An Assessment of Three Portable Peak Flow Meters* - Chest ...

An Assessment of Three Portable Peak Flow 

Meters* 

M. S. Eichenhorn, M.D.; R. K. Beauchamp, R.-C.P.T.;f 

P. A. Harper, R.-C.P.T.;t and I. C. Ward, M.D. 

Peak flow has become widely used an independent 

measure of lung function, particularly In asthma, because 

It can be quickly and easily determined by simple 

portable lnsfrumentaflon. Three relatively inexpensive 

devices, the Armstrong mini-Wright peak flow meter, 

Vitalograph pulmonary monitor, and HealthScan peak 

flow meter, were tested for accuracy and reproducibility. 

Five units of each type were individually connected in 

series to a pneumotachograph, and 20 measurements 

(five in each of four flow ranges) were made on each 

unit at pulsatile flows ranging from 120 to 480 Lpm. 

The mean percentage of discrepancy (D%) for each 

P eak expiratory flow has been accepted as an 

independent measure of lung function for some 

time,’ with more recent applications being found in 

the emergency room, clinic, and home evaluation 

For editorial comment see page 262 

and management of asthma.27 Three light-weight, 

relatively inexpensive, and compact instruments are 

now commercially available for use in this regard. 

These instruments are the mini-Wright peak flow 

meter manufactured by Armstrong Industries 

(ARM ), the pulmonary monitor by Vitalograph, 

Ltd (VIT), and the HealthScan peak flow meter 

( distributed by Organon, Inc. [HS-O]). The Arm- 

strong and Vitalograph units operate through air 

pressure directed ‘against a diaphragm, which dis- 

places a light-weight piston. The Armstrong units 

measure peak flow from 60-800 liters per minute 

( Lpm), while the Vitalograph scale ranges from 

150 to 700 Lpm, though higher flows can also be 

recorded following the removal of two plastic plugs. 

The HealthScan instrument is, in effect, a rotameter, 

with air flow directed through a precisely-drilled 

orifice. Two scales are provided together with a 

removable end piece so that flow ranging from 80- 

520 Lpm can be determined. The Armstrong unit 

sells for about $50, while the Vitalograph and 

HealthScan units sell for about $15 each. 

#{176}Frornthe Division of Pulmonary Medicine, Henry Ford 

Hospital, Detroit. 

tPresently at the University of Wisconsin Center for Health 

Sciences. Madison. 

Reprint requests: Dr. Eichenhorn, Pulmonary DIVISIOn, 2799 

West Grand Blvd, Detroit 48202 

instrument of a particular model was calculated at 

each flow range, and these subsequendy averaged to 

give an inter-Instrument percentage of discrepancy at 

each flow for each modeL Intra-Instrument variability 

was also assessed as the mean percentage of discrep- 

ancy for all flow rates for each individual insfrument. 

While only the Armstrong mini-wright peak flow meter 

meets flow range criteria established by the American 

Thoracic Society and American College of Chest Physi- 

slans for flow devices, only the HealthScan-()rganon 

peak flow meter meets the established criteria for accuracy 

and reproducibility. 

The accuracy and reproducibility of each of these 

instruments was compared to a pneumotachograph 

(calibrated through a rotameter) to determine the 

reliability and, hence, clinical utility of each. Ideal- 

ly, such devices should meet the guidelines for flow 

devices established by the American College of 

Chest Physicians (ACCP) and the American Thoracic 

Society (ATS ), providing a flow range of 0-720 

Lpm, and reproducibility of ± 5 percent.8’#{176} 

301 Assesament of Thre Portable Peak Flow Meters (E!chenhom at a!) 

Downloaded From: http://journal.publications.chestnet.org/ on 01/02/2013 

Mnmons 

Five unused units of each type were randomly selected 

from a group of instruments available at Henry Ford 

Hospital. Each unit was connected in series to a No. 3 

Fleisch pneumotachograph ( Hewlett Packard model 

21073B) which had been calibrated both directly (flow), 

using a rotameter (CPI model hOC flow calibrator), and 

indirectly ( integrated volume), using a calibrated 3 liter 

syringe. The slight alinearity above 360 Lpm was corrected 

for mathematically by the construction of a calibration 

curve. Flow rates of 120, 180, 300, and 480 Lpm were 

selected for study, as it was felt these were representative 

of flows apt to be evident during clinical bronchospasm. A 

calibrated 3-liter syringe was then manually activated to 

provide pulsatile flow through the test instrument and 

pneumotachograph. Multiple pulses were then delivered 

until five measurements approximating each of the four 

pre-determined flow rates were recorded on the pneumotachograph. 

Thus, 20 measurements were recorded for each 

instrument. It was felt that multiple repetitions at each 

flow rate were necessary to avoid isolated errors in measurement 

that might otherwise occur. 

The discrepancy between the measured and actual (pneumotachograph) 

flow rates was then computed at each flow 

rate for each instrument by dividing the difference between 

measured and actual flow by the actual flow ( , then

Table 1-.Mini-Wright Meter 

Flow (Lpm) 120 180 300 480 

Overall 5 D%= -2.7 

Percentage of Discrepancy (D%) 

Instrument 

Mean 

D% 

1 18.1 24.8 11.8 #{149} 1.4 14.0 

2 8.1 16.5 7.7 1.9 8.6 

3 24.2 30.7 13.8 8.9 19.4 

4 26.4 38.3 Malfunctioned 32.4 

5 17.3 22.4 11.7 5.2 14.2 

Models 18.8 26.5 11.3 4.4 

Overall D%= 15.3 


Table 2-Pulmonary Monitor 


Instrument 

Mean 

D% 

1 -27.5 8.2 0.4 5.1 -3.7 

2 -45.4 -12.3 13.4 8.2 -9.0 

3 -55.7 -6.9 7.7 -2.2 -14.3 

4 -54:5 -7.4 2.4 -4.4 -16.0 

5 -55.3 -8.1 4.0 1.3 -145 

Model -47.7 -5.3 5.4 1.6 

Overall D%=-11.5 


Table 3-Peak Flow Meter 


Instrument 

Mean 

D% 

1 -1.9 -5.1 -1.9 -4.9 -3.5 

2 0.5 -1.1 0.0 0.7 0.0 

3 -6.4 -2.1 -4.2 -0.6 -3.3 

4 -7.4 0.6 1.3 0.4 -1.3 

5 -2.9 -4.1 -6.2 -8.3 -5.4 

Model -3.6 -2.4 -2.2 -2.5 

converted to percentages (percent discrepancy, D%). 

Under-readings, thus, were negative values compared to 

actual, while over-readings were positive. The mean D% 

for each of the five measurements at each flow rate for 

each instrument was then calculated. The mean D% for 

each flow range between instruments (inter-instrument 

variability) of similar manufacture, as well as the mean 

D% for all flows on a single instrument (intra-instrument 

20- 

10. 

w 

30. 

0 

U, -10- 

-20- 

-30- 

-40- 

-50- 

#{149}a- 

I 

I 

I 

I 

I 

-ARM 

10 240 360 480 

Flow (I/rn) 

Ficunx 1. Inter-instrument variability, D%. 

RESULTS 

The percentage of discrepancy for each of the 

Armstrong, Vitalograph, and HealthScan peak flow 

meters are depicted in Tables 1-3. Intra-instrument, 

as well as inter-instrument means are also displayed. 

Graphic depictions of results are displayed for inter- 

instrument D% in Figure 1, and for intra-instrument 

D% in Figure 2. As can be seen, only the Health- 

Scan peak flow meter had acceptable mean interand 

intra-instrument D% of less than 5 percent. 

In testing the Armstrong Industries’ mini-Wright 

peak flow meter, one malfunctioned during the 

testing. The diaphragm became displaced from the 

cylindrical housing, and could not be manually 

replaced. Though the widest recorded ranges were 

>- 

C.) 

z 

aw 

C.) 

Cl) 

30- 

20’ 

10 

-ARM 

-- VIT 

-.- HS-O 

variability) were then determined. Ficuas 2. Intra-instrument variability, D%. 


1 __.-1#{149}-..,#{149} -I;_._44.. I 

noted on this particular instrument prior to mal- 

function, elimination of all data from the defective 

instrument would not significantly alter the net 

results for the model as a whole. 

The Vitalograph pulmonary monitor data are ob- 

viously biased by extremely poor performance at the 

120 Lpm flow range. The instrument scale begins at 

150 Lpm, and hence, results were extrapolated back 

to include the 120 Lpm range, assuming the same 

linearity of scale to apply at flows below, as well as 

above the scale minimum. This may not, in fact, be 

the case. The length-tension relationship of the 

spring within the cannister may be such that quite 

a large initial force must be directed to overcoming 

inertia. Hence, all flow measurements at 120 Lpm 

may have little validity. 

Ignoring the flows at 120 Lpm, the Vitalograph 

pulmonary monitor’s performance improves signifi- 

cantly. The instrument tends to underestimate flows 

at 180 Lpm, and overestimate flows above this 

range. Though inter-instrument and intra-instrument 

mean percentages of discrepancy meet ACCP and 

ATS standards (0.57 and 2.2, respectively), this was 

achieved only through wide variation in D% at the 

180 Lpm flow range. No single percentage of dis- 

crepancy met the established standards at this 

range, though there were sufficient positive and 

negative values so that the mean that resulted was 

acceptable. Likewise, though intra-instrument van- 

ability was acceptable, this was often the result of 

averaging significantly varied individual results (in- 

struments 2 and 3 especially). This factor limits 

model acceptability. 

The HealthScan peak flow meter performed more 

uniformly. Though some units tended to vary from 

actual readings at either high or low flow ranges, 

there were no wide swings in results evident as was 

the case for the Vitalograph product. HealthScan 

instruments generally tended toward slight under- 

estimation of true values. Overall, both inter- and 

intra-instrument accuracy was quite good. 

DiscussioN 

Results of peak flow measurements are now widely 

accepted for following the course of bronchial 

asthma.7 Alterations in peak flow provide an ob- 

jective means of documenting patient status, and 

with the development of portable instrumentation 

to achieve this purpose, close monitoring of pulmo- 

nary function at home can be made. Three light- 

weight, inexpensive devices for peak flow measure- 

ment are currently widely marketed as described. 

Ideally, these devices should meet ATS and ACCP 

standards. The results of our studies performed at 

varying flow rates for multiple instruments support 

the accuracy and reproducibility of only the Health- 

Scan instrument, though only the Armstrong unit 

meets the established criteria for flow range. 

Prior documentation of performance of both the 

Armstrong and Vitalograph products have been 

previously described. In the original description 

of the Armstrong mini-Wright device, documentation 

of an underestimation of peak flow of 17 per- 

cent was made, though allowance for this was pro- 

vided in calibration.’#{176} Subsequent studies showed 

correlation between the standard Wright and mini- 

Wright peak flow meters, but the study design in- 

volved the comparison of separate maximal efforts 

by a trained subject into each device, rather than 

recording flow in series into both, as done in our 

study.” This may have introduced some variability 

in the actual flow delivered, since the studies as- 

sumed the subject produced the exact peak flow 

each time. Likewise, significant variation between 

instruments for presumably similar flows was also 

documented. Perks et al’2 also found significant 

inter-instrument variability for the mini-Wright 

unit, but felt that this difference remained constant 

for any given machine so that deviations in measurements 

were valid, though exact accuracy was not 

necessarily so. 

Similar studies are also available for the Vitalo- 

graph pulmonary monitor. When initially described, 

arbitrary units of measurements were used, rather 

than liters per minute, which probably limited 

clinical utilization.13 When revised to provide read- 

lug in Lpm, Perks et al’ found fair correlation with 

a standard Wright peak flow meter ( again on suc- 

cessive peak flow maneuvers, rather than in series), 

but again found significant inter-instrument varia- 

bility. They also stated that the inability to meas- 

ure flows below 150 Lpm would limit the clinical 

utility of the unit. This is particularly apt to be 

true in management of asthma.3 

Burns15 compared the Armstrong and Vitalograph 

products and found that significant errors of estimate 

existed for both devices, being larger for the 

pulmonary monitor. He concluded that though the 

accuracy of both devices was low, they could be of 

use in determining discrete peak flow changes from 

308 Assessment of Three Portable Peak Flow Meters (E!chenhorn .t a!) 


baseline. 

Our studies support the inter-instrument van- 

ability of both the Armstrong and Vitalograph de- 

vices when compared to a pneumotachograph. 

Likewise, significant intra-instrument variability ex- 

ists for both devices. Much of the problem in accu- 

racy and reproducibility may stem from the design 

of both which utilizes a single expanding spring to 

measure flow. Variability of the length-tension rela- 

tionship for any particular spring might well be

expected. 

On the other hand, the HealthScan peak flow 

meter operates as a rotameter. Though inaccuracies 

could result from imprecision in establishing orifice 

size, this does not seem to be the case, as only this 

device meets ATS and ACCP standards, both in 

inter- and intra-measurement studies. Though removing 

the end-piece to permit scale changes may 

be an inconvenience, at this time, only the Health- 

Scan-Organon instrument seems sufficiently accu- 

rate to be recommended for clinical use, recogniz- 

ing, however, its inability to record flows greater 

than 520 Lpm. 

Rmiucs 

1 Wright BM, McKerrow CB. Maximum forced expiratory 

flow rate as a measure of ventilatory capacity. Br Med 

J 1959; 2:1041-47 

2 Hetzel MR, Clark TJH, Branthwaite MA. Asthma: 

Analysis of sudden deaths and ventilatory arrests in 

hospitaL Br Med J 1977; 1:808-11 

3 Banner AS, Shah RS, Addington WW. Rapid prediction 

of need for hospitalization in acute asthma. JAMA 1976; 

235:1337-38 

4 Nowak RM, Pensler MI, Sarkar DD, Anderson JA, Kvale 

PA, Ortiz AE, et aL Comparison of peak expiratory flow 

and FEV1 : Admission criteria for acute bronchial asthma. 

Ann Emergency Med 1982; 11:64-69 


S Murray AB, HardWick DF, Pine GE, Fraser BM. Assessing 

severity of asthma with Wright peak flow meter. 

Lancet 1977; 1:708 

6 Taplin PS, Creer TL. A procedure for using peak expiratory 

flow rate data to increase the predictability of 

asthma episodes. J Asthma Res 1978; 16:15-19 

7 Hetzel MR, Williams IP, Shakespeare RM. Can patients 

keep their own peak flow records reliably? Lancet 1979; 

1:597-99 

8 Permutt S, Chester E, Anderson W, Cugell D, Petty 

TL, Sharp JT. Office spirometry in clinical practice. 

Chest 1978; 74:298 

9 Gardner RM, Baker CD, Broennie AM, Burrows B, Ferris 

BG, Gaensler EA, et aL ATS statement-Snowbird workshop 

on standardization of spirometry. Am Rev Respir 

Dis 1979; 119:831-38 

10 Wright BM. A miniature Wright-peak flow meter. Br 

Med J 1978; 2:1627-28 

11 Brown LA, Sly RM. Comparison of mini-Wright and 

standard Wright peak flow meters. Ann Allergy 1980; 

45:72-74 

12 Perks WH, Tams IP, Thompson DA, Prowse K. An 

evaluation of the mini-Wright peak flow meter. Thorax 

1979; 34:79-81 

13 Haydu SP, Chapman Ti’, Hughes DTD. Pulmonary 

monitor for assessment of airways obstruction. Lancet 

1976; 2: 12.25-26 

14 Perks WH, Cole M, Steventon 1W, Tams IF, Prowse E 

An evaluation of the Vitalograph pulmonary monitor. 

Br J Dis Chest 1981; 75:161-64 

15 Burns KL. An evaluation of two instruments for assesslug 

airway flow. Ann Allergy 1979; 43:246-49 

CHEST I 82 1 3 I SEPTEMBER, 1982 309

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