Teresa Feixas

Use of electrical impedance tomography (EIT) for the assessment of unilateral pulmonary function

We describe a fully automatable quantification process for the assessment of unilateral pulmonary function (UPF) by means of EIT and propose a measurement protocol for its clinical implementation. Measurements were performed at the fourth and sixth intercostal levels on a first group of ten healthy subjects (5M, 5F, ages 26-48 years) to define the proper protocol by evaluating the most common postures and ventilation modes. Several off-line processing tools were also evaluated, including the use of digital filters to extract the respiratory components from EIT time series. Comparative measures were then carried out on a second group consisting of five preoperatory patients with lung cancer (4M, IF, ages 25-77 years) scheduled for radionuclide scanning. Results show that measurements were best performed with the subject sitting down, holding his arms up and breathing spontaneously. As regards data processing, it is best to extract Fourier respiratory components. The mean of the healthy subject group leads to a left-right division of lung ventilation consistent with literature values (47% left lung, 53% right lung). The comparative study indicates a good correlation (r = 0.96) between the two techniques, with a mean difference of (-0.4+/-5.4)%, suggesting that the elimination of cardiac components from the thoracic transimpedance signal leads to a better estimation of UPF.

Determinación de óxido nítrico en aire espirado (FENO) mediante un equipo portátil (NIOX-MINO® Aerocrine) en población sana

La determinacion de oxido nitrico en aire espirado (FENO) es una tecnica no invasiva que se utiliza en la evaluacion clinica y el tratamiento del asma. El objetivo de este estudio ha sido determinar los valores de referencia de FENO en un grupo de voluntarios sanos mediante la utilizacion de un nuevo equipo portatil (NIOX-MINO® Aerocrine), asi como determinar el grado de relacion que presenta con el equipo de determinacion habitual en nuestro laboratorio de funcion pulmonar (sensor de quimioluminiscencia N-6008® SIR). Segun los resultados obtenidos, los valores de FENO que da el equipo portatil son siempre superiores a los que ofrece el sensor habitual, con un valor de corte de 34 ppb (media + 2 desviacion estandar). Existe un relacion directa y significativa de la determinacion de FENO entre ambos equipos (r = 0,92; p = 0,001) con un factor de correccion de: FENO (NIOX-MINO®) = 10 + 1,5 FENO (N-6008®). La relacion entre los valores de FENO y la edad, el sexo, el indice de masa corporal y los valores espirometricos no fue estadisticamente significativa.

Measuring Breathing Pattern in Patients With Chronic Obstructive Pulmonary Disease by Electrical Impedance Tomography

a b s t r a c t Background and Objective: The measurement of breathing pattern in patients with chronic obstructive pulmonary disease (COPD) by electrical impedance tomography (EIT) requires the use of a mathematical calibration model incorporating not only anthropometric characteristics (previously evaluated in healthy individuals) but probably functional alterations associated with COPD as well. The aim of this study was to analyze the association between EIT measurements and spirometry parameters, static lung volumes, and carbon monoxide diffusing capacity (DLCO) in a group of male patients to develop a calibration equation for converting EIT signals into volume signals. Materials and Methods: We measured forced vital capacity (FVC), forced expiratory volume in 1 second (FEV1), FEV1/FVC, residual volume, total lung capacity, DLCO, carbon monoxide transfer coefficient (KCO) and standard anthropometric parameters in 28 patients with a FEV1/FVC ratio of <70%. We then compared tidal volume measurements from a previously validated EIT unit and a standard pneumotachometer. Results: The mean (SD) lung function results were FVC, 72 (16%); FEV1, 43% (14%); FEV1/FVC, 42% (9%); residual volume, 161% (44%); total lung capacity, 112% (17%); DLCO, 58% (17%); and KCO, 75% (25%). Mean (SD) tidal volumes measured by the pneumotachometer and the EIT unit were 0.697 (0.181) L and 0.515 (0.223) L, respectively (P<.001). Significant associations were found between EIT measurements and CO transfer parameters. The mathematical model developed to adjust for the differences between the 2 measurements (R 2 =0.568; P<.001) was compensation factor=1.81 - 0.82 × height (m) - 0.004×KCO (%). Conclusions: The measurement of breathing pattern by EIT in patients with COPD requires the use of a previously calculated calibration equation that incorporates not only individual anthropometric characteristics but gas exchange parameters as well.

Duration of pulmonary rehabilitation to achieve a plateau in quality of life and walk test in COPD

OBJECTIVE To address the minimum duration of pulmonary rehabilitation necessary for patients with chronic obstructive pulmonary disease (COPD) to achieve a plateau in Health-Related Quality of Life (HRQL) and exercise tolerance. METHODS COPD patients with a dyspnea rating of at least 2 on the Medical Research Council scale participated in an outpatient rehabilitation program of 3 weekly sessions for 12 weeks. Measurements included HRQL and exercise tolerance 2 weeks before the program started and every 2 weeks thereafter. Patients were considered to have reached a plateau if they showed no improvement beyond 20% of the minimal important difference between 2 consecutive evaluations on HRQL score or walk tests. RESULTS Twenty-eight patients participated. The number of patients achieving stability after 8 weeks, showing continued improvement after 8 weeks, and demonstrating an erratic pattern of change was as follows: for physical function 16 (56%), 10 (37%) and 2 (7%) patients; for emotional function 22 (79%), 5 (18%) and 1 (4%); and for 6-min walk test 21 (75%), 5 (18%) and 2 (7%). More severe patients demonstrated a greater likelihood (76%) of achieving stability in physical function at 12 weeks than did less severe patients (27%; p on difference=0.003). The likelihood of stability at 12 weeks in emotional function and the 6-min walk test did not differ by severity. CONCLUSIONS A program of 3 weekly 3-h sessions of outpatient pulmonary rehabilitation program should last at least 8 weeks in order to achieve optimal HRQL and exercise tolerance for most patients.

Medición del patrón ventilatorio mediante tomografía por impedancia eléctrica en pacientes con EPOC

BACKGROUND AND OBJECTIVE The measurement of breathing pattern in patients with chronic obstructive pulmonary disease (COPD) by electrical impedance tomography (EIT) requires the use of a mathematical calibration model incorporating not only anthropometric characteristics (previously evaluated in healthy individuals) but probably functional alterations associated with COPD as well. The aim of this study was to analyze the association between EIT measurements and spirometry parameters, static lung volumes, and carbon monoxide diffusing capacity (DLCO) in a group of male patients to develop a calibration equation for converting EIT signals into volume signals. MATERIALS AND METHODS We measured forced vital capacity (FVC), forced expiratory volume in 1 second (FEV(1)), FEV(1)/FVC, residual volume, total lung capacity, DLCO, carbon monoxide transfer coefficient (KCO) and standard anthropometric parameters in 28 patients with a FEV(1)/FVC ratio of <70%. We then compared tidal volume measurements from a previously validated EIT unit and a standard pneumotachometer. RESULTS The mean (SD) lung function results were FVC, 72 (16%); FEV(1), 43% (14%); FEV(1)/FVC, 42% (9%); residual volume, 161% (44%); total lung capacity, 112% (17%); DLCO, 58% (17%); and KCO, 75% (25%). Mean (SD) tidal volumes measured by the pneumotachometer and the EIT unit were 0.697 (0.181)L and 0.515 (0.223)L, respectively (P<.001). Significant associations were found between EIT measurements and CO transfer parameters. The mathematical model developed to adjust for the differences between the 2 measurements (R(2)=0.568; P<.001) was compensation factor=1.81# - 0.82# height (m)# -0.004 x KCO (%). CONCLUSIONS The measurement of breathing pattern by EIT in patients with COPD requires the use of a previously calculated calibration equation that incorporates not only individual anthropometric characteristics but gas exchange parameters as well.

Measurement of Fraction of Exhaled Nitric Oxide With the Portable NIOX-MINO Monitor in Healthy Adults

Measurement of the fraction of exhaled nitric oxide (FENO) provides a noninvasive way to monitor asthma treatment in clinical practice. The aim of this study was to determine FENO reference values for measurements recorded with the portable NIOX MINO monitor in a group of healthy volunteers. We also assessed the association between values recorded by the portable monitor and the N-6008 chemiluminescence analyzer used in our pulmonary function laboratory. The FENO values obtained with the portable monitor were consistently higher than those recorded by the N-6008 analyzer; the cutoff value for the portable monitor was 34 ppb (mean + 2 SD). We detected a direct correlation (r=0.92) between the FENO measurements recorded by the 2 monitors (P=.001). The following equation expresses the relationship between measurements from the 2 devices: FENO(NIOX MINO) = 10 + [1.5 FENO(N-6008)]. We did not observe statistically significant correlations between FENO measurements and age, sex, body mass index, or spirometry.

Assessment of Differential Lung Function by Electrical Impedance Tomography

OBJECTIVE To compare unilateral lung function estimated by 2 methods: electrical impedance tomography (EIT) and ventilation-perfusion lung scintigraphy. PATIENTS AND METHODS This prospective clinical study was carried out in the pulmonary function laboratory of a general hospital. Twenty patients diagnosed with lung cancer (17 men and 3 women, ranging in age from 25 to 77 years) who were candidates for lung resection underwent ventilation-perfusion lung scanning breathing a radioactive gas. Differential lung function was estimated based on images taken at 2 intercostal spaces in which ventilation and perfusion were represented by changes in bioelectrical impedance. Each lungs contribution to overall respiratory function was also calculated based on scintigraphy. RESULTS The right lung contributed a mean (SD) of 54% (9%) of ventilation (range, 32%-71%) according to EIT. Scintigraphy similarly estimated the right lungs contribution to be 52% (10%) of total ventilation (range, 31%-80%) and 50% (9%) of perfusion (range, 37%-71%). The difference between the 2 estimates was not significant (t test), and the correlation coefficients between them were r=0.90 for ventilation and r=0.72 for perfusion (P< .05 in both cases). The analysis of agreement showed that the mean difference between the methods was 1.9% (95% confidence interval [CI], 10.5% to -6.8%) for ventilation and 3.4% (95% CI, 17.1% to -10.3%) for perfusion. CONCLUSIONS EIT is able to estimate differential lung function as accurately as ventilation-perfusion scintigraphy.

Determinación de la concentración de óxido nítrico alveolar en aire espirado: procedimiento y valores de referencia en personas sanas

Nitric oxide (NO) production has been described using a 2-compartment model for the synthesis and movement of NO in both the alveoli and the airways. The alveolar concentration of NO (Ca(NO)), an indirect marker of the inflammatory state of the distal portions of the lung, can be deduced through exhalation at multiple flow rates. Our objective was to determine reference values for Ca(NO). The fraction of exhaled NO (Fe(NO)) was measured in 33 healthy individuals at a rate of 50mL/s; the subjects then exhaled at 10, 30, 100, and 200mL/s to calculate Ca(NO). A chemiluminescence analyzer (NIOX Aerocrine) was used to perform the measurements. The mean (SD) Fe(NO) was 15 (6)ppb. The mean Ca(NO) was 3.04 (1.30)ppb. These values of Ca(NO) measured in healthy individuals will allow us to analyze alveolar inflammatory behavior in respiratory and systemic processes.

Monitoring of breathing pattern at rest by electrical impedance tomography

OBJECTIVE Electrical impedance tomography (EIT) involves the application of a small alternating current to produce a series of chest images that can be used to monitor breathing pattern. The relation between chest images and tidal volume has not been sufficiently validated. The aim of the present study was to analyze the correlation between EIT images and the volume-time signal measured with a pneumotachometer in 13 healthy volunteers. MATERIAL AND METHODS The following measurement devices were used: a) MedGraphics preVent Pneumotach, with special software for recording the volume-time signal (reference test), and b) EIT-4, a fourth-generation prototype unit designed by the Department of Electronic Engineering at the Universidad Politécnica de Cataluña, Spain that records the volume-time signal and produces a graphic depiction of a cross section of the thorax at the sixth intercostal space. RESULTS The mean (SD) tidal volume measured by the pneumotachometer and the EIT-4 was 0.523 (0.102) L and 0.527 (0.106) L, respectively (P value not significant). The linear correlation coefficient between the 2 measurements was 0.923 (P=.001), and the mean of the differences between the 2 procedures was -0.003 L (95% confidence interval, -0.045 to 0.038). The greatest differences were associated with female gender, body mass index, and chest circumference. In view of these differences, a different equation based on these variables was needed for calibration of the EIT-4. CONCLUSIONS The EIT-4 provides an alternative means of monitoring breathing pattern, although a number of issues related to the circumference of the rib cage need to be resolved.

Determining the Alveolar Component of Nitric Oxide in Exhaled Air: Procedures and Reference Values for Healthy Persons

Nitric oxide (NO) production has been described using a 2-compartment model for the synthesis and movement of NO in both the alveoli and the airways. The alveolar concentration of NO (CANO), an indirect marker of the inflammatory state of the distal portions of the lung, can be deduced through exhalation at multiple flow rates. Our objective was to determine reference values for CANO. The fraction of exhaled NO (FENO) was measured in 33 healthy individuals at a rate of 50 mL/s; the subjects then exhaled at 10, 30, 100, and 200 mL/s to calculate CANO. A chemiluminescence analyzer (NIOX Aerocrine) was used to perform the measurements. The mean (SD) FENO was 15 (6) ppb. The mean CANO was 3.04 (1.30) ppb. These values of CANO measured in healthy individuals will allow us to analyze alveolar inflammatory behavior in respiratory and systemic processes.