THE SHORTER-TERM BIOLOGICAL HAZARDS OF A FALLOUT FIELD
60 percent of the experiments did the mean
tidal volume increase as the mean respiratory
frequency decreased. (It should be pointed
The hygro-
scopic nature of this aerosol is undoubtedly
responsible for some of this increased value,
but estimates of this contribution do not account for the difference scon.
out that these experiments were frequently
weeks or months apart.) Consequently, it appears that the tidal solume is as relevant a
factor as is the respiratory frequency. It is
The relation of deposition ta respiratory
characteristics is shown in Figures 3 and 4.
In Figure 3 is seen a plotof the percent of the
aerosol mass deposited as a functionof the mean
respiratory frequencies and the mean tidal
volume from the 17 experiments.
Each exper-
same individual are interconnected.
The heavy
rexsonable to explain this on the basis that as
the tidal volumeincreases, the numberof particles inhaled increases, and that a deeper, fuller
respiratory tidal volume provides for a more
intimate contact of aerosol particles with the
vast. mucosal surfaces of the hing. Both of
iment provides a single point, and those on the
(Remember particle den-
sity is of no importance at these sizes.)
atory frequencies and/or higher tidal volumes.
This inverse relationship may be due to an
interdependence of these two variables. In
In Figure4 is anotherset of parameters which
appear interesting; the mean respiratory air
flow rates ag plotted against percent mass deposition. As seen in the figure, in the case of
other words, the deposition may be a function
of tidal volumo and since an increased tidal
volumeis generally associated with a decreased
respiratory frequency, such a relation would be
expected. However, unlike previous reports (at
larger particle sizes) wherein these were in-
E
o
~.
inspixation, an increase in the mean air flow
whereas in the case of expiration, a decrease in
the mean air flow rate was associated with an
incrersed deposition. Again, there is a prob-
ex
&
“oF
S 40
—?
°o
A.
4.
4
300
100
(co. RTPS air/sec)
i
i
i
12
I
al
16
MEAN RESPIRATORY
FREQUENCY (cycles /min.)
j
400
L
i
600
i
MEAN TIDAL VOLUME
{ec.R TPS air)
Figur» 3.-—~Effect of tidal volume and respiratory frequency on aerosol deposition.
i
800
A
he
200
a
300
(cce.RTPS air/sec)
Fiaure 4.-- Effect of respiratory air flowrates on aerosal deposition.
able interdependence; one which may involve
particles are less than 0.4 «4 diameter but only
instance, it was found that as the respiratory
frequency decreased, it was generally associated
with an increase in the expiratory phase duration, more so than with the inspiratory phase
due to these particles. In other words, a mass
the tidal volume or respiratory frequency. For
duration; thereby tending to produce an increased mean inspiratory air flow rate particularly if the tidal volume increased. One may
50 percent of the aerosol mass is presumably
deposilion value of 50 percent could be based.
on the nasal-pharyngeal deposition of a few
thousand particles greater than 0.4 u diameter
or it could be due to millions of small particles
depositing in the lung parenchyma. This point
serves to illustrate, first, the need for particle
size deposition data instead of, or along with,
mass deposition data.
It demonstrates that.
impaction process might be so efficient. during
mass deposition measurements are based on
the recognition of a relatively few particles
portant during the expiration. Even more possible is the idea that particle deposition would
Such measurements ignore the contribution of
be improved by the increased turbulence induced by highair flows.
8
1
MEAN INSPIRED AIR FLOW RATE - MEAN EXPIRED AIR FLOW RATE
inspiration that it would be relatively unim-
2= 20
o!
4.
200
tory velocities by impaction and possibly the
ow
xs
i
100
hypothesize that the deposition of the larger
particles would be increased by higher inspira-
™
ul
20
generally resulted in an increased deposition
100
80
40
these conditions tend to promote Brownian
motion deposition.
arrow is to denote the general trend, which is
toward dnercased deposition with lower respir-
z
°
tion of not more than 55 percent.
oO
variably related in an inverse manner, only in
tion value for this particular aerosol distribu-
193
DEPOSITION
o
Ss
oa
cepted relations predict a percent mass deposi-
RETENTION OF SUB-MICRON ABROSOLS IN HUMAN RESPIRATORY TRACT
¥% MASS
192
DISCUSSION
Somepointsin this experimental studyrelate
to the fallout problem. One is best seen by
returning to Figure 2. Observe the mass dis-
tribution of this aerosol: 99 percent of the
which are generally believed to only rarely
penetrate beyond the anatomical dead space.
the greater percentage of the particles which
can presumably penetrate into the lung paren-
chyma.?*
Thus, to return to the original considerations,
4 There ts increasing evidence that radioactive nuclei adsorb onto
avallahle dust as a function of thet total diameter rather than total crosssectlon (Smoluchowski, 19).
In our ense, equivalent total diameters
occur at about 0.09 4 glee so that the first (smaller) 65 percent of the
particles provide 50 percent of the total diameter but only a few percant
of the mass (<3%).