Ill. Heart Work Henry A. Bent North Carolina State University Raleigh, 27650
Many problems of personal health, the urban environment, the national economy, and world peace would be eased if we worked our heads, and hearts, harder. It is useful to know, therefore, how hard a heart can work, safely. Calculations suggest, and experience confirms, that a sound heart always outperforms other muscles. A heart's power output equals the rate that it pumps blood multiplied by the blood's pressure (Box. 10). Taking, after the young German physician, Robert Mayer, the first person to
---
.-
~
Power= P X -
v Time
Work power = Time WDrk = F w s X Distance Force = (Pressure of blwd). P X (Area of aortal. A
(2)
(3)
(4) A X Dist. Blood moves in aorta = Vol. of
-Force=
PX-
-Work= -Power=
blood pumped,
v Disl.
P X V PX-
v Time
Cp - Cu = PV
V
by (31 by (2) by (11
make this calculation, in the 1840'8, blood's pressure to be 150 mmHg, one calculates for a pumping rate of 7 llmin (100 mllbeat X 70 beatslmin) a power output for the heart's left ventrical of 34 callmin Heart's Power Output
= (Fluid Pumping Rate)(Fluid's Pressure) = (7 Ilmin)
(150 mmHd .X
1 atm 24.2 caln X760 mmHg l atml
While 34 callmin mav seem like a small power output for the heart's left ventricai compared to some2000 callmin for skeletal muscles during a typical work day (see Box 2 in Part I), the leftventrical, Mayer pointed out, only weighs about 0.14 kg compared to some 30 kg for skeletal muscles. Kilogram for kilogram, in the long runror long ride, or long work session, heart muscles work much harder than skeletal muscles cal mm
34 -
For the left ventrical: --- = 240 0.14 kg
I
cal kg mm
-
Fluid's Pressure derived as follows: ( 1 Newton = I Jlm) 101 325 Newtons/m2 I cal 10-km" - 24.2 call1 = lOl325JlmW-X--
1atm
4.185
11
586 I Journal of Chemical Education
Indeed, it is a fact known to everybody, remarks Mayer, that if one tries to work a skeletal muscle isochronously with heart beats one will soon be forced to refrain from this concurrence with the heart. since the muscle -gets so lame it will refuse to serve even the strongest will. Circulation velocity of blood to the heart, adds Mayer, is greater [twice as great per gram of muscle] than to all other organs of the body. Mayer's First Law of Exercise Physiology Robert Mayer, father of biophysics, was the first person to calculate the mechanical equivalent of heat, by comparing the PV-work done by a gas expanding a t constant pressure with the experimentally determined difference between the heat capacity of a gas measured a t constant pressure (CJ and the heat capacity . . of the gas measured a t constant volume ( C , ) : i.e., Mayer assumed (correctly, for ideal gases) that
Box 10. Power Output of the Heart ~~
cal 2000 mm eal For skeletal muscles: = 66 30 kg kg mm
- uork of expansion per degree
With James Joule, Mayer often receives credit for establishing as a useful principle the First Law of Thermodynamics: the Conservation of Energy. The following law may he of more immediate practical value to many sedentary adults. You can't run t o death
if healthv. No species that could would long survive. None of [he distance runners who collapsed durin; ihe Mexicu City Olvmpics held ar an altitude 01' over 8O(W leer showed cwonary indufiiciencies in EKGs taken immediately after collapse On the other hand You con sit to death
unless healthy. Inactivity kills. Avoid inactivity as you would severe illness urges van Aaken, world-famous advocate of aerobic trainine. I n modern, over-industr~alieedsocieties we nred to seek uut activities that require physical effort and learn to disregard the social stigma bf labor:stress is necessary for life. "Every cardiolgist I know," writes a noted physiologist, "exercises." Much "aging," he adds, is simply deconditioning. The average American knows what he wants (an easy, exertionless life), not what he needs. Activity is less risky than cuntinuous inactiuity emphasize Astrand and Rodahl in their classic textbook on exercise physiology. I t is advisable to pass a careful medical examination if one intends to he sedentarv, thev continue, to establish if one's health is good enough to tolerate the inactivity! Heart disease.. thev- observe, is in some respects a deficiency disease. Americans may have gold in their hearts, silver in their hair, but lead in their pants. T o a striking degree we've become a sit-down natiun addicted to gas-guzzling vehicles and other labor-saving, health-damaging devices. More and mure Americans lead a (modern) dog's life (Box 11). "It is not the rich and the great, not those who depend on
Box 12. "Not Poems" by Adele Aldrldge
Box 11. "Your Dog: His Health and Happiness" by Dr. Louls L. Vine, Veterinarian
EAT
"With the advent of son and easy living, some of our dogs are losing their girlish and boyish figures.and I am daily seeing in my clinic dogs at many breeds who are fatalmcst to the point of obesity . . . Dogs that are allowed plenly of exerciw will keep trim all their lives. Dogs b t just lie arwnd all day become obese.Dogs arc meam to be active. "Over feeding and insufficientexercise are the principal causes of fat,lazy, sluggish puppies [and people] . . .The dog's body is geared lor running and playing. a M bath ate necessary far his well-being.Lack of exercise Can bring on all Kinds of digestive disorders and physical and mental sluggishness."
medicine, who become old," wrote Seneca, Roman statesman and philosopher, 4 B.C.-65 A.D., "hut such as use much exercise, are exposed to the fresh air, and whose f w d is plain and moderate." Time and modern technology have not suhstantially altered the wisdom of that remark. Substantially better health cannot he hought with an $118.5 billion National Health Plan wrote Philip Ahelson, editor of Science. in 1976. Unfo&umtely, if understandably, modern medicine focuses attention on disease (where the dollars are--118.5 billion from the U.S. government alone in 1976), not health. Isn't it time, asks Ahelson. to . oav" more attention to simnle measures that promise great improvement a t little cost?:except possibly to ohvsicians' incomes. i)u; greatest henlth prohlern todey in the US. is nut the It is the .~hvsical fitness of financial fitness of our . nhvsicians. . . our citizens. Our greatest killers today in the U.S. are not under-funded hospitals and over-worked doctors. Our greatest killers are under-used muscles and over-used mouths. T h e lonser the belt. the shorter the life (Box 12). ~ussian-~hkasians; famed for their longevity, are simple people who live close to the land, are physically active all their lives, eat relatively little meat, and are downright skinny hy U.S. standards. Whenever an Ahkasian becomes even moderately fat all his friends and relatives think he is ill and inquire ahuut his state of health. Sugar is almost unknown among them. Sweet Death
S o dangerous is sugar to the human body, remarked the president of the North Carolina Dental Society recently, it would he labeled a poison if discovered today. Nutritionally, refined sugars have no redeeming qualities-no vitamins, no minerals, no amino acids, no essential fatty acids, no roughage, only the ahility with oxygen to yield 4 kcal of energy per .gram oxidized. ... America's sueet twth--and itiaffluence,and the financrsl interest< oicunfcctionary, sntt-drink, cold c e r e d and other
EAT
EAT
EAT
EAT
FAT
FAT
FAT
FATAL sugary-snack industries-has led to a consumption of sugar in the U.S. in excess of 120 Ihlpersonlyear, approximately one quarter of an average American's needed caloric intake! 1201b -X454 g 1 yr 1 lb
4
kcal X 1yr X
Ig
,365 days
1 = 0.25 2400 kcal
Produced have been large corporate profits; large mal-nourished customers; and large incidences of dental diseases, cardiovascular diseases, diabetes, and other diet-related diseases. Sugar kills, through human greed-and through osmosis. Added to gardens-where with ground water it forms syrup-sugar kills nematodes, by dehydrating them. Water spontaneously diffuses from nematodes' cells, where its concentration is relatively high, to the deadly sweet syrup, where its concentration is lower. Added to processed garden produce-canned and frozen vegetables, baked beans, peanut butter, jellies and jams, and a host of other sweetened things-sugar preserves them for human consumption, by killing bacteria. Suggested Readings Ill Mayer. R. J.."The MofimaoiOrganirmr and their Relation toMetaholism. A n E s a y in NaturalSrienee." ITrmsiolnr 1.indaav. R.R.1 in "Julius RobertMager: P r o ~ h e t of Enerey."Po.~amnn Prem. NPWY m k . 1 9 7 . 3 . ~ ~76145. . (2) Antrand. P., and Rndahl. K.. "Texthook ofWork Physidogy." McCraw-Hill Book Co.. NPW Ysrk, 1970. (3) Mnrchoura, I.. F... and Gross. 1. .. "Total Fitnerr in :30Minutes a Week."Simon and Schuster. New Ynrk. 1975. (4) Hisdon. H.. "Fitnerr Aiier Forty: W ~ r l dPohlicafiuns. Mountain View, California, 1917.
Volume 55, Number 9. September 1978 / 587
