Posted by MHK on June 28, 2001 at 17:17:40:
In Reply to: Re: Thanks Bill.... posted by John Walker on June 26, 2001 at 14:01:36:
Effects of Deep Air on The Body
Ben,
You raise some very interesting questions regarding blood viscosity and the behavior of blood within the microcirculation. The reality may be a lot worse than any of us may have imagined. Fortunately, for vertebrates, the apparent viscosity of whole blood decreases in tubes with diameters less than 0.1cm. This observation is known as the Fahraeus-Lindqvist effect and implies that the shear stress at the capillary wall decreases as the tube diameter decreases. On the contrary suspensions of rigid particles display no such behavior. Mammalian capillaries range in diameter from 10 micrometers down to 3 micrometers so that blood cells have to flow down them in single file. For those capillaries whose diameters are less than that of a cell (7 - 8 micrometers) Red blood cells must deform to pass through the vessel. High pressures must be generated locally within the thin layer of fluid around the cell in order to deform it and therefore depend considerably on the elastic properties of the cell. Anything which impairs the elastic characteristics of the blood cell may have a profound mechanical effect on both the cell and the blood vessel.
Abnormal cells which are hardened or almost spherical cannot be deformed so easily and therefore cannot pass through the smallest vessels. In experiments performed to determine the size of the smallest vessel through which a red blood cell can transit it was found that anything smaller than 3 micrometers caused damage to the cells. Cells which are artificially hardened or made to swell into a spherical shape (osmosis), impairing flexibility, cannot pass through pores less than 8 micrometers in diameter without suffering haemolysis (cell destruction).
In view of the above scenario it would seem that any action which would artificially "stiffen" blood cells could have a potentially negative impact in terms of both the mechanical damage to the cells and capillaries themselves as well as decreased perfusion of the surrounding tissues. Where critical tissues are concerned, such as those subserving neurological processes (your brain for instance) the effects of diminished mass transport could be profound. Since the capillary micro-circulation plays an essential role in gas transfer during compression and decompression one might be further concerned as to the effects of red blood cell rigidity associated with hyperbaric exposures to air.
Blood is forced to flow through capillaries as little as 3 micrometers across in the splenic pulp. Normal cells can do this with little haemolysis; however abnormal spherical cells cannot, such as what occurs in the disease known as hereditary spherocytosis (sickle cell anemia is another disease which distorts blood cells). The spleen filters out blood borne debris as well as housing a large population of B cells, the immune soldiers which manufacture antibodies in response to an alert by the T cells. There was some speculation recently in the DAN journal regarding "Divers Disease", a flu-like illness which sometimes accompanies hyperbaric exposures. I wouldn't be at all surprised if the cause of this problem turns out to be the aftereffects of red blood cell rigidity and the consequent build up of haemolized cells in the spleen and lymph nodes.
Maybe its just a coincidence, but deep air diving carries obvious and subtle neurological effects and it poses very problematical decompression issues for long exposures (empirically and anecdotal observations). I personally have experienced fatigue and other flu-like symptoms following exposures to air diving and attribute this to some form of immune system response.
Eventually, physiologists and hematologists will understand the specific underlying effects of excessive hyperbaric air. For the mean time I think its a safe bet to avoid deep air at all costs.
Regards,
Bill Mee