Max Weinmann, an Undercurrent subscriber and
a critical care specialist in Atlanta, GA, writes, "I am
grateful for John Bantin's timely thoughts on computer
reliability and DCS avoidance (Undercurrent March). The
challenge does, indeed, go beyond the ability to achieve
mathematical manipulations of algorithms, which have
always been difficult to test in humans, and in particular,
those of us who present ubiquitous but growing
challenges; namely aging, at least in physiological terms.
"This has been clearly demonstrated recently by
the increasing morbidity and mortality of older divers.
Change in weight, fitness, cardiovascular and organ
health, and the indignation of a growing medicine cabinet
replete with blood pressure, cholesterol, prostate
and hormone replacement medication, to name a few.
All of which collude to alter our physiology and the
nature of gas uptake and release as we dive. Since the
introduction of computers, we have largely become
passive travelers of a tour governed utterly by the laws
espoused by these algorithms, where personalization
is based upon standard deviation manipulation rather
than on the increasingly complex diversity of our own
body physiology."
"Hence, adhering to computer-driven dives is not
a guarantee of avoiding DCS. Specifically because
our physiology is a dynamic environment constantly
changing from moment to moment and compensating
for changes in body fluid balance, chemical intake,
hormone levels, external temperature, cardiac health,
vascular sufficiency, etc. This leaves many computer
algorithms wanting. "Indeed, as Bantin points out,
'The problem with all of this is no algorithm writer
can write one specifically tailored for you. It's all
based on hypothesis and Haldane's original research
from more than 100 years ago.'"
As a diver and critical care/hyperbaric physician,
I've seen firsthand the vagaries of DCS and the incredulity
of divers, both young and old, who have developed
the condition, despite adhering religiously to a
computer profile a statistically-derived calculation that
is incapable of taking into account individual factors such as dehydration; previous injury; the increased work the heart must perform in the setting of high
blood pressure -- these are all important determinants
of gas exchange, and hence, personal DCS risk.
"Only recently has Scubapro incorporated the monitoring
of health factors, which brings this dynamic personalization
much closer. By monitoring heart rate and
air consumption (indirect measures of body 'work,' and
hence, gas uptake and consumption), the algorithm that
will determine Joe Diver's underwater profile is based
upon actual biologic measurement and not statistics. For
the first time, the profile will be based upon dynamic
real-time measures of the individual diver's physiology,
and not just the average of accrued statistical data. This
is highly impactful in terms of safety, especially for the
over-50 age group."
"While I have no commercial interest in this device, I
am invested in diver safety. I sincerely believe the future
of safe diving lies in real-time monitoring of an individual
diver's physiological determinants of gas handling.
That requirement transcends mere statistics. Diving is
itself a dynamic and highly variable experience, as is
our physiologic response, both between different divers,
and with different dives for the same diver. It therefore
demands a similarly dynamic computer able to integrate
our own unique physiology in order to avoid morbidity
and mortality."
John Bantin replies: "I absolutely agree that not enough
divers bother to understand how their computer works or
what it is really telling them. Too many people buy one, take
it out of the box and blindly use it, without even appreciating
what might be displayed. I met a diver recently who wanted
his computer sent back to the manufacturer because it went
into 'Error Mode.' He assumed it had gone faulty because it
had locked him out from using it for 24 hours. I'm not entirely
sure he believed me when I told him it was telling him that he
was in error mode. He must have come up faster than the prescribed
ascent-rate limit and not done the added time required
on the safety stop. Luckily it had not been sent into 'SOS
mode' -- although I once witnessed a diver try to hide his computer
after it displayed SOS."