R e s e a r c h A r t i c l e C J EALES M.Sc (Physiotherapy) RAND Senior Lecturer, Department of Physiotherapy, University o f the W itw atersrand A V STEWART B.Sc (Physiotherapy) RAND DPE (RAND) M.Sc (Medicine) RAND Senior Lecturer, Department of Physiotherapy, University of the W itw atersrand CORRESPONDENCE Mrs C J Eales Department of Physiotherapy, Faculty of Health Sciences, University of the W itw atersrand 7 York Rd PARKTOWN 2 1 9 3 South Africa A P r o p o s e d F ie l d T e s t f o r E v a l u a t in g F i t n e s s in E l d e r l y H y p e r t e n s i v e Pa t i e n t s "3 ] he in cid en ce o f h y p erten ­ sion in S o u th Africa is as high as 8 2 .1 % in elderly b la ck w om en and 7 6 .9 % in eld er­ ly b la ck m en , (Bester and W eich 1 9 9 1 ) P atients were con sid ered h y p e rte n s iv e if b lo o d p ressu re exceed ed 1 4 0 / 9 0 Hg mm . H ypertension is a m ajor c o n ­ trib u tin g factor for strokes and d ea th from stro k e s. S tro k e s b e c o m e fam ily c a ta stro p h es am on gst the rural p opu lation in SA b ecau se o f the unavailability of approp riate rehabilitative services. H yperten sion is also a risk factor for congestive heart failure, c h ro n ­ ic occlu siv e p erip h eral vascular disease and renal failure. T here is in creasin g evid ence show ing that effective treatm en t o f hy p ertension sig nificantly low ers m orbid ity and m ortality due to these diseases (Bester and W eich 1 9 9 1 ). Regular aerobic exercise low ers the b lo od pressure in hypertensive patients by as m u ch as 11 m m Hg sy sto lic pressu re and 8 m m Hg diastolic pressure. T he proposed m ech an ism s in clu d e red uction in ren in -an gioten s in activity, resting sy m p a th etic to n e , b a ro -re c e p to r sen sitiv ity an d to ta l p e rip h era l resistance (H ou ston 1 9 9 2 ). In Sou th A frica there is a m ove aw ay from te rtia ry m e d icin e towards com m u n ity -b ased p rim a­ ry health care. W ith in this c on tex t exercise cou ld b eco m e an in e x p e n ­ sive in terv en tio n for the treatm ent o f h y p ertension. In order for a p re­ scribed exercise program m e to be safe and effective, patients' exercise p e rfo rm a n c e m u st b e assessed . W ith a view to prescribing exercise for hypertensive patients in a c o m ­ m u nity-based setting it b eco m es im p ortan t to design an exercise lest that can m easure their exercise capacity, in an effective and in e x ­ pensive m anner. T h e criteria for su ch a test w ould b e the follow ing • valid in both a hospital and com - m u n ity -clin ic setting. • inexpensive. C J EALES; A V STEWART Key words: Hypertension, exercise tests, Duke Activity Status Index, six minute walking test. ABSTRACT There is a very high incidence o f hypertension amongst the black population in South Africa. Regular aerobic exercise has been shown to be an effective method of lowering blood pressure. In order to be able to prescribe exercise for patients in a community- based setting, an easily administered exercise test needs to be used. In this study the 6 minute walking test in conjunction with the Borg scale and the Duke Activity Status Index (DASI) were tested on three groups of hypertensive patients from different socio-econom­ ic communities. The mean age of the cohort was 64.1 years (SD±7.9) and males and females were included. The outcome was evaluated by determining the degrees of agree­ ment between the DASI and the age predicted V 0 2 m a x (-0.3295) as well as between the calculated V 0 2 m a x and the age predicted V 0 2 m a x (-0.3045). The tests were easy to administer and the calculations easily done. The agreement between the 6 minute w alking test and the DASI test was clinically acceptable (-0.0250) . There was no agree­ ment between the values obtained and the age-predicted values. It was concluded that the walking test is a useful field test for exercise performance. • easily ad m inistered so that vari­ ou s levels o f h e a lth p e rs o n n e l w ould be con fid en t to use the test. • e ld e rly h y p e rte n siv e p a tie n ts w ould have to un derstand the test in stru ctio n s and safely com p lete the test. A w alking test seem s to be an ideal test to use. T h is is a test of physical co n d itio n that is relevant to the d em and s o f daily living and is a realistic m eth od o f c o n tin u o u s a s se s sm e n t o f e x e rc ise p e r fo r ­ m an ce. B assey et al ( 1 9 7 6 ) and C u n n in g h am et al ( 1 9 8 6 ) suggest­ ed that a self selected w alkin g pace cou ld b e an ad equ ate m easure of cardiovascular fitness and physical activity in the elderly. T h ey also su g g ested th a t th is te c h n iq u e cou ld be useful as a screen in g device to assess cardiovascular fit­ ness in older su b je c ts un able or un w illin g to w alk on a tread m ill or ride a c y c le erg om eter. In the S o u th A frican c lin ic a l situ atio n su ch eq u ip m en t is frequently not a v a ila b le and it w as th erefo re d ecided on a w alkin g test. A s ix m in u te w a lk in g test appears to fit the above criteria. A ccord in g to G uyatt et al ( 1 9 8 5 ) a six m inu te w alking test is a valid m easure o f exercise cap acity in p atients w ith ch ron ic lu n g disease an d c h ro n ic h eart failu re. T h e value o f this test in the d eterm in a ­ tion o f exercise capacity in elderly p atients with ch ro n ic h y p ertension has n o t b een established . T h e Borg scale s u b jectiv ely m ea­ sures the patient's p ercep tio n of exercise exertio n and also gives an in d ic a tio n o f e x e r c is e in te n s ity (D em ello et al 1 9 8 7 ). U sin g the Borg Scale to d eterm in e th e p er­ ceived intensity o f e x ertio n , the p re d icte d m a x im u m oxy gen uptake o r M ET (m eta b o lic equ iva­ le n t) level c a n be c a lc u la te d (W enger and H ellerstein 1 9 8 4 ). T h is can also be calcu lated using 16 SA Jo u r n a l o f Ph y s io t h e r a p y V o l 53 No 2 R ep ro du ce d by S ab in et G at ew ay u nd er li ce nc e gr an te d by th e P ub lis he r (d at ed 2 01 3. ) R e s e a r c h J o n e s ' form u la (Jo n e s and C am pbell 1 9 8 2 ). A ccord in g to Borg ( 1 9 8 2 ) , p er­ ceived exertio n is the single best in d icator o f the degree o f physical strain. T he overall perceived ex er­ tion rating integrates various in fo r­ m ation in clu d in g the m any signals elicited from the peripheral w o rk ­ ing m u scles and jo in ts , from the cen tral cardiovascular and respira­ tory system s and from the central nervous system . T h e rate o f perceived exertion (RPE) at the ventilatory thresholds and the lactate thresholds is c o n ­ stant and corresp on d s to a Borg scale rating o f 1 3 -1 4 . T he onset of h y p e rv e n tila tio n a n d /o r la cta te accu m ulation in m u scle and blood d uring exercise may provide an o b je c tiv e , p h y sio lo g ica l a n c h o r p oint for the su b jectiv e RPE. A reported RPE o f 9 - 1 0 w h ich is the very light to fairly light feeling of effort suggests that oxygen trans­ port and uptake are n o t at training levels ( Birk and B irk 1 9 8 7 ). E x e rc ise in ten sity , w ith o u t a graded exercise test, is prescribed by d eterm ining the age predicted m axim al heart rate and then c a lc u ­ lating the training heart rate. T h is p ro c e d u re m ay n o t alw ays be accu rate and m axim al heart rate by this calculation could result in an error o f as m u ch as 10 beats/m in standard deviation for each age category (B irk and B irk 1 9 8 7 ). Pulse rate is som etim es difficu lt for elderly people to m easure. T h is lends credibility to the use o f the RPE for assessing exercise intensity and prescribing exercise. An RPE o f less than 11 c o rre­ sponds to a heart rate o f less than 7 0 % o f the patient's m axim al heart rate. Sim ilarly an RPE o f 1 2 - 1 4 corresp on ds to a heart rate o f 7 0 - 8 0 % o f the patient's m axim um . Available evid ence suggests that the RPE ind ep en den tly or in c o m ­ bination w ith pulse rate can be effectively utilised for p rescribing exercise intensity (B irk and Birk 1 9 8 7 ). To c h e ck the accu racy o f the six m inu te w alking test as a m easure o f e x e rc ise c a p a city in eld erly h y p erten siv e p atien ts the D uke Activity Status In d ex can also be adm inistered. T h is is a b rief self­ ad m in istered q u e s tio n n a ire that m easures fun ctional capacity and assesses aspects o f quality o f life. T h is in d ex correlates significantly w ith p eak oxygen up take and is m easured in M ETS (H latky et al 1 9 8 9 , F ro eh lich er et al 1 9 9 3 ). A stu d y was u n d e rta k e n to assess the efficacy o f these tests in the su bp op u lation chosen. MATERIALS AND METHODS Subjects Patients were selected from a ter­ tiary care hospital in a m etro p o li­ tan area, a com m u n ity health c lin ­ ic in a depressed soc io -ec o n o m ic area and a hospital situated in a rem ote rural com m unity. Male and fem ale patients in the age group 5 5 -7 5 were inclu ded. All had blood pressure readings above 1 4 0 /9 0 H gm m . All the patients attending the hy p ertension clin ic on a sp ecif­ ic day at the above three venues were asked to participate in the study. All the patients from the rural hospital agreed to participate but there were patients from the o th er two clin ics who refused. A total o f 4 4 p a tie n ts w ere selected from the three areas. At the tertiary care hospital we assessed 17 patients. T he sam ple included 3 b lack patients and 14 w hite p atients (G roup 1). At the c o m m u n ity c lin ic we assessed 14 patients (G roup 2) and at the rural hospital 13 patients (G roup 3 ). T hese patients were all b la c k (Table 1). T he p ro ject was passed by the C o m m ittee for H um an E th ics at the U niversity o f the W itw aters- ran d. (C le a ra n c e c ertific a te no. M 9 4 1 1 3 0 ) . All p articipan ts signed a con sen t form after b ein g fully in fo rm ed o f the n atu re o f the study. Method All patients were seated and the D uke Activity Status Index was com pleted . T h e researchers read the qu estion s to the patients and reco rd ed th e ir resp o n ses. Im m ed iately after the com p letio n o f the DASI, w ith the patient still seated, the resting b lo od pressure m easurem ents were taken on the left arm. T h e p ro c e d u re for the six m in u te w a lk in g test was th en explained to the patient. T h e restin g pulse rate was taken m anually w ith the patient standing at the startin g p o in t o f the distance to be covered. T he p atient then com pleted the six m inu te w alking test . D irectly on com p letio n o f the test the pulse rate was taken. T he p atient was again seated and the post exercise blood pressure m ea­ sured. T h e patient rated his/her perceived exertion during the test on the Borg scale. The distance w alked was record ­ ed in m etres. TABLE 1: Mean Age (±SD) o f hypertensive patients in three groups recruited from three different clinical sites Groups Mean Age ( yrs) SD Sample Size 1 63.3 ± 7.02 17 2 63.1 ± 6.30 14 3 66.2 ± 10.3 13 TOTAL 64.1 ± 7.9 44 Group 1 = Tertiary Hospital Group 2 = Urban Community Group 3 = Rural Community A r t i c l e > A w alking test is a test o f physi­ cal condition that is relevant to the dem ands o f daily living C) SA J o u r n a l o f Ph y s io t h e r a p y V o l 53 No 2 17 R ep ro du ce d by S ab in et G at ew ay u nd er li ce nc e gr an te d by th e P ub lis he r (d at ed 2 01 3. ) R e s e a r c h A r t i c l e TABLE 2 Mean (±SD) duration of hypertension in years in all three groups of patients Groups Mean ± SD (yrs) 1 14.9 ± 7.9 2 8.2 ± 4.3 3 7.9 ± 3.8 TOTAL 10.7 ± 7.4 CALCULATION OF THE DATA T h e DASI score was obtained by adding the sum o f w eights for the "yes" replies. T h e oxygen uptake was calculated in the follow ing way: V O 2 = 0 . 4 3 x DASI + 9 .6 This fo rm u la was su g g ested b y the research ers w ho designed the test (H latky et al 1 9 8 9 ) To con v ert the result to M ET val­ ues the V O 2 was divided by 3 .5 . T he M ET value o f the w alking test was calculated using the follow ing form ula: V O 2 m l/kg. m in = (distance in m etres)/ Tim e x 0 .1 + 3 .5 = x M ETS = x / 3 . 5 (A m erican C ollege o f Sports M edicine 1991) U sing this M ET value and the rate o f perceived exertion as scored on the Borg Scale by the patient it was p ossible to calculate the p re­ d icted m ax im u m oxygen up take using the con version m eth od as d es c rib ed b y W en g er and H ellerstein ( 1 9 8 4 ) T h is con version was d one in the follow ing way: T here is a c o n stan t relationship betw een the RPE and the p ercen t­ age o f m axim u m oxygen uptake. From the RPE the percentage of m ax im u m oxygen u p take can be read from the con version graph and thus the m axim u m oxygen up take can be calculated as the test M ETS are know n. T h e age p re d icte d m ax im u m oxygen up take (M E T S) was also calculated using the form ula by Jo n e s and C am p bell (1 9 8 2 ) : Fem ale = ( 4 8 - 0 .3 7 x age)/ 3 .5 Male = ( 6 0 -3 .7 x a g e )/ 3 .5 T h e fo llo w in g in fo rm a tio n on exercise capacity was thu s avail­ able: 1. Patients' Test M ETS 2 P atients' V O 2 m ax calcu lated from the test and the RPE (M E T S) 3. Age p red icted m axim um oxygen u p take (M ET S) 4 . DASI M ETS TABLE 3 Tabulation o f Exercise test, DASI, calc VO2 m ax and age predicted peak METS in hypertensive patients from three groups. D istance m etres Test METS DASI METS VO2 m a x calcu lated in METS Age pred peak METS Tertiary Hosp 433 3.0 6.6 6.9 7-1 U rban Clinic 3 5 4 2.7 6.3 6.2 7.0 ' Rural Hosp 246 2.6 7.0 6.8 6.7 Mean 382 2.8 6.6 6.6 6.9 SD ±79.1 ± 0 .3 8 ± 1 .5 0 ± 2 .0 8 ±0 .9 6 P 0.0 0 6 6 0.0 0 9 1 0 .5 4 0 5 0.6 3 0 1 0.5121 RESULTS T he m ean age o f the patients was slightly h ig h er at the rural hosp ital b u t n o t significantly so ( p = 0 .5 2 2 2 ) (Table 1). T h e hy p ertensive patients at the tertiary care h o sp ita l had been identified and treated for a sig nifi­ cantly longer period o f tim e than the p a tie n ts in the o th e r two groups (p = 0 . 0 1 6 8 ) . Perhaps this im plies that m ed ical care was m ore readily available. (Table 2 ) T h e a g re em e n t b e tw e e n tw o tests can be establish ed by c a lc u ­ lating the lim its o f agreem ent as proposed by Bland and A ltm an, ( 1 9 8 6 ) . T he c a lcu latio n is as fol­ lows: U pper lim it = d + 1 .9 6 x SE Low er lim it = d - 1 .9 6 x SE W h ere d is the m ean o f the d if­ ferences in the scores for two tests and SE is the standard error of these differences (sd /V m ) T h e average distance covered in the six m inu te w alking test was the greatest for the tertiary hospital group ( 4 3 3 m etres), 3 5 4 m etres for the u rb an group and 3 4 7 for the rural group. T h is difference in d istan ce w alked was sig n ifican t (p = 0 0 0 6 6 ) and therefore the test M ET S also d iffered sig nificantly (p = 0 0 0 9 1 ) . DISCUSSION In a study by G uyatt et al ( 1 9 8 5 ) the m ean distance covered by c a r­ diac patients in the six m inu te w a lk in g test was 4 5 0 m etres, w h ich is con sid erably m ore than the distance covered by the h y p e r­ tensive patients in this study. It w ould appear that the exercise capacity of the groups stu d ied was im paired. T h e variation betw een the M ET values for the DASI and the V O 2 m ax M ET values calcu lated from the w alking test is sm all and c lin i­ cally accep table and therefore the results o f these two m eth od s were ju d g ed to be in agreem ent (Table 4 ). T h is ind icates that the w alking test results w hen con v erted to V O 2 m ax, yields resu lts th at are in agreem ent w ith the DASI results and that the V O 2 m ax values from the w alking test m inu s the m ean of the differences betw een the two 18 SA Jo u r n a l o f Ph y s io t h e r a p y V o l 53 No 2 R ep ro du ce d by S ab in et G at ew ay u nd er li ce nc e gr an te d by th e P ub lis he r (d at ed 2 01 3. ) R e s e a r c h A r t i c l e TABLE 4 Limits o f agreement between the tests DASI - VCh m ax. calc DASI - Age pred VO2 m ax VO2 m a x .c a lc - Age pred VO2 m ax m ean (d) -0 .0 2 5 0 -0 .3 2 9 5 -0 .3 0 4 5 stan d ard erro r (sd/rn) 0.2621 0 .1 8 5 5 0 .2 7 1 0 Limits of agreement (-0 .5 3 9 ; 0.4 8 9 ) (-0 .7 0 1 ; 0.3 7 1 ) (-0 .8 4 7 ; 0.2 3 8 ) tests will equal the DASI value (V O 2 m ax calc - 0 .0 2 5 = DASI) The Duke Activity Scale In d ex gives a valuable assessm ent o f the V O 2 m ax and one could argue that this test alone would suffice (Hlatky et al, 1 9 8 9 ). Peak oxygen uptake is the gold standard against which exercise cap acity is m easured. Because the DASI has been validat­ ed against peak oxygen uptake and there exists a significant correlation betw een the two tests we feel that the six m inute walking test has potential as a field test. The exercise test provided very valuable inform a­ tion on patients' responses to exer­ cise and would be essential to use when form ulating an individual exercise prescription. REFERENCES 1. Bassey E J, Fentem P H, MacDonald I C, Scriven P M 1976 Self-paced walking as a method for exercise testing in elderly and young men. Clinical Science and M olecular M edicine vol 51: 6 0 9 - 61 2. 2. Bester F C J, Weich D J V 1 991 Prevalence o f hypertension among elderly blacks in the O range Free State. Cardiovascular Journal o f Southern Africa. 2 (4): 154-156. 3 . Birk TJ, Birk CA 1987 Use o f ratings o f perceived exertion for exercise prescription. Sports Medicine 4: 1 -8. 4. Bland MJ, Altman DG 1986 Statistical methods for assessing agreement between two methods o f clinical measurement. The Lancet: 3 0 7 - 310. 5. Borg GAV 1982 Psychophysical bases o f perceived exertion. Medicine and Science in Sport and Exercise. 14 (5): 377- 381. 6. Cunningham DA, Reichnitzer PA, Donner AP 1986 Exercise training and the speed of self-selected w alking pace in men at retirement. Canadian Journal on A g in g 5(1): 19 - 25. 7. Demello J J, Cureton K J, Boineau R E 1 987 Ratings o f perceived exertion at the lactate threshold in trained and untrained men and women. Medicine and Science in Sport and Exercise 19(4): 354- 362. 8. Froehlicher VT, Myers J, Follansbee WP, Labovitz AJ 1993 Exercise and the Heart. 3rd edn M osby Year Book Inc St Louis Missouri: 91 - 92. 9. Guidelines for exercise testing and prescription 1991 The American College o f Sports Medicine. 4th edn. Lee and Febriger: 296. 10. Guyatt G H, Sullivan M J, Thompson P J, Fallen E L, Pugsley S O , Taylor D W , Berman L B 1985 The six minute walk: A new measure of exercise capacity in patients with chronic heart failure. Canadian M edical Association Journal. 132: 9 1 9 -923. 11. Hlatky M A, Boineau R E, Higginbotham M B, Lee K L, Mark D B, C aliff R M, Cobb F R, Pryor D B 1989 A Brief Self-Administered Questionnaire to Determine Functional Capacity (The Duke Activity Status Index). The American Journal o f C ardiology September 15: 651- 654. 1 2. Houston M C 1992 Exercise and Hypertension. Postgraduate M edicine 92 (6): 139 - 150 13. Jones N L and Campbell E J M 1982 Clinical Exercise Testing. W B Saunders Co. Philadelphia London Toronto Mexico City. 14. Wenger N K, Hellerstein H K 1984 Rehabilitation o f the C oronary Patient. 2 edn John W ile y and Sons N ew York: 241. 15. Weich D J V, Nienkemper M J, Bester F C J, 1991 Hipertensie by die bejaarde Continuing M edical Education. 9 ( 1 ) 6 0 -69 T he variation in lim its o f agree­ m en t betw een the DASI and the age p re d icte d V O 2 m ax and betw een the calculated V O 2 m ax and the age predicted V O 2 m ax was clinically un accep table esp e­ cially the low er lim it in b o th cases ( - 0 .7 0 1 ; and - 0 .8 4 7 , Table 4 ). The V O 2 m ax calculated from the six m in u te w alking test and the V O 2 calculated from the DASI reflected the values o f hypertensive patients. T he age predicted V O 2 m ax is a value for healthy people and does not reflect the V O 2 m ax o f patients w ith h y p e rte n s io n . T h is w ould explain the lack o f agreem ent illu s­ trated in the results. T hese results w ould require further validation by direct m easurem ent. CONCLUSION T he w alking test seem s to have potential as a useful field test. The m a jo r ity o f the p a tie n ts w ere enth u siastic about particip atin g in the test and no c om p lication s were exp erien ced d uring the test p ro ce­ dures. The test was not difficult to ad m inister or to calculate and spe­ cialised p ersonnel w ould n o t be requ ired for the testin g p ro c e ­ dures. ❖ SA Jo u r n a l o f Ph y s io t h e r a p y V o l 53 No 2 19 R ep ro du ce d by S ab in et G at ew ay u nd er li ce nc e gr an te d by th e P ub lis he r (d at ed 2 01 3. )