Some final references

[Martin Baeker <martin.baeker@tu-bs.de>]

Forgot to forward this to the list although it might be of some
interest concerning RTs...


Unfortunately, I only could access the abstract of the first, but I
think it makes the point that RTs work well quite clearly by bypassing
them.


Nasal Respiratory Turbinate Function in Birds
Author(s)       Nicholas R. Geist
Identifiers     Physiological and Biochemical Zoology, volume 73 (2000), pages 
581

Nasal respiratory turbinates are complex, epithelially lined
structures in nearly all birds and mammals that act as intermittent
countercurrent heat exchangers during routine lung ventilation. This
study examined avian respiratory turbinate function in five large bird
species (1151,900 g) inhabiting mesic temperate climates. Evaporative
water loss and oxygen consumption rates of birds breathing normally
(nasopharyngeal breathing) and with nasal turbinates experimentally
bypassed (oropharyngeal breathing) were measured. Water and heat loss
rates were calculated from lung tidal volumes and nasal and
oropharyngeal exhaled air temperatures (Tex). Resulting data indicate
that respiratory turbinates are equally adaptive across a range of
avian orders, regardless of environment, by conserving significant
fractions of the daily water and heat budget. Nasal Tex of birds was
compared to that of lizards, which lack respiratory turbinates. The
comparatively high nasal Tex of the lizards in similar ambient
conditions suggests that their relatively low metabolic rates and
correspondingly reduced lung ventilation rates may have constrained
selection on similar respiratory adaptations.


Or if you prefer mammals:

The contribution of nasal countercurrent heat exchange to water
balance in the northern elephant seal, Mirounga angustirostris

AC Huntley, DP Costa and RD Rubin

Elephant seals fast completely from food and water for 1-3 months
during terrestrial breeding. Temporal countercurrent heat exchange in
the nasal passage reduces expired air temperature (Te) below body
temperature (Tb). At a mean ambient temperature of 13.7 degrees C, Te
is 20.9 degrees C. This results in the recovery of 71.5% of the water
added to inspired air. The amount of cooling of the expired air (Tb -
Te) and the percentage of water recovery varies inversely with ambient
temperature. Total nasal surface area available for heat and water
exchange, located in the highly convoluted nasal turbinates, is
estimated to be 720 cm2 in weaned pups and 3140 cm2 in an adult
male. Nasal temporal countercurrent heat exchange reduces total water
loss sufficiently to allow maintenance of water balance using
metabolic water production alone.

This latter paper I could access in full. It shows nicely how
temperature is reduced in the turbinates and water is retained by
this. The discussion starts with the sentence

Nasal countercurrent heat exchange results in a significant reduction
of respiratory evaporative water loss (EWL) in the northern elephant
seal. Reduction in Te and calculated water savings are comparable to
those reported for several large and small animals adapted to arid
habitats (Jackson & Schmidt-Nielsen, 1964; Collins et al.  1971;
hangman et al. 1978, 1979).


I have to admit, though, that the RTs may not be as efficient as
theory predicts: (here again I only can access the abstract)

The Role of the Nasal Passages in the Water Economy of Crested Larks and Desert 
Larks
Author(s)       B. Irene Tieleman, Joseph B. Williams, Gilead Michaeli, and 
Berry Pinshow
Identifiers     Physiological and Biochemical Zoology, volume 72 (1999), pages 
219

Condensation of water vapor in the exhaled air stream as it passes
over previously cooled membranes of the nasopharynx is thought to be a
mechanism that reduces respiratory water loss in mammals and
birds. Such a mechanism could be important in the overall water
economy of these vertebrates, especially those species occupying
desert habitats. However, this hypothesis was originally based on
measurements of the temperature of exhaled air (Tex), which provides
an estimate of water recovered from exhaled air as a proportion of
water added on inhalation but does not yield a quantitative measure of
the reduction in total evaporative water loss (TEWL). In this study,
we experimentally occluded the nares of crested larks (Galerida
cristata), a cosmopolitan species, and desert larks (Ammomanes
deserti), a species restricted to arid habitats, to test the
hypothesis that countercurrent heat exchange in the nasal passages
reduces TEWL. Tex of crested larks increased linearly with air
temperature, (Ta): Tex=8.93+0.793ÃTa. Following Schmidt-Nielsen and
based on measurements of Tex, we predicted that crested larks would
recover 69%, 49%, 23%, and -5% of the water added to the inhaled air
at Ta's of 15Â, 25Â, 35Â, and 45ÂC, respectively. However, with the
nares occluded, crested larks increased TEWL by only 27%, 10%, and 6%
at Ta's of 15Â, 25Â, and 35ÂC, respectively. At Ta=45C, TEWL of the
crested lark was not affected by blocking the nares. In contrast to
our expectation, occluding the nares of desert larks did not affect
their TEWL at any Ta.


Despite the discrepancies between expected and measured water loss, this
still shows that *some* water is obviously retained by the RTs.


I rest my case.



                   Priv.-Doz. Dr. Martin BÃker
                   Institut fÃr Werkstoffe
                   Technische UniversitÃt Braunschweig
                   Langer Kamp 8
                   38106 Braunschweig
                   Germany
                   Tel.: 00-49-531-391-3073                      
                   Fax   00-49-531-391-3058
                   e-mail <martin.baeker@tu-bs.de>