Previous studies during head-out immersion have shown closing volume (
CV) to either increase or remain unchanged. We hypothesized that these
inconclusive results might be related to differences in the ages of t
he subjects tested. To elucidate this we studied single-breath argon w
ashout tests performed by a younger group (n=8, age 23-26) and an olde
r group (n=8, age 40-54) of males every 5 min during 30 min of seated,
thermoneutral head-out immersion. No temporal changes in CV during im
mersion were observed in either group, therefore values within each gr
oup during immersion were combined. In the younger group, CV increased
77% (dry, 0.26+/-0.11 L; wet, 0.46+/-0.10 L; Delta=0.20 L) (P<0.001)
but remained less than the tidal breathing range upper limit [expirato
ry reserve volume + tidal volume (ERV + VT)]. In the older group, CV i
ncreased 34% (dry, 0.83+/-0.29 L; wet, 1.11+/-0.19 L; Delta=0.28 L) (P
<0.05) and was not different from ERV + VT, The absolute increase in C
V during immersion did not differ between the groups. ERV decreased du
ring immersion in both groups and was lower in the older than younger
group (P<0.001). Alveolar plateau (phase III) slope became steeper in
the younger (P<0.001) but not in the older group. We conclude that dur
ing immersion: (1) The absolute increase in CV is independent of age,
and (2) in subjects over 40, CV approaches the highest lung volumes re
ached during tidal breathing. Older subjects may be more likely to dev
elop atelectasis during immersion and/or under other conditions in whi
ch CV is increased and tidal breathing occurs at low lung volumes.