANOVA with LSD post-hoc, p=0.024). There was a non-significant trend towards increased lung tissue resistance after 200 mGy, with no significant effect on pulmonary oedema, cellular or proteinaceous infiltrate, nor other aspects of respiratory mechanics (two-way ANOVA with LSD post-hoc, p>0.05).
A clear understanding of these immunological and physiological effects informs the responsible use of medical diagnostic procedures in modern medicine. Establishment of this model for the elucidation of acute immune effects of low-dose radiation will facilitate future work evaluating these parameters in disease models, mimicking patients in intensive care. / Thesis / Master of Science (MSc) / Diagnostic procedures such as computed tomography (CT) and X-ray imaging are a common part of intensive and critical care medicine. Some physicians are concerned that this exposure to diagnostic radiation may negatively affect the health of their patients, who are prone to infection and who often need a machine to breathe for them. In order for doctors to make informed decisions, the possible effects of these levels of radiation must be understood. To improve this understanding, this study looked at the short-term effects of X-ray doses on key organs affected by critical illness, the lungs, and the spleen, which is an important organ of the immune system that helps fight infection.
Using an animal model, doses of X-rays in the range of diagnostic radiation (0-200 mGy) were examined and no significant effect on lung health was found. However, the highest dose of X-rays tested, which is greater than that expected for a single CT scan, did have an effect on cells from the spleen. Spleen cells are designed to multiply when they detect various types of infection, so that there are more immune cells to fight that infection. The cells from animals that were given the highest dose of X-rays didn’t multiply as much in response to infective stimulus as those from animals that received lower doses, or no X-rays at all.
Overall, it seems that diagnostic radiation doesn’t have an effect in the lungs, but very high diagnostic doses could slightly affect a patient’s ability to fight infection. It is important to remember that patients in critical care are very sick, so doctors have good reason to use diagnostic tools available to them. Missing a diagnosis has major and immediate consequences, which must be balanced against the potential small risks of using radiation to make that diagnosis.
| Identifer | oai:union.ndltd.org:mcmaster.ca/oai:macsphere.mcmaster.ca:11375/20971 |
| Date | January 2017 |
| Creators | Muise, Stacy |
| Contributors | Boreham, Douglas, Radiation Sciences (Medical Physics/Radiation Biology) |
| Source Sets | McMaster University |
| Language | English |
| Detected Language | English |
| Type | Thesis |
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