Normal values of exhaled carbon monoxide in healthy subjects: comparison between two methods of assessment

Abstract

BackgroundIn a previous study, exhaled carbon monoxide (eCO) has been assessed in healthy non-smokers with a photo acoustic spectrometer Brüel&Kjær 1312. Unexpectedly, values were higher than those reported in literature, which were mostly obtained with electrochemical analysers. This study was aimed to compare eCO values obtained with Brüel&Kjær 1312 and PiCO + Smokerlyzer, a largely utilized electrochemical analyser.MethodsThirty-four healthy subjects, 15 non-smokers and 19 smokers, underwent eCO assessment with Brüel&Kjær 1312 and PiCO + Smokerlyzer during a prolonged expiration (15 seconds). Brüel&Kjær 1312 assessed CO concentration 7 and 12 seconds after the beginning of expiration and displayed the mean value. PiCO + Smokerlyzer was utilized according to the manufacturer’s recommendations. In vitro, the two devices were tested with standard concentrations of CO in nitrogen (5, 9.9, 20, and 50 ppm), and the time needed by PiCO + Smokerlyzer readings to stabilize was assessed at different gas flows.ResultsBoth Brüel&Kjær 1312 and PiCO + Smokerlyzer presented very good internal consistency. The values provided were strictly correlated, but at low test concentrations, the Brüel&Kjær 1312 readings were greater than the PiCO + Smokerlyzer, and vice versa. PiCO + Smokerlyzer overestimated the CO standard concentrations at 5 and 9.9 ppm by 20%, while Brüel&Kjær 1312 measures were correct. PiCO + Smokerlyzer readings stabilized in 12 seconds during in vitro tests and in 15 seconds during in vivo measurements, suggesting that the values displayed corresponded to the initial phase of expiration.ConclusionsDifferences between Brüel&Kjær 1312 and PiCO + Smokerlyzer may be explained because Brüel&Kjær 1312 measured CO levels in the middle and at the end of expiration while PiCO + Smokerlyzer assessed them in the initial part of expiration.

Analysis of Agreement between Expired-Air Carbon Monoxide Monitors

“…Values obtained from the Bedfont monitor were consistently higher than those from the Vitalograph monitor. The elevated CO values obtained from the Bedfont monitors are consistent with a previous study finding overestimation of CO by roughly 20% when measuring known concentrations of carbon monoxide of 5 ppm and 9.9 ppm (Moscato et al, 2014). …”

“…According to each respective CO monitor’s manual, the BreathCO monitor is accurate ±3 ppm (Vitalograph, n.d.) and the pico+ Smokerlyzer is accurate ±2% (CoVita, 2010). Previous studies have found both monitors to have high internal consistency, with intraclass correlation coefficients for the Vitalograph ranging from 0.935 to 0.994 (Javors, et al, 2005) and 0.985 for the Bedfont monitor (Moscato et al, 2014)…”

“…Bland-Altman analysis determines the level of agreement in measurement between monitors rather than their accuracy (i.e., closeness to true value) or precision (i.e., closeness between repeated measures) (Mantha, Roizen, Fleisher, Thisted, & Foss, 2000), both of which have been reported elsewhere per each monitor (CoVita, 2010; Javors, et al, 2005; Moscato, Poscia, Gargaruti, Capelli, & Cavaliere, 2014; Vitalograph, n.d.). Knowing whether these monitors agree (e.g., 4 ppm for one is 4 ppm for the other) will allow for the monitors and diagnostic criteria to be used interchangeably.…”

Evaluation of smoking status: comparison of self-reports with exhaled carbon monoxide analysis in university students in the Islamic Republic of Iran

“…In the present study, men showed higher exhaled CO levels than the total participants (around 2-fold) and women (around 3-fold). These findings were consistent with the results reported by Moscato et al (25); however, the CO values were not comparable between the studies. Typical exhaled CO values certainly differ across studies even if they used a piCO+ Smokerlyzer because mean levels in nonsmokers vary from < 1.5 ppm (26) to 3 ppm (27).…”

Exhaled nitric oxide and carbon monoxide in lung transplanted patients

“…However, different devices were used to measure eCO and possible factors affecting eCO levels (such as current therapy and active-passive smoking exposure) were not considered. It is known that different methodologies of eCO assessment can lead to significantly different results [31] and, to make reliable comparisons among studies on eCO, there is a need to use standardized instruments and methods [4].…”