NiTi Alloys Exposure Alters miR-124 Expression in Physiological and Osteoarthritic Osteoblasts.

PURPOSE OF THE STUDY Nitinol (NiTi) is a biomaterial widely used in medicine based on super-elastic and shape memory properties. miR-124 has a key role in inflammatory process, osteoblasts differentiation, and mineralization. The aim of study was evaluating the differences in gene expression of miR-124 of human physiological osteoblasts (HOB) and human osteoarthritic osteoblasts (OSBA) as a response to NiTi alloy in different heat treatments. MATERIAL AND METHODS The cells were cultivated with NiTi discs with/without addition of bacterial lipopolysaccharide (LPS) for 72 hours. MicroRNAs were isolated, underwent reverse transcription and were analyzed by RT-PCR. RESULTS As a response to LPS, HOB overexpressed miR-124, while in OSBA expression change did not occur. Overexpression was also observed in both cell lines as a response to hydrogen and helium treated NiTi discs. HOB expressed significantly higher amount of miR-124 than OSBA as a response to hydrogen treatment of NiTi discs. In addition, hydrogen treatment caused significantly higher expression in HOB than LPS. The combination of NiTi disc and LPS treatment in HOB didn't cause any expression changes. Comparing to LPS-only treatment, the expression in HOB with combination of LPS and alloy was significantly lower. In OSBA, the expression was increased by the combination of LPS and hydrogen disc, in case of helium disc, the expression was decreased. CONCLUSIONS In conclusion, human physiological and osteoarthritic osteoblasts respond to NiTi alloy with both surface (hydrogen and helium atmosphere) treatment by overexpression of miR-124. The effect of LPS as inflammatory modulator suggests the presence of an "anti-inflammatory preconditioning" in osteoarthritic osteoblasts, as physiological osteoblasts overexpression was significantly higher. Key words: nitinol, osteoblast, miR-124, lipopolysaccharide.

Free-breathing Pulmonary MR Imaging to Quantify Regional Ventilation.

Purpose To measure regional specific ventilation with free-breathing hydrogen 1 (1H) magnetic resonance (MR) imaging without exogenous contrast material and to investigate correlations with hyperpolarized helium 3 (3He) MR imaging and pulmonary function test measurements in healthy volunteers and patients with asthma. Materials and Methods Subjects underwent free-breathing 1H and static breath-hold hyperpolarized 3He MR imaging as well as spirometry and plethysmography; participants were consecutively recruited between January and June 2017. Free-breathing 1H MR imaging was performed with an optimized balanced steady-state free-precession sequence; images were retrospectively grouped into tidal inspiration or tidal expiration volumes with exponentially weighted phase interpolation. MR imaging volumes were coregistered by using optical flow deformable registration to generate 1H MR imaging-derived specific ventilation maps. Hyperpolarized 3He MR imaging- and 1H MR imaging-derived specific ventilation maps were coregistered to quantify regional specific ventilation within hyperpolarized 3He MR imaging ventilation masks. Differences between groups were determined with the Mann-Whitney test and relationships were determined with Spearman (ρ) correlation coefficients. Statistical analyses were performed with software. Results Thirty subjects (median age: 50 years; interquartile range [IQR]: 30 years), including 23 with asthma and seven healthy volunteers, were evaluated. Both 1H MR imaging-derived specific ventilation and hyperpolarized 3He MR imaging-derived ventilation percentage were significantly greater in healthy volunteers than in patients with asthma (specific ventilation: 0.14 [IQR: 0.05] vs 0.08 [IQR: 0.06], respectively, P < .0001; ventilation percentage: 99% [IQR: 1%] vs 94% [IQR: 5%], P < .0001). For all subjects, 1H MR imaging-derived specific ventilation correlated with plethysmography-derived specific ventilation (ρ = 0.54, P = .002) and hyperpolarized 3He MR imaging-derived ventilation percentage (ρ = 0.67, P < .0001) as well as with forced expiratory volume in 1 second (FEV1) (ρ = 0.65, P = .0001), ratio of FEV1 to forced vital capacity (ρ = 0.75, P < .0001), ratio of residual volume to total lung capacity (ρ = -0.68, P < .0001), and airway resistance (ρ = -0.51, P = .004). 1H MR imaging-derived specific ventilation was significantly greater in the gravitational-dependent versus nondependent lung in healthy subjects (P = .02) but not in patients with asthma (P = .1). In patients with asthma, coregistered 1H MR imaging specific ventilation and hyperpolarized 3He MR imaging maps showed that specific ventilation was diminished in corresponding 3He MR imaging ventilation defects (0.05 ± 0.04) compared with well-ventilated regions (0.09 ± 0.05) (P < .0001). Conclusion 1H MR imaging-derived specific ventilation correlated with plethysmography-derived specific ventilation and ventilation defects seen by using hyperpolarized 3He MR imaging. © RSNA, 2018 Online supplemental material is available for this article.

Respiration of thermogenic inflorescences of skunk cabbage Symplocarpus renifolius in heliox.

The respiration rate of the thermogenic inflorescences of Japanese skunk cabbage Symplocarpus renifolius can reach 300 nmol s-1 g-1 , which is sufficient to raise spadix temperature (Ts ) up to 15 °C above ambient air temperature (Ta ). Respiration rate is inversely related to Ta , such that the Ts achieves a degree of independence from Ta , an effect known as temperature regulation. Here, we measure oxygen consumption rate (Mo2 ) in air (21% O2 in mainly N2 ) and in heliox (21% O2 in He) to investigate the diffusive conductance of the network of gas-filled spaces and the thermoregulatory response. When Ts was clamped at 15 °C, the temperature that produces maximal Mo2 in this species, exposure to high diffusivity heliox increased mean Mo2 significantly from 137 ± 17 to 202 ± 43 nmol s-1 g-1 FW, indicating that respiration in air is normally limited by diffusion in the gas phase and some mitochondria are unsaturated. When Ta was clamped at 15 °C and Ts was allowed to vary, exposure to heliox reduced Ts 1 °C and increased Mo2 significantly from 116 ± 10 to 137 ± 19 nmol s-1 g-1 , indicating that enhanced heat loss by conduction and convection can elicit the thermoregulatory response.

Acute respiratory muscle unloading by normoxic helium-O2 breathing reduces the O2 cost of cycling and perceived exertion in obese adolescents.

PURPOSE: In obesity, an increased work of breathing contributes to a higher O2 cost of exercise and negatively affects exercise tolerance. The purpose of the study was to determine whether, in obese adolescents, acute respiratory muscle unloading via normoxic helium-O2 breathing reduces the O2 cost of cycling and perceived exertion. METHODS: Nine males [age 16.8 ± 1.6 (x ± SD) years, body mass 109.9 ± 15.0 kg] performed on a cycle ergometer, breathing room air (AIR) or a 21 % O2-79 % helium mixture (He-O2): an incremental exercise, for determination of [Formula: see text]O2 peak and gas exchange threshold (GET); 12 min constant work rate (CWR) exercises at 70 % of GET (GET) determined in AIR. RESULTS: [Formula: see text]O2 peak was not different in the two conditions. From the 3rd to the 12th minute of exercise (both during CWR < GET and CWR > GET), [Formula: see text]O2 was lower in He-O2 vs. AIR (end-exercise values: 1.40 ± 0.14 vs. 1.57 ± 0.22 L min(-1) GET). During CWR > GET in AIR, [Formula: see text]O2 linearly increased from the 3rd to the 12th minute of exercise, whereas no substantial increase was observed in He-O2. The O2 cost of cycling was ~10 % (GET) lower in He-O2 vs. AIR. Heart rate and ratings of perceived exertion for dyspnea/respiratory discomfort and leg effort were lower in He-O2. CONCLUSIONS: In obese adolescents, acute respiratory muscle unloading via He-O2 breathing lowered the O2 cost of cycling and perceived exertion during submaximal moderate- and heavy-intensity exercise.

Oxygen diffusion limitation triggers ventilatory movements during spiracle closure when insects breathe discontinuously.

During discontinuous gas exchange cycles in insects, spiracular opening follows a typical prolonged period of spiracle closure. Gas exchange with the environment occurs mostly during the period of full spiracular opening. In this study we tested the hypothesis that recently reported ventilatory movements during the spiracle closure period serve to mix the tracheal system gaseous contents, and support diffusive exchanges with the tissues. Using heliox (21% O2, 79% He), we found that by increasing oxygen diffusivity in the gas phase, ventilatory movements of Schistocerca gregaria were significantly delayed compared with normoxic conditions. Exposure to hyperoxic conditions (40% O2, 60% N2) resulted in a similar delay in forced ventilation. Together, these results indicate that limits to oxygen diffusion to the tissues during spiracle closure trigger ventilatory movements, which in turn support tissue demands. These findings contribute to our understanding of the mechanistic basis of respiratory gas exchange between insect tissues and the environment.

Decompression models: review, relevance and validation capabilities.

INTRODUCTION/BACKGROUND: For more than a century, several types of mathematical models have been proposed to describe tissue desaturation mechanisms in order to limit decompression sickness. These models are statistically assessed by DCS cases, and, over time, have gradually included bubble formation biophysics. This paper proposes to review this evolution and discuss its limitations. METHODS: This review is organized around the comparison of decompression model biophysical criteria and theoretical foundations. Then, the DCS-predictive capability was analyzed to assess whether it could be improved by combining different approaches. RESULTS: Most of the operational decompression models have a neo-Haldanian form. Nevertheless, bubble modeling has been gaining popularity, and the circulating bubble amount has become a major output. By merging both views, it seems possible to build a relevant global decompression model that intends to simulate bubble production while predicting DCS risks for all types of exposures and decompression profiles. CONCLUSIONS: A statistical approach combining both DCS and bubble detection databases has to be developed to calibrate a global decompression model. Doppler ultrasound and DCS data are essential: i. to make correlation and validation phases reliable; ii. to adjust biophysical criteria to fit at best the observed bubble kinetics; and iii. to build a relevant risk function.

Development and testing of hyperbaric atomic force microscopy (AFM) and fluorescence microscopy for biological applications.

A commercially available atomic force microscopy and fluorescence microscope were installed and tested inside a custom-designed hyperbaric chamber to provide the capability to study the effects of hyperbaric gases on biological preparations, including cellular mechanism of oxidative stress. In this report, we list details of installing and testing atomic force microscopy and fluorescence microscopy inside a hyperbaric chamber. The pressure vessel was designed to accommodate a variety of imaging equipment and ensures full functionality at ambient and hyperbaric conditions (≤85 psi). Electrical, gas and fluid lines were installed to enable remote operation of instrumentation under hyperbaric conditions, and to maintain viable biological samples with gas-equilibrated superfusate and/or drugs. Systems were installed for vibration isolation and temperature regulation to maintain atomic force microscopy performance during compression and decompression. Results of atomic force microscopy testing demonstrate sub-nanometre resolution at hyperbaric pressure in dry scans and fluid scans, in both contact mode and tapping mode. Noise levels were less when measurements were taken under hyperbaric pressure with air, helium (He) and nitrogen (N(2) ). Atomic force microscopy and fluorescence microscopy measurements were made on a variety of living cell cultures exposed to hyperbaric gases (He, N(2) , O(2) , air). In summary, atomic force microscopy and fluorescence microscopy were installed and tested for use at hyperbaric pressures and enables the study of cellular and molecular effects of hyperbaric gases and pressure per se in biological preparations.

Some Beneficial Effects of Inert Gases on Blood Oxidative Metabolism: In Vivo Study.

The aim of the study was to assess the effect of external use of inert gases (helium and argon) on the state of free radical processes in vivo. The experiment was performed on 30 male Wistar stock rats (age-3 months, weight-200-220 g.), randomly distributed into 3 equal groups. The first group of animals was intact (n = 10). The animals of the second and third groups were treated with argon and helium streams, respectively. Our research has allowed us to establish that the studied inert gases have a modulating effect on the state of oxidative metabolism of rat blood, and the nature of this effect is directly determined by the type of gas. The results of this study allowed us to establish the potential antioxidant effect of the helium stream, mainly realized due to the activation of the catalytic properties of the enzymatic link of the antioxidant system of rat blood plasma. At the same time, the revealed features of shifts in oxidative metabolism during treatment with argon flow include not only stimulation of the antioxidant system but also the pronounced induction of free radical oxidation. Thus, the conducted studies made it possible to verify the specificity of the response of the oxidative metabolism of blood plasma to the use of inert gases, depending on their type.

A new, vapour-phase mechanism for stomatal responses to humidity and temperature.

A new mechanism for stomatal responses to humidity and temperature is proposed. Unlike previously-proposed mechanisms, which rely on liquid water transport to create water potential gradients within the leaf, the new mechanism assumes that water transport to the guard cells is primarily through the vapour phase. Under steady-state conditions, guard cells are assumed to be in near-equilibrium with the water vapour in the air near the bottom of the stomatal pore. As the water potential of this air varies with changing air humidity and leaf temperature, the resultant changes in guard cell water potential produce stomatal movements. A simple, closed-form, mathematical model based on this idea is derived. The new model is parameterized for a previously published set of data and is shown to fit the data as well as or better than existing models. The model contains mathematical elements that are consistent with previously-proposed mechanistic models based on liquid flow as well as empirical models based on relative humidity. As such, it provides a mechanistic explanation for the realm of validity for each of these approaches.

Transmit gain calibration for nonproton MR using the Bloch-Siegert shift.

Transmit gain (B 1+) calibration is necessary for the adjustment of radiofrequency (RF) power levels to the desired flip angles. In proton MRI, this is generally an automated process before the actual scan without any user interaction. For other nuclei, it is usually time consuming and difficult, especially in the case of hyperpolarised MR. In the current work, transmit gain calibration was implemented on the basis of the Bloch-Siegert phase shift. From the same data, the centre frequency, line broadening and SNR could also be determined. The T(1) and B(0) insensitivity, and the wide range of B 1+ over which this technique is effective, make it well suited for nonproton applications. Examples are shown for hyperpolarised (13)C and (3)He applications.

Comparison of hyperpolarized (3)He MRI with Xe-enhanced computed tomography imaging for ventilation mapping of rat lung.

Lung ventilation was mapped in five healthy Brown Norway rats (210-377 g) using both hyperpolarized (3)He MRI and Xe-enhanced computed tomography (Xe-CT) under similar ventilator conditions. Whole-lung measurements of ventilation r obtained with (3)He MRI were not significantly different from those obtained from Xe-CT (p = 0.1875 by Wilcoxon matched pairs test). The ventilation parameter r is defined as the fraction of refreshed gas per unit volume per breath. Regional ventilation was also measured in four regions of the lung using both methods. A two-tailed paired t-test was performed for each region, yielding p > 0.05 for all but the upper portion of the right lung. The distribution of regional ventilation was evaluated by calculating ventilation gradients in the superior/inferior (S/I) direction. The average S/I gradient obtained using the (3)He MRI method was found to be 0.17 ± 0.04 cm(-1) , whereas the average S/I gradient obtained using the Xe-CT method was found to be 0.016 ± 0.005 cm(-1) . In general, S/I ventilation gradients obtained from both methods were significantly different from each other (p = 0.0019 by two-tailed paired t-test). These regional differences in ventilation measurements may be caused by the manner in which the gas contrast agents distribute physiologically and/or by the imaging modality.

Effect of isobaric breathing gas shifts from air to heliox mixtures on resolution of air bubbles in lipid and aqueous tissues of recompressed rats.

Deep tissue isobaric counterdiffusion that may cause unwanted bubble formation or transient bubble growth has been referred to in theoretical models and demonstrated by intravascular gas formation in animals, when changing inert breathing gas from nitrogen to helium after hyperbaric air breathing. We visually followed the in vivo resolution of extravascular air bubbles injected at 101 kPa into nitrogen supersaturated rat tissues: adipose, spinal white matter, skeletal muscle or tail tendon. Bubbles were observed during isobaric breathing-gas shifts from air to normoxic (80:20) heliox mixture while at 285 kPa or following immediate recompression to either 285 or 405 kPa, breathing 80:20 and 50:50 heliox mixtures. During the isobaric shifts, some bubbles in adipose tissue grew marginally for 10-30 min, subsequently they shrank and disappeared at a rate similar to or faster than during air breathing. No such bubble growth was observed in spinal white matter, skeletal muscle or tendon. In spinal white matter, an immediate breathing gas shift after the hyperbaric air exposure from air to both (80:20) and (50:50) heliox, coincident with recompression to either 285 or 405 kPa, caused consistent shrinkage of all air bubbles, until they disappeared from view. Deep tissue isobaric counterdiffusion may cause some air bubbles to grow transiently in adipose tissue. The effect is marginal and of no clinical consequence. Bubble disappearance rate is faster with heliox breathing mixtures as compared to air. We see no reason for reservations in the use of heliox breathing during treatment of air-diving-induced decompression sickness.

Effect of atmospheric pressure plasma on inactivation of pathogens inoculated onto bacon using two different gas compositions.

Atmospheric pressure plasma (APP) is an emerging non-thermal pasteurization method for the enhancement of food safety. In this study, the effect of APP on the inactivation of pathogens inoculated onto bacon was observed. Sliced bacon was inoculated with Listeria monocytogenes (KCTC 3596), Escherichia coli (KCTC 1682), and Salmonella Typhimurium (KCTC 1925). The samples were treated with APP at 75, 100, and 125 W of input power for 60 and 90 s. Two gases, helium (10 lpm) or a mixture of helium and oxygen, (10 lpm and 10 sccm, respectively) were used for the plasma generation. Plasma with helium could only reduce the number of inoculated pathogens by about 1-2 Log cycles. On the other hand, the helium/oxygen gas mixture was able to achieve microbial reduction of about 2-3 Log cycles. The number of total aerobic bacteria showed 1.89 and 4.58 decimal reductions after plasma treatment with helium and the helium/oxygen mixture, respectively. Microscopic observation of the bacon after plasma treatment did not find any significant changes, except that the L∗-value of the bacon surface was increased. These results clearly indicate that APP treatment is effective for the inactivation of the three pathogens used in this study, although further investigation is needed for elucidating quality changes after treatment.

A review of recent neurochemical data on inert gas narcosis.

Nitrogen narcosis occurs in humans at around 0.4 MPa (4 ATA). Hydrogen narcosis occurs between 2.6 and 3.0 MPa. In rats, nitrogen disturbances occur from 1 MPa and a loss of righting reflex around 4 MPa. Neurochemical studies in striatum of rats with nitrogen at 3 MPa (75% of anesthesia threshold) with differential pulse voltammetry have demonstrated a decrease in dopamine (DA) release by neurons originated from the substantia nigra pars compacta (SNc). Such a decrease is found also with compressed argon, which is more narcotic than nitrogen and with the anesthetic gas nitrous oxide. Inversely, compressed helium with its very low narcotic potency induces DA increase. Microdialysis studies in the striatum have indicated that nitrogen also induces a decrease of glutamate concentration. Nitrogen pressure did not modify NMDA glutamate receptor activities in SNc or striatum but enhanced GABAA receptors activities in SNc. Repetitive exposures to nitrogen narcosis suppressed the DA decrease and induced an increase. This fact and the lack of improvement of motor disturbances did not support the hypothesis of a physiological adaptation. The desensitization of the GABAA receptors on DA cells during recurrent exposures and the parallel long-lasting decrease of glutamate coupled to the increase in NMDA receptor sensitivity suggest a nitrogen neurotoxicity or addiction induced by recurrent exposures. The differential changes produced by inert gases indifferent neurotransmitter receptors would support the binding protein theory.

Axial distribution heterogeneity of nitric oxide airway production in healthy adults.

Model simulations of nitric oxide (NO) transport considering molecular diffusion showed that the total bronchial NO production needed to reproduce a given exhaled value is deeply influenced by its axial distribution. Experimental data obtained by fibroscopy were available about proximal airway contribution (Silkoff PE, McClean PA, Caramori M, Slutsky AS. Zamel N. Respir Physiol 113: 33-38, 1998), and recent experiments using heliox instead of air gave insight on the peripheral airway production (Shin HW, Condorelli P, Rose-Gottron CM, Cooper DM, George SC. J Appl Physiol 97: 874-882, 2004; Kerckx Y, Michils A, Van Muylem A. J Appl Physiol 104: 918-924, 2008). This theoretical work aimed at obtaining a realistic distribution of NO production in healthy adults by meeting both proximal and peripheral experimental constraints. To achieve this, a model considering axial diffusion with geometrical boundaries derived from Weibel's morphometrical data was divided into serial compartments, each characterized by its axial boundaries and its part of bronchial NO production. A four-compartment model was able to meet both criteria. Two compartments were found to share all the NO production: one proximal (generations 0 and 1; 15-25% of the NO production) and one inside the acinus (proximal limit, generations 14-16; distal limit, generations 16 and 17; 75-85% of the NO production). Remarkably, this finding implies a quasi nil production in the main part of the conducting airways and in the acinar airways distal to generation 17. Given the chosen experimental outcomes and reliant on their accuracy, this very inhomogeneous distribution is likely the more realistic one that may be achieved with a "one-trumpet"-shaped model. Refinement should come from a more realistic description of the acinus structure.

Use of inert gases and carbon monoxide to study the possible influence of countercurrent exchange on passive absorption from the small bowel.

The purpose of the present study was to quantitate the influence of countercurrent exchange on passive absorption of highly diffusible substances from the small intestine of the rabbit. The absorption of carbon monoxide, which is tightly bound to hemoglobin and therefore cannot exchange, was compared to the absorption of four unbound gases (H(2), He, CH(4), and (133)Xe), which should exchange freely. The degree to which the observed absorption of the unbound gases falls below that predicted from CO absorption should provide a quantitative measure of countercurrent exchange.CO uptake at high luminal Pco is flow-limited and, assuming that villus and central hemoglobin concentrations are equal, the flow that equilibrates with CO (F(co)) was calculated to equal 7.24 ml/min/100 g. The observed absorption rate of the unbound gases was from two to four times greater than would have been predicted had their entire uptake been accounted for by equilibration with F(co). This is the opposite of what would occur if countercurrent exchange retarded absorption of the unbound gases. The unbound gases have both flow- and diffusion-limited components, and F(co) should account for only the fraction of absorption that is flow limited. A simple model of perfusion and diffusion made it possible to calculate the fraction of the total uptake of unbound gases that was flow limited. This fraction of the total observed absorption rate was still about 1.8 times greater than predicted by CO absorption. A possible explanation for this discrepancy is that plasma skimming reduces the hemoglobin of villus blood to about 60% of that of central blood. Thus, F(co) is actually about 1.7 times greater than initially calculated, and with this correction, there is close agreement between the predicted and observed rates of absorption of each of the unbound gases. We conclude that countercurrent exchange does not influence passive absorption under the conditions of this study.

Use of inert gases to study the interaction of blood flow and diffusion during passive absorption from the gastrointestinal tract of the rat.

Measurement of the relative absorption rates of inert gases (H(2), He, CH(4), SF(6), and (133)Xe) was used to investigate the interaction between diffusion and blood flow during passive absorption from the stomach, small bowel, and colon of the rat. If uptake is blood flow limited, the gases should be absorbed in proportion to their solubilities in blood, but if diffusion limited, uptake should be proportional to the diffusion rate of the gases in mucosal tissues. The observed absorption data were fitted to a series of models of interaction between perfusion and diffusion. A simple model accurately predicted the absorption rates of the gases from all segments of bowel. In this model, gas is absorbed into two distinct blood flows: one which flows in proximity to the lumen and completely equilibrates with the lumen, and a second which is sufficiently rapid and distant from the lumen that its gas uptake is entirely diffusion limited. The fraction of the total absorption attributable to the equilibrating flow can be readily calculated and equalled 93%, 77%, and 33% for the small bowel, colon, and stomach, respectively. Thus the rate of passive absorption of gases from the small bowel is limited almost entirely by the blood flow to the mucosa, and absorption from the stomach is largely limited by the diffusion rate of the gases. The flow which equilibrates with the lumen can be quantitated, and this flow may provide a useful measure of "effective" mucosal blood flow.

Reproducibility of cardioventilatory measurements using a respiratory mass spectrometer.

The aim of this study was to assess the within subject reproducibility of cardioventilatory measurements and the maximum permitted 'normal' variability over time at rest and exercise using the respiratory mass spectrometer (RMS). Ten subjects underwent an incremental exercise test on three separate occasions utilising rebreathing (RB) and helium dilution mixed expired gas analysis (HME) functions of the RMS. Measurements included heart rate (HR), oxygen consumption (V(O2)), carbon dioxide excretion (V(VO2)), effective pulmonary blood flow (Q(eff)), stroke volume (SV), arteriovenous oxygen content difference (AVO), transfer factor (Dl(CO)), functional residual capacity (FRC), minute ventilation (VE), tidal volume (VT) and respiratory quotient (RQ). The coefficients of variation for each variable for the 10 subjects were calculated. At rest, the 90th centile variability for measured cardiopulmonary variables (RB only) was <35%. During exercise, the 90th centile for variability for measured cardiopulmonary variables for HME and RB were < or =20 and <40%, respectively. These measurements in healthy adults should inform sample size in research studies.

The accuracy of the oxygen washout technique for functional residual capacity assessment during spontaneous breathing.

BACKGROUND: Measurement of functional residual capacity (FRC) is of considerable interest for monitoring patients with lung injury. The lack of instruments has impeded routine bedside FRC measurement. Recently, a simple automated method for FRC assessment by O2 washout has been introduced. We designed this study to evaluate the accuracy of FRC measurement using the O2 washout technique. METHODS: The LUFU system (Draeger, Luebeck, Germany) estimates FRC by O2 washout, a variant of multiple breath nitrogen washout. This technique uses a sidestream O2-analyzer to calculate FRC from end-inspired and end-expired O2 concentrations during fast changes of Fio2. We measured FRC in 23 healthy, spontaneously breathing volunteers in the sitting position using three techniques: 1) helium dilution (FRC-He), 2) body plethysmography (FRC-bp), 3) oxygen washout (FRC-O2). RESULTS: FRC-O2 (mean 4.1 +/- 1.1 L, range 2.4-6.9 L) corresponds with FRC-He (mean 4.0 +/- 1.0 L, range 2.4-6.2 L; bias of FRC-O2: -0.2 +/- 0.4 L) and FRC-bp (mean 4.2 +/- 1.0 L, range 2.8-6.1 L; bias of FRC-O2: 0.1 +/- 0.6 L). CONCLUSIONS: The bias and precision of the O2 washout technique using the LUFU system were clinically acceptable when compared with FRC-He and FRC-bp for FRC assessment in spontaneously breathing volunteers.

A simple method to reconstruct the molar mass signal of respiratory gas to assess small airways with a double-tracer gas single-breath washout.

For the assessment of small airway diseases, a noninvasive double-tracer gas single-breath washout (DTG-SBW) with sulfur hexafluoride (SF6) and helium (He) as tracer components has been proposed. It is assumed that small airway diseases may produce typical ventilation inhomogeneities which can be detected within one single tidal breath, when using two tracer components. Characteristic parameters calculated from a relative molar mass (MM) signal of the airflow during the washout expiration phase are analyzed. The DTG-SBW signal is acquired by subtracting a reconstructed MM signal without tracer gas from the signal measured with an ultrasonic sensor during in- and exhalation of the double-tracer gas for one tidal breath. In this paper, a simple method to determine the reconstructed MM signal is presented. Measurements on subjects with and without obstructive lung diseases including the small airways have shown high reliability and reproducibility of this method.