Schematic a. and image b. of the closed gas loop.

<p>The valves V1 and V2 are used for switching between venting, i.e., flushing the system with ambient air in (blue arrows) or closed-loop for sample testing (red arrows). The septum is used for sample injection using a syringe.</p

The UGGA system; a. simplified schematic of the UGGA gas loop (shaded area is the partially evacuated loop zone), and b.instrument case interior (note: image distorted due to wide-angle lens).

<p>The UGGA system; a. simplified schematic of the UGGA gas loop (shaded area is the partially evacuated loop zone), and b.instrument case interior (note: image distorted due to wide-angle lens).</p

Variability, accuracy of all closed-loop tests for three different instruments (F, R, and I) and for all instruments.

<p>X_meas and X_exp (in ppm) are the means of the measured and expected instrument PP, and V_loop gives estimated mean loop volume (ml) (SD and SE have the same units as their respective variables). Coefficient of variation CV(%) = 100(SD/X_exp), standard error is SE = SD/√n.</p

Measuring CO₂ and CH₄ with a portable gas analyzer: Closed-loop operation, optimization and assessment

<div><p>The use of cavity ring-down spectrometer (CRDS) based portable greenhouse gas analyzers (PGAs) in closed-loop configuration to measure small sample volumes (< 1 l) for CH₄ and CO₂ concentrations is increasing and offers certain advantages over conventional measurement methods in terms of speed as well as the ability to measure directly in field locations. This first systematic assessment of the uncertainties, problems and issues associated with achieving reliable and repeatable measurement with this technique presents the adaptation, measurement range, calibration and maintenance, accuracy and issues of efficient operation, for one example instrument. Regular open-loop calibration, a precise loop volume estimate, leak free system, and a high standard of injection practices are necessary for accurate results. For 100 μl injections, measured values ranging from 4.5 to 9 x10⁴ ppm (CH₄), and 1000 ppm to 1 x10⁶ ppm (CO₂) are possible with uncertainties ±5.9% and ±3.0%, respectively, beyond 100 ppm CH₄ correction may be necessary. Uncertainty arising from variations water vapour content and atmospheric pressure are small (0.24% and -0.9% to +0.5%, respectively). With good practice, individual operator repeatability of 1.9% (CH₄) and 2.48% (CO₂) can be achieved. Between operator injection error was around 3% for both gases for four operators. Slow syringe plunger operation (> 1s) is recommended; generally delivered more (ca. 3–4%) sample into the closed instrument loop than did rapid operation. Automated value retrieval is recommended; we achieved a 3 to 5-fold time reduction for each injection cycle (ca. <2 min), and operator reading, recording, and digitization errors are eliminated.</p></div

Measured and expected methane ΔX demonstrating instrumental drop-off (indicated by arrow) for X_CH4 values > 100 ppm (shaded area = linear range).

<p>Data for three instruments A, B, and C. Equations for A and B give the correction from measured to expected values. The table inset shows percentage error for A and B.</p

a. and b. measured ΔX (a. CH₄ and b. CO₂) concentration (y-axis) vs. sample concentration (x-axis) for three injection volumes 100, 200 and 500 μl, respectively.

<p>Legend values in brackets are the dilution factor (V_loop-V_sample)/V_sample. The shaded area in (a.) shows the linear response range for CH₄.</p

Coefficient of variation (CV) of a. CH₄ and b. CO₂ instrument readings in ambient air as a function of ring down time (RD).

<p>The data were obtained from different instruments, the dotted lines show least-square power-law fits of the data to RD.</p

Comparative injection measurement variability/error, for: A—Worn gastight syringe; B—New liquid syringe; and C—New gas tight syringe (see text for details), and 4 syringe operators (indicated by numbers 1 to 4).

<p>X_mean is the mean test gas PP in ppm. Expected test values were 50.1 ppm CH₄ and 970.4 ppm CO₂. Measurement error ε(%) is a given by <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0193973#pone.0193973.e003" target="_blank">Eq 3</a>. CV is coefficient of variation (SD/X_mean) standard error is SE = SD/√n, and SD is standard deviation.</p

Patient distribution according to results of right heart catheterization; flow chart of the study design.

<p> <i>PH, postcapillary pulmonary hypertension; RHC, right heart catheterization; TTE, transthoracic echocardiography; sPAP, systolic pulmonary arterial pressure; RVaSl, apical right ventricular longitudinal strain.</i></p

Baseline data, groups divided with regard to findings from right heart catheterization.

<p>BMI, body mass index; CAD, coronary artery disease; NYHA FC, NYHA functional class; CCB, calcium channel blocker; ARB/ACEI, angiotensin receptor blockers/angiotensin converting enzyme inhibitor; mPAP, mean pulmonary arterial pressure; sPAP, systolic pulmonary arterial pressure; PCWP, pulmonary capillary wedge pressure; RV, right ventricle; RA, right atrium; LVEF, left ventricular ejection fraction; E, early; A, atrial; MV, mitral velocity; RVDs/d, systolic/diastolic right ventricular diameter; LAV, left atrial volume; IVSd, diastolic interventricular septum thickness.</p