DEPOSITION OF MMMF (CERAMIC FIBERS)
IN THE LUNGS OF GUINEA PIGS
DISSERTATION CONCLUSIONS AND RECOMMENDATIONS
The design of the chamber and the tubes to hold the guinea pigs was satisfactory
for exposing the animals by inhalation (nose only).
The exposure for six hours had no apparent physical effects on the well being
of the animal.
The overall concentration and size distribution of the dust cloud were within the
desired range. The average concentration of the air in the exposure chamber was
297 fibers/ml with CML of 13.3
μm and CMD of 0.92 μm.
The CML and CMD in the (LRT) slightly decreased from group I to group III.
In the (URT) the CML for groups I and II was the same and slightly increased in
the third group. The CMD increased from group I to group II and then sharply
decreased to group III. In the (ERT) the trend was similar to that of the (LRT).
With the exception of the upper left and right lobes the CML and CMD in the lobes
were not dependent on the weight of the lobe nor on its location within the lung.
Fiber retention in the animals as percent of inhaled fibers were 30.8 ± 1.61,
27.1 ± 1.33 and 21.9 ± 1.66 for groups I, II and III respectively.
Fiber retention in the lungs of animals as a whole and in individual lobes increased
with increasing fiber length up to 6.5 μm and then decreased with increasing fiber
length. Retention by diameter peaked at 0.5 μm and rapidly decreased as the
Retention in the lobes was found to be dependent on the location and the average
distance of the lobe from the principal bronchus and trachea, and not on the size
of the lobe.
Pulmonary deposition in the guinea pig is higher than that obtained for rats.
Pulmonary deposition by fiber size is comparable to that reported for man.
In terms of short-term fiber clearance, fibers with length >10 μm and diameter
>1.5 μm cleared faster than shorter and thinner fibers.
For better measurements of short-term clearance, retention should have been
measured at more frequent intervals.
Fiber clearance in the respiratory tract appears to be associated with two
clearance half-lives: t1/2 of 25 hours in the URT and t1/2 of 362 hours in the LRT.
The impaction equivalent diameter and mass equivalent diameter are better
descriptors of fiber deposition in relation to fiber dimensions than the conventional
aerodynamic equivalent diameter.