CLIN. AND EXPER.-THEORY AND PRACTICE, A7(2&3), 381-385 (1985)

DATA ANALYSIS OF LONG-TERM BLOOD PRESSURE MONITORIKG

G . K . M6rieK CardioConcept Research Group PO Box 155 1211 GENEVA 1 2 (Swi t ze r l and)

G . Abetel Group P r a c t i c e P lace du Marchi., 6 1350 ORBE (Swi t ze r l and)

J . C . Bousquet Sandoz Product C l i n i c a l Research 4010 BASLE (Swi t ze r l and)

Ke9 words: Datu analysis, anhulatory i5P

INTRODUCTION

Ambulatory systems f o r long-term b lood p r e s s u r e moni tor ing produce a l a r g e volu- m e of d a t a , u s u a l l y d i s p l a y i n g a wide i n t e r - i n d i v i d u a l and in te r -group v a r i a b i l i t y . U n t i l r e c e n t l y , most i n v e s t i g a t o r s involved in such s t u d i e s were conten t t o reduce t h i s da t a t o the mean, s t anda rd d e v i a t i o n , c o e f f i c i e n t of v a r i a t i o n , median, range and d i s t r i b u t i o n . However, t h e s e va lues do n o t adequa te ly r e f l e c t drug-induced chan- ges i n c i r c a d i a n p r e s s u r e r ead ings and s u b s t i a n t i a l l y reduce the power of s t a t i s t i c a l a n a l y s i s .

As an a i d t o r e s e a r c h i n t h i s f i e l d , our group has dev i sed a s y s t o l i c and d i a s - t o l i c p r e s s u r e s c o r i n g method which i n t e g r a t e s t ime-s tandard ized blood p r e s s u r e d a t a and the i n t e r v a l of obse rva t ions us ing prede termined th re sho lds . Such an approach i s independent of t h e number of blood p r e s s u r e (BPI r ead ings , t h e average i n t e r v a l b e t - ween two read ings and the t o t a l d u r a t i o n of obse rva t ion .

METHOD

1. Analys is of blood p r e s s u r e p r o f i l e s . I n o rde r t o compare BP p r o f i l e s o b t a i - ned by i n d i r e c t measurement, a uniform method of e v a l u a t i o n must be employed and a common s t anda rd accepted by a l l p a r t i c i p a n t s ( a s in e l e c t r o c a r d i o g r a p h y ) . We o f f e r t he fo l lowing model a s meet ing these requi rements .

Recording c o n d i t i o n s . The p a t i e n t wears a r eco rd ing device f o r 12-24 hours wh i l e going about h i s normal a c t i v i t i e s . A t 8 am and 6 pm he a t t e n d s h i s d o c t o r ' s o f f i c e , where h i s blood p res su re i s a l s o measured conven t iona l ly us ing a usua l mercu- r y manometer l i nked t o the p o r t a b l e device (Remler 2000) f o r c a l i b r a t i o n purposes .

Measured v a r i a b l e s . For s y s t o l i c and d i a s t o l i c BP: o f f i c e BP. HgBP s imul taneous c o n t r o l v a l u e s , mean c o r r e l a t i o n device/HgBP, mean o f f i c e r ead ings and s t anda rd devi - a t i o n (SD) , mean ambulatory r ead ings and SD, mean p r o f i l e and SD, range. For pu l se : mean ambulatory r ead ings and SD, o f f i c e r ead ings and SD, mean p r o f i l e and SD.

by g radua t ions of 1-g ( a b s o l u t e and % v a l u e s ) . The r e s u l t a n t curve i s n o t always gauss i an in shape; i t r e v e a l s any d i f f e r e n c e between the mean and the median of t h e r ead ings . Th i s method of p r e s e n t a t i o n t a k e s no account t o the d u r a t i o n of a given r ead ing , which may be an impor tan t i t e m .

Data p r e s e n t a t i o n . The d a y ' s r ead ings are p resen ted i n a f requency d i s t r i b u t i o n

2 . S t anda rd ized S y s t o l i c and D i a s t o l i c Scor ing (SSDS) method.

Hathemat ica l p r i n c i p l e . The S tanda rd ized S y s t o l i c and D i a s t o l i c Scor ing (SSDS) method i s based on t h e t ime-re la ted s u r f a c e a r e a of blood p res su re above o r below the fo l lowing a r b i t r a r y t h r e s h o l d s curves : P o s i t i v e s y s t o l i c s co re : 160 , 150, 140 nnnHg, n e g a t i v e s y s t o l i c score : 100 d g , d i a s t o l i c s co re : 95, 90 , 85 d g . According

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Copyright 0 1985 by Marcel Dekker, Inc. 0730-0077/85/0702-038 I $ 3 . S O / O

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382 MERIER, ABETEL, AND BOUSQWT

04.05.83 DISTRIBUTION MESURES JOURNALIERES 12) SVSTOLIPUES 20101/42

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DATA ANALYSlS OF LONG-TERM BP M O N I T O R I N G 383

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384 MERIER, ABETEL, AND BOUSQUET

t o t h i s d e f i n i t i o n each s c o r e r e p r e s e n t s t h e ArmnHgltime u n i t above o r below t h e g iven th re sho ld , i . e . t he t o t a l s u r f a c e a r e a above o r below t h e t h r e s h o l d cu rve d iv ided by the t ime of obse rva t ion . This approach makes t h e SSDS method independent of t h e num- be r of blood p r e s s u r e measurements pe r hour and t h e t i m e of obse rva t ion . Consequently i t pe rmi t s v a l i d comparisons between d i f f e r e n t r e s e a r c h s t u d i e s i n t h i s f i e l d .

Computing process . We de f ine :

n

X S

X. 1

ti Ax. =

Ax. = 1

A t i =

SCORE

number of d a t a (b lood p r e s s u r e r ead ings )

t h r e s h o l d v a l u e s 160 , 150 and 140 f o r t h e P o s i t i v e s y s t o l i c s c o r e 100 f o r t h e Negat ive s y s t o l i c s co re 95 , 90 and 85 f o r t h e D i a s t o l i c s co re

i n d i v i d u a l d a t a ( i = l , 2 , ..., n)

t ime of measurement (hour , dec imal )

xi - xs; x . > 0 ( s y s t o l i c o r d i a s t o l i c , p o s i t i v e )

100 - x . X. > 0 ( s y s t o l i c , n e g a t i v e ) i' 1

t . - ti-l titl - t . 2 +-

(Represent ing t h e t i m e i n t e r v a l between two blood p res su re r ead ings . The f i r s t and l a s t r ead ings a r e s p e c i a l c a s e s , computed acco rd ing ly )

i = n 1 . 1 (Axi . Ati) = -

i=n i=l

i-1 1 A t ;

A BASIC-language computer program was dev i sed and implemented on desk and pocket computers ( a v a i l a b l e on r e q u e s t ) .

Mathematical e v a l u a t i o n . The mathematical i m p l i c a t i o n s of t h e SSDS method were eva lua ted by means of r e g r e s s i o n / c o r r e l a t i o n a n a l y s i s . The r e s u l t shows a v e r y good c o r r e l a t i o n between t h e mean and t h e s c o r e s i n cases wi th d i f f e r e n t means and the same s t anda rd d e v i a t i o n , and a t t h e o p p o s i t e , a v e r y good c o r r e l a t i o n between the s t anda rd d e v i a t i o n (which i s an e s t i m a t o r of t h e b lood p r e s s u r e v a r i a b i l i t y ) and t h e s c o r e s i n cases wi th t h e same mean and d i f f e r e n t s t anda rd d e v i a t i o n . Consequently, i n t h e s e two extreme t h e o r e t i c a l blood p r e s s u r e p a t t e r n s , t he SSDS method c o r r e l a t e s w e l l w i th t h e mean BP i n c a s e s wi th t h e same v a r i a b i l i t y and c o r r e l a t e s w e l l w i th t h e v a r i a b i l i t y i n c a s e s wi th t h e same mean BP. This r e f l e c t s t he b a s i c p r i n c i p l e of t h e SSDS method, which i s t o g ive a b e t t e r estimate of t h e c o n t r i b u t i o n of each i n d i v i d u a l measurement t o t h e t o t a l long-term b lood p r e s s u r e p r o f i l e and t o enhance t h e d i sc r imi - n a n t power of t he d a t a a n a l y s i s p rocess .

C l i n i c a l e v a l u a t i o n and r e l evance . I n o rde r t o e v a l u a t e the c l i n i c a l r e l evance of t h e SSDS method, p a r t i c u l a r l y w i t h i n the framework of a c l i n i c a l t r i a l of a n t i - hype r t ens ive d rugs , w e app l i ed t h e method t o the Swiss bop indo lo l / a t eno lo l coope ra t i - ve s tudy , i n which a t e n o l o l 5Omg and lOOmg w a s compared w i t h bopindolo l lmg and 2mg i n r e s p e c t t o t h e an t i -hype r t ens ive e f f e c t . Regard less of t he f i n a l r e s u l t s , which i s n o t t he purpose of t h i s pape r , t h e a n a l y s i s demonst ra ted t h e a b i l i t y of t h e SSDS method t o d e t e c t f i n e d i f f e r e n c e s i n t h e blood p r e s s u r e c o n t r o l a f fo rded by these two drugs . We conclude t h a t t he SSDS method appears t o be a more s e n s i t i v e and accu ra t e ins t rument f o r ana lys ing long-term blood p r e s s u r e d a t a , a s compared wi th t h e conven- t i o n a l "mean/ s tandard dev ia t ion" method .

SUMMARY

1 Long-term blood p r e s s u r e mon i to r ing p rov ides a l a r g e q u a n t i t y of d a t a wi th a wide i n t e r - i n d i v i d u a l o r i n t e r -g roup v a r i a b i l i t y .

2 The convent iona l "mean/standard dev ia t ion" approach t o d a t a a n a l y s i s i s a r e l a - t i v e l y i n s e n s i t i v e ins t rument f o r d e t e c t i n g c i r c a d i a n d i f f e r e n c e s i n blood p res - s u r e p r o f i l e , mainly because t h e mean and t h e v a r i a b i l i t y around t h e mean a r e processed s e p a r a t e l y .

3 The proposed Standard ized S y s t o l i c and D i a s t o l i c Scor ing (SSDS) method enhances the a n a l y t i c a l p o s s i b i l i t i e s .

P re l imina ry e v a l u a t i o n of t h e SSDS method u s i n g d a t a ob ta ined i n an anti-hyper- t e n s i v e drug t r i a l sugges t s c l i n i c a l r e l evance .

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DATA ANALYSIS OF LONG-TERM BP MONITORING

REFERENCES

1 A b e t e l G.F.: I n t e r s t du p r o f i l t e n s i o n n e l . Schweiz. med. Wschr. 1980; 110:1935- 1938.

2 Clement D.L.: How s h a l l we d e f i n e b lood p r e s s u r e v a r i a b i l i t y ? Round t a b l e d i s - c u s s i o n . I n Ref 6 : 607, 611-619.

3 Gould B . A . , Hornung R.S . , Kieso H . A . , e t a l : E v a l u a t i o n of t h e Remler M2000 blood p r e s s u r e r e c o r d e r . H y p e r t e n s i o n ; 1984:6:209-215.

4 M a l l i o n J . M . , de Gaudemaris R . , Vi l lemain P . : Automat ic ambula tory non- invas ive b lood p r e s s u r e r e c o r d i n g method, methodology, c l i n i c a l a p p l i c a t i o n s . I n Ref 6: 522-528.

5 Nann S . , M i l l a r - C a r i g M.W., Gould B . A . , e t a l : The assessment o f b l o o d p r e s s u r e v a r i a b i l i t y from h o u r l y mean v a l u e s . I n Ref 6 : 572-581.

6 S t o t t F.D., R a f t e r y E . B . , Clement D . L . , Wright S . L . , e d . : P r o c e e d i n g s o f t h e 4 t h I n t e r n a t i o n a l Symposium on Ambulatory M o n i t o r i n g and t h e 2nd Gent Workshop on Blood P r e s s u r e V a r i a b i l i t y . Academic P r e s s , New-York: 1982.

7 Van Maele G . O . , Clement D . L . : Methods of p r o c e s s i n g semi-cont inuous blood p r e s - s u r e r e c o r d i n g . In Ref 6: 608-611.

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