Re: Ruben was right

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

This is probably my last comment on this matter due to time
restrictions and the fact that the tone of the discussion seems to be
becoming something I don't like to be involved in.

> > Imagine the blood-air-barrier were completely impenetrable to water,
> > then there would be no water exhaled. Imagine it were completely
> > impenetrable to CO2, there would be no CO2 exhaled. So is it clear
> > that partial pressures must be the same?
> No comments.

Why not? If I understood correctly, your argument was that the same
amount of water and CO2 is produced in the body, therefore the same
amount (partial pressure) must come out of the lungs. (If I
misunderstood again, tell me). My argument shows that this is not
necessarily the case - the blood could loose much more water than CO2
to the air in the lung - thsi water would then have to come from
somewhere else.

> > BTW, these are questions that could be easily answered by
> > experiment. Here's an abstract I found with google:
> No. Any experiment deals with more than one hypothesis but with multiple.
> Care must be taken.

Even though I am a theoretical physicist, I'll always prefer
experiment (if well-laid out) to back-of-the-envelope estimates.


> The both abstracts you have posted do not state CO2 pressure in exhausted
> air and body temperatureof animals. 

Since what comes in must go out, the CO2 exhaled must equal the O2
taken in - since there is no other way the body can loose CO2 or get
O2.

>That makes is slightly incomplete.
> At 35ÂC, hovering (not resting!) hummingbirds apparently face the danger
> of overheating. As they do not have sweat glands, they _have to_
> hyperventilate their lungs. (CO2 pressure should decrease)

So you say that in this case what comes in does not equal what goes out?


> > At 0 Â C the respiratory water loss and metabolic water production were
> equal
> If hummingbirds were endotherms that would disprove my analysis.
> But I was reffering to lung temperature, not ambient air temperature.
> In my generic 4%CO2 animal model, that could be interpreted as: at ambient
> T=0ÂC the bird has
> body T of about 41ÂC and lung T about 29ÂC,

You don't believe that, do you? A lung temperature 12ÂC below body
core temperature? How would this be maintained?

> > similar to oxygen consumption. At 30ÂC, total evaporative water loss
> > was 5.4 mg H2O gâ1 hâ1. Nonrespiratory evaporative water loss was 5.1
> > mg H2O gâ1 hâ1 and accounted for 94% of total evaporative water
> 
> > Whereas water loss is 5.4mg which is 30 times larger (the difference
> Again you compare wrong values... My generic animal model does not predict
> nonrespiratory water losses (the goal was to testify Ruben's claim).
> And in the second abstract we do not know respiratory water loss.
> We could substract 5.1 from 5.4 but result is highly unreliable as both
> numbers are approximate and we get what is "Loss of precision in
> substraction".
> (Please don't ask me to tell about metrology and ariphmetic. -> Google)

Spare me your patronising, please...

> This does not contribute to Ruben's claim that ectotherms do not have to
> worry about respiratory water loss. Rather reverse.

No, it simply shows that it is not obvious that respiratory water loss
is always given once you know CO2 output. That, IIUC, was your claim.

Martin.

                   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>