A comparison of two noninvasive methods of blood pressure measurement in the triage area A u t h o r s : D o n n a J o n e s , RN, MSN, M a r t h a K e e h n e r E n g e l k e , RN, PhD, Sy lv ia T. B r o w n , RN, EdD, a n d

M e l S w a n s o n , PhD, G r e e n v i l l e , N o r t h C a r o l i n a

Objective In t r iage of pa t i en t s in the emergency depar tment , nu r ses can identify condit ions such as e levated blood pressure tha t can lead to serious hea l th problems. It is imperat ive tha t the method used to evalua te blood pressure is dependab le and accurate. The in t roduct ion of n e w technology may yield resul ts tha t are not comparable to tradit ional measures . Therefore we compared the t radi t ional auscul ta tory me thod of measur ing blood pressure wi th the use of an au toma ted device.

Methods The blood pressure of 100 heal thy adul t vo lunteers was m e a s u r e d first wi th the t radi t ional cuff me thod and t h e n wi th an au toma ted device (IVAC model 4200). The m e a s u r e m e n t s were recorded and then compared for each individual.

Results The m e a n difference b e t w e e n the paired systolic m e a s u r e m e n t s was 4.3 m m Hg (p = 0.0001). The m e a n difference b e t w e e n the paired diastolic m e a s u r e m e n t s was 1.3 m m Hg. There was a clinically significant difference (>9 mm Hg) in 37% of the systolic readings and 26% of the diastolic readings. In 76% of those clinically significant systolic differences, the IVAC 4200 m e a s u r e m e n t exceeded the m a n u a l method. For the clinically signif icant diastolic differences, 58% of the IVAC 4200 m e a s u r e m e n t s were greater than the m a n u a l method.

Conclusion Clinicians mus t be caut ious w h e n us ing n e w technology to measu re blood pressure. Results may not be comparable wi th resul ts ob ta ined wi th the t radi t ional method. (J Emery Nurs 1996;22:111-5)

Donna Jones is staff nurse, emergency department, Pitt County Memorial Hospital, Greenville, North Carolina. Martha Engelke is associate professor, and Sylvia Brown and Mel Swanson are profes- sors, East Carolina University School of Nursing, Greenville, North Carolina. For reprints, write Martha Keehner Engelke, RN, PhD, 220 Pineview Dr., Greenville, NC 27834. Copyright �9 1996 by the Emergency Nurses Association. 0099-1767/96 $5.00 + 0 18/1/72107

A l though the pr imary miss ion of the emergency d e p a r t m e n t is the t r ea tmen t of l i fe- threatening

illnesses, it is e s t ima ted that 43% of ED visits through- out the country are for pr imary heal th care. 1 Through initial nu r s ing a s s e s s m e n t in the tr iage area, pa t ien ts may be identif ied as hav ing condi t ions tha t could place t h e m at risk for serious illness. A rout ine part of a nu r s i ng a s s e s s m e n t is the a s s e s s m e n t of vital signs, inc lud ing blood pressure. Triage nurses frequently identify pa t ien ts who have elevated blood pressure and refer t hem to resources for follow-up and treat- ment . Therefore it is critical that nurses provide accu- rate a nd precise heal th s c r een ing to these pat ients .

A n es t imated 50 million A me r i c a ns have hyper- tension. 2 Many pa t i en t s with elevated blood pressure

are una w a r e of the problem unti l they come to a health care agency for t r e a t me n t of an unre la ted physical problem. The prevalence of pa t ien ts who come to the e me r ge nc y d e p a r t m e n t wi th previously und i a gnosed hyper tens ion ranges from 18.8% 3 to 31.7%. 4 Further-

more, Chernow et al. 5 found that 68% of 239 pa t ien ts whose hyper tens ion was d iagnosed in the emergency depa r tmen t had con t inued elevated blood pressure dur ing follow-up care ei ther in the e m e r g e n c y depart- m e n t or in a phys i c i an ' s office.

Al though the "gold s t andard" for blood pressure m e a s u r e m e n t is the direct intraarterial method, it is ne i ther pract ical nor appropriate for use in the tr iage

area. Instead, the a s s e s s m e n t of blood pressure in ambula tory se t t ings has traditionally b e e n performed by the auscul ta tory method. Auscu l ta t ion of blood pressure involves p lac ing a cuff, which encloses a bladder, a round the b icep musc le of a pa t i en t ' s arm. The bladder is inflated wi th air unt i l a palpable pulse can no longer be ob ta ined distally, and an addi t ional 20 m m Hg of air t hen is instilled into the bladder. A s te thoscope is p laced over the brachial artery and the air is slowly released from the cuff unt i l tones are heard and con t inues to be released unti l the tones disappear. The systolic pressure is the point at which Korotkoff sounds beg in and the diastolic pressure is the point at which the sounds disappear. Al though this method is

subject ive, it is the tradit ional a nd most commonly used method of blood pressure de terminat ion . 6

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Table 1 S u m m a r y of prev ious s tudies compar ing tradit ional and automated dev ices for m e a s u r i n g blood pressure

Marx et al. 7 Laboring women Nonpregnant/pregnant women

Whincup et al. 8 Children Adults

Crews and Harrison 9 DS-175 DS-145 DS-115

Weaver et al. 1~

Systol ic pressure Diastol ic pres sure

A > M A < M A = M A > M A < M

& +

A = M

+ +

+ +

+ +

+ +

+ +

+ +

+ +

A, Automated; M, manual; A > M, automated significantly greater than manual; A < M, automated significantly less than manual A = M, no significant difference between automated and manual.

Recent ly , a u t o m a t e d d e v i c e s tha t moni to r blood p re s su re by the osc i l lometr ic m e t h o d have b e e n in t roduced . This m e t h o d involves the u se of an elec- t ronic i n s t r u m e n t c o n n e c t e d to a blood p re s su re cuff t ha t con ta ins a sensor . The sensor is a m i c r o p h o n e tha t s e n s e s the Korotkoff s o u n d s or the pu l sa t ions of t he blood flow th rough the ar te ry whi le the cuff slowly deflates . This m e t h o d is u s e d mos t often w h e n very f requen t b lood p r e s s u r e r e a d i n g s are b e i n g obta ined .

After the in t roduc t ion of an a u t o m a t e d m e t h o d of b lood p re s su re a s s e s s m e n t in our t r i age area, the n u m b e r of p a t i e n t s w i th e l eva t ed blood p re s su re i n c r e a s e d from 18% to 26%. We d id not know w h e t h e r th is i n c r e a s e r e p r e s e n t e d a t rue i nc rea se in t he inci-

d e n c e of e l eva t ed b lood p r e s s u r e or w h e t h e r i t w a s re la ted to an i n c o n s i s t e n c y b e t w e e n the t rad i t iona l and a u t o m a t e d me thods . Therefore th is s t u d y was u n d e r t a k e n to c o m p a r e two ind i r ec t m e t h o d s of mon- i tor ing blood pressure : the auscu l t a to ry m e t h o d and the osci l lometr ic me thod .

Literature r e v i e w

Previous repor ts c o m p a r i n g the auscu l t a to ry m e t h o d wi th t he osci l la tory m e t h o d have s u g g e s t e d tha t the m e t h o d s m a y yield s ign i f ican t ly different read ings . The resul t s from severa l s tud i e s are s u m m a r i z e d in Table 1.

A compar i son of t he auscu l t a to ry and osci l la tory m e t h o d s of b lood p re s su re mon i to r ing in n o n p r e g n a n t (n=20) , p r e g n a n t (n=20) , a n d labor ing w o m e n (n = 30) found no s ign i f i can t d i f ferences b e t w e e n the n o n p r e g n a n t and the p regnan t , non labor ing subjec ts . However , in t he l abor ing women , systol ic p r e s su re s w e r e s ign i f ican t ly h ighe r and d ias to l ic p r e s s u r e s we re s ign i f ican t ly lower w i th the osci l la tory m e t h o d t han wi th the auscu l t a to ry me thod . 7

W h i n c u p et al. s c o m p a r e d the D inamap mode l

1846SX a u t o m a t i c b lood p re s su re moni to r (Critikon, Inc., Tampa, Fla.) and auscu l t a to ry m e t h o d s on 141 adu l t s and 152 ch i ldren in o u t p a t i e n t clinics. They found tha t sys tol ic p r e s su re s we re s igni f icant ly h igher for bo th chi ldren a n d adul t s w i th the D i n a m a p dev ice bu t t ha t the re w a s no s ign i f ican t d i f ference in the di- as to l ic read ings . Resul ts from th ree different tr ials d e m o n s t r a t e d s imi lar results.

Crews and Harr i son 9 c o m p a r e d th ree e lect ronic blood p re s su re mon i to r s (models DS-175, DS-145, and DS-115; Nisse i Commerce , Ltd., Tokyo, Japan) wi th t he auscu l t a to ry m e t h o d in 21 vo lun teers from 20 to 53 yea r s of age. The m o d e l DS-175 dev ice ove re s t ima t ed sys to l ic and d ias to l ic p r e s s u r e s s ignif icant ly . All th ree m o d e l s o v e r e s t i m a t e d low blood p r e s s u r e s and un- d e r e s t i m a t e d h igh blood pressures .

Ano the r s t u d y c o m p a r i n g the D i n a m a p mode l 1846SX wi th the auscu l t a to ry m e t h o d involved 381 f i f th-grade chi ldren in w h i c h th ree r e a d i n g s were ob- t a i n e d wi th bo th t he D ina ma p dev ice and the auscul- t a tory m e t h o d of b lood p re s su re m e a s u r e m e n t , i~ Sys- tolic b lood p re s su re s were s ign i f ican t ly h igher and di- as to l ic p re s su re s ign i f ican t ly lower wi th the a u t o m a t e d me thod . The au thors cau t i oned tha t r e a d i n g s from the D i n a m a p dev ice m i g h t be u s e d to classify some chil- d ren as h y p e r t e n s i v e w h e n t hey were normotens ive .

Finally, Rebenson-P iano , e t al. 11 c o m p a r e d the d i r ec t m e t h o d of b lood p re s su re d e t e r m i n a t i o n wi th bo th the osci l la tory a n d the auscu l t a to ry me thods in a s a m p l e of 32 i n t ens ive care pa t ien ts . They found tha t bo th ind i rec t m e t h o d s u n d e r e s t i m a t e d systol ic pres- sures in no rmotens ive p a t i e n t s bu t only the osci l latory resu l t s were s igni f icant . Diastol ic p r e s su re s were not s ign i f ican t ly different in no rmotens ive pa t ien ts . In t he hype r t e ns ive popula t ion , the d i rec t m e t h o d for sys- tolic p re s su re s w a s s igni f icant ly h igher than both in- d i r ec t me thods .

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In summary , resu l t s of p rev ious r e sea rch com- p a r i n g the auscu l t a to ry and osci l latory m e t h o d s of b lood p r e s s u r e m e a s u r e m e n t a re conflict ing. There is s o m e e v i d e n c e tha t osci l la tory m e a s u r e m e n t s m a y yield different resul ts t han the auscu l t a to ry method . No s tud ie s have speci f ica l ly a d d r e s s e d the relat ion- sh ip b e t w e e n the a u t o m a t e d dev ice u sed at our hos- pi ta l (model 4200; IVAC Lilly Mediz in Technik GMBH, Giessen , Germany) and the auscu l t a to ry m e t h o d of b lood p r e s s u r e de te rmina t ion .

Method Setting This s t u d y w a s c o n d u c t e d in the t r i age room of an e m e r g e n c y d e p a r t m e n t a t a 750-bed level I t r a u m a cen te r in a rural a r ea of t he Southeas t .

Sample The p a r t i c i p a n t s we re a c o n v e n i e n c e s a m p l e of vol- un t ee r s i nc lud ing e m e r g e n c y med ica l t echn ic ians , nurses , phys ic i ans , and o ther ED staff. Sub jec t s we re s e l e c t e d if t hey m e t t he following criteria: older t han 18 yea r s of age, no h i s tory of hype r t ens ion or an t ihy- pe r t en s ive the rapy , n o n p r e g n a n t s ta te .

Procedure After ob t a in ing in formed consent , the sub j ec t ' s b lood p re s su re w a s m e a s u r e d wi th the mercu ry s p h y g m o - m a nome te r . The b lood p re s su re was t aken in the m a n n e r d e s c r i b e d earlier. The cuff s ize w a s de te r - m i n e d by the s ize of t he individual ; both adul t and large adul t cuffs we re used. The blood p re s su re m e a - s u r e m e n t w a s t hen r e p e a t e d 1 m i n u t e la ter in t he s a m e arm wi th the IVAC mode l 4200 device . Both m e a s u r e m e n t s were pe r fo rmed by the s a m e re- searcher . By pe r fo rming the auscu l t a t ion m e t h o d first, some r e sea rche r b i a s w a s e l imina ted b e c a u s e the re- s ea rche r w a s u n a w a r e of the resul ts from the oscil la- tory me thod . The door to the t r i age room w a s c losed dur ing the s t u d y pe r iod to min imize no ise and dis- t r ac t ions from the e m e r g e n c y a rea and the sub jec t w a s a s k e d not to talk du r ing the m e a s u r e m e n t read- ings.

Instnmlents The IVAC 4200 is the osc i l lometr ic dev ice u s e d to ob- ta in a u t o m a t e d blood pressures . The IVAC 4200 is m a n u f a c t u r e d by the IVAC Corpora t ion and is cali- b r a t e d a c c o r d i n g to m a n u f a c t u r e r ' s spec i f i ca t ions b y the hosp i t a l ' s b i o m e d i c a l eng inee r s every 6 months . The m e r c u r y s p h y g m o m a n o m e t e r is the Trimline mode l (PyMah Corp., Somerville, N.J.) and is cali- b r a t e d b y the hosp i ta l b i o m e d i c a l eng inee r s every month. The cuff is a t t a c h e d to the s p h y g m o m a n o m -

eter b y a rubber air hose. The cuff con ta ins a p n e u m a t i c b ladder b a g tha t is a t t a c h e d to a s e c o n d air

hose tha t ends in a h a n d - h e l d bulb for inflation of the b ladder .

The d a t a were col lec ted dur ing a 2-week pe r iod on a modi f i ed vers ion of the t r i age s h e e t u s e d in the e m e r g e n c y d e p a r t m e n t . The s u b j e c t ' s n a m e w a s s u b s t i t u t e d wi th c o n s e c u t i v e n u m b e r s to m a i n t a i n confident ia l i ty . The s u b j e c t ' s age, weight , and sex were also recorded.

Data analysis The d a t a were ana lyzed wi th the Sta t i s t ica l P a c k a g e for the Social Sc i ences (SPSS Inc., Chicago, Ill.) af ter d a t a col lect ion was comple te . Systol ic and d ias to l ic r e a d i n g s for each sub j e c t o b t a i n e d b y the IVAC 4200 and the manua l cuff m e t h o d s were compared . We ex- a m i n e d resul ts for the to ta l s a m p l e and for s u b g r o u p s wi th va lues >140 m m H g sys tol ic or >90 m m Hg dias- tolic. We p r o p o s e d tha t any di f ference b e t w e e n the IVAC 4200 and the m a n u a l m e t h o d grea te r than 9 m m Hg w a s clinically s ign i f i can t and m i g h t result in a dif- fe rence in t r ea tment . Finally, w e s t u d i e d the p e r c e n t - a g e of var ia t ion in the m a n u a l m e a s u r e tha t could be exp la ined or a c c o u n t e d for b y know ing the va lues for the a u t o m a t e d method .

Results Of the 100 sub jec t s enrolled in th is s tudy, 38 were m e n and 62 were women . The sub jec t s r a n g e d in age from 18 to 54 yea r s (mean a g e 32.7 years). The total s a m p l e m e a n sys to l ic blood p re s su re was 125 m m Hg by the m a n u a l m e t h o d and 129.3 m m Hg by the IVAC 4200 e lec t ronic ins t rument . The m e a n dias to l ic p r e s su re w a s 74.7 m m Hg and 76 m m Hg b y the manua l a n d e lec t ronic method , respect ive ly .

The IVAC i n s t r u m e n t p r o d u c e d h igher m e a n p re s su re m e a s u r e m e n t s for the total sample , and for all s u b g r o u p s excep t for m a n u a l d ias to l ic p re s su re s >90 m m Hg. For systol ic p r e s s u r e s >140 m m Hg and d ias- tolic p r e s su re s >90 m m Hg by the m a n u a l method, the c o r r e spond ing IVAC 4200 m e a s u r e m e n t s were over tw ice as var iable w h e n m e a s u r i n g systol ic pressure , and over six t imes more var iable w h e n m e a s u r i n g di- as tol ic p r e s su re (Table 2).

For the total s amp le of 100 m e a s u r e m e n t s , the m e a n di f ference b e t w e e n the pa i r ed systol ic m e a - s u r e m e n t s was 4.3 m m H g (p < 0.0001); the m e a n dif- fe rence b e t w e e n the p a i r e d d ias to l ic m e a s u r e m e n t s was only 1.3 m m Hg. When cons ide r ing the abso lu te d i f ference b e t w e e n the pa i r ed m e a s u r e m e n t s , the m e a n abso lu t e systol ic d i f ference w a s 8.7 m m Hg and the m e a n dias to l ic d i f ference was 6.9 m m Hg. The la rges t o b s e r v e d abso lu te d i f ference w a s 12.2 m m Hg

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Table 2 Mean, SD, and range of manua l and IVAC automated dev ice m e a s u r e m e n t s

Mean M e a s u r e m e n t N (mm Hg)

R an ge SD (ram Hg)

Total sample Systolic (manual) 100 125.0 16.25 98-162 Systolic (IVAC) 100 129.3 14.70 102-182 Diastolic (manual) 100 74.7 10.82 50-96 Diastolic (IVAC) 100 76.0 10.56 46-104

Systolic (manual -<140 mm Hg) Manual 81 119,8 10.83 98-140 IVAC 81 124.1 11.94 102-150

Systolic (manual >140 mm Hg) Manual 19 147.1 5.67 142-162 IVAC 19 151.3 13.63 129-162

Diastolic (manual -<90 mm Hg) Manual 95 73.7 10.07 50-95 IVAC 95 75.1 9.84 46-99

Diastolic (manual >90 mm Hg) Manual 5 94.4 1.67 92-96 IVAC 5 92.4 11.26 74-104

Table 3 Percent of m e a s u r e m e n t s e x c e e d i n g the 9 m m Hg criterion, m e a n and range of absolute dif ference, m e a n dif ference, paired t t e s t p value , and Pearson correlation of manua l and IVAC automated dev ice blood pressure m e a s u r e m e n t s

>9 m m Hg Abso lute di f ference m e a n (range) Mean di f ference

M e a s u r e m e n t N N % (ram Hg) (mm Hg) p r Total sample

Systolic 100 37 37.0 8.7 (0-40) 4,3 0.0001 0.77 Diastohc 100 26 26.0 6.9 (0-27) 1.3 0.15 0.66

Systolic -<140 mm Hg 81 28 34.6 7.9 (0-28) 4.3 0.0001 0.69 >140 mm Hg 19 9 47.4 12.2 (1-40) 4.3 0.26 -0.22

Diastolic <--90 mm Hg 95 24 25.3 7.0 (0-27) 1.5 0.11 0.61 >90 mm Hg 5 2 40.0 6.8 (0-20) 2.0 0.71 0.20

for the pai red systolic di f ferences whe re the systolic

m e a s u r e s e x c e e d e d 140 m m Hg by the manua l

method . For the total sample, the Pearson correlation

coeff ic ient b e t w e e n the two m e t h o d s was 0.77 for the

systol ic m e a s u r e m e n t s and 0.66 for the diastolic mea-

s u r e m e n t s (p < 0.0001) (Table 3). The IVAC 4200

read ings e x c e e d e d the manua l read ings in 61% of the

systol ic m e a s u r e m e n t s and 60% of the diastolic mea-

surements .

We had p roposed tha t any difference b e t w e e n the

IVAC 4200 m e t h o d and the manua l m e t h o d >9 m m Hg

was clinically significant . With this di f ference as a

criterion, 37% of the systolic di f ferences and 26% of

the diastol ic d i f ferences e x c e e d e d 9 m m Hg. For sys-

tolic p ressures >140 m m Hg, more than 47% of the

d i f ferences e x c e e d e d the 9 m m H g cri terion (Table 3).

Of those di f ferences grea te r than 9 m m Hg in the total

sample, 76% of the IVAC 4200 systolic m e a s u r e m e n t s

were g rea te r than the manua l measu remen t s , w he rea s

58% of the IVAC 4200 diastol ic m e a s u r e m e n t s ex-

c e e d e d the manua l m easu rem en t s .

Finally, a l though there were s ignif icant correla-

t ions b e t w e e n the total sample systolic and diastol ic

m e a s u r e m e n t s , the coeff ic ient of de te rmina t ion is

only 0.59 for the systolic correlat ion and 0.44 for the

diastolic correlation, ind ica t ing that only 59% of the

var ia t ion in the manua l systolic m e a s u r e s can be ex-

plained, or a c c o u n t e d for, by knowing the values for

the IVAC 4200 systolic measures . Similarly, only 44%

of the var ia t ion in the manua l diastolic m easu re can

be expla ined by knowing the value for the a u t o m a t e d

method .

D i s c u s s i o n

The resul ts of this s tudy ind ica te that there were both

stat is t ical ly s ignif icant and clinically s ignif icant dif-

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ferences b e t w e e n the two methods of blood pressure measu remen t . The IVAC 4200 had signif icantly higher systolic m e a s u r e m e n t s compared with the manua l

measu remen t s . In addit ion, more than 60% of the IVAC 4200 systolic and diastolic m e a s u r e m e n t s were greater than the cor responding manua l measure- ments . Al though there were s ignif icant correlations b e t w e e n the total sample systolic and diastolic mea- surements , only 59% of the variat ion in the m a n u a l systolic measu res can be explained by knowing the values for the IVAC 4200 systolic measures . Similarly, only 44% of the variat ion can be accoun ted for in the diastolic measures . When the criterion of 9 m m Hg difference in m e a s u r e m e n t s is used, 37% of the sys- tolic and 26% of the diastolic differences exceeded this criterion. When the manua l systolic measu rem e n t was greater than 140 m m Hg, more than 46% of the differences were greater than 9 m m Hg. Similarly, 40% of the systolic differences were greater than 9 m m Hg when the manua l diastolic was greater than 90 m m Hg.

Results of this s tudy m u s t be in terpre ted with caut ion b e c a u s e of several l imitations. Few volunteers were hyper tens ive and n o n e were hypotensive. The s tudy should be repl icated wi th a larger sample size and with pa t i en t s who are hypertensive, normoten- sive, and hypotensive . It is possible that the two methods do not yield equiva len t results in the assess- m e n t of hypotens ive pat ients , such as those in shock.

Al though we tried to min imize researcher bias, we migh t have improved reliability by hav ing the in- s t rumen t s recal ibrated after each reading or by us ing

s p h y g m o m a n o m e t e r s de s igned for research; such in- s t rumen t s are more sens i t ive to more subt le varia- tions. Compar ing both indi rec t me thods with the gold s tandard of direct arterial m e a s u r e m e n t would allow us to draw clearer conclus ions on which method is more accurate . Current ly we know that the tradit ional and au toma ted me thods are different bu t are unsu re which is the mos t accurate .

The results of this s tudy sugges t that blood pres-

sure m e a s u r e m e n t s ob ta ined with an au tomated de- vice may differ from those ob ta ined with the tradi- t ional cuff method. Staff nurses should consider this possibi l i ty dur ing tr iage of pa t i en t s in the emerge nc y depar tment . The d iagnos is of hyper tens ion should be m a d e with cau t ion and only after repeated measures are taken. Nurses who not ice an increase in the inci-

de nc e of h igh blood pressure wi th the in t roduct ion of n e w e q u i p m e n t mus t consider the possibil i ty that the increase is related to the c h a n g e in m e a s u r e m e n t de- vice rather than a t rue increase in inc idence . Finally, w h e n nurses monitor blood pressures over t ime they need to consider that the tradit ional method and the au toma ted device ma y not yield equivalent readings. It is impor tan t to use the s ame i n s t r u m e n t cons is tent ly so that real change i n p a t i e n t blood pressure migh t not be masked by variabili ty in the equipment .

References

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2. Joint National Commission on Detection, Evaluation, and Treatment of High Blood Pressure. The fifth report of the Joint National Committee on Detection, Evaluation, and Treatment of High Blood Pressure (JNC V). Arch Intern Med 1993;153:154-83.

3. Franklin CM. Prevalence of previously undetected hy- pertension in patients with nonacute conditions. J Emerg Nurs 1987;13:283-5. 4. Capriotti TA. Prevalence and referral of nonurgent ED

patients with previously undetected hypertension. J Emerg Nurs 1989;15:238-40.

5. Chernow SM, Iserson KV, Criss E. Use of the emergency department for hypertension screening: a prospective study. Ann Emerg Med 1987;16:180-2.

6. Perloff D, Grim C, Flack J, et al. Human blood pressure determination by sphygmomanometry. Circulation 1993; 88:2460-70.

7. Marx GF, Schwable SS, Cho E, Whitty JE. Automated blood pressure measurements in laboring women: Are they reliable? Am J Obstet Gynecol 1993;168:796-8.

8. Whincup PH, Bruce NG, Cook DG, Shaper AG. The Di- namap 1846SX automated blood pressure recorder: com- parison with the Hawksley random zero sphygmomanome- ter under field conditions. J Epidemiol Community Health 1992;46:164-9.

9. Crews WD, Harrison DW. An evaluation of the DS-175, DS-145, and DS-115, digital blood pressure/pulse meter de- vices. Biomed Instrum Technol 1991;25:211-4. 10. Weaver MG, Park MK, Lee DH. Differences in blood pressure levels obtained by auscultatory and oscillometric methods. Am J Dis Child 1990;144:911-4. 11. Rebenson-Piano M, Holm K, Foreman MD, Kirchhoff KT. An evaluation of two indirect methods of blood pressure measurement in ill patients. Nurs Res 1989;38:42-5.

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