Assessment of Accuracy of the Vacu-Med 17053 Calibrator for Ventilation, Oxygen Uptake (V̇O2), and Carbon Dioxide Production (V̇CO2)
======================================================================================================================================

* Jennifer A Bunn
* Jesse L Pittsley
* Scott V Baker
* JW Yates

## Abstract

**BACKGROUND:** Few have examined the accuracy of mechanical calibrators used to calibrate metabolic monitors.

**OBJECTIVE:** To evaluate the Vacu-Med 17053 motorized syringe calibrator for accuracy against the accepted standard method: the Douglas bag.

**METHODS:** We tested oxygen consumption (V̇O2) values of 522–3,210 mL/min. We mixed room air and calibration gases in the pumping syringes of the Vacu-Med 17053 and evacuated those gases into a Douglas bag, measured the Douglas bag volumes and concentrations, and converted to pulmonary ventilation, V̇O2, and carbon dioxide production (V̇CO2).

**RESULTS:** The Vacu-Med 17053 calibrator overestimated V̇O2 by a mean 28.6 mL/min (1.3% error), underestimated V̇CO2 by 6.9 mL/min (−1.7% error), and underestimated pulmonary ventilation by 0.98 L/min (−1.4% error). The V̇O2 and V̇CO2 differences between the calibrator and the Douglas bag were larger at higher V̇O2 levels.

**CONCLUSIONS:** The V̇O2 and V̇CO2 differences might be attributable to fluctuations of the calibrator settings. The Vacu-Med 17053 calibrator was accurate with the application of a mathematical correction.

*   calibration
*   oxygen consumption
*   carbon dioxide production
*   pulmonary ventilation
*   tidal volume
*   respiratory rate

## Introduction

During the past 30 years, laboratories have switched from the cumbersome but accepted standard method (the Douglas bag) to automated systems to measure oxygen consumption (V̇O2), carbon dioxide production (V̇CO2), and pulmonary ventilation. However, questions remain regarding the accuracy and reliability of automated calibration systems because of differences in flow, volume, and gas concentration measurement methods.1 The various instrumentation employed by each system causes different V̇O2 and V̇CO2 values between systems.2

The diversity of available calibration systems necessitates an accepted standard method to calibrate metabolic monitors for accuracy and reliability. With the Douglas-bag method the clinician must either use calibration gas or obtain expiratory gas from humans and measure that gas with the metabolic monitor and the Douglas-bag method for volume and concentrations. The best technique to measure accuracy involves connecting the Douglas bag directly to the metabolic monitor's mixing chamber3–6 and simultaneously measuring the gas with the metabolic monitor and the Douglas bag. However, some metabolic monitors do not allow for simultaneous collection, so a cumbersome but often used method is to switch from measurement by the metabolic monitor to collection in the Douglas bag during an exercise test.7–11 In that method, the expired gas is not measured simultaneously by the metabolic monitor and the Douglas bag, so the measured volumes and concentrations are not directly comparable.

Several mechanical calibrators have been developed to overcome the limitations of the Douglas-bag method to calibrate a metabolic monitor. Some calibrators are accurate, but all have limitations, including delivery of calibration gas without correction for pulmonary air saturation, over-reliance on complex equations, and failing to prove accuracy of pulmonary ventilation in conjunction with V̇O2 and V̇CO2.12–15 None of the available calibrators has been found to be as accurate or reliable as the Douglas-bag method. A recently released calibrator (model 17053, Vacu-Med, Ventura, California) was designed to work with various metabolic monitors, but the manufacturer has not provided accuracy and reliability data, nor has the 17053 been validated in independent academic research. In previous studies of mechanical calibrators, none of the instruments were validated for pulmonary ventilation, V̇O2, and V̇CO2 against the accepted standard method: Douglas bag.12–15

The 17053 calibrator's method differs from the Douglas-bag method in that it serves as the source of gas, and the clinician can calculate and alter pulmonary ventilation, V̇O2, and V̇CO2 output with the calibrator. We compared the 17053 calibrator to the Douglas-bag method.

## Methods

This study was conducted in the Department of Kinesiology at the University of Kentucky, Lexington, Kentucky. Vacu-Med was not involved in designing the study, data collection, analysis, interpretation, or preparing the manuscript.

### Calibrator Set-up and Operation

The 17053 calibrator was designed to calibrate and evaluate the accuracy of automated metabolic monitors of all types. The 17053 digitally displays tidal volume (VT) in L, respiratory frequency in breaths/min, and flow in L/min. The 17053 has two 4.0-L syringes that draw in room air and calibration gas. Figure 1 shows a schematic of the 17053 calibrator, with arrows indicating the direction of air flow. Two actions occur simultaneously during inspiration: room air flows into syringe barrel 2 through a 2-way valve, and syringe barrel 1 fills with room air from the 5.0-L storage bag and calibration gas (which, ideally, is 21% CO2 and 79% N2) from the 1.0-L storage bag. The 2 gases flowing into syringe barrel 1 mix together at the bypass valve and the inspiratory restrictor, and enter syringe barrel 1 through 2-way valve 1.

![Fig. 1.](http://rc.rcjournal.com/http://rc.rcjournal.com/content/respcare/56/4/472/F1.medium.gif)

[Fig. 1.](http://rc.rcjournal.com/content/56/4/472/F1)

Fig. 1. 
Flow diagram of the Vacu-Med 17053 motorized syringe calibrator. SB1 = syringe barrel 1. SB2 = syringe barrel 2. B = bumpers. ER = expiratory restrictor. IR = inspiratory resistor (variable). M = motor. REV = reverser. RRD = rolling ring drive. 2WV = 2-way valve. 1WV = 1-way valve. BV = bypass valve. OV = overflow valve.

During expiration there are also 2 simultaneous events: room air from syringe barrel 2 flows back through 2-way valve 2, into the 5.0-L reservoir bag; and air from syringe barrel 1 flows through the 2-way valve 1 past the expiratory restrictor and out of the calibrator into a metabolic monitor or a Douglas bag for measurement. If the 5.0-L bag becomes full, excess room air empties through the overflow valve. The respiratory cycle is controlled by the motor and rolling ring drive. The 17053 calibrator can be adjusted for respiratory frequency and VT. The flow of calibration gas is controlled by a rotometer, next to the 1.0-L reservoir bag.

### Evaluation of Calibrator Accuracy

We created a standard protocol (Table 1) to study a wide physiological range of V̇O2 (512–3,150 mL/min), V̇CO2 (522–3,210 mL/min), and pulmonary ventilation (8–122 L/min), with 3 VT and frequency settings, and 7 rotometer settings to control the calibration gas. As suggested by the manufacturer, to obtain realistic and accurate values, the rotometer was never set below 20 or above 140. At each setting, mixed gas from the calibrator was collected in the Douglas bag for one minute, beginning with expiration and ending with inspiration. Gas concentrations were analyzed with a paramagnetic O2 analyzer and an infrared CO2 analyzer (AEI Technologies, Quogue, New York). The gas was then emptied from the Douglas bag by a vacuum (Shop-Vac, Williamsport, Pennsylvania) that pulled the air from the bag through a Rayfield meter (Rayfield Equipment, Whitsfield, Vermont) at 2.5 L/s. Both the Rayfield meter and Douglas-bag method were previously evaluated to ensure proper assessment of the mechanical calibrator (pulmonary ventilation error 0.09%, V̇O2 error 0.08% after the V̇O2 correction equation).

View this table:
[Table 1.](http://rc.rcjournal.com/content/56/4/472/T1)

Table 1. 
Sample Calibration Protocol*

We conducted the protocol in its entirety 7 times, and entered the data into the software that accompanies the 17053 calibrator (O2Cal.xls, Vacu-Med, Ventura, California) and predicts the V̇O2 and V̇CO2 values based on information entered by the investigator, including room temperature, barometric pressure, relative humidity, and calibration gas flow.

### Data Analysis

With statistics software (SPSS 16.0, SPSS, Chicago, Illinois) we analyzed the differences between the measured (via Douglas bag) and predicted (by Vacu-Med) pulmonary ventilation, V̇O2, and V̇CO2 values, with a one-sample Student *t* test. Statistical significance was set at α = .05. We used linear regression to further assess potential sources of error, and created Bland-Altman plots to evaluate trends and outliers.

## Results

Table 2 shows the mean pulmonary ventilation, V̇O2, and V̇CO2 differences and the *P* values for those differences. The mean difference in pulmonary ventilation was −0.98 ± 1.78 L/min (*P* < .001), representing a −1.4% error. There was close agreement between the Douglas bag and Vacu-Med 17053 values for ventilations less than 60 L/min. However, between 85 and 120 L/min the difference increased to approximately 5–10 L/min. Overall, there was a 2.4% error at the higher pulmonary-ventilation values, compared to a −1.0% error at the lower pulmonary-ventilation values. The mean V̇O2 difference was 28.6 ± 75.2 mL/min (*P* < .001), indicating a 1.3% error. The mean V̇CO2 values differed by −6.9 ± 60.9 mL/min (*P* = .17) between the Douglas-bag and 17053 calibrator, signifying a −1.7% error. Linear regression analyses showed that respiratory rate (*P* = .048) and VT (*P* = .008) were the source of error for pulmonary ventilation, whereas respiratory rate impact was the source of error for V̇O2 (*P* < .001) and V̇CO2 (*P* = .02). Essentially, the respiratory rate impacted the error in pulmonary ventilation, V̇O2, and V̇CO2. Figure 2 shows the Bland-Altman plot of the Douglas-bag values versus the Vacu-Med-17053-minus-Douglas-bag values. At V̇O2 500 mL/min the difference between the Douglas-bag and Vacu-Med 17053 values was close to zero, but at values above 500 mL/min the difference averaged 36.3 mL/min. Thus, as V̇O2 increased, calibrator error increased. The 17053's mean V̇CO2 was 6.9 mL/min greater than that of the Douglas bag (*P* = .17).

View this table:
[Table 2.](http://rc.rcjournal.com/content/56/4/472/T2)

Table 2. 
Differences in Pulmonary Ventilation, V̇O2, and V̇CO2, and *P* Values for Those Differences

![Fig. 2.](http://rc.rcjournal.com/http://rc.rcjournal.com/content/respcare/56/4/472/F2.medium.gif)

[Fig. 2.](http://rc.rcjournal.com/content/56/4/472/F2)

Fig. 2. 
Bland-Altman plot of oxygen uptake (V̇O2) and carbon dioxide production (V̇CO2) values measured with a Douglas bag versus with the Vacu-Med 17053 motorized syringe calibrator.

## Discussion

Our major finding is that the Vacu-Med 17053 calibrator overestimated V̇O2 by 1.3%, and that error increased as V̇O2 increased, and it underestimated V̇CO2 by −1.7%. Ideally, the V̇O2 difference should match the V̇CO2 difference, since the Vacu-Med 17053 was designed to produce a respiratory exchange ratio of 1.0, but that was not the case. There was a trend of increasing V̇O2 and V̇CO2 variability with rising pulmonary ventilation. This may have been caused by the pumping of the rolling ring drive, which forcefully moves air through the calibrator, which shakes the calibrator and thereby might cause fluctuations in the volume of calibration gas entering the calibrator. The calibrator was secured to a hard surface, and pressure from the gas tank was adjusted to minimize the shaking, but some fluctuation was unavoidable. In addition, the calibrator uses tubing that creates dead space within the device, which also may have contributed to differences between the calibrator and the Douglas-bag method. We measured the tubing dead space by filling the connectors and tubing with water and measuring the volume with a graduated cylinder, and the dead-space volume was 260 mL. The dead space may have contributed to calibrator error because upon expiration air remains in the tubing rather than moving into the Douglas bag, and that air then mixes with the air in the following inspiration.

The Vacu-Med 17053 calibrator underestimated pulmonary ventilation by −1.4%, and we attribute that error to VT and respiratory rate. As with V̇O2 and V̇CO2, the error was greater at the higher pulmonary ventilation levels (−2.4%) than at the lower pulmonary-ventilation levels (−1.0%), so the forceful movement of the rolling ring drive and shaking of the calibrator at the higher frequencies may have altered the air volume flowing into the calibrator.

### Limitations

While our protocol covers a realistic physiological range of pulmonary ventilation, V̇O2, and V̇CO2 in an average human, the values are not as high as those in a highly trained athlete, in whom V̇O2 may exceed 5,000 mL/min. Such values cannot be produced by the Vacu-Med 17053 calibrator because the manufacturer limited the rotometer scale to 140, which allows calibration gas into the system via the 1.0-L balloon at 15.75 mL/min.16 Despite this inability to match athletic V̇O2 values, 3,151 mL/min is above the maximum values obtained by average humans and is acceptable for evaluating metabolic monitors.

## Conclusions

The Vacu-Med 17053 calibrator exhibited small errors versus the Douglas-bag method for pulmonary ventilation (−1.4% error), V̇O2 (1.3% error), and V̇CO2 (−1.7% error) across resting and exercising levels. However, the Vacu-Med 17053 exhibited larger errors at higher breathing frequencies, and the highest available V̇O2 calibration value is 3,151 mL/min, which is not as high as needed for assessing elite athletes. Therefore, the Vacu-Med 17053 may be useful to test the accuracy and validity of a metabolic monitor, but is limited at very high exercise values.

## Footnotes

*   Correspondence: Jennifer Bunn PhD, Department of Exercise Science, Campbell University, PO Box 414, Buies Creek NC 27506. E-mail: bunnj{at}campbell.edu.
*   This research was partly funded by a Research Equipment Initiative Grant from the University of Kentucky.

*   Jennifer Bunn PhD presented a version of this paper at the annual meeting of the American College of Sports Medicine, held May 31 through June 3, 2006, in Denver, Colorado.

*   The authors have disclosed no conflicts of interest.

*   Copyright © 2011 by Daedalus Enterprises Inc.

## References

1.  1. Macfarlane DJ. Automated metabolic gas analysis systems: a review. Sports Med 2001;31(12):841–861.
    
    [CrossRef](http://rc.rcjournal.com/lookup/external-ref?access_num=10.2165/00007256-200131120-00002&link_type=DOI) 
    
    [PubMed](http://rc.rcjournal.com/lookup/external-ref?access_num=11665912&link_type=MED&atom=%2Frespcare%2F56%2F4%2F472.atom) 
    
    [Web of Science](http://rc.rcjournal.com/lookup/external-ref?access_num=000171581500002&link_type=ISI) 

2.  2. Jones NL. Evaluation of a microprocessor-controlled exercise testing system. J Appl Physiol 1984;57(5):1312–1318.
    
    [Abstract/FREE Full Text](http://rc.rcjournal.com/lookup/ijlink/YTozOntzOjQ6InBhdGgiO3M6MTQ6Ii9sb29rdXAvaWpsaW5rIjtzOjU6InF1ZXJ5IjthOjQ6e3M6ODoibGlua1R5cGUiO3M6NDoiQUJTVCI7czoxMToiam91cm5hbENvZGUiO3M6MzoiamFwIjtzOjU6InJlc2lkIjtzOjk6IjU3LzUvMTMxMiI7czo0OiJhdG9tIjtzOjIzOiIvcmVzcGNhcmUvNTYvNC80NzIuYXRvbSI7fXM6ODoiZnJhZ21lbnQiO3M6MDoiIjt9) 

3.  3. Bassett DR Jr., Howley ET, Thompson DL, King GA, Strath SJ, McLaughlin JE, et al. Validity of inspiratory and expiratory methods of measuring gas exchange with a computerized system. J Appl Physiol 2001;91(1):218–224.
    
    [Abstract/FREE Full Text](http://rc.rcjournal.com/lookup/ijlink/YTozOntzOjQ6InBhdGgiO3M6MTQ6Ii9sb29rdXAvaWpsaW5rIjtzOjU6InF1ZXJ5IjthOjQ6e3M6ODoibGlua1R5cGUiO3M6NDoiQUJTVCI7czoxMToiam91cm5hbENvZGUiO3M6MzoiamFwIjtzOjU6InJlc2lkIjtzOjg6IjkxLzEvMjE4IjtzOjQ6ImF0b20iO3M6MjM6Ii9yZXNwY2FyZS81Ni80LzQ3Mi5hdG9tIjt9czo4OiJmcmFnbWVudCI7czowOiIiO30=) 

4.  4. Bredbacka S, Kawachi S, Norlander O, Kirk B. Gas exchange during ventilator treatment: a validation of a computerized technique and its comparison with the Douglas bag method. Acta Anaesthesiol Scand 1984;28(4):462–468.
    
    [PubMed](http://rc.rcjournal.com/lookup/external-ref?access_num=6435385&link_type=MED&atom=%2Frespcare%2F56%2F4%2F472.atom) 
    
    [Web of Science](http://rc.rcjournal.com/lookup/external-ref?access_num=A1984TD99400024&link_type=ISI) 

5.  5. Kawakami Y, Nozaki D, Matsuo A, Fukunaga T. Reliability of measurement of oxygen uptake by a portable telemetric system. Eur J Appl Physiol Occup Physiol 1992;65(5):409–414.
    
    [PubMed](http://rc.rcjournal.com/lookup/external-ref?access_num=1425645&link_type=MED&atom=%2Frespcare%2F56%2F4%2F472.atom) 

6.  6. Rietjens GJ, Kuipers H, Kester AD, Keizer HA. Validation of a computerized metabolic measurement system (Oxycon-Pro) during low and high intensity exercise. Int J Sports Med 2001;22(4):291–294.
    
    [CrossRef](http://rc.rcjournal.com/lookup/external-ref?access_num=10.1055/s-2001-14342&link_type=DOI) 
    
    [PubMed](http://rc.rcjournal.com/lookup/external-ref?access_num=11414673&link_type=MED&atom=%2Frespcare%2F56%2F4%2F472.atom) 
    
    [Web of Science](http://rc.rcjournal.com/lookup/external-ref?access_num=000168964800011&link_type=ISI) 

7.  7. Carter J, Jeukendrup AE. Validity and reliability of 3 commercially available breath-by-breath respiratory systems. Eur J Appl Physiol 2002;86(5):435–441.
    
    [CrossRef](http://rc.rcjournal.com/lookup/external-ref?access_num=10.1007/s00421-001-0572-2&link_type=DOI) 
    
    [PubMed](http://rc.rcjournal.com/lookup/external-ref?access_num=11882930&link_type=MED&atom=%2Frespcare%2F56%2F4%2F472.atom) 
    
    [Web of Science](http://rc.rcjournal.com/lookup/external-ref?access_num=000174871800010&link_type=ISI) 

8.  8. Jensen K, Jorgensen S, Johansen L. A metabolic cart for measurement of oxygen uptake during human exercise using inspiratory flow rate. Eur J Appl Physiol 2002;87(3):202–206.
    
    [CrossRef](http://rc.rcjournal.com/lookup/external-ref?access_num=10.1007/s00421-002-0616-2&link_type=DOI) 
    
    [PubMed](http://rc.rcjournal.com/lookup/external-ref?access_num=12111279&link_type=MED&atom=%2Frespcare%2F56%2F4%2F472.atom) 
    
    [Web of Science](http://rc.rcjournal.com/lookup/external-ref?access_num=000177173200002&link_type=ISI) 

9.  9. Versteeg PG, Kippersluis GJ. Automated systems for measurement of oxygen uptake during exercise testing. Int J Sports Med 1989;10(2):107–112.
    
    [PubMed](http://rc.rcjournal.com/lookup/external-ref?access_num=2722322&link_type=MED&atom=%2Frespcare%2F56%2F4%2F472.atom) 

10. 10. Unnithan VB, Wilson J, Buchanan D, Timmons JA, Paton JY. Validation of the sensormedics (S2900Z) metabolic cart for pediatric exercise testing. Can J Appl Physiol 1994;19(4):472–479.
    
    [PubMed](http://rc.rcjournal.com/lookup/external-ref?access_num=7849663&link_type=MED&atom=%2Frespcare%2F56%2F4%2F472.atom) 

11. 11. Lucia A, Fleck SJ, Gotshall RW, Kearney JT. Validity and reliability of the Cosmed K2 instrument. Int J Sports Med 1993;14(7):380–386.
    
    [PubMed](http://rc.rcjournal.com/lookup/external-ref?access_num=8244604&link_type=MED&atom=%2Frespcare%2F56%2F4%2F472.atom) 
    
    [Web of Science](http://rc.rcjournal.com/lookup/external-ref?access_num=A1993LZ82500005&link_type=ISI) 

12. 12. Boutellier U, Gomez U, Mader G. A piston pump for respiration simulation. J Appl Physiol 1981;50(3):663–664.
    
    [FREE Full Text](http://rc.rcjournal.com/lookup/ijlink/YTozOntzOjQ6InBhdGgiO3M6MTQ6Ii9sb29rdXAvaWpsaW5rIjtzOjU6InF1ZXJ5IjthOjQ6e3M6ODoibGlua1R5cGUiO3M6MzoiUERGIjtzOjExOiJqb3VybmFsQ29kZSI7czozOiJqYXAiO3M6NToicmVzaWQiO3M6ODoiNTAvMy82NjMiO3M6NDoiYXRvbSI7czoyMzoiL3Jlc3BjYXJlLzU2LzQvNDcyLmF0b20iO31zOjg6ImZyYWdtZW50IjtzOjA6IiI7fQ==) 

13. 13. Gore CJ, Catcheside PG, French SN, Bennett JM, Laforgia J. Automated VO2max calibrator for open-circuit indirect calorimetry systems. Med Sci Sports Exerc 1997;29(8):1095–1103.
    
    [PubMed](http://rc.rcjournal.com/lookup/external-ref?access_num=9268968&link_type=MED&atom=%2Frespcare%2F56%2F4%2F472.atom) 
    
    [Web of Science](http://rc.rcjournal.com/lookup/external-ref?access_num=A1997XR03500016&link_type=ISI) 

14. 14. Prieur F, Busso T, Castells J, Bonnefoy R, Benoit H, Geyssant A, et al. A system to simulate gas exchange in humans to control quality of metabolic measurements. Eur J Appl Physiol Occup Physiol 1998;78(6):549–554.
    
    [PubMed](http://rc.rcjournal.com/lookup/external-ref?access_num=9840411&link_type=MED&atom=%2Frespcare%2F56%2F4%2F472.atom) 

15. 15. Huszczuk A, Whipp BJ, Wasserman K. A respiratory gas exchange simulator for routine calibration in metabolic studies. Eur Respir J 1990;3(4):465–468.
    
    [Abstract/FREE Full Text](http://rc.rcjournal.com/lookup/ijlink/YTozOntzOjQ6InBhdGgiO3M6MTQ6Ii9sb29rdXAvaWpsaW5rIjtzOjU6InF1ZXJ5IjthOjQ6e3M6ODoibGlua1R5cGUiO3M6NDoiQUJTVCI7czoxMToiam91cm5hbENvZGUiO3M6MzoiZXJqIjtzOjU6InJlc2lkIjtzOjc6IjMvNC80NjUiO3M6NDoiYXRvbSI7czoyMzoiL3Jlc3BjYXJlLzU2LzQvNDcyLmF0b20iO31zOjg6ImZyYWdtZW50IjtzOjA6IiI7fQ==) 

16. 16. Vacu-Med. Operating and service manual: motorized syringe no. 17053 with metabolic calibration kit no. 17051.