Effects of low frequency noise upon the reaction of pleural milky spots to mycobacterial infection.

INTRODUCTION

Milky Spots (m.s.), also known as Kampmeier's foci, are confined to the parietal leaflet and act as a barrier to mediastinum infections, having very important phagocytic functions. Previous studies have made clear that large pressure amplitude and low frequency (LPALF) noise (> or = 90 dB, < or = 500 Hz) induces morphofunctional changes on the pleural mesothelium. The purpose of this study was to investigate the dynamics of m.s., namely the response to infectious agents reaching the pleural space under noise stress.

METHODS

Wistar rats (n = 20) were used; 5 as control and sham operated, 5 exposed to infection but not to noise, 5 exposed to 1696 cumulative hours of LPALF noise, and 5 exposed to 2184 cumulative hours. Following noise exposures, all rats except the 5 controls were injected with 0.2 ml of saline solution containing 2 x 10(8) viable mycobacterium avium bacilli (ATCC-25291 strain, sereotype 2). The rats were sacrificed 21 d after infection and sections of the retrocardiac pleural leaflets were observed with a light microscope using the Ziehl-Neelsen staining method.

RESULTS

There was an increase in the number and diameter of the m.s. due to hypercellularity, mainly caused by the increase of mononuclear cells, and there was formation of large granulomas containing many mycobacteria. Rats submitted to noise also presented alterations of the standard morphological changes, namely partial necrosis of the m.s.

CONCLUSION

The data suggest that exposure to LPALF noise can interfere with the normal immune response to bacterial infection in rats. This can be an important contribution to the understanding of the disorders in the pleural space of vibroacoustic disease patients.