Download The physiology and pathophysiology of the hyperbaric and diving

J Appl Physiol 106: 274 –275, 2009;
doi:10.1152/japplphysiol.91477.2008.
Editorial
HIGHLIGHTED TOPIC
The Physiology and Pathophysiology of the Hyperbaric and
Diving Environments
The physiology and pathophysiology of the hyperbaric
and diving environments
David R. Pendergast1,2 and Claes E. G. Lundgren1,2
1
Center for Research and Education in Special Environments and 2Department of Physiology and Biophysics, University at
Buffalo, Buffalo, New York
Address for reprint requests and other correspondence: D. R. Pendergast,
Center for Research and Education in Special Environments and Dept. of
Physiology and Biophysics, Univ. at Buffalo, Buffalo, NY 14214 (e-mail:
[email protected]).
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crush injury, poorly healing wounds, necrotizing soft tissue,
osteomyelitis, ischemic skin grafts and retinal vascular occlusion, and, in promising pilot studies, stroke. The current
list of indications paid for by insurers numbers 13 and is
growing. It is only to be expected that the results of ongoing
research concentrating on evidence-based and mechanistic
studies of the physiology and medicine of diving and clinical hyperbaric medicine are intensely cross fertilizing.
This series on “The Physiology and Pathophysiology of
the Hyperbaric and Diving Environments,” although for
space reasons not entirely comprehensive, offers reviews
dealing with topic areas that are central to the general theme
of the series. The review entitled “The underwater environment: cardiopulmonary, thermal, and energetic demands” (6) gives
an overview of effects of water surrounding the body. Another
study will deal with simplest form of diving, i.e., breath-hold
diving, and is entitled “The physiology and pathophysiology of
human breath-hold diving” (4). A subsequent paper in the
series will be “Pulmonary gas exchange in diving” (5), dealing
with the effects of depth, including immersion and pressure, on
respiration. Increased pressure of the respired gas typically
exposes the diver to high partial pressures of oxygen and
nitrogen during air breathing or other inert gases when special
breathing mixtures are used.
Increased nitrogen pressure in the lungs generates higher
tissue nitrogen pressure, and during ascent, this leads to an
excess of nitrogen that must be eliminated via the lungs. If this
elimination does not keep pace with the reduction in depth,
decompression sickness might ensue. Various aspects of how
to prevent this outcome and some of the insights into decompression physiology gained in studies of decompression to
altitude, which has applications also to decompression in diving,
are dealt with in “Decompression to altitude: assumptions,
experimental evidence, and future directions” (3).
Recent advances in physiological research methods are
now allowing much improved understanding of the mechanisms of action of oxygen and oxygen toxicity and the
so-called inert gases as illustrated by the following two
papers: “Two faces of nitric oxide: implications for cellular
mechanisms of oxygen toxicity” (1) and “Effects of hyperbaric gases on membrane nanostructure and function in
neurons” (2). The advances in hyperbaric oxygen therapy
will without doubt be much furthered by the deepening
insight in the mechanisms of action of high oxygen tensions
on important pathological processes as discussed in “Oxidative stress is fundamental to hyperbaric oxygen therapy”
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HUMAN EXPOSURE to the challenges of the underwater world
has been traced back thousands of years (e.g., the diving
women of Japan). However, the last century has seen an
acceleration of activities with disparate foci on the “Silent
World.” The variety and beauty of marine life attract growing numbers of recreational divers, and the pressing need for
exploitation of new energy sources has led to technical
development and physiological research allowing divers to
work at over 500 m of depth. The physical properties of
water favor stealth military operations but have also inspired
competitive diver-athletes to compete in overcoming enormous challenges (the current world record in deep breathhold diving subjected the diver to a pressure of 21 atm). The
severity of these challenges is greater than for any other
human activity and are due to pressure (depth), temperature
extremes, and the unbreathable ambient medium. They affect locomotion, respiration, circulation, renal and nervous
systems, and water and thermal balance due to the physical
properties of water. Direct hydrostatic effects have been
demonstrated, as well as physical and pharmacological or
toxic actions of respired gases at increased pressures. Physiological adaptations to the strains caused by the underwater
environment are achievable, sometimes to an amazing degree, while other challenges require an artificially created
“microenvironment” (breathing gear, diving suit, etc.), and
yet, adjustment is not always sufficient, resulting in injury
and even death.
Some insights into the physiology and medicine of diving
have had marked impacts on the theory and practice of
traditional medicine. The application of increased ambient
pressure, typically in a surface-based pressure chamber, has
been used for over a century to eliminate the gas bubbles
causing decompression sickness in divers but has more
recently been applied, preferably in combination with oxygen breathing, to treat nosocomial gas embolism in the
clinic. A further development of this methodology is the
application of hyperbaric oxygen, currently available at over
900 facilities in this country, to treat a variety of conditions
that might benefit from enhanced tissue oxygenation, or
other pressure-mediated effects. These conditions include,
among others, carbon monoxide poisoning, gas gangrene,
Editorial
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J Appl Physiol • VOL
REFERENCES
1. Allen BW, Demchenko IT, Piantadosi CA. Two faces of nitric oxide:
implications for cellular mechanisms of oxygen toxicity. J Appl Physiol
(October 9, 2008). doi:10.1152/japplphysiol.91109.2008.
2. D’Agosstino DP, Colomb DG, Dean JB. Effects of hyperbaric gases on
membrane nanostructure and function in neurons. J Appl Physiol (September 25, 2008). doi:10.1152/japplphysiol.91070.2008.
3. Foster PP, Butler BD. Decompression to altitude: assumption, experimental evidence, and future directions. J Appl Physiol;
doi:10.1152/japplphysiol.91099.2008.
4. Lindholm P, Lundgren CE. The physiology and pathophysiology of human breath-hold diving. J Appl Physiol (October 30, 2008).
doi:10.1152/japplphysiol.90991.2008.
5. Moon RE, Cherry AD, Stolp BW, Camporesi EM. Pulmonary gas exchange in diving. J Appl Physiol (November 13, 2008).
doi:10.1152/japplphysiol.91104.2008.
6. Pendergast DR, Lundgren CE. The underwater environment: cardiopulmonary, thermal, and energetic demands. J Appl Physiol (November
26, 2008). doi:10.1152/japplphysiol.90984.2008.
7. Spiess B. Perfluorocarbon emulsions as a promising technology: a review of tissue and vascular gas dynamics. J Appl Physiol;
doi:10.1152/japplphysiol.90995.2008.
8. Thom SR. Oxidative stress is fundamental to hyperbaric oxygen therapy.
J Appl Physiol (October 9, 2008). doi:10.1152/japplphysiol.91004.2008.
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(8). Finally, a relatively recent advancement in medical
technology, namely the development of perfluorocarbon
emulsions with high gas-dissolving capacity, for intravenous administration, shows promise, not only in enhancing
inert gas elimination in divers, but also for relief of tissue
hypoxia in a host of clinical conditions unrelated to diving,
as described in “Perfluorocarbon emulsions as a promising technology: a review of tissue and vascular gas dynamics” (7).
Despite modest public funding support for research related to human productivity and safety in undersea activities
(mostly from the US Navy) and for the use of hyperbaric
oxygen treatment in terrestrial medicine, very important
gains in these areas have been made and are accelerating,
especially in the latter field. For instance, the exploitation of
oil and natural gas fields under the sea bottom is critically
dependent on divers, and there is a rapidly growing application of hyperbaric oxygen that now, supported by sound
mechanistic research, is setting its sights on some of the
major public health challenges, such as stroke and the sequelae of
diabetes.