"jcarlyle" wrote in message
oups.com...
Thanks, Hartley, I appreciate that!

-John

On Jan 28, 1:54 pm, "HL Falbaum" wrote:
Udo, John:

I'll do a bit of review and try to formulate a clear answer in "educated
layman's" terms. The full technical explanation is a bit soporific and
not
really necessary for the purpose at hand..


Well--here it is FWIW:
Sorry its long but it does not lend itself well to a one paragraph answer.

This is the short explanation of renal function and water management for
glider pilots. First a few explanations and basic facts.
Water exists in the human body in two basic "compartments". Inside the cells
( intracellular fluid "ICF") and outside the cells (extracellular fluid
"ECF"). Visualize this as small, close together, islands in a vast swamp.
This fluid is not just water, but ions and small protien molecules. The
major players are Sodium, Potassium, Bicarbonate, and Ammonium. These
regulate cell function and acid-base balance, among other things. They
(water and solutes)are transported back and forth across cell membranes by
active "pumps", which are part of the cell, and osmotic pressure gradients,
which transfers water.

We gain water by drinking, and by metabolism of foods, as well as extraction
of water from the foods (think watermelon, celery, oranges, etc). We lose
water by breathing out water vapor, by direct transpiration from skin,
sweating, and urine production. The amounts vary with temperature, air
moisture content, ambient pressure, and exercise.

Breathing, at sea level pressure, and standard atmosphere temperature and
moisture, and at rest loses us about 375 to 500 cc per day. Much more at
high altitude and on oxygen.Transpiration, about 250 to 350 cc per day,
while sweating and urination can be quite variable, as we all know. The US
Army Surgeons Handbook suggests that total losses can approach 15 liters per
day in combat troops--flack vests, equipment, heat, exertion and the like.
Sweat contains salt, but not as concentrated as in the plasma, or ECF/ICF.

The body produces, just by metabolizing, a certain amount of wastes per day
which the kidneys must remove. This requires about 400 cc of urine per day,
assuming normal kidney function.

So here's how it works---blood flows through capilliaries in the kidney,
surrounding the glomerulus. This is a filter, allowing out water and the
solutes mentioned above. Then the filtrate passes to the renal tubule (a
little tube) and the capilliaries follow. The tubule is an active structure
and pumps water back into the capps but leaves some for the tubule. Under
the influence of the pituitary gland, the water is regulated by Vasopressin
(AntiDiuretic Hormone) and the Sodium by Angiotensin. ADH is a osmotic
regulator, and Angiotension is a blood pressure regulator. Acid base balance
is controlled by pumping Bicarbonate and Ammonium ( and also by the lungs,
adjusting CO2). Once the tubules have done their job, the remainder is
pumped by pressure and peristalsis (muscular contraction waves in a tubular
structure) down the ureter into the bladder.

The bladder is a muscular-walled sack which can contract involuntarily, and
this contraction can be inhibited or facilitated by conscious control. The
sphincter (think of a O-ring which can change diameter and thickness)
controls the flow, and is under voluntary control and well as involuntary
control. (This is the secret of toilet training.). When the bladder begins
to get full, it sigmals the spinal cord to produce the "micturition"
(peeing) reflex, and you get the signal. This starts at about 150 cc and
comes and goes untill 4-500 cc, when the bladder is full. The reason it
comes and goes is that it is a pressure signal, not a volume signal. The
bladder, being a muscle, can relax, pressure will decrease and it becomes
larger in capicty. (this is the other secret of toilet training).
Eventually, it cannot be ignored, as you all know! You relax the sphincter,
command bladder contraction facilitation and abdominal wall
contraction--and, whew! relief!

If we don't provide a sufficient flow rate to the tubules, they will
concentrate the wastes as best they can, until the pumps can no longer
overcome the osmotic pressure gradient, then they give up! If we don't empty
the bladder, we eventually cannot overcome the pressure gradient and the
tubules and the glomeruli give up. If the wastes are too concentrated too
long, we form Calcium or Oxalate stones.

So what do we need to do? We must provide mild excesses of water and
electrolytes to the system and let it take what it needs. How do we know we
have done that--? Well, we know that we need to excrete at least 400-500 cc
of urine per 24hr. We know that urine should not be overly concentrated. We
know that when we sleep, our blood pressure, heart rate and respiratory rate
is decresed, thereby requiring less urine output. Therefore we need to
excrete more urine during the day. Plan 35-50 cc per hour, and moderate
concentration--light to medium yellow. If we do that, we are well hydrated
and our urinary system is functioning well-no danger. Acid-base balance is
maintained (another source of cognitive impairment).If we drink enough to
maintain those pasameters, we should be fine. Water is good if we are not
doing muscular effort (as we are not losing electrolytes much), Gatorade or
Powerade if we are doing heavy muscular effort (assemble 3 ASW20B's in a
row)--but be careful. The glucose can cause an insulin spike, and drop your
blood sugar.

In the final analysis, it's really simple. Drink enough to maintain about a
40-50cc/ hr urine output. For those who say "I don't pee much", I
say--measure--maybe it's enough after all-maybe not. To those who measure
their flights by "pee bags", well-enjoy, but you may be overdoing it. (I
have seen a FULL 1 gallon ziplock bag come out of a glider after landing!)

I hope this helps

Hartley Falbaum