Analysis of exhaled nitric oxide by the helium bolus method

STUDY OBJECTIVES: The precise anatomic sites contributing to exhaled nitric oxide (eNO) are still unknown. The present study was designed to analyze profiles of eNO by referring to the He exhalation curve and examining the effects of breath-holding and expiratory flow rates on eNO. PARTICIPANTS: Healthy volunteers and patients with stable asthma. MEASUREMENTS AND RESULTS We used the He bolus method of the closing volume, and simultaneously analyzed the concentrations of exhaled He and nitric oxide (NO). By referring to the He exhalation curve, the expired gas was divided into three parts: airway dead space (phase 1), a mixture of airway and alveolar gas (phase 2), and alveolar gas (phase 3 and phase 4). The eNO profiles showed a peak in phase 2 (peak eNO) and decreased gradually to a plateau in the latter half of phase 3 (plateau eNO). The levels of peak eNO were higher than those of plateau eNO in both normal subjects and asthmatic patients. Breath-holding increased levels of peak eNO 2.5-fold in both normal subjects and asthmatic patients, but it did not affect the levels of plateau eNO. The levels of peak eNO increased as the expiratory flow rate decreased, and the levels of plateau eNO showed a similar flow dependency. CONCLUSION: A peak value of eNO concentration profiles may directly express the production of NO in the airway.     

Respiratory heat loss is not the sole stimulus for bronchoconstriction induced by isocapnic hyperpnea with dry air

It is uncertain if respiratory heat loss or respiratory water loss is the stimulus for bronchoconstriction induced by isocapnic hyperpnea or exercise with dry air in subjects with asthma. We partially separated these 2 stimuli by having 18 subjects with asthma breathe dry air (0 mg/L water content) at increasing ventilations by isocapnic hyperpnea while we measured the increase in specific airway resistance (SRaw). The study was divided into 2 phases. In Phase 1, we used an apparatus with a single respiratory valve and evaluated the subjects' responses at 3 different inspired temperatures (-8.4, 20.5, and 39.4 degrees C). Seven of the subjects had esophageal catheters with 2 thermocouples in place to measure retrocardiac and retrotracheal temperatures. In this phase, we found that there were no significant differences in the ventilation required to cause a 100% increase in SRaw among the 3 different inspired temperatures (48.4 L/min, cold; 47.5 L/min, room temperature; 44.2 L/min, hot), even though the retrotracheal temperature fell more when the subjects breathed cold air at 40 L/min (2.1 degrees C) than when they breathed hot air (1.2 degrees C), suggesting greater airway cooling with the cold air. In Phase 2, in order to accurately measure inspired and exhaled temperatures and exhaled water content, we used 2 separate systems for delivering the inspired air and collecting the exhaled air at 2 different inspired temperatures (-21.4 and 38.9 degrees C). Again, we found that there was no significant difference in the ventilation required to cause a 100% increase in SRaw between the 2 different inspired temperatures (28.3 L/min, cold; 33.6 L/min, hot). When the subjects inhaled cold air, exhaled temperature was warmer than previously reported.(ABSTRACT TRUNCATED AT 250 WORDS)     

Breath tests and airway gas exchange

Measuring soluble gas in the exhaled breath is a non-invasive technique used to estimate levels of respiratory, solvent, and metabolic gases. The interpretation of these measurements is based on the assumption that the measured gases exchange in the alveoli. While the respiratory gases have a low blood-solubility and exchange in the alveoli, high blood-soluble gases exchange in the airways. The effect of airway gas exchange on the interpretation of these exhaled breath measurements can be significant. We describe airway gas exchange in relation to exhaled measurements of soluble gases that exchange in the alveoli. The mechanisms of airway gas exchange are reviewed and criteria for determining if a gas exchanges in the airways are provided. The effects of diffusion, perfusion, temperature and breathing maneuver on airway gas exchange and on measurement of exhaled soluble gas are discussed. A method for estimating the impact of airway gas exchange on exhaled breath measurements is presented. We recommend that investigators should carefully control the inspired air conditions and type of exhalation maneuver used in a breath test. Additionally, care should be taken when interpreting breath tests from subjects with pulmonary disease.     

Dynamics of soluble gas exchange in the airways: II. Effects of breathing conditions

A mathematical model of the airways is developed which focuses on the dynamic exchange characteristics of heat, water and soluble gas. A typical airway segment is divided radially into three regions: the airway lumen, a thin mucous layer of variable thickness coating the airway wall, and an underlying nonperfused tissue layer. A bronchial circulation capillary bed lies beyond the nonperfused tissue layer. The simultaneous exchange of water, heat and soluble gas is dealt with using the model of Tsu et al. (Ann. Biomed. Eng. 16:547-571, 1988). In the case of excretion of ingested ethyl alcohol from the bronchial and pulmonary circulations, the model predicts that during inspiration, because of the alcohol flux from the airway mucosa, a concentration of alcohol in equilibrium with mucus is achieved in the inspired air before the respiratory bronchioles are reached. During exhalation, much of this alcohol redeposits on the airway surface. The net flux of alcohol from the airway surface exceeds the flux of alcohol from the mouth in the exhaled gas indicating that the exhaled alcohol comes from the airways and bronchial circulation rather than from the alveoli and the pulmonary circulation. Alcohol flux moves farther into the airways with oral breathing compared to nasal breathing. Increased ventilation shifts the alcohol flux more alveolarward. Changes in inspired air temperature and humidity have almost no effect on the distribution of alcohol flux in the airways.     

Human heart-lung transplantation: physiologic aspects of the denervated lung and post-transplant obliterative bronchiolitis

Eighteen sequential follow-up measurements of pulmonary function were obtained over a period of 21 months after heart-lung transplantation in a patient who had undergone surgery for end-stage pulmonary lymphangioleiomyomatosis. In the early postoperative period, there was a moderate decrease in VC and TLC but gas exchange was maintained at essentially normal levels. The most conspicuous features of postoperative lung function were a very low airway resistance and an increase in FEV1/VC ratio above 95%. These alterations were associated with an unusual shape of the maximal expiratory flow-volume (MEFV) curve. Instead of showing a uniform decrease in expiratory flow as expiration proceeds to residual volume, the post-transplant MEFV curve showed a peak followed by a gently sloping plateau ending at a knee where flow suddenly fell. The knee occurred after exhalation of 80% VC. From the sixth postoperative month, the patient developed rapidly increasing air-flow obstruction, which proved to be due to obliterative bronchiolitis. As air-flow obstruction worsened, the knee on the MEFV curve progressively occurred at a higher lung volume, the flow plateau shortened, and flow after the knee became smaller at a given volume. From the ninth postoperative month, it was no longer possible to identify a plateau-knee configuration on the MEFV curve, which resembled that seen in severe obstructive airway disease.(ABSTRACT TRUNCATED AT 250 WORDS)     

Flow-dependency of exhaled nitric oxide in children with asthma and cystic fibrosis.

The concentration of nitric oxide in exhaled air, a marker of airway inflammation, depends critically on the flow of exhalation. Therefore, the aim of this study was to determine the effect of varying the flow on end-expiratory NO concentration and NO output in children with asthma or cystic fibrosis (CF) and in healthy children. Nineteen children with stable asthma, 10 with CF, and 20 healthy children exhaled from TLC while controlling expiratory flow by means of a biofeedback signal at approximately 2, 5, 10 and 20% of their vital capacity per second. NO was measured in exhaled air with a chemiluminescence analyser. Comparisons between the three groups were made by analysing the NO concentration at the endexpiratory plateau and by calculating NO output at different flows. Exhaled NO decreased with increasing flow in all children. Children with asthma had significantly higher NO concentrations than healthy children, but only at the lowest flows. Asthmatics using inhaled steroids (n=13) tended to have lower median exhaled NO than those without steroids. The slope of linearized (log-log transformed) NO/flow plots was significantly steeper in asthmatics than in healthy controls. CF patients had a significantly lower NO concentration and output over the entire flow range studied, compared to asthmatic and control subjects, with a similar NO/flow slope as control subjects. In conclusion, the nitric oxide concentration in exhaled air is highly flow-dependent, and the nitric oxide-flow relationship differs between asthmatics versus cystic fibrosis patients and control subjects. Assessment of the nitric oxide/flow relationship may help in separating asthmatics from normal children.     

Simultaneously recorded single-exhalation profiles of ethanol, water vapour and CO(2) in humans: impact of pharmacokinetic phases on ethanol airway exchange

The breath alcohol concentration (BrAC) standardized to the alveolar water vapour concentration has been shown to closely predict the arterial blood alcohol (ethanol) concentration (ABAC). However, a transient increase in the ABAC/BrAC ratio has been noted, when alcohol is absorbed from the gastrointestinal tract (absorption phase) and the ABAC rapidly rises. We analysed the plot of simultaneously recorded alcohol, water vapour and CO(2)?against exhaled volume (volumetric expirogram) for respiratory dead space volume (VD), cumulative gas output and phase III slope within one breath to evaluate whether changes in the BrAC profile could explain this variability. Eight healthy subjects performed exhalations through pre-heated non-restrictive mouthpieces and the concentrations were measured by infrared absorption. In the absorption phase, the respiratory VD of alcohol was transiently increased and the exhaled alcohol was displaced to the latter part of the expirogram. In the post-absorption phase, the respiratory VD for alcohol and water vapour was stable and always less than the respiratory VD for CO(2), indicating that the first part of the exhaled alcohol and water originated from the conducting airway. The position of the BrAC profile between water vapour and CO(2)?in the post-absorptive phase indicates an interaction within the conducting airway, probably including a deposition of alcohol onto the mucosa during exhalation. We conclude that the increase in the ABAC/BrAC ratio during the absorption phase of alcohol coincides with a transient increase in respiratory VD of alcohol and a delay in the appearance of alcohol in the exhaled air as the exhalation proceeds compared with the post-absorption phase.     

Nasal heat exchange in the giraffe and other large mammals.

The respiratory air of the giraffe is exhaled at temperatures substantially below body core temperature. As a consequence, the water content of the exhaled air is reduced to levels below that in pulmonary air, resulting in substantial reductions in respiratory water loss. Measurements under outdoor conditions showed that at an ambient air temperature of 24 degrees C, the exhaled air was 7 degrees C below body core temperature, and at ambient air temperature of 17 degrees C, the exhaled air was 13 degrees C below core temperature. The observations were extended to two additional species of wild and four species of domestic ungulates. All these animals exhaled air at temperatures below body core temperature. The average amount of water recovered due to cooling of the air during exhalation, calculated as per cent of the water loss that would occur if air were exhaled at body core temperature, amounted to between 24 and 58%, the average value for the giraffe being 56%.     

Isoprene and acetone concentration profiles during exercise on an ergometer

A real-time recording setup combining exhaled breath volatile organic compound (VOC) measurements by proton transfer reaction-mass spectrometry (PTR-MS) with hemodynamic and respiratory data is presented. Continuous automatic sampling of exhaled breath is implemented on the basis of measured respiratory flow: a flow-controlled shutter mechanism guarantees that only end-tidal exhalation segments are drawn into the mass spectrometer for analysis. Exhaled breath concentration profiles of two prototypic compounds, isoprene and acetone, during several exercise regimes were acquired, reaffirming and complementing earlier experimental findings regarding the dynamic response of these compounds reported by Senthilmohan et al (2000 Redox Rep. 5 151-3) and Karl et al (2001 J. Appl. Physiol. 91 762-70). While isoprene tends to react very sensitively to changes in pulmonary ventilation and perfusion due to its lipophilic behavior and low Henry constant, hydrophilic acetone shows a rather stable behavior. Characteristic (median) values for breath isoprene concentration and molar flow, i.e., the amount of isoprene exhaled per minute are 100 ppb and 29 nmol min(-1), respectively, with some intra-individual day-to-day variation. At the onset of exercise breath isoprene concentration increases drastically, usually by a factor of ～3-4 within about 1 min. Due to a simultaneous increase in ventilation, the associated rise in molar flow is even more pronounced, leading to a ratio between peak molar flow and molar flow at rest of ～11. Our setup holds great potential in capturing continuous dynamics of non-polar, low-soluble VOCs over a wide measurement range with simultaneous appraisal of decisive physiological factors affecting exhalation kinetics. In particular, data appear to favor the hypothesis that short-term effects visible in breath isoprene levels are mainly caused by changes in pulmonary gas exchange patterns rather than fluctuations in endogenous synthesis.     

Exhaled carbon monoxide is not elevated in patients with asthma or cystic fibrosis.

Increased levels of exhaled carbon monoxide (fractional concentration of CO in expired gas (FE,CO)), measured with an electrochemical sensor, have been reported in patients with inflammatory airway disorders, such as asthma, rhinitis and cystic fibrosis. This study aimed to evaluate these findings by using a fast-response nondisperse infrared (NDIR) analyser, and to compare these measurements with the fractional concentration of nitric oxide in exhaled air (FE,NO). Thirty-two steroid-na?ve asthmatics, 24 steroid-treated asthmatics (16 patients with allergic rhinitis, nine patients with cystic fibrosis), and 30 nonsmoking healthy controls were included. CO measurements with the NDIR analyser were performed simultaneously with nitric oxide (NO) analysis (chemiluminescence technique). After 15 s of breath-hold, single-breath exhalations over 10 s were performed at two flow rates and end-tidal plateau concentrations were registered. An electrochemical CO sensor was used independently with an exhalation to residual volume, after a 15 s breath-hold. None of the two CO analysers gave a significant increase in FE,CO in the groups of patients with inflammatory airway disorders compared to controls. FE,NO was significantly elevated in steroid-na?ve asthmatics and subjects with allergic rhinitis, but not in steroid-treated asthmatics and subjects with cystic fibrosis. Reducing exhalation flow rate by 50% gave a two-fold increase in FE,NO, while FE,CO was unaffected. A significant increase was seen in FE.CO, but not in FE,NO, when comparing with and without a 10 s breath-hold. In conclusion, the fractional concentration of carbon monoxide in expired gas was not increased in any of the patient groups, while the fractional concentration of nitric oxide in expired gas was significantly elevated in patients with steroid-na?ve asthma and allergic rhinitis. Moreover, carbon monoxide was unaffected by flow rate but increased with breath-hold, suggesting an origin in the alveoli rather than the conducting airways.     

Off-line exhaled nitric oxide measurements in children

The concentration of exhaled nitric oxide (eNO) is a useful marker of asthmatic bronchial inflammation. eNO can now be measured away from the laboratory (off-line), even in children. Short exhalation maneuvers (8 sec) and small samples (1 L) of exhaled gas are probably sufficient in children, but more information is needed about the effect of different measurement conditions. As a preliminary step before conducting epidemiological studies in schoolchildren, we investigated the effects of expiratory flow, dead space, and expiratory time on eNO concentrations collected in 1-L mylar collection bags. We studied 101 cooperative subjects (62 males) aged 5-18 years (30 healthy volunteers, 51 asthmatics, and 20 children with various other respiratory diseases) in our pulmonary function laboratory. On-line and off-line eNO were compared in a single session, and analyzed with a Sievers NOA 280 nitric oxide analyzer. For both methods of collecting expired gas, subjects did a single exhalation without breath-holding against an expiratory pressure 10 cm H(2)O. We investigated the effects of expiratory flow, dead space, and exhalation time on eNO; we also compared on-line and off-line eNO measurements, and the repeatability of both techniques at a given flow rate. Expiratory flows of 58 mL/sec provided more reproducible data than lower flows (coefficient of repeatability 1.1 ppb for 58 mL/sec vs. 2.8 for 27 mL/sec vs. 5.7 for 18 mL/sec). eNO concentrations were about 25% higher in off-line than in on-line recordings if the initial 250 mL of exhaled gas were not eliminated, and 37% higher if exhalation lasted longer (16 sec vs. 8 sec). Eliminating 250 mL of dead space and shortening the filling time to 8 sec yielded off-line eNO values close to those on-line (geometric mean off-line eNO 14.4 ppb, 95% confidence interval: 12.2-17.0) vs. on-line eNO 13.8 ppb (95% confidence interval: 11.6-16.5). On-line and off-line results were highly correlated (r = 0.996, P = 0.000) and had similar coefficients of variation (on-line eNO 2.6%, off-line 2.8%). Neither agreement nor repeatability of eNO measurements were affected by disease status or baseline FEV(1) (% predicted values). Once standardized, the off-line eNO technique using 1-L gas collection bags will provide results similar to those recorded on-line.     

Comment on 'The effect of temperature on exhaled breath condensate collection'

Vyas et al [1] reported that the collection of exhaled breath condensates (EBCs) can be increased 79% by cooling their condenser with dry ice rather than ice water. This was accompanied by what may have been a modest decrease in EBC conductivity and protein concentrations, suggesting that some but not all of the increases in EBC volume were due to the addition of water vapor to the condensate. It is possible that water vapor is trapped more readily than airway droplets at cold temperatures. Alternatively, water vapor in ambient air could have entered through the top of the condenser, which appears to be open to the atmosphere. Despite these decreases in concentration, cold temperatures do appear to increase the rates at which some airway solutes can be collected in the EBC. It should be noted that volatile constituents (e.g., NH(4)(+)?and HCO(3)(-)), normally account for ～90% of the total conductivity of EBC samples [2-5]. These ions must be removed before measuring conductivity because they are derived primarily from the oral cavity by diffusion. When we originally introduced the conductivity approach [2], the samples were freeze-dried (lyophilized) at < -50?°C and a pressure below 0.133 kPa. Lyophilization removes water molecules from ice (sublimation) rather than liquid water (evaporation). To validate this approach, we showed that more than >?99% of NH(4)(+)?in the samples was removed by lyophilization and that the ratios of plasma conductivities to those of lyophilized EBC concentrations were similar to the ratios for 2 other indicators which are used to estimate the dilution of airway droplets by water vapor, namely urea and total cations [2]. In their current study, Vyas et al [1] chose to remove volatiles from their samples by centrifugal evaporation at room temperature and a pressure of 1.3?kPa. They report conductivity values that are approximately an order of magnitude greater than those found when the samples are lyophilized and what would be expected from studies in which urea or total cations are used [2-9]. Since they failed to indicate how much NH(4)(+)?remains in their samples after evaporation or measure dilutional indicators other than conductivity, retention of some oral volatiles may have occurred, complicating interpretation of their data. Dry ice failed to significantly change nitrate/nitrite concentrations and this approach may not be particularly useful for measuring these biomarkers. Interconversion between NO(3)(-), NO(2)(-)?and their derivatives could greatly complicate interpretation of the effect of low temperatures on NO(3)(-)?and NO(2)(-)?concentrations in the EBC. Concentrations of hydrogen peroxide doubled when dry ice rather than ice water was used. This may be due in part to increased solubility of H(2)O(2)?in cold water. It is probably more appropriate to measure the rates (V(E,x) moles min(-1)) at which each of the volatile solutes (for example, x = NH(3), CO(2), NO(2), H(2)O(2)) are exhaled from the lungs than to estimate airway fluid concentrations (moles/liter). If most of the exhaled indicator is in the gas phase, V(E,x) can be calculated from the product of the expiratory flow rate and the fractional concentration of the indicator in the exhaled gas. Furthermore, it would probably be better if the rates of exhalation of volatile indicators were directly measured in the gas phase (e.g., GC-MS after droplet formation is minimized by warming the exhaled air) rather than in condensates. Most volatile substances (including water) are rapidly lost from alveolar and airway surfaces as gases rather than in airway droplets. Because gases readily diffuse between the blood and airspaces in the lungs, exhaled concentrations may reflect concentrations in the blood and extrapulmonary sites of production and may be influenced by local ventilation to perfusion ratios in the lungs. Many factors can affect the efficiency with which different volatiles are collected in condensates including: [1] the air: EBC distribution coefficients and the volume of water in the condenser during condensation, [2] temperature, flow rate and turbulence of air flow through the condenser, [3] the presence of buffers in the lungs, exhaled air and fluid lining the condenser, which is particularly important for weak acids and bases. EBCs cannot be used to estimate losses of volatile solutes from the lungs unless the rates of efflux out of the condenser in both the air and fluid dripping from the condenser are also known. In contrast to nonvolatiles excretion rates of volatiles should not be significantly affected by dilution of airway droplets by condensed water vapor. We would argue that EBC measurements should be largely confined to non-volatile indicators, using a dilutional indicator to estimate concentrations (moles L(-1)) in the airway fluid. Although excretion of nonvolatile solutes is largely from the airways and is limited by the miniscule volumes of airway fluid in the EBC, estimates of airway concentrations of nonvolatile markers are relatively immune to the multitude of variables listed above and there is no need to measure losses from the condenser. As illustrated in this study, greater cooling could presumably enhance recovery of nonvolatile EBC indicators. Alternatively, droplet formation might be augmented by intentional coughing, depth or rate of respiration, or chest vibration of one sort or another. Salivary contamination should be routinely monitored with sensitive amylase measurements. Of the greatest importance would be the development of sufficiently sensitive assays of EBC biomarkers and dilution. Acknowledgments This work was supported by the National Institutes of Health (grants HL75405 and HD51857). RC occupies the Grancel/Burns Chair in the Rehabilitative Sciences at LA Biomed. References [1] Vyas D et al 2012 The effect of temperature on exhaled breath condensate collection J. Breath Res. 6 036002 [2] Effros R M, Biller J, Foss, B, Hoagland K, Dunning M B, Castillo D, Bosbous M, Sun F and Shaker R 2003 A simple method for estimating respiratory solute dilution in exhaled breath condensates Am. J. Respir. Crit. Care Med. 168 1500-5 [3] Effros R M, Casaburi R, Su J, Dunning M, Torday J, Biller J and Shaker R 2006 The effects of volatile salivary acids and bases on exhaled breath condensate pH Am. J. Respir. Crit. Care Med. 173 386-92 [4] Effros R M, Wahlen K, Bosbous M, Castillo D, Foss B, Dunning M, Gare M, Lin W and Sun F 2002 Dilution of respiratory solutes in exhaled condensates Am. J. Respir. Crit. Care Med. 165 663-9 [5] Effros R M, Peterson B, Casaburi R, Su J, Dunning M, Torday J, Biller J and Shaker R 2005 Epithelial lining fluid solute concentrations in chronic obstructive lung disease patients and normal subjects J. Appl. Physiol. 99 1286-92 [6] Dwyer T M 2004 Sampling airway surface liquid: non-volatiles in the exhaled breath condensate Lung 182 241-50 [7] Baker E H, Clark N, Brennan A L, Fisher D A, Gyl K, Hodson M E, Philips B J, Baines D L and Wood D M 2007 Hyperglycemia and cystic fibrosis alter respiratory fluid glucose concentrations estimated by breath condensate analysis J. Appl. Physiol. 7102 1969-75 [8] Esther C R, Boysen G, Olsen B M, Collins L B, Ghio A J, Swenberg J W and Boucher R C 2009 Mass spectrometric analysis of biomarkers and dilution markers in exhaled breath condensate reveals elevated purines in asthma and cystic fibrosis Am. J. Physiol. Lung. Cell. Mol. Physiol. 296 L987-93 [9] Esther C R, Lazaar A L, Bordonali E, Qaqish B and Boucher R C 2011 Elevated airway purines in COPD Chest 140 954-60.     

Effect of thoracentesis on respiratory mechanics and gas exchange in the patient receiving mechanical ventilation

BACKGROUND: This study reports the effect of thoracentesis on respiratory mechanics and gas exchange in patients receiving mechanical ventilation. Study design: Prospective. SETTING: University hospital. PATIENTS: Eight patient receiving mechanical ventilation with unilateral (n = 7) or bilateral (n = 1) large pleural effusions. INTERVENTION: Therapeutic thoracentesis (n = 9). MEASUREMENTS: Resistances of the respiratory system measured with the constant inspiratory flow interrupter method measuring peak pressure and plateau pressure, effective static compliance of the respiratory system (Cst,rs), work performed by the ventilator (Wv), arterial blood gases, mixed exhaled Pco2, and pleural liquid pressure (Pliq). RESULTS: Thoracentesis resulted in a significant decrease in Wv and Pliq. Thoracentesis had no significant effect on dynamic compliance of the respiratory system; Cst,rs; effective interrupter resistance of the respiratory system, or its subcomponents, ohmic resistance of the respiratory system and additional (non-ohmic) resistance of the respiratory system; or intrinsic positive end-expiratory pressure (PEEPi). Indices of gas exchange were not significantly changed by thoracentesis. CONCLUSIONS: Thoracentesis in patients receiving mechanical ventilatory support results in significant reductions of Pliq and Wv. These changes were not accompanied by significant changes of resistance or compliance or by significant changes in gas exchange immediately after thoracentesis. The reduction of Wv after thoracentesis in patients receiving mechanical ventilation is not accompanied by predictable changes in inspiratory resistance and static compliance measured with routine clinical methods. The benefit of thoracentesis may be most pronounced in patients with high levels of PEEPi.     

The current single exhalation method of measuring exhales nitric oxide is affected by airway calibre.

The authors have observed that some patients with acute exacerbations of asthma do not have substantially higher levels of exhaled nitric oxide (NO). The study examined whether this could be explained by the effect of airway calibre on exhaled NO. Exhaled NO, height and forced expiratory volume in one second (FEV1) were measured in 12 steroid-naive asthmatics and 17 normal subjects. For comparison, another group of patients with airways disease (34 cystic fibrosis patients) were also studied. In 20 asthmatics (on various doses of inhaled steroids, 0-3,200 microg x day-1), exhaled NO was measured before and after histamine challenge (immediately after reaching the provocative concentration causing a 20% fall in FEV1) and in 12 of these patients, also after nebulized salbutamol to restore FEV1 to baseline. Studies were also conducted to examine possible confounding effects of repeated spirometry (as would occur in histamine challenge) and nebulized salbutamol alone in exhaled NO levels. Exhaled NO was measured using a single exhalation method with a chemiluminescence analyser at a constant flow rate and mouth pressure. There was a significant correlation between FEV1 and exhaled NO in steroid naive asthmatics (r=0.9, p<0.001) and cystic fibrosis patients (r=-0.48, p<0.05) but not in normal subjects (r=-0.13, p=0.61). Exhaled NO decreased significantly after histamine challenge and returned to baseline after bronchodilation by nebulized salbutamol (mean+/-SEM: 23.6+/-3.6 parts per billion (ppb) (prehistamine), 18.2+/-2.7 ppb (posthistamine) and 23.6+/-3.8 ppb (postsalbutamol) p=0.001). Repeated spirometry and nebulized salbutamol did not affect exhaled NO measurements significantly. Exhaled nitric oxide levels appear to be lower in circumstances of smaller airway diameter. Hence, within a subject nitric oxide levels may be artefactually decreased during bronchoconstriction. This may be caused by increased airflow velocity in constricted airways when the exhalation rate is kept constant.     

低流速法测定急性呼吸窘迫综合征静态肺压力-容积曲线的比较性实验研究

目的 探讨低流速法代替气道闭合法测定急性呼吸窘迫综合征(ARDS)静态肺压力-容积曲线的可行性.方法 采用内毒素(LPS)诱导的绵羊ARDS模型,利用低流速法和气道闭合法测定肺压力-容积曲线,并用双向直线回归法确定相应曲线低位转折点压力(Pinf), 低流速法和气道闭合法测定的Pinf分别表示为Pinfd和Pinfb.结果 Pinfd与Pinfb分别为(8.91±0.82) cm H2O与(8.59±0.78) cm H2O ,两者比较差异无显著性,具有显著相关性(r=0.93, P<0.05).相同潮气量情况下,两种方法 测定的相应气道压力呈正相关(r=0.99, P<0.005).低流速法和气道闭合法测定的肺顺应性分别为(19±7) L/cm H2O和(20±7) L/cm H2O,差异无显著性(P>0.05).低流速法测定肺压力-容积曲线的时间需3～4 min,气道闭合法需30～35 min.结论 低流速法测定肺压力-容积曲线准确安全,简便省时,可代替气道闭合法.     

Effect of smoking on exhaled nitric oxide and flow-independent nitric oxide exchange parameters.

It is a well-known fact that smoking is associated with a reduction in exhaled nitric oxide (NO) levels. There is, however, limited knowledge relating to the smoking-induced changes in production or exchange of NO in different compartments of the airways. This study comprised 221 adult subjects from the European Community Respiratory Health Survey II, who were investigated in terms of their exhaled NO, lung function, immunoglobulin E sensitisation and smoking habits. The following parameters were determined using extended NO analysis: airway tissue nitric oxide concentration (Caw,NO), airway transfer factor (or diffusing capacity) for nitric oxide (Daw,NO), alveolar nitric oxide concentration (CA,NO) and fractional exhaled nitric oxide concentration at a flow rate of 50 mL x s(-1) (FeNO,0.05). Maximum total airway nitric oxide flux (J'aw,NO) was calculated from Daw,NO(Caw,NO-CA,NO). Current smokers (n = 35) exhibited lower (geometric mean) FeNO,0.05 (14.0 versus 22.8 ppb), Caw,NO (79.0 ;versus 126 ppb) and J'aw,NO (688 versus 1,153 pL x s(-1)) than never-smokers (n = 111). Ex-smokers (n = 75) were characterised by lower FeNO,0.05 (17.7 versus 22.8 ppb) and Jaw,NO (858 versus 1,153 pL x s(-1)) than never-smokers. These relationships were maintained after adjusting for potential confounders (sex, age, height, immunoglobulin E sensitisation and forced expiratory volume in one second), and, in this analysis, a negative association was found between current smoking and CA,NO. Snus (oral moist snuff) consumption (n = 21) in ex-smokers was associated with an increase in Daw,NO and a reduction in Caw,NO, after adjusting for potential confounders. Passive smoking was associated with a higher CA,NO. Using extended nitric oxide analysis, it was possible to attribute the reduction in exhaled nitric oxide levels seen in ex- and current smokers to a lower total airway nitric oxide flux in ex-smokers and reduced airway and alveolar nitric oxide concentrations in current smokers. The association between snus (oral tobacco) use and reduced nitric oxide concentrations in the airways and increased nitric oxide transfer from the airways warrants further studies.     

Dissociation of temperature-gradient and evaporative heat loss during cold gas hyperventilation in cold-induced asthma

We examined temperature-gradient and evaporative energy losses during cold gas inhalation challenges in patients with exercise-induced asthma by using gases with similar water-carrying capacities but significantly different volume heat capacities. Seven subjects were asked to hyperventilate mixtures of 80% helium/20% oxygen (HeO2) or 80% sulfur hexafluoride/20% oxygen (SF6O2) for 5 min at a fixed target minute ventilation of 20 x FEV1 and an inspired gas temperature of 0 degrees C. Each subject equilibrated his or her lungs with the appropriate gas mixture prior to testing: PETCO2 and FIO2 were monitored and maintained at constant values (CO2 = 0.05; O2 = 0.20) by CO2 scrubbing and addition of compressed gas to the system. Gas composition, inspired and expired flow rates, and gas temperatures at the airway opening were recorded in real time using a computer-based data collection system that calculated respiratory heat loss on a per breath basis. Bronchoconstriction was quantitated using specific airway conductance measured before and serially after each challenge. The degree of bronchoconstriction correlated closely with evaporative respiratory heat loss (r = 0.658 p less than 0.05), but poorly with both temperature-gradient (r = 0.114, p greater than 0.20) and total (r = 0.268, p greater than 0.15) heat loss. These findings suggest that total respiratory heat loss is not the primary stimulus in exercise-induced asthma, and further suggest that total water loss, or focal heat/water loss, may be important in inducing bronchospasm in this subset of asthmatics.     

The effects of hyperpnea on exhaled nitric oxide synthesis in normal subjects

STUDY OBJECTIVES: To determine if the concentration of nitric oxide (NO) in the lungs increases with hyperpnea by contrasting calculated production (ie, the product of the fractional expired NO concentration [FeNO] and minute ventilation [Ve]) [Vno] with the amount of NO in equilibrium with the conducting airways (eNOair) and the amount of NO diffusing from the alveoli (eNOalv). DESIGN: Observational study. SETTING: University teaching hospital. PARTICIPANTS: Normal subjects. INTERVENTIONS: Measurements were made in 16 healthy people during and after 4 min of tidal breathing (10 L/min) and isocapnic hyperventilation of 60 L/min. MEASUREMENTS AND RESULTS: FeNO was measured by collecting the exhaled air during the last minute of each trial and passing it through a chemiluminescence analyzer. The expired NO levels in the plateau phases of slow (30 mL/s) and fast (200 mL/s) single-breath exhalations were also obtained before and after hyperventilation. The Vno (mean +/- SEM) increased from 89.8 +/- 12.3 to 329.1 +/- 36.2 nL/min as Ve rose (p < 0.001). However, neither the quantities of eNOair nor eNOalv changed with hyperventilation (eNOair range before to after, 34.9 +/- 7.7 to 30.9 +/- 6.4 parts per billion [ppb], p = 0.96; eNOalv range before to after, 7.3 +/- 1.5 to 6.5 +/- 1.1 ppb, p = 0.97). CONCLUSIONS: These data demonstrate that the amount of NO in equilibrium with the airway walls and alveoli are not altered by hyperpnea. Rather, the apparent augmentation in Vno in such circumstances appears to be an arithmetic artifact.     

Salivary contribution to exhaled nitric oxide.

Dietary and metabolic nitrate is distributed from the blood to the saliva by active uptake in the salivary glands, and is reduced to nitrite in the oral cavity by the action of certain bacteria. Since it has been reported that nitric oxide may be formed nonenzymatically from nitrite this study aimed to determine whether salivary nitrite could influence measurements of exhaled NO. Ten healthy subjects fasted overnight and ingested 400 mg potassium nitrate, equivalent to approximately 200 g spinach. Exhaled NO and nasal NO were regularly measured with a chemiluminescence technique up to 3 h after the ingestion. Measurements of exhaled NO were performed with a single-breath procedure, standardized to a 20-s exhalation, at a flow of 0.15 L x s(-1), and oral pressure of 8-10 cmH2O. Values of NO were registered as NO release rate (pmol x s(-1)) during the plateau of exhalation. Exhaled NO increased steadily over time after nitrate load and a maximum was seen at 120 min (77.0+/-15.2 versus 31.2+/-3.0 pmol x s(-1), p<0.01), whereas no increase was detected in nasal NO levels. Salivary nitrite concentrations increased in parallel; at 120 min there was a four-fold increase compared with baseline (1.56+/-0.44 versus 0.37+/-0.09 mM, p<0.05). The nitrite-reducing conditions in the oral cavity were also manipulated by the use of different mouthwash procedures. The antibacterial agent chlorhexidine acetate (0.2%) decreased NO release by almost 50% (p<0.01) 90 min after nitrate loading and reduced the preload control levels by close to 30% (p<0.05). Sodium bicarbonate (10%) also reduced exhaled NO levels, but to a somewhat lesser extent than chlorhexidine acetate. In conclusion, salivary nitric oxide formation contributes to nitric oxide in exhaled air and a large intake of nitrate-rich foods before the investigation might be misinterpreted as an elevated inflammatory activity in the airways. This potential source of error and the means for avoiding it should be considered in the development of a future standardized method for measurements of exhaled nitric oxide.