Document RJJ056e8Kaqq8K6BN5R1m0rqV

150 FRANK A. PATTY it has entered the blood stream and then been transported to the tissues, it is j evident that the circulation rate is an important factor in respiration. The blood '; volume is usually slightly greater than the lung capacity. For a normal man it.jgf approximately 6 to 7 liters.8 The time required for a complete circuit of the blood varies with exercise*, the part of the body supplied, and many other factors, but averages somewhat less than 1 minute. The normal heart stroke is about 60 to 70 ml., with a resting, pulse of 68 to 72 per minute, giving a minute volume of 4 to 5 liters. Exercise canl increase the heart stroke to 100 or 200 ml. and the pulse rate to 170 or 180.1 Environmental temperatures above 30 C. increase the minute volume 5 to' 3(k per cent. Digestion of food increases the basal minute volume by 30 to 40 pepl cent for about 3 hours. Emotional strain causes an increase of 15 to 25 per cent;! pH changes have an effect, as do naturally occurring, as well as foreign, chemicals! having a vasoconstrictor or vasodilator reaction. Also, just as the amount aniP content of the venous supply to the lungs play a major role in regulating thdjij breathing required to keep the arterial blood constant, so does the circulation! depend on breathing, and any retardation of breathing will be quickly followedf by a change in circulation. Henderson4,8 strikingly demonstrated the control .ol circulation by breathing when he showed that excessive pulmonary ventilation! could induce failure of the circulation. The part played by respiration in the] action of atmospheric contaminants upon the body will be discussed later, __ ___________ IP.-.AhBOicpUiop^-Jjistrihutio'o, and Elimination A. MODES OF EXPRESSING CONCENTRATIONS The extent of atmospheric contamination in the gaseous phase is frequently! expressed as parts per million (p.p.m.), denoting units of volume in 1,000,000; volumes, .and is usually corrected to 25 C. and 760 mm. Hg pressure. Thisui a convenient mode of expression and, for routine examinations of workroom atmospheres, the actual conditions- are frequently not sufficiently removed^rom this standard to require temperature-pre8Sure r.cprrections. Since comparisons via p.p.m. are on a volume--hence molecular--basis they have no direct relation t| the weight-volume expression of milligrams per liter occasionally used, especialM in foreign technical pnb}io'ldqn.33^tqail^a;afflajiggtlitgr unit,has thei advantagi of being.-mpre .rcjadflyff oomparedj^t^5ttda^^eteffacdloneali<ftnd`.~dosat><^gl8 expressed as. milligrams per kilogram of bodyfweigljt On the ,wholey-howeflj| the p.p.m. unit has proved much more convenient and expressive in industrial hygiene, where low concentrations of contaminants are the rule, Variations-d'h' the expression of -parts by volume are: per'cent'byVoliM thdusSSS! parts per ten thousand, parts per hundred thousand, parts per hundred million! and parts per billion. The excuse for employing so many units is the desire to' * Y. Henderson, Am. J. Physiol., 25, 310 (1910). * Y. Henderson and H. W. Haggard, J. Biol. Chem., 33, 355 (1918). M.teUfeW' ENTRY AND ACTION OF TOXIC MATERIALS 151 Ete^^^se^'rhall whole numbers. However, this multiplicity of units is confusing and s^nigifftBetter be confined to not more than three units: per cent, parts per million, billion. Per cent by volume is generally used when the concern are on the orderxof 0.1 per cent or greater. Parts per million is a logical concentrations ranging from 1,000 down to 1 or even 0.1 p.p.m. For1 Mn||ations less than 1 p.p.m., parts per billion (p.p.b.) appears to be the afflffihlt. One million p.p.b. = 1,000 p.p.m. = 0.1 per cent = a partial pres- J'ii^^p|'0.i76 mm. Hg at sea level. One gram mole of a perfect gas or vapor has a 24.45 liters at 25 C. and a pressure of 760 mm. Hg. Therefore under SCffTi^rSqgnddiittiioonnss:: ?*> - molecular weight 1 p.p.m. = - ----- , ,, mg. per liter; ^ * 1000 X 24.45 6 24.45 X 1000 1 mg. per liter = p.p.m. molecular weight efiljtmylflion table for gases (p.p.m. to mg. per liter and mg. per liter to p.p.m.) oil pages xvi-xvii. Another method of expressing gas concentrations is the i isure method, using the unit of the pressure exerted by one millimeter j$33fSirury.' This is convertible directly to per cent by volume by multiplying by ''Odyarid')(jividing by the barometric pressure; or to p.p.m. by multiplying by 'v''ii,^^nd-*dividiBg-by--the-barometrio pressure:.......... .pressure of one constituent X 1,000,000 = p.p.m. of constituent Tunff* t,||l|pn|the contaminant is dispersed in the atmosphere in solid or liquid form, jg|j|j^isfer|ust. or fume, its concentration must be expressed either on a weight "'^'"''njlbasis or particles per volume basis. Liqmile- and toxic solids are as milligrams per cubic meter, or per 10 cu. m. to approximate jpK^jnaximtlm amount inhaled in one 8-hour day by a workman doing moderately " ^SjMfejIi^This standard was originally based on 20" liters per minute X 60 ililkSurs = 9600 liters = 9.6 cu. m. Henderson and Haggard1 estimate l^ljfeathfhg rate to be 8 liters per minute or about 4 cu7m. per 8-hour Iffismaoniy the minute volume, but also retention, the physiological dead u^jother factors must be considered in computing daily.^stpjniq-intake, gdityjof, the figure, 10 cu. m., is open to question. Those 3usts that exert lungs, rather than 't,hroughnufiJ,the"system as a ^^^Msually counted microscopically and expressed as miliipn particles per ?f<^ISair. Outdoor air contaminants and stack effluent's-are, frequently cssMSi|;Wgrams, milligrams, or micrograms per cubic meter, ounces p^er ^llijpbic feet, pounds per thousand pounds of air, and grains per cubic m- ' ir B*., m 1?S