On the
27.11.14 I had the great pleasure of meeting and having a seminar from Suzy
Munns. She is a comparative respiratory physiologist and started off by
studying a bachelor of science majoring in Zoology. Suzy struck me as a very
intelligent and charismatic person and her fields of study proved to also be very
interesting.
In her
research on the respiratory system in crocodiles she discovered something and
was then faced with the reality of having to prove years and years of accepted
knowledge wrong.
It had
been believed that crocodile respiration, explained by the term hepatic piston
pump was a completely new and unique mechanism for respiration only found in
crocodiles. It was thought that a muscle
call the Diaphragmaticus muscle was used to pull the internal organs such as
the liver backwards (caudally), which in turn pulled the bottom of the lungs
backwards and expands them.
But on
dissection of a crocodile Suzy noticed that this Diaphragmaticus muscle which
was thought to be so crucial in the respiration of crocodile was thin and
almost transparent.
On seeing
this it seems impossible that such a small muscle could be capable of pulling
organs around and being the main mechanism used in respiration.
The main
reason why this Diaphragmaticus muscle was assumed to be the main mechanism for
inspiration in crocodiles was because previous studies had shown that it fired
during inspiration. But the issue was that technology has advanced a lot since
this these studies were undertaken, and it was likely that this information was
inaccurate due to the technology and information present back then. To test the
impacts of the hepatic piston pump on respiration a number of test were
run.
One of
the hardest things that Suzy had to undertake in this research was training
crocodiles in the lab to run on a treadmill in order to be able to monitor the
different parameters such as, blood gases and EMG. Breathing masked were also
placed on the crocodiles, these measured pressure changes and collected expired
air. Basically anything that could be measured during activity they
measured.
The tests
were run under two different conditions. The crocodiles where monitored with
their Diaphragmaticus muscle still intact and then they were tested again after
the muscle had been severed. In order to severe the muscle the crocodiles
underwent an operation under anesthesia. And of course I thought I must add
that the these individuals had a couple of days to recover after their
operation before the tests were run.
The
results from these tests showed that there were no significant differences in
ventilation or blood gases after inactivation of the Diaphragmaticus muscle.
This was tested under the conditions:
- At rest
- Under reduced respiratory drive (low temp)
- Under increased respiratory drive (exercise/ hypercapnia (increased carbon dioxide))
From
these studies it could be concluded that the hepatic piston pump may act as a
supplement in ventilation but it is not the primary ventilation mechanism.
Costal ventilation was found to be the primary ventilation mechanism in
crocodiles.