Real-time detection of nitric oxide isotopes in lung function tests.

In lung function tests, the determination of the pulmonary diffusing capacity (D) using the single-breath method is a commonly applied technique. The calculation of D is performed on the basis of accurate measurements of indicator gas concentrations. In this chapter, we demonstrate the appropriateness of the stable nitric oxide (NO) isotopes 14NO and 15NO in revealing reliable data of D. We performed studies on animals (14NO) by using respiratory mass spectrometry (M3) and on humans (15NO) by applying laser magnetic resonance spectroscopy (LMRS). The equipment was characterized by sufficient detection limits of 70 parts/billion at [14NO] = 0.001% (M3) and 40 parts/billion at [15NO] = 0.002 % (LMRS), respectively. Lastly, we were able to show that D-values for 14NO indeed reveal the entire diffusive properties of the alveolar-capillary membrane and that 15NO is a useful indicator gas for reflecting disturbances of pulmonary gas exchange.

Pulmonary diffusing capacities for oxygen-labeled CO2 and nitric oxide in rabbits.

We determined the pulmonary diffusing capacity (DL) for 18O-labeled CO2 (C18O2) and nitric oxide (NO) to estimate the membrane component of the respective gas conductances. Six anesthetized paralyzed rabbits were ventilated by a computerized ventilatory servo system. Single-breath maneuvers were automatically performed by inflating the lungs with gas mixtures containing 0.9% C18O2 or 0.05% NO in nitrogen, with breath-holding periods ranging from 0 to 1 s for C18O2 and from 2 to 8 s for NO. The alveolar partial pressures of C18O2 and NO were determined by using respiratory mass spectrometry. DL was calculated from gas exchange during inflation, breath hold, and deflation. We obtained values of 14.0 +/- 1.1 and 2.2 +/- 0.1 (mean value +/- SD) ml.mmHg-1.min-1 for DL(C18O2) and Dl(NO), respectively. The measured DL(C18O2)/DL(NO) ratio was one-half that of the theoretically predicted value according to Graham's law (6.3 +/- 0.5 vs. 12, respectively). Analyses of the several mechanisms influencing the determination of DL(C18)2 and DL(NO) and their ratio are discussed. An underestimation of the membrane diffusing component for CO2 is considered the likely reason for the low DL(C18O2)/DL(NO) ratio obtained.

Alveolar slope and dead space of He and SF6 in dogs: comparison of airway and venous loading.

Series (Fowler) dead space (VD) and slope of the alveolar plateau of two inert gases (He and SF6) with similar blood-gas partition coefficients (approximately 0.01) but different diffusivities were analyzed in 10 anesthetized paralyzed mechanically ventilated dogs (mean body wt 20 kg). Single-breath constant-flow expirograms were simultaneously recorded in two conditions: 1) after equilibration of lung gas with the inert gases at tracer concentrations [airway loading (AL)] and 2) during steady-state elimination of the inert gases continuously introduced into venous blood by a membrane oxygenator and partial arteriovenous bypass [venous loading (VL)]. VD was consistently larger for SF6 than for He, but there was no difference between AL and VL. The relative alveolar slope, defined as increment of partial pressure per increment of expired volume and normalized to mixed expired-inspired partial pressure difference, was larger by a factor of two in VL than in AL for both He and SF6. The He-to-SF6 ratio of relative alveolar slope was generally smaller than unity in both VL and AL. Whereas unequal ventilation-volume distribution combined with sequential emptying of parallel lung regions appears to be responsible for the sloping alveolar plateau during AL, the steeper slope during VL is attributed to the combined effects of continuing gas exchange and ventilation-perfusion inequality coupled with sequential emptying. The differences between He and SF6 point at the contributing role of diffusion-dependent mechanisms in intrapulmonary gas mixing.

Pulmonary diffusing capacities for nitric oxide and carbon monoxide determined by rebreathing in dogs.

Pulmonary diffusing capacities (DL) of NO and CO were determined simultaneously from rebreathing equilibration kinetics in anesthetized paralyzed supine dogs (mean body wt 20 kg) after denitrogenation (replacement of N2 by Ar). During rebreathing the dogs were ventilated in closed circuit with a gas mixture containing 0.06% NO, 0.06% 13C18O, and 1% He in Ar for 15 s, with tidal volume of 0.5 liter and frequency of 60/min. The partial pressures of NO, 13C18O, 16O18O, N2, Ar, CO2, and He in the trachea were continuously analyzed by mass spectrometry. Measurements were performed at various O2 levels characterized by the mean end-expired PO2 during rebreathing (PE'O2). In control conditions ("normoxia," PE'O2 = 67 +/- 8 Torr) the following mean +/- SD values were obtained (in ml.min-1.Torr-1): DLNO = 52.4 +/- 11.0 and DLCO = 15.4 +/- 2.9. In hypoxia (PE'O2 = 24 +/- 7 Torr) DLNO increased by 11 +/- 8% and DLCO by 19 +/- 10%, and in hyperoxia (PE'O2 = 390 +/- 26 Torr) DLNO decreased to 87 +/- 3% and DLCO to 56 +/- 8% with respect to values in normoxia. DLNO/DLCO of 3.24 +/- 0.06 (hypoxia), 3.38 +/- 0.31 (normoxia), and 5.54 +/- 1.04 (hyperoxia) were significantly higher than the NO/CO Krogh diffusion constant ratio (1.92) predicted for simple diffusion through aqueous layers. With increasing O2 uptake elicited by 2,4-dinitrophenol, DLNO and DLCO increased and DLNO/DLCO remained close to unchanged. The results suggest that the combined effects of diffusion and chemical reaction with hemoglobin limit alveolar-capillary transport of CO. If it is assumed that reaction kinetics of NO with hemoglobin (known to be extremely fast) are not rate limiting for NO uptake, the contribution of the slow chemical reaction with hemoglobin to the total CO uptake resistance (= 1/DLCO) was estimated to be 38% in hypoxia, 41% in normoxia, and 64% in hyperoxia. The various factors expected to restrict the validity of this analysis are discussed, in particular the effects of functional inhomogeneity.

Cardiogenic oscillations in He and SF6 expirograms during airway and venous loading.

Cardiogenic oscillations in the expired partial pressure profiles of two inert gases (He and SF6) were monitored in seven anesthetized paralyzed mechanically ventilated dogs. He and SF6 were administered either intravenously by a membrane oxygenator and partial arteriovenous bypass [venous loading (VL)] or by washin into lung gas [airway loading (AL)]. The single-breath expirograms obtained during constant-flow expiration after inspiration of test gas-free air displayed distinct and regular cardiogenic oscillations. The relative oscillation amplitude (ROA), calculated as oscillation amplitude divided by mixed expired-inspired partial pressure difference, was in the range of 1-8%. The ROA for both He and SF6 was approximately 4.2 times higher in VL than in AL, which indicated that among lung units that emptied sequentially in the cardiac cycle, the effects of alveolar ventilation-perfusion (VA/Q) inequality were more pronounced than those of alveolar ventilation-alveolar volume (VA/VA) inequality. In AL, He and SF6 oscillations were 180 degrees out of phase compared with CO2 and O2 oscillations and with He and SF6 oscillations in VL, which suggests that regions with low VA/VA had high VA/Q and very low Q/VA. The ROA was practically unaffected by breath holding in both AL and VL, which indicates that there was little diffusive or convective (cardiogenic) mixing between the lung units that were responsible for cardiogenic oscillations. The ROA was consistently higher for He than for SF6, and the He-to-SF6 ratio was independent of route of test gas loading, averaging 1.6 in both AL and VL. This result may be explained by laminar Taylor dispersion, whereby oscillations generated in peripheral lung regions are dissipated in inverse proportion to diffusion coefficient during transit through the proximal (larger) airways.

The overall fractionation effect of isotopic oxygen molecules during oxygen transport and utilization in humans.

The aim of the study was to clarify (1) whether fractionation effects of isotopic oxygen molecules due to respiratory processes can be neglected in tracer studies, (2) whether additional information about respiratory processes can be obtained from measuring isotope fractionations. Experiments were performed on 7 healthy humans at rest. Samples were taken from inspiratory and expiratory gas. After having removed the carbon dioxide from the samples, the oxygen was completely burnt with graphite to CO2, and the 16O18O/16O2 ratio of the CO2 generated was analysed by mass spectrometry. The 16O18O/16O2 ratio of the expiratory gas was 0.21 +/- 0.07% greater than that of the inspiratory air. The overall rate constant for uptake, subsequent transport and utilization was higher for 16O2 by 0.91 +/- 0.24% than for 16O18O. These results together with model calculations including data from literature suggest: (1) the fractionation effects between 16O18O and 16O2 as well as between 18O2 and 16O2 are small enough for both isotopic species to be considered appropriate labels in the investigation of respiratory processes, (2) the effect measured could be due to limitations of oxygen transport by utilization, (3) additional processes such as the reaction of oxygen with hemoglobin could be involved in forming the overall fractionation effect.

Fractionation of oxygen isotopes due to equilibration of oxygen with hemoglobin.

The aim of the study was to answer the question as to whether the chemical reaction of oxygen with hemoglobin exhibits a source of isotopic fractionation, which could be of significance in forming the overall fractionation effect of respiration recently determined in man. Investigations were performed on bovine hemoglobin solutions adjusted to normal values of Hb concentration and pH. After degassing in vacuo, the hemoglobin solution was equilibrated in a closed system with pure oxygen of suitable pressure so that oxygen saturation levels of 30, 50 and 100% were achieved. After complete equilibration, isotope analysis of oxygen by mass spectrometry resulted in 16O18O/16O2 ratios which were 0.35 +/- 0.02% lower in the oxygen bound to hemoglobin than that of the gas phase during all levels of oxygenation. Model calculations suggest the following: (1) the fractionation during oxygen uptake in the lung at rest is primarily determined by the reaction with hemoglobin, (2) the overall fractionation effect of respiration can be explained as due to single effects of the constituent processes when assuming the oxygen transport to be limited by utilization.

Assessment of stratified inhomogeneity within distal alveolar space with respect to oxygen uptake.

Investigations were made as to whether or not there is a limitation of oxygen transport by stratified inhomogeneity in distal alveolar gas. Experiments were performed on 2 subjects. Single breath manoeuvres were carried out with similar phases of inspiration and expiration but varying breath-hold times. The inspiratory gas contained a small amount of oxygen labeled carbon dioxide, C18O2. End-expiratory gas was analysed on its residual C18O2 partial pressure by mass spectrometry. For evaluating a stratificational conductance, compartment model analysis was applied on the breath-hold data. Stratificational conductance has been found to be higher than 553 ml.mmHg-1. min-1. When transferred to oxygen transport, this means that stratificational conductance is more than 10 times higher than oxygen diffusing capacity. It can be concluded that (i) stratified inhomogeneity in distal alveolar space does not exhibit a limiting factor of oxygen uptake in lungs, (ii) a contribution of stratificational effects to sloping alveolar plateau is expected to be of minor importance.

Investigation of the human oxygen transport system during conditions of rest and increased oxygen consumption by means of fractionation. Effects of oxygen isotopes.

The aim of the study was to assess various pathways of the oxygen transport system at rest and ergometer work by the utility of information derivable from different behaviour of the isotopic oxygen molecules 16O2 and 16O18O during transport. 6 healthy humans were studied at rest and at different levels of ergometer work, ranging from 50 to 250 W. Isotope analysis was performed by applying a reference technique. Samples of inspiratory and expiratory gas, taken during steady state conditions, were analysed by a respiratory mass spectrometer on their 16O18O/16O2 ratios by comparing them with a reference gas of appropriate composition. Ventilatory minute volume, oxygen consumption and end-expiratory oxygen partial pressure were also measured. At rest, the delta IU-value quantifying the isotope effect of the overall oxygen transport amounted to 0.74 +/- 0.08%. During ergometer work, the fractionation factor steadily decreased with increasing oxygen consumption, yielding the regression line delta IU [%] = 0.74 -1.3.10(-4).VO2, where VO2 is oxygen consumption given in ml/min. With respect to oxygen transport from inspiratory gas to tissue, this result suggests: convective processes of oxygen transport become more limiting with increasing oxygen consumption, whereas diffusion does not become a major limiting step up to oxygen consumption rates of 3600 ml/min, otherwise a reverse relationship between fractionation factor and oxygen consumption should have been found.

Dependency of overall fractionation effect of respiration on hemoglobin concentration within blood at rest.

In this study it was investigated in which way varying hemoglobin concentrations within blood influence overall fractionation effect of respiration, meaning a change in composition of isotopic oxygen molecules 16O2 and 16O18O within oxygen transported during entire respiration. Since overall fractionation effect of respiration is known to consist of different fractionating and non-fractionating processes, measuring it under condition of anemia could be useful in relating changes in isotopic compositions of oxygen to limitations of entire oxygen transport caused by one or more of these processes. Experiments were performed on 6 patients suffering from various degrees of anemia of a variety of etiologies and on 6 healthy humans. All test subjects breathed air at rest. Samples from inspiratory and expiratory gas were taken in order to analyse 16O18O/16O2 ratios with the aid of respiratory mass spectrometry. Values of overall fractionation effect decreased with respect to a drop in hemoglobin concentration from 17.6 to 6.6 g/100 ml in terms of a linear relationship (r = 0.79) provided that values of overall fractionation effect were normalized so as to exclude the influence of varying ventilatory conditions. It could be shown that at a value of hemoglobin content of 6.6 g/100 ml, 16O2 was transported in preference to 16O18O with a 0.57% higher rate compared to a value of 0.78% obtained at a hemoglobin concentration of 17.6 g/100 ml.(ABSTRACT TRUNCATED AT 250 WORDS)

Cardiogenic oscillations of He and SF6 in expired gas in dogs.

Quantitative analysis of cardiogenic oscillations of He and SF6 during airway and venous loading demonstrated that both VA/Q and VA/VA inequalities were involved in the lung gas inhomogeneity producing cardiac oscillations in the expirogram. Both inequalities were coupled in such a manner that low VA/Q units had high VA/VA. The oscillations were modified in conducting airways where SF6 oscillations were attenuated more than He oscillations, probably by laminar Taylor dispersion.

Functional inhomogeneities in interstitial lung disease, assessed using (16)o(18)o.

Abstract We investigated the contribution of diffusion limitation and functional inhomogeneities to the impairment of pulmonary oxygen (O(2)) transfer in interstitial lung disease (ILD). Analyses of (16)O(18)O/(16)O(2) ratios were performed on expiratory gas mixtures obtained from 6 ILD patients and 6 healthy humans at rest, applying respiratory mass spectrometry. We assessed O(2) transport by using the overall fractionation factor of respiration (α(0)) which is predicted to increase in the case of diffusion limitation. α(0) was reduced in patients (1.0065±3.10(-4)) when compared to the value for healthy subjects (1.0071±7.10(-4), P <0.05), pointing away from a diffusion limitation of O(2) transport. On the basis of a two-compartment model we interpreted our findings by assuming an unequal distribution of diffusion and convective O(2) transport in the pulmonary gas exchange of the patients.

Model analysis on alveolar-capillary O2 equilibration during exercise.

The present article was aimed at determining the alveolar-capillary PO2 difference (deltaP(AcO2)) during exercise. The working hypothesis was that values of the pulmonary NO diffusing capacity can be used to calculate (deltaP(AcO2)) data on the basis of well-known laws of pulmonary gas exchange. For this purpose, we analysed the pertinent data of three studies performed on 35 healthy, non-athletic non-smokers of similar age at seven different exercise intensities. Calculated mean values of alveolar-capillary PO2 difference aggravated from deltaP(AcO2) at rest to (deltaP(AcO2))=18 mmHg at a performance capacity amounting to 90% of the maximum level. Regression analysis revealed (deltaP(AcO2))=0.31* (V O2/V O2 max)2 at a very high significance level (n=7, r=0.999, P<0.0000082). Due to the non-linear increase of (deltaP(AcO2)) with inclining O(2) consumption, our model analysis confirms the opinion that pulmonary diffusion decreasingly determines maximal aerobic power.

Determination of alveolar-capillary O2 partial pressure gradient by using 15NO.

We propose an approach for determining the alveolar-mean capillary oxygen (O(2)) partial pressure gradient to evaluate the efficiency of O(2) equilibration between alveolar space and pulmonary capillary blood. For this purpose, measurements of the pulmonary [(15)N]nitric oxide diffusing capacity are to be interpolated into the recording of O(2) consumption. We expect the O(2) partial pressure gradient amounting to 3.3 mmHg for breathing room air at rest, a third of that commonly given. The simplicity of our method allows its application to children or even artificially ventilated patients. Therefore, it will enable a new insight into pulmonary O(2) equilibration.

Pre and post operative occupational therapy for a toe to hand transplantation.

Thumb loss is a significant disability for the hand. This paper describes a traumatic thumb injury and amputation after which the occupational therapist placed an orthotic device to substitute for the thumb. When the patient was undecided about a proposed toe-to-hand transplant, the occupational therapist fabricated a mold of the toe, and attached it to the patient's hand. After training with the mold, the patient was ready to accept the toe-to-hand transplant. The post transplant occupational therapy program and patient's return to work was described.