This paper presents a method for predicting an individual's cardiac response to a series of fixed intensity tasks. It was determined that cardiac responses to exercise at given work loads are similar for subjects of the same sex and level of physical fitness when they are expressed in terms of resting heart rate. Using this observation as a basis, a prediction model was developed by extrapolating from emperically derived heart rate patterns. The prediction error was no more than five to ten percent of the actual heart rate value in ninety percent of the predictions.Yeshttps://us.sagepub.com/en-us/nam/manuscript-submission-guideline

Larry E. Long

LaVerne L. Hoag

English

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PREDICTION OF CARDIAC RESPONSE TO PHYSICAL STRESS Larry  E.  Long and Laverne L. Hoag Univers i ty  of  Oklahoma, Norman, Oklahoma 73069 ABSTRACT This  paper p r e s e n t s  a method f o r  p r e d i c t i n g  an i n d i v i d u a l ' s  c a r d i a c  r e s -  ponse t o  responses  t o  e x e r c i s e  a t  given work l o a d s  a r e  s i m i l a r  f o r  s u b j e c t s  of t h e  same sex and l e v e l  of p h y s i c a l  f i t n e s s  when they a r e  expressed i n  terms of r e s t i n g  h e a r t  r a t e .  Using t h i s  observa t ion  a s  a b a s i s ,  a p r e d i c t i o n  model was developed by e x t r a p o l a t i n g  from emperical ly  der ived  h e a r t  r a t e  p a t t e r n s .  a s e r i e s  of  f i x e d  i n t e n s i t y  tasks .  It was determined t h a t  c a r d i a c  The p r e d i c t i o n  e r r o r  was no more than f i v e  to  ten  percent  n i n e t y  percent  of t h e  p r e d i c t i o n s .  INTRODUCTION Protec t ion  of t h e  worker ' s  h e a l t h  through proper  job  des ign ,  workplace des ign ,  and c o n t r o l  of t h e  en- vironment i s  a b a s i c  r e s p o n s i b i l i t y  of t h e  human f a c t o r  s p e c i a l i s t .  An important  cons idera t ion  i n  e v a l u a t i n g  both t h e  job  and t h e  worker ' s  capac i ty  t o  perform t h e  job is t h e  assessment of t h e  worker ' s  phys io logica l  response t o  p h y s i c a l l y  demanding t a s k s ;  however, t h e  measurement of a worker ' s  response i s  o f t e n  i m p r a c t i c a l  i n  product ion f l o o r  s i t u a t i o n s .  In  such s i t u a t i o n s ,  p r e d i c t i o n  of t h e  worker ' s  response is t h e  only a l t e r n a t i v e ,  b u t  extreme i n t e r p e r s o n a l  v a r i a t i o n s  has  made a v a i l a b l e  p r e d i c t i o n  techniques unacceptably inaccura te .  The e l imina t ion  of t h i s  i n t e r p e r s o n a l  v a r i a t i o n  was a necessary p r e r e q u i s i t e  t o  t h e  development of an a c c u r a t e  p r e d i c t i o n  technique.  A p r e d i c t i o n  model, which minimizes i n t e r p e r s o n a l  v a r i a t i o n  by using a s imple t ransformat ion  was devel -  oped to p r e d i c t  a worker ' s  c a r d i a c  response t o  phys- i c a l  t a s k s  in  t h e  a e r o b i c  range.  The model permi ts  s e v e r a l  s t e p  changes i n  work load t o  occur b u t  i s  r e s t r i c t e d  t o  a t o t a l  per iod  of a c t i v i t y  of no more than four  minutes i n  order  t o  avoid  complicat ions due t o  f a t i g u e .  Because of  t h e  s i z e  of t h e  r e q u i r e d  d a t a  base  and t h e  complexity of t h e  computat ional  proced- u r e s ,  t h e  model is computer dependent. MODEL DEVELOPMENT The most apparent  d e t e r r e n t  t o  p r e d i c t i n g  an i n d i v i d u a l ' s  h e a r t  r a t e  response ( h e a r t  r a t e  p a t t e r n )  t o  work i s  t h e  extreme v a r i a t i o n  i n  a b s o l u t e  h e a r t  r a t e  between i n d i v i d u a l s  working on t h e  same job.  This  v a r i a t i o n  can be s u b s t a n t i a l l y  reduced by viewing c a r d i a c  responses  t o  e x e r c i s e  i n  terms of t h e  percent  of an i n d i v i d u a l ' s  average r e s t i n g  h e a r t  r a t e  (%RIB). This  t ransformat ion  provides  a common o r i g i n  f o r  h e a r t  r a t e  p a t t e r n s  produced by d i f f e r e n t  i n d i v i d u a l s .  The reduct ion  i n  i n t e r p e r s o n a l  v a r i a t i o n  caused by t h i s  t ransformat ion  i s  i l l u s t r a t e d  i n  F i g u r e  1. 2 I1O 100 3 c - . . . - - - - - 80 P v , , -  Subjec t  A Subject  B _-_  W 70 , 20 40 60 80 Time (Sec.) A 3 6o +o'=-' ' ' ' ' ' ' ' of t h e  a c t b a l  h e a r t  r a t e  v i l u e  i n  _ -  130 I, __ Subject  A Subject  B 110 100 Y > > 0 20 40 60 80 Time (Sec.) B F i g u r e  1. Heart  r a t e  p a t t e r n s  f o r  two s u b j e c t s  performing a t a s k  of l i g h t  i n t e n s i t y .  Of t h e  numerous environmental and human v a r i a b l e s  which a f f e c t  t h e  magnitude and r a t e  of change of h e a r t  r a t e s ,  only t h e  human v a r i a b l e s  of sex ,  p h y s i c a l  f i t -  n e s s ,  and r e s t i n g  h e a r t  r a t e  were included in  t h i s  s tudy.  The s u b j e c t  c a t e g o r i e s  which can be def ined  by two l e v e l s  each of sex  and p h y s i c a l  f i t n e s s  were:  (1) male of good p h y s i c a l  f i t n e s s  (MG), (2) sedentary  male (MS), (3) female of good phys ica l  f i t n e s s  (FG), and (4) sedentary  female (FS). The experiment was designed t o  minimize v a r i a t i o n  w i t h i n  o t h e r  v a r i a b l e s  which might e f f e c t  h e a r t  r a t e  response to e x e r c i s e .  The a b i l i t y  t o  e v a l u a t e  phys ica l  f i t n e s s  by tech-  n iques  not  r e q u i r i n g  ex tens ive  medical  f a c i l i t i e s  i s  poor. This  i n a b i l i t y  t o  e a s i l y  measure p h y s i c a l  f i t -  ness  n e c e s s i t a t e d  t h e  use  of an e a s i l y  i d e n t i f i a b l e  dichotomy in  c l a s s i f y i n g  phys ica l  f i t n e s s  of t h e  s u b j e c t  . The only phys io logica l  measurement r e q u i r e d  by t h e  p r e d i c t i o n  model i s  t h e  i n d i v i d u a l ' s  r e s t i n g  h e a r t  r a t e .  For t h e  purpose of t h i s  s tudy r e s t i n g  h e a r t  r a t e  was def ined  a s  t h e  average s e a t e d  h e a r t  r a t e  over a f i v e  minute per iod  fol lowing f i f t e e n  minutes of r e s t .  A l l  e x e r c i s e  d a t a  f o r  t h e  development of t h e  pre-  d i c t i v e  model were gathered w h i l e  t h e  s u b j e c t  was e x e r c i s i n g  on a b i c y c l e  ergometer. Two types  of da ta  were r e q u i r e d .  F i r s t ,  i t  was necessary  t o  develop a r e l a t i o n s h i p  between a work load and t h e  s teady  s t a t e  %RHR, t h e  dependent v a r i a b l e .  Regression equat ions  a r e  a s  fol lows:  For M S =.47W + 106 r = .95 MS S =.26W + 100 r = .99 FG S =.48W + 108 r = .97 FS S =.43W + 103 r = .98 Where, S = Steady s t a t e  %RHR W = Work load  ( w a t t s  ) r = Corre la t ion  c o e f f i c i e n t  225  at UNIV OF OKLAHOMA LIBRARIES on January 20, 2016pro.sagepub.comDownloaded from There i s  no s t a t i s t i c a l l y  s ign i f i can t  d i f fe rence  in the  slopes of the  MG, FG, and FS equations.  However, t he  slope of the  than the  slopes of the  MG, FG, and FS equations.  Con- s i s t e n t  pa t te rns  in the  data s t rongly  suggest t ha t  when a l a rge r  data base has been developed, these slopes w i l l  be shown t o  be s ign i f i can t ly  d i f f e ren t  from each o ther .  Based on t h i s  observation, the model was developed using separa te  r e l a t ionsh ips  f o r  each subjec t  category. A l a t e r  comparison of pred ic t ive  r e s u l t s  with a model which combined the  regression equations in to  an average equation showed t h a t  t he re  was no loss i n  accuracy in  using separa te  equations,  Second, the pred ic t ive  model required espec ia l ly  derived hea r t  r a t e  pa t t e rns  from which a predicted card iac  response could be extrapolated.  t e rns , in  terms of %RHR, having one of four poss ib le  i n i t i a l  values (IV = 100, 120, 140 o r  160% RHR) and one of four possible steady s t a t e  values ( SS=lOO, 120,  and 140, or 160% RHR),were derived by t a s t ing .  equation is s ign i f i can t ly  d i f f e ren t  Twelve pa t -  THE PREDICTIVE METHOD The predic t ion  i s  accomplished by ex t rapola t ing  an expected card iac  response, in terms of %RHR, from an appropr ia te  pa i r  of emperically derived hea r t  r a t e  pa t t e rns .  The derived pa t t e rns  a r e  se lec ted  from those of a pa r t i cu la r  subjec t  category such t h a t  t he  p a i r  of pa t te rns  bracket the  pred ic t ion  t o  be made. The only information needed f o r  s e l ec t ing  the pa i r  of pa t t e rns  i s  the i n i t i a l  value of the  pred ic t ion ,  which i s  known, and the  expected steady s t a t e  value which i s  obtained from the  workload versus steady s t a t e  %RHR r e l a t i o n -  ships.  A graphic example of the der iva t ion  of a pre- d ic ted  hea r t  r a t e  pa t te rn  i s  shown i n F i g u r e  2. The pa t te rn  t o  be predicted (P) has an i n i t i a l  value of 129% RHR (given) and a steady s t a t e  value of 146%RHR (100 wat t  worklmd f o r  FS). A pa t te rn  not ad jus ted  f o r  time (Z) with the  required steady s t a t e  value of 146%RHR can be obtained by l i nea r  in te rpola t ion  between the  high (140 t o  16O%RHR) and low (120 t o  140% RHR) 0 0 0 . 0  WOW LOAD (WATTS) r 3 0  12  p' 0 110 1 pa t te rns .  However i t  can be observed t h a t  the  r e s u l t a n t  i n i t i a l  Galue of L i s  126% RHR and not the  required 129%RHR. Therefore it i s  necessary t o  s h i f t  Z t o  the  l e f t  such tha t  the  in t e rcep t  a t  time zero  f o r  pa t te rn  Z is 129%RHR. The r e su l t an t  pa t -  t e rn  P is the pa t te rn  t o  be predicted.  A l l  pa t t e rns ,  f o r  e i t h e r  pos i t i ve  o r  negative s t ep  changes in  work load a r e  determined in  a s imi l a r  manner and a r e  ex- pressed in terms of %RHR. Given the  r e s t i n g  hea r t  r a t e  of a pa r t i cu la r  ind iv idua l ,  P can be t r ans l a t ed  i n t o  ac tua l  hea r t  r a t e  values.  of f ixed  in t ens i ty  tasks  with a combined duration of no more than four minutes. The only purpose of the four minute time r e s t r i c t i o n  is t o  avoid the  e f f e c t s  of fa t igue .  A s  long a s  f a t igue  is  not  s i g n i f i c a n t ,  the  model w i l l  y i e l d  an accura te  pred ic t ion .  predicted hea r t  r a t e  pa t te rn  f o r  each task  i s  derived according t o  the  aforementioned procedures and then they a r e  combined t o  obtain a pred ic t ion  f o r  t he  s e r i e s .  Suppose tha t  it is des i red  t o  p red ic t  t he  card iac  response of a sedentary male with a r e s t i n g  hea r t  r a t e  of 76 bea ts  per minute t o  a s e r i e s  compo- sed of t he  tasks  requi r ing  work loads of 110 wa t t s  f o r  70 seconds, 175 wat t s  f o r  80 seconds, and zero wa t t s  f o r  90 seconds. F i r s t ,  t he  hea r t  r a t e  pa t -  t e rn  f o r  the 110 wat t  t ask  i s  predicted f o r  70 seconds. The hea r t  r a t e  value a t  time equal t o  70 seconds becomes the  i n i t i a l  value f o r  the  second task ,  and the  hea r t  r a t e  pa t te rn  f o r  the second task  i s  determined. Task three  is recovery t o  a r e s t i n g  s t a t e  s t a r t i n g  a t  time equals 150 seconds. Table 1 presents  the  predicted card iac  response a s  produced by the  pred ic t ion  model. Figure 3 i s  a p lo t  of the  predicted and observed hea r t  r a t e  values - f o r  t he  subject and tasks  of the  example. The predic t ive  model w i l l  accommodate a s e r i e s  The Table 1 : Prediction model output f o r  t he  subjec t  and tasks  of the  example. o = Pattern Z 0 = Pat te rn  P = high & low pa t t e rns  c = s h i f t  i n  time 100 4 I , I I 0 10 20 30 t o  5b  Qo 7 b  ' TIME (sec) Figure 2: Graphic example of der iva t ion  of predicted hea r t  r a t e  pa t te rn .  Arrows represent  s h i f t  of Z t o  in te rcept  a t  an i n i t i a l  value of 129. .-_- 110 110 110 110 110 110 110 175 175 175 175 175 175 175 1?5 0 0 0 0 0 0 0 0 0 0 CARDlAC RESPONSE VALE SEDENTARY PAR IS 76 ELAPSED TIEE H U R T  RATE (SECONDS) ( B W  0 76 10 88 20 94 30 97 40 98 so 99 60 99 70 99 80 104 90 100 110 120 107 110 111 112 130 112 190 89 200 86 210 82 220 81 230 79 240 77 EVALUATXON OF THE PREDICTIVE ACCURACY ZRHR 100 11s 123 127 129 130 , 130 130 136 141 145 145 147 147 147 ib7 138 131 125 118 113 ioa ...106 104 102 In order t o  ve r i fy  the accuracy of t he  prediction model, a subjec t  representa t ive  of each of t he  four subjec t  ca tegor ies  performed s i x  exerc ise  s e r i e s  s imi la r  t o  the  above example. Upon examining the  d i s t r ibu t ion  of t h e  e r r o r ,  i t  was determined t h a t   at UNIV OF OKLAHOMA LIBRARIES on January 20, 2016pro.sagepub.comDownloaded from 90% of t h e  time e r r o r s  of t h e  p r e d i c t i o n  model were no more than 5% t o  10% of t h e  observed h e a r t  r a t e  va lue .  SUMMARY The purpose of t h i s  s tudy was t o  i n v e s t i g a t e  t h e  f e a s i b i l i t y  of developing a p r e d i c t i v e  technique f o r  h e a r t  r a t e  which r e q u i r e d  a minimum of d e s c r i p t i v e  information.  By express ing  t h e  h e a r t  r a t e  d a t a  i n  terms of t h e  percent  of r e s t i n g  h e a r t  r a t e ,  a p r e d i c -  t i o n  model was developed and v e r i f i e d  t o  be accura te .  However, t h e  p r e d i c t i o n  mode1,in i t s  present  form, accommodates only a segment of t h e  a d u l t  working populat ion and a J imi ted  range of phys ica l  a c t i v i t i e s .  Much work remains t o  be done b e f o r e  t h e  p o t e n t i a l  a p p l i c a b i l i t y  of t h i s  technique can be f u l l y  r e a l i z e d .  110- 0 observed * p r e d i c t e d  0 0 0 0 0  0 . .  0 0 Figure  3:  P l o t  of p r e d i c t e d  and observed h e a r t  r a t e  responses  f o r  t h e  s u b j e c t  and t a s k s  of the  example. 227  at UNIV OF OKLAHOMA LIBRARIES on January 20, 2016pro.sagepub.comDownloaded from 

Prediction of Cardiac Response to Physical Stress

 This paper presents a method for predicting an individual's cardiac response to a series of fixed intensity tasks. It was determined that cardiac responses to exercise at given work loads are similar for subjects of the same sex and level of physical fitness when they are expressed in terms of resting heart rate. Using this observation as a basis, a prediction model was developed by extrapolating from emperically derived heart rate patterns. The prediction error was no more than five to ten percent of the actual heart rate value in ninety percent of the predictions. </jats:p

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Proceedings of the Human Factors Society Annual Meeting

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Prediction of Cardiac Response to Physical Stress

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