An algebraic solution to dead space determination according to Fowler's graphical method

A simplified 4-parameter model of volumetric capnograms improves calculations of airway dead space and slope of Phase III

To evaluate a compact and easily interpretable 4-parameter model describing the shape of the volumetric capnogram, and the resulting estimates of anatomical dead space (VD_AW) and Phase III (alveolar plateau) slope (S_III). Data from of 8 mildly-endotoxemic pre-acute respiratory distress syndrome sheep were fitted to the proposed 4-parameter model (4p) and a previously established 7-parameter model (7p). Root mean square error (RMSE) and Akaike information criterion (AIC), as well as VD_AW and S_III derived from each model were compared. Confidence intervals for model's parameters, VD_AW and S_III were estimated with a jackknife approach. RMSE values were similar (4p: 1.13 ± 0.01 mmHg vs 7p: 1.14 ± 0.01 mmHg) in the 791 breath cycles tested. However, the 7p overfitted the curve and had worse AIC in more than 50% of the cycles (p < 0.001). The large number of degrees of freedom also resulted in larger between-animal range of confidence intervals for 7p (VD_AW: from 6.1 10^-12 to 34 ml, S_III: from 9.53 10^-7 to 1.80 mmHg/ml) as compared to 4p (VD_AW: from 0.019 to 0.15 ml, S_III: from 3.9 10^-4 to 0.011 mmHg/ml). Mean differences between VD_AW (2.1 ± 0.04 ml) and S_III (0.047 ± 0.004 mmHg/ml) from 7 and 4p were significant (p < 0.001), but within the observed cycle-by-cycle variability. The proposed 4-parameter model of the volumetric capnogram improves data fitting and estimation of VD_AW and S_III as compared to the 7-parameter model of reference. These advantages support the use of the 4-parameter model in future research and clinical applications.

Effects of pulmonary inhalation on hyperpolarized krypton-83 magnetic resonance T1 relaxation

The (83)Kr magnetic resonance (MR) relaxation time T(1) of krypton gas in contact with model surfaces was previously found to be highly sensitive to surface composition, surface-to-volume ratio, and surface temperature. The work presented here explored aspects of pulmonary (83)Kr T(1) relaxation measurements in excised lungs from healthy rats using hyperpolarized (hp) (83)Kr with approximately 4.4% spin polarization. MR spectroscopy without spatial resolution was applied to the ex vivo lungs that actively inhale hp (83)Kr through a custom designed ventilation system. Various inhalation schemes were devised to study the influence of anatomical dead space upon the measured (83)Kr T(1) relaxation times. The longitudinal (83)Kr relaxation times in the distal airways and the respiratory zones were independent of the lung inhalation volume, with T(1) = 1.3 s and T(1) = 1.0 s, depending only on the applied inhalation scheme. The obtained data were highly reproducible between different specimens. Further, the (83)Kr T(1) relaxation times in excised lungs were unaffected by the presence of up to 40% oxygen in the hp gas mixture. The results support the possible importance of (83)Kr as a biomarker for evaluating lung function.

Fractionated exhaled breath condensate collection shows high hydrogen peroxide release in the airways

BACKGROUND

Exhaled breath condensate (EBC) allows noninvasive monitoring of inflammation in the lung. Activation of inflammatory cells results in an increased production of reactive oxygen species, leading to the formation of hydrogen peroxide (H(2)O(2)). In addition, cigarette smoking causes an influx of inflammatory cells, and higher levels of H(2)O(2) have been found in EBC of smokers. However, there are still unresolved issues reflected by large variations in exhaled H(2)O(2) and uncertainties about the origin of H(2)O(2) release in the lung.

METHODS

We collected EBC as fractionated samples from the airways and from the lung periphery in 10 nonsmokers, eight asymptomatic smokers, and in eight chronic obstructive pulmonary disease (COPD) patients, and H(2)O(2) concentration and acidity (pH) were analyzed in the airway and the alveolar fraction.

RESULTS

In all subjects studied, H(2)O(2) was 2.6 times higher in the airway versus the alveolar fraction. Airway H(2)O(2) was twofold higher in smokers and fivefold higher in COPD patients compared to nonsmokers. In all study groups, there was no significant difference in deaerated pH between the airway and the alveolar sample.

CONCLUSIONS

Exhaled H(2)O(2) is released at higher concentrations from the airways of all subjects studied, implying that the airways may be the dominant location of H(2)O(2) production. Because many lung diseases cause inflammation at different sites of the lung, fractionated sampling of EBC can reduce variability and maintain an anatomical allocation of the exhaled biomarkers.

Hyperpolarized 83Kr MRI of lungs

Hyperpolarized (hp) (83)Kr (spin I=9/2) is a promising gas-phase contrast agent that displays sensitivity to the surface chemistry, surface-to-volume ratio, and surface temperature of the surrounding environment. This proof-of-principle study demonstrates the feasibility of ex vivo hp (83)Kr magnetic resonance imaging (MRI) of lungs using natural abundance krypton gas (11.5% (83)Kr) and excised, but otherwise intact, rat lungs located within a custom designed ventilation chamber. Experiments comparing the (83)Kr MR signal intensity from lungs to that arising from a balloon with no internal structure inflated to the same volume with krypton gas mixture suggest that most of the observed signal originated from the alveoli and not merely the conducting airways. The (83)Kr longitudinal relaxation times in the rat lungs ranged from 0.7 to 3.7s but were reproducible for a given lung. Although the source of these variations was not explored in this work, hp (83)Kr T(1) differences may ultimately lead to a novel form of MRI contrast in lungs. The currently obtained 1200-fold signal enhancement for hp (83)Kr at 9.4T field strength is found to be 180 times below the theoretical upper limit.

Uptake of Ozone in Human Lungs and Its Relationship to Local Physiological Response

To investigate whether intersubject variations in the dose of inhaled ozone (O(3)) cause corresponding variations in the physiological response, 28 female and 32 male nonsmokers participated in a 1-h continuous inhalation of clean air or 0.25 ppm O(3) while exercising on a cycle ergometer at a constant ventilation rate of 30 L/min. The exposure protocols included continuous monitoring of respiratory flow rate and O(3) concentration from which O(3) uptake (OZU) and fractional uptake efficiency (UE) were computed. Pre-to-post changes in forced expired volume in 1 s (%DeltaFEV(1)), peripheral cross section for carbon dioxide diffusion (%Delta A(P)), and Fowler dead space volume (V(D)) were also measured for each exposure. Individual values of UE ranged from .70 to .98 among all the subjects, with significant differences (p<.05) existing between men and women. These intersubject differences were inversely correlated with breathing frequency and directly correlated with tidal volume. The mean +/- SD values of %Delta FEV(1), %Delta A(P), and %Delta V(D) were all significantly more negative in the O(3) exposure session (-13.31 +/- 13.40, -8.14 +/- 7.62, and -4.20 +/- 5.12, respectively) than in the air exposure session (-0.06 +/- 4.56, 0.22 +/- 10.82, and -0.70 +/- 6.88, respectively). Finally, our results showed that neither %DeltaFEV(1) nor %Delta V(D) was correlated OZU, whereas there was a significant relationship (rho = -0.325, p = .0257) between %Delta A(P) and OZU. We conclude that the overall uptake of O(3) is a weak predictor of intersubject variations in distal airspace response, but is not a predictor of intersubject variations in conducting airway responses.

Implementation of Fowler's method for end-tidal air sampling

The design, realization and testing of a CO(2)-triggered breath sampler, capable of a separate collection of dead space and end-tidal air on multiple breaths, is presented. This sampling procedure has advantages in terms of the sample volume, insights regarding the origin of compounds, increased reproducibility and higher concentrations of compounds. The high quality of design and the speed of the components ensure a breath-by-breath estimate of dead volume, as well as the comfort and safety of the subject under test. The system represents a valid tool to contribute to the development of a standardized sampling protocol needed to compare results obtained by the various groups in this field.

Unevenness of ventilation assessed by the expired CO(2) gas volume versus V(T) curve in asthmatic patients

Recently, we have shown that the expired CO2 gas volume versus tidal volume (VCO2-VT) curve is a useful tool for assessing unevenness of ventilation because it allows the separation of tidal volume into three functional compartments: (a) the CO2-free expired air (V0), (b) the transitional volume (Vtr), (c) the alveolar volume (VA) and the measurement of alveolar FCO2 during resting breathing in normal subjects and patients with COPD. In this paper, we have investigated whether changes pertaining to unevenness of ventilation taking place immediately after the administration of methacholine can be assessed using the VCO2-VT curve in asthmatic patients. The VCO2-VT curve was obtained during tidal breathing from 16 stable asthmatic patients who underwent a methacholine challenge test. It has been found that the Vtr, and hence Bohr's dead space (VD,Bohr = V0 + Vtr), over tidal volume ratios were significantly increased immediately after the methacholine administration, whilst the V0 over tidal volume ratio was not affected. The change of the above ratios was not related to the percentage decrease of FEV1.0 following methacholine administration.

Effects of ventilation on the collection of exhaled breath in humans

A computerized system has been developed to monitor tidal volume, respiration rate, mouth pressure, and carbon dioxide during breath collection. This system was used to investigate variability in the production of breath biomarkers over an 8-h period. Hyperventilation occurred when breath was collected from spontaneously breathing study subjects ( n = 8). Therefore, breath samples were collected from study subjects whose breathing were paced at a respiration rate of 10 breaths/min and whose tidal volumes were gauged according to body mass. In this “paced breathing” group ( n = 16), end-tidal concentrations of isoprene and ethane correlated with end-tidal carbon dioxide levels [Spearman's rank correlation test ( rs) = 0.64, P = 0.008 and rs = 0.50, P = 0.05, respectively]. Ethane also correlated with heart rate ( rs = 0.52, P < 0.05). There was an inverse correlation between transcutaneous pulse oximetry and exhaled carbon monoxide ( rs = -0.64, P = 0.008). Significant differences were identified between men ( n = 8) and women ( n = 8) in the concentrations of carbon monoxide (4 parts per million in men vs. 3 parts per million in women; P = 0.01) and volatile sulfur-containing compounds (134 parts per billion in men vs. 95 parts per billion in women; P = 0.016). There was a peak in ethanol concentration directly after food consumption and a significant decrease in ethanol concentration 2 h later ( P = 0.01; n = 16). Sulfur-containing molecules increased linearly throughout the study period (β = 7.4, P < 0.003). Ventilation patterns strongly influence quantification of volatile analytes in exhaled breath and thus, accordingly, the breathing pattern should be controlled to ensure representative analyses.

Differential contribution of dead space ventilation and low arterial pCO2 to exercise hyperpnea in patients with chronic heart failure secondary to ischemic or idiopathic dilated cardiomyopathy

In chronic heart failure (CHF), the abnormally large ventilatory response to exercise (VE/VCO(2) slope) has 2 conceptual elements: the requirement of restraining arterial partial pressure of carbon dioxide (pCO(2)) from increasing (because of an increased ratio between increased physiologic dead space and tidal volume [VD/VT]) and the depression of arterial pCO(2) by further increased ventilation, which necessarily implies an important non-carbon dioxide stimulus to ventilation. We aimed to assess the contribution of these 2 factors in determining the elevated VE/VCO(2) slope in CHF. Thirty patients with CHF underwent cardiopulmonary exercise testing (age 65 +/- 11 years, left ventricular ejection fraction 34 +/- 15%, peak oxygen uptake 15.2 +/- 4 ml/kg/min, VE/VCO(2) slope 36.4). At rest and during exercise, arterial pCO(2) was measured and VD was calculated and separated into serial and alveolar components. VD/VT decreased from 0.57 at rest to 0.44 at peak exercise (p <0.01). VE/VCO(2) slope was correlated with peak exercise VD/VT (r = 0.67), the serial VD/VT ratio (r = 0.64), and alveolar VD/VT ratio (r = 0.51) at peak exercise (all p <0.01). VE/VCO(2) slope was also correlated with arterial pCO(2) (r = -0.75, p <0.001). Despite this, arterial pCO(2) was not related to peak oxygen uptake (r = 0.2) or to arterial lactate (r = -0.25) and only weakly to New York Heart Association functional class (F = 3.7). First, the increased VE/VCO(2) slope was caused by both the high VD/VT ratio and by other mechanisms, as shown by low arterial pCO(2) during exercise. Second, this latter component (depression of arterial pCO(2)) was not related to conventional measures of heart failure severity.