Vol. 276, Issue 1, L207-L212, January 1999
SPECIAL COMMUNICATION
Time domain reflectometry: measurement of free water in normal lung
and pulmonary edema
Nobuhiro
Miura1,2,
Sumie
Shioya1,
Daisaku
Kurita1,
Teruyoshi
Shigematsu1, and
Satoru
Mashimo
,2
1 Department of Internal
Medicine, Tokai University School of Medicine, Isehara, Kanagawa
259-1193; and 2 Department of
Physics, Tokai University, Hiratsuka, Kanagawa 259-1292, Japan
The free water content of lung tissue was
investigated by dielectric spectroscopy in normal lungs and in
pulmonary edema induced by oleic acid in rats. The dielectric
relaxation in a frequency range of
107 to
1010 Hz was measured
with the time domain reflectometry method at 25°C.
Three dielectric relaxation processes were analyzed for the lung
tissue. A high-frequency process around 10 GHz was attributed to the
orientation of free water molecules based on the relaxation time
[log 
h (in
s) = 
11.03]. The dielectric
strength (
) of this high-frequency peak
(h) should reflect the
amount of free water in the tissue. Because the measured
h depended on the air
content of the lung samples, the value of
h was corrected for the air
content of each sample as determined by the point-counting method in
the area where the time domain reflectometry data were obtained. The
lungs of rats that received an injection of oleic acid had a
significantly increased free water content
[(h of lung/ of
pure water) × density of pure water] compared with that in
the normal lung (0.76 vs. 0.59 g/cm3). These results indicate
that free water occupies ~60% of the total volume of normal lung
tissue and that there is an increase in free water in pulmonary edema.
lung tissue water; oleic acid-induced lung injury
Deceased 29 March 1996.
