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From Fellrnr.com, Running tips
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The advice given to runners on hydration has changed over time and looks set to continue to change. There are competing forces at work - sports drink manufacturers, event organizers (often sponsored by the manufacturers) and scientists (some also sponsored by the manufacturers). One thing is clear about hydration - it is important. Incorrect hydration can lead to impaired performance, and in extreme cases, death. A condition related to dehydration is [[Hyponatremia]], which is where the sodium (salt) level in the blood becomes too dilute. This is a dangerous condition that has killed a number of runners. This entry is a follow on to [[Practical Hydration]] which should be read first.
=Effects of dehydration=
=Sodium loss through sweat=
The amount of salt that is lost through sweating varies a lot. It varies from individual to individual, and for an individual it will vary depending on fitness and heat acclimation<ref name="ref9"/>. This means that you may have to experiment with your salt intake, both during and after exercise.
==Anatomy of Sweating==
[[File:Sweat Gland.jpg|right|thumb|500px|A drawing of the sweat gland. (C=clear cells, D=dark cells, IC=Intracellular canaliculi, M=Myoepitherial cell, Mc=Mitochondria. )]]
==Sodium Loss Table==
The table below is based on the research showing that sweat sodium concentration increases with sweat rate. The table below is for a runner who is 174cm/70inches high and weighs 60Kg/132lbs, but you can create a customized chart at [[Sodium Loss]]. To check your sweat rate, simply weigh yourself before and after a run. Dropping 1 Kg or 2.2 pounds equates to 1 liter of sweating. (Obviously you need to adjust for any fluid intake and avoid urination.)
{| class="wikitable"
!
!
==Sodium Loss and Sweat Rate==
The concentration of sodium in sweat depends on the sweat rate. This is believed to be because the sweat is released with a high sodium concentration, then the sodium is reabsorbed before it reaches the surface. The faster the sweating, the less chance for reabsorption.
[[File:Sweat Rate Sodium Concentration - adjusted.jpg|none|thumb|400px|Sweat rate and sodium concentration<ref name="sweatrateBuono-2008"/>, adjusted using the formula for regional patch collection<ref name="WBWandPatchBaker-2009"/>.]]
===Converting per-area sweat rates to whole body sweat rates===
We can convert from per-area sweat rates to whole body sweat rates by using a [http://www.halls.md/body-surface-area/bsa.htm Body Surface Area Calculator]. For example, a 135 pound, 70 inch high person has a skin surface area of 1.74 m<sup>2</sup>, which is 17,400 cm<sup>2</sup>. Therefore 1 mg/cm<sup>2</sup>/min is 17,400 mg/min, or 17.4 g/min or 1,044 g/hour, or 1 liter/hour.
==Sodium Loss and Fitness==
While some sources suggest that increased fitness reduces the sodium concentration in sweat research<ref name="trainingHamouti-2011"/> shows this is not the case. For both trained and untrained individuals sodium concentration depends mainly on sweat rate. In fact, for a given relative intensity (% of [[VO2max|V̇O<sub>2</sub>max]]) trained individuals will be performing a greater absolute work rate and therefore have a greater sweat rate and sodium concentration.
[[File:Sodium in sweat trained and untrained.jpg|none|thumb|400px|Sweat sodium concentration against sweating rate, showing for three different work intensities and for trained and untrained individuals. Note that this data is not adjusted for regional patch collection, so the rates are too high and should be scaled by 0.67.]]
==Sodium Loss and Heat Acclimation==
A study<ref name="sweatheatBuono-2007"/> shows that the sodium concentration of sweat is reduced by [[Heat Acclimation Training]]. The study used three bouts of 30 min. of exercise in environmental chamber with 10 min. of rest between each bout.[[File:Sweat Rate Sodium Concentration for heat adaptation - adjusted.jpg|none|thumb|400px|Sweat sodium concentration against sweating rate, before and after 10 days of heat acclimation training, adjusted using the formula for regional patch collection<ref name="WBWandPatchBaker-2009"/>.]]
==Sodium Loss and Skin Temperature==
A study<ref name="skintempShamsuddin-2005"/> of sweating great sodium concentration for different temperatures has shown that sodium reabsorption is greater at high temperatures. Unfortunately the units used in this study are not comparable with other studies. The mechanism behind this is unclear, but the implication is that the sodium concentration of sweat in cooler weather may be higher than expected from the above studies.
[[File:Sweat Rate Sodium Concentration for skin temperatures.jpg|none|thumb|400px|Sweat sodium concentration against sweating great, shown for two different skin temperatures.]]
=Sodium Retention=
The human body has mechanisms to try to maintaining its sodium balance. Greater sodium intake results in the excess being excreted in the sweat and urine. Conversly, restricted sodium intake will result in a reduction of the sodium concentration of the sweat<ref name="a1946CONN-1946"/>. This reduction in the sodium concentration occurs at all sweating rates, but the relationship between sodium concentration and sweat rate remains a straight line<ref name="SweatSaltIntakeSigal-1968"/>. So at any given sweat rate, a restricted sodium intake will result in less sodium in the sweat. However, even on a restricted sodium intake, the more you sweat, the greater the sodium concentration. Comparing the maximum sodium concentration of sweat between a salt intake of 500mg/day and 20,000mg/day, the low salt intake reduced the sodium concentration by 30-48%<ref name="SweatSaltIntakeSigal-1968"/>. [[File:SodiumIntakeSweatConcentration.jpg|none|thumb|500px|The effect of high (20,000mg/day NaCL) and low (500mg/day NaCL) on the sodium concentration of sweat at various sweat rates<ref name="SweatSaltIntakeSigal-1968"/>. Three subjects were put on the diet for a week, then tested for five days while remaining on that diet. The two tests were separated by a month.]]
=Sodium Intake=
Below are some sample sources of Sodium, with the concentrations defined.
{| class="wikitable"
! Source
! Sodium - mmol per liter
There is a table showing a range of values at [[Sodium Loss]].
=Hyponatremia=
[[Hyponatremia]] is where the sodium (salt) levels becomes in the blood become too dilute. Initial The symptoms of mild hyponatremia tend to be a gain in weight and a general swelling and 'puffiness', most noticeable in the hands. More However, mild Hyponatremia may have no clinical symptoms, or just weakness, dizziness, headache, nausea/vomiting, but more severe Hyponatremia is likely to have symptoms are caused by a swelling of the brain (cerebral edema) , including nauseaaltered mental status, seizures, pulmonary edema, vomitingcoma, headache and malaisedeath<ref name="ref10RosnerKirven2006"/>.
=HypERnatremia - the opposite of HypOnatremia=
Generally, Hypernatremia (too much sodium in the blood) seems to be a result of dehydration rather than excessive salt intake<ref name="ref17Kratz-2005"/>. It should be noted that taking [[Electrolyte Capsules]] bypasses the body's taste. This sense of taste seems to reflect our body's internal sensors; our desire for salty foods reflects our salt requirements.
=Salt and High Blood Pressure=
There is evidence that increased salt intake can increase blood pressure<ref name="ref4"/>, and the common recommendation is to restrict your salt intake if you have high blood pressure. However, a recent study<ref name="JAMAStolarz-Skrzypek-2011"/> has shown that reducing your salt intake may increase your risk of a heart attack rather than lower it. For more on the health risks of low salt diets see http://www.drmirkin.com/public/ezine050811.html
As an aside, if you have low blood pressure, which I do, increasing your salt intake can really help.
=Caffeine and Alcohol=The scientific evidence shows that [[Caffeine]] is generally not a diuretic<ref name="ref5Graham-1998"/><ref name="ref14"/><ref name="ref15Falk-1990"/>. Previous studies have shown that if you don't normally take [[Caffeine]] and then get a large dose, there is some diuretic effect. However normal intakes of [[Caffeine]] by non-users and use by regular users is not a diuretic<ref name="ref16Maughan-2003"/>. (If you urinate more because you drink a 20oz Latte, it is because of the 20oz of fluid, not the [[Caffeine]].)=Alcohol=Alcohol is another story; drinking anything stronger than 2% will cause dehydration. Because alcohol takes 36 hours a diuretic due to the suppression of vasopressin secretion<ref name="ROBERTS-1963"/><ref name="RubiniKleeman1955"/>, and the volume of urine produced is proportional to clear the bodyalcohol consumed<ref name="Eggleton-1942"/>. However, it should the diuretic effect of alcohol may be avoided for 48 hours before you wish to avoid impaired performancereduced when consumed when suffering from post-exercise dehydration. A study looked at consuming water or an alcoholic beverage of 1%, 2%, and 4% after 1 hour of moderate exercise<ref name="ref5Shirreffs-1997"/>. The study found that urine production tended to increase with alcohol content, but the difference was not statistically significant. The alcohol tended to reduce the rate of recovery for both blood and plasma volume, though tendency was only statistically significant at 4%. In summary, alcoholic beverages of up to 2% appear to have little impact on rehydration rate compared with the equivalent volume of water, but 4% beverages tend to delay recovery.= Cramps =
The evidence for hydration and electrolyte status causing [[Cramps]] is somewhat ambiguous, but supplementing your electrolyte intake may help.
=Blisters and black toe nails=
The volume of extracellular fluid is typically 15 liters in a 70 kg human, and the 50 grams of sodium it contains is about 90% of the body's total sodium content.
=Symptoms of Dehydration=
These symptoms are for the general public<ref name="CLINC"/>, and there is evidence<ref name="SYMPT"/> that they may not apply to athletes suffering from mild dehydration.{| class="wikitable"
! symptom
! mild dehdration dehydration (3-5% body weight) ! Moderate dehdration dehydration (6-9% body weight) ! Severe dehdration dehydration (>10% body weight)
|-
| Level of consciousness
=References =
<references>
<ref name="RosnerKirven2006">M. H. Rosner, J. Kirven, Exercise-Associated Hyponatremia, Clinical Journal of the American Society of Nephrology, volume 2, issue 1, 2006, pages 151–161, ISSN [http://www.worldcat.org/issn/1555-9041 1555-9041], doi [http://dx.doi.org/10.2215/CJN.02730806 10.2215/CJN.02730806]</ref>
<ref name="CLINC">Clinical Studies in Fluid and Electrolyte Balance</ref>
<ref name="SYMPT">J. McGarvey, J. Thompson, C. Hanna, T. D. Noakes, J. Stewart, D. Speedy, Sensitivity and specificity of clinical signs for assessment of dehydration in endurance athleteshttp://bjsm.bmj.com/content/early/2010/04/22/bjsm., British Journal of Sports Medicine, volume 44, issue 10, 2008.053249.abstract</ref><ref name="ref5">Caffeine dehydration : Caffeine and alcohol - just how dehydrating are they?, pages 716–719, ISSN [http://www.pponlineworldcat.co.ukorg/encycissn/caffeine0306-dehydration.htm http://www.pponline.co.uk/encyc/caffeine3674 0306-dehydration.htm3674]</ref><ref name="ref7">Hydration - fluid intake advice and tips, doi [http://wwwdx.pponlinedoi.co.ukorg/encyc/hydration-fluid-intake-advice-and-tips-40789 http://www.pponline.co10.uk1136/encyc/hydration-fluid-intake-advice-and-tips-40789]</ref><ref name="ref8">The Relation Of Glycogen To Water Storage In The Liver[http://wwwbjsm.jbc2008.org/cgi/reprint/96/2/367053249 10.pdf http:1136//wwwbjsm.jbc2008.org/cgi/reprint/96/2/367.pdf053249]</ref><ref name="ref9Nilsson-1973">Cracking LH. Nilsson, Liver glycogen content in man in the Code on Hydrationpostabsorptive state., Scand J Clin Lab Invest, volume 32, issue 4, pages 317-23, Dec 1973, PMID [http://www.activencbi.com/cycling/Articles/Cracking-the-Code-on-Hydrationnlm.htm http://wwwnih.active.comgov/cycling/Articlespubmed/Cracking-the-Code-on-Hydration.htm4771101 4771101]</ref><ref name="ref10González-Alonso-1995">Hyponatremia[http://enJ.wikipediaGonzález-Alonso, R.org/wiki/Hyponatremia http://enMora-Rodríguez, PR.wikipediaBelow, EF.org/wiki/Hyponatremia]</ref><ref name="ref11">Coyle, Dehydration reduces cardiac output and increases systemic and cutaneous vascular resistance during exercise[http://www.edb.utexas.edu/coyle/pdf%20library/%286329%20Dehydration%20reduces%20cardiac%20output%20&%20increases%20systemic%20&%20cutaneous%20vascular%20resistance%20during%20exercise,%20J%20Appl%20Physiol%2079J Appl Physiol (1985), volume 79, issue 5,%201487pages 1487-96,%201995.pdf Nov 1995, PMID [http://www.edbncbi.nlm.utexasnih.edugov/coyle/pdf%20librarypubmed/%2863%29%20Dehydration%20reduces%20cardiac%20output%20&%20increases%20systemic%20&%20cutaneous%20vascular%20resistance%20during%20exercise,%20J%20Appl%20Physiol%2079,%201487-96,%201995.pdf8594004 8594004]</ref><ref name="ref14Graham-1998">TE. Graham, E. Hibbert, P. Sathasivam, Metabolic and exercise endurance effects of coffee and caffeine ingestion[http://jap.physiology.org/cgi/content/full/, J Appl Physiol (1985), volume 85/, issue 3/, pages 883 -9, Sep 1998, PMID [http://japwww.ncbi.nlm.physiologynih.orggov/cgi/content/full/85/3pubmed/8839729561 9729561]</ref><ref name="ref15Falk-1990">B. Falk, R. Burstein, J. Rosenblum, Y. Shapiro, E. Zylber-Katz, N. Bashan, Effects of caffeine ingestion on body fluid balance and thermoregulation during exercise., Can J Physiol Pharmacol, volume 68, issue 7, pages 889-92, Jul 1990, PMID [http://www.ncbi.nlm.nih.gov/pubmed/2383801 http://www.ncbi.nlm.nih.gov/pubmed/2383801]</ref><ref name="ref16Maughan-2003">RJ. Maughan, J. Griffin, Caffeine ingestion and fluid balance: a review., J Hum Nutr Diet, volume 16, issue 6, pages 411-20, Dec 2003, PMID [http://ptwww.wkhealthncbi.com/pt/re/jhnd/abstractnlm.00009862-200312000-00004nih.htm;jsessionid=KNhWhGQSZnXhY11p2f7qnnmn1Q7z376shvhsK7hTWDLVGQhWpGGJ%21811725889%21181195628%218091%21-1 http:gov/pubmed/pt.wkhealth.com/pt/re/jhnd/abstract.00009862-200312000-00004.htm;jsessionid=KNhWhGQSZnXhY11p2f7qnnmn1Q7z376shvhsK7hTWDLVGQhWpGGJ!811725889!181195628!8091!-119774754 19774754]</ref><ref name="ref17Kratz-2005">A. Kratz, AJ. Siegel, JG. Verbalis, MM. Adner, T. Shirey, E. Lee-Lewandrowski, KB. Lewandrowski, Sodium Status status of Collapsed Marathon Runnerscollapsed marathon runners., Arch Pathol Lab Med, volume 129, issue 2, pages 227-30, Feb 2005, doi [http://arpadx.allenpressdoi.com/arpaonlineorg/?request=get-document&doi=10.1043%2F1543/1543-2165%282005%29129%3C227(2005)129<227:SSOCMR%3E2>2.0.CO%3B2 http://arpa.allenpress.com/arpaonline/?request=get-document&doi=;2 10.1043%2F1543/1543-2165%282005%29129%3C227(2005)129<227:SSOCMR%3E2>2.0.CO%3B2;2], PMID [http://www.ncbi.nlm.nih.gov/pubmed/15679427 15679427]</ref>
<ref name="acsm">http://journals.lww.com/acsm-msse/_layouts/oaks.journals/ImageView.aspx?k=acsm-msse:2007:02000:00022&i=TT2
</ref>
http://lpi.oregonstate.edu/infocenter/minerals/sodium/
</ref>
<ref name="JAMAStolarz-Skrzypek-2011">K. Stolarz-Skrzypek, T. Kuznetsova, L. Thijs, V. Tikhonoff, J. Seidlerová, T. Richart, Y. Jin, A. Olszanecka, S. Malyutina, Fatal and Nonfatal Outcomesnonfatal outcomes, Incidence incidence of Hypertensionhypertension, and Blood Pressure Changes blood pressure changes in Relation relation to Urinary Sodium Excretion urinary sodium excretion., JAMA, volume 305, issue 17, pages 1777-85, May 2011, doi [http://dx.doi.org/10.1001/jama.ama-assn2011.574 10.1001/jama.2011.org574], PMID [http:/content/305www.ncbi.nlm.nih.gov/17pubmed/177721540421 21540421]</ref><ref name="sweatrateBuono-2008">MJ. Buono, R. Claros, T. Deboer, J. Wong, Na+ secretion rate increases proportionally more than the Na+ reabsorption rate with increases in sweat rate ., J Appl Physiol (1985), volume 105, issue 4, pages 1044-8, Oct 2008, doi [http://japdx.physiologydoi.org/content10.1152/japplphysiol.90503.2008 10.1152/105japplphysiol.90503.2008], PMID [http:/4/1044www.ncbi.nlm.nih.fullgov/pubmed/18653750 18653750]</ref><ref name="trainingHamouti-2011">SpringerLink N. Hamouti, J. Del Coso, JF. Ortega, R. Mora- European Journal of Applied PhysiologyRodriguez, Sweat sodium concentration during exercise in the heat in aerobically trained and untrained humans., Eur J Appl Physiol, Volume volume 111, Number issue 11 , pages 2873-81, Nov 2011, doi [http://dx.doi.org/10.1007/s00421-011-1911-6 10.1007/s00421-011-1911-6], PMID [http://www.springerlinkncbi.comnlm.nih.gov/content/mxj56211q04v4455pubmed/21431880 21431880]</ref><ref name="a1946CONN-1946">JW. CONN, MW. JOHNSTON, LH. LOUIS, Relationship between salt intake and sweat salt concentration under conditions of hard work in humid heat., Fed Proc, volume 5, issue 1 Pt 2, pages 230, 1946, PMID [http://www.ncbi.nlm.nih.gov/pubmed/2098457120984571]</ref><ref name="skintempShamsuddin-2005">SpringerLink - European Journal AK. Shamsuddin, T. Kuwahara, A. Oue, C. Nomura, S. Koga, Y. Inoue, N. Kondo, Effect of skin temperature on the ion reabsorption capacity of Applied Physiologysweat glands during exercise in humans., Volume Eur J Appl Physiol, volume 94, Number issue 4 , pages 442-7, Jul 2005, doi [http://dx.doi.org/10.1007/s00421-005-1354-z 10.1007/s00421-005-1354-z], PMID [http://www.springerlinkncbi.nlm.nih.comgov/content/n569w2538g13516rpubmed/15843956 15843956]</ref><ref name="sweatheatBuono-2007">MJ. Buono, KD. Ball, FW. Kolkhorst, Sodium ion concentration vs. sweat rate relationship in humans ., J Appl Physiol (1985), volume 103, issue 3, pages 990-4, Sep 2007, doi [http://japdx.physiologydoi.org/content10.1152/103japplphysiol.00015.2007 10.1152/japplphysiol.00015.2007], PMID [http:/3/990www.ncbi.nlm.nih.fullgov/pubmed/17600161 17600161]</ref><ref name="WBWandPatchBaker-2009">LB. Baker, JR. Stofan, AA. Hamilton, CA. Horswill, Comparison of regional patch collection vs. wwhole body washdown for measuring sweat sodium and potassium loss during exercise... [, J Appl Physiol(1985), volume 107, issue 3, pages 887-95, Sep 2009, doi [http://dx.doi.org/10.1152/japplphysiol.00197.2009 10.1152/japplphysiol.00197. 2009] - PubMed - NCBI , PMID [http://www.ncbi.nlm.nih.gov/pubmed/1954173819541738]</ref>
<ref name="Fitzpatrick">Fitzpatrick's Dermatology in General Medicine, Chapter 81. Biology of Eccrine, Apocrine, and Apoeccrine Sweat Glands</ref>
<ref name="SweatSaltIntakeSigal-1968">CB. Sigal, RL. Dobson, The effect of salt intake on sweat gland function., J Invest Dermatol, volume 50, issue 6, pages 451-5, Jun 1968, PMID [http://www.ncbi.nlm.nih.gov/pubmed/5652824 5652824]</ref><ref name="Goulet2012">E. D. B. Goulet, Effect of exercise-induced dehydration on endurance performance: evaluating the impact of exercise protocols on outcomes using a meta-analytic procedure, British Journal of Investigative Dermatology Sports Medicine, volume 47, issue 11, 2012, pages 679–686, ISSN [http://www.worldcat.org/issn/0306-3674 0306-3674], doi [http://dx.doi.org/10.1136/bjsports- The 2012-090958 10.1136/bjsports-2012-090958]</ref><ref name="Goulet2011">E. D. B. Goulet, Effect of Salt Intake exercise-induced dehydration on time-trial exercise performance: a meta-analysis, British Journal of Sports Medicine, volume 45, issue 14, 2011, pages 1149–1156, ISSN [http://www.worldcat.org/issn/0306-3674 0306-3674], doi [http://dx.doi.org/10.1136/bjsm.2010.077966 10.1136/bjsm.2010.077966]</ref><ref name="Convertino-1996">VA. Convertino, LE. Armstrong, EF. Coyle, GW. Mack, MN. Sawka, LC. Senay, WM. Sherman, American College of Sports Medicine position stand. Exercise and fluid replacement., Med Sci Sports Exerc, volume 28, issue 1, pages i-vii, Jan 1996, PMID [http://www.ncbi.nlm.nih.gov/pubmed/9303999 9303999]</ref><ref name="WallWatson2013">B. A. Wall, G. Watson, J. J. Peiffer, C. R. Abbiss, R. Siegel, P. B. Laursen, Current hydration guidelines are erroneous: dehydration does not impair exercise performance in the heat, British Journal of Sports Medicine, 2013, ISSN [http://www.worldcat.org/issn/0306-3674 0306-3674], doi [http://dx.doi.org/10.1136/bjsports-2013-092417 10.1136/bjsports-2013-092417]</ref><ref name="beverageWWW">How to Calculate Your Sweat Gland Function1 Rate - Beverage Institute for Health and Wellness, http://www.naturebeverageinstitute.comorg/jidarticle/journalhow-to-calculate-your-sweat-rate/, Accessed on 25 June 2015</ref><ref name="Shirreffs-1997">SM. Shirreffs, RJ. Maughan, Restoration of fluid balance after exercise-induced dehydration: effects of alcohol consumption., J Appl Physiol (1985), volume 83, issue 4, pages 1152-8, Oct 1997, PMID [http://www.ncbi.nlm.nih.gov/pubmed/9338423 9338423]</ref><ref name="ROBERTS-1963">KE. ROBERTS, mechanism of dehydration following alcohol ingestion., Arch Intern Med, volume 112, pages 154-7, Aug 1963, PMID [http://www.ncbi.nlm.nih.gov/v50pubmed/n614044808 14044808]</fullref><ref name="RubiniKleeman1955">Milton E. Rubini, Charles R. Kleeman, Ezra Lamdin, Studies on alcohol diuresis. I. The effect of ethyl alcohol ingestion on water, electrolyte and acid-base metabolism 12, Journal of Clinical Investigation, volume 34, issue 3, 1955, pages 439–447, ISSN [http:/jid196873a/www.worldcat.org/issn/0021-9738 0021-9738], doi [http://dx.doi.org/10.1172/JCI103092 10.html 1172/JCI103092]</ref><ref name="Eggleton-1942">MG. Eggleton, The diuretic action of alcohol in man., J Physiol, volume 101, issue 2, pages 172-91, Aug 1942, PMID [http://www.ncbi.nlm.nih.gov/pubmed/16991552 16991552]</ref><ref name="Shirreffs-1996">SM. Shirreffs, AJ. Taylor, JB. Leiper, RJ. Maughan, Post-exercise rehydration in man: effects of volume consumed and drink sodium content., Med Sci Sports Exerc, volume 28, issue 10, pages 1260-71, Oct 1996, PMID [http://www.ncbi.nlm.nih.gov/pubmed/8897383 8897383]</ref><ref name="Maughan-1995">RJ. Maughan, JB. Leiper, Sodium intake and post-exercise rehydration in man., Eur J Appl Physiol Occup Physiol, volume 71, issue 4, pages 311-9, 1995, PMID [http://www.ncbi.nlm.nih.gov/pubmed/8549573 8549573]</ref><ref name="Nose-1988">H. Nose, GW. Mack, XR. Shi, ER. Nadel, Role of osmolality and plasma volume during rehydration in humans., J Appl Physiol (1985), volume 65, issue 1, pages 325-31, Jul 1988, PMID [http://www.ncbi.nlm.nih.gov/pubmed/3403476 3403476]</ref>
</references>