Tidal expired airflow patterns in adults with airway obstruction

Pediatric population with cystic fibrosis in the centre of Portugal: candidates for new therapies

OBJECTIVES

Cystic fibrosis (CF) is a severe autosomal recessive disease that results from mutations in a gene encoding the Cystic Fibrosis Transmembrane Conductance Regulator (CFTR) protein, a chloride channel. This study aims to characterize the clinical and genetic features of a cohort of pediatric people with CF (PwCF) in the center of Portugal and to determine which ones are candidates for the new drugs modulating the CFTR channel.

METHODS

A review of the demographic, genetic and clinical characteristics of PwCF undergoing follow-up at a CF reference center was carried out.

RESULTS

Twenty-three PwCF (12 male), with a median age of 12 years, were followed up. All patients carry the F508del mutation in at least one allele. Fifteen PwCF were F508del-homozygous, median BMI z-score was -0.13, all are pancreatic insufficient and median FEV1 value was 78.1%. These PwCF are eligible for dual therapy (lumacaftor/tezacaftor+ivacaftor) and for triple therapy (tezacaftor+ivacaftor+elexacaftor). PwCF with 711 +1G->T (n = 2), 2184insA (n = 1) mutations and a novel mutation c.3321dup (n = 1) have minimal function mutation and patients with a residual function mutation: R334W (n = 3) and P5L (n = 1) have a less severe phenotype. All these patients, because they also carry F508del mutation, are elegible to triple therapy.

CONCLUSIONS

Genetic and molecular characterization of PwCF poses an important step not just for CF diagnosis and prognosis which is tightly correlated with the clinical phenotype, but also for the eligibility of CFTR modulator drugs.

Tidal breathing flow profiles during sleep in wheezing children measured by impedance pneumography

For the first time, impedance pneumography (IP) enables a continuous analysis of the tidal breathing flow volume (TBFV), overnight. We studied how corticosteroid inhalation treatments, sleep stage, and time from sleep onset modify the nocturnal TBFV profiles of children. Seventy children, 1-5 years old and with recurrent wheezing, underwent three, full-night TBFVs recordings at home, using IP. The first recorded one week before ending a 3-months inhaled corticosteroids treatment, and remaining two, 2 and 4 weeks after treatment. TBFV profiles were grouped by hour from sleep onset and estimated sleep stage. Compared with on-medication, the off-medication profiles showed lower volume at exhalation peak flow, earlier interruption of expiration, and less convex middle expiration. The differences in the first two features were significant during non-rapid eye movement (NREM), and the differences in the third were more prominent during REM after 4 h of sleep. These combinations of TBFV features, sleep phase, and sleep time potentially indicate airflow limitation in young children.

Classification of Tidal Breathing Airflow Profiles Using Statistical Hierarchal Cluster Analysis in Idiopathic Pulmonary Fibrosis

In idiopathic pulmonary fibrosis (IPF) breathing pattern changes with disease progress. This study aims to determine if unsupervised hierarchal cluster analysis (HCA) can be used to define airflow profile differences in people with and without IPF. This was tested using 31 patients with IPF and 17 matched healthy controls, all of whom had their lung function assessed using spirometry and carbon monoxide CO transfer. A resting tidal breathing (RTB) trace of two minutes duration was collected at the same time. A Euclidian distance technique was used to perform HCA on the airflow data. Four distinct clusters were found, with the majority (18 of 21, 86%) of the severest IPF participants (Stage 2 and 3) being in two clusters. The participants in these clusters exhibited a distinct minute ventilation (p < 0.05), compared to the other two clusters. The respiratory drive was greatest in Cluster 1, which contained many of the IPF participants. Unstructured HCA was successful in recognising different airflow profiles, clustering according to differences in flow rather than time. HCA showed that there is an overlap in tidal airflow profiles between healthy RTB and those with IPF. The further application of HCA in recognising other respiratory disease is discussed.

Expiratory Flow Limitation During Mechanical Ventilation

Expiratory flow limitation (EFL) is present when the flow cannot rise despite an increase in the expiratory driving pressure. The mechanisms of EFL are debated but are believed to be related to the collapsibility of small airways. In patients who are mechanically ventilated, EFL can exist during tidal ventilation, representing an extreme situation in which lung volume cannot decrease, regardless of the expiratory driving forces. It is a key factor for the generation of auto- or intrinsic positive end-expiratory pressure (PEEP) and requires specific management such as positioning and adjustment of external PEEP. EFL can be responsible for causing dyspnea and patient-ventilator dyssynchrony, and it is influenced by the fluid status of the patient. EFL frequently affects patients with COPD, obesity, and heart failure, as well as patients with ARDS, especially at low PEEP. EFL is, however, most often unrecognized in the clinical setting despite being associated with complications of mechanical ventilation and poor outcomes such as postoperative pulmonary complications, extubation failure, and possibly airway injury in ARDS. Therefore, prompt recognition might help the management of patients being mechanically ventilated who have EFL and could potentially influence outcome. EFL can be suspected by using different means, and this review summarizes the methods to specifically detect EFL during mechanical ventilation.

Tidal breathing patterns derived from structured light plethysmography in COPD patients compared with healthy subjects

PURPOSE

Differences in tidal breathing patterns have been reported between patients with chronic obstructive pulmonary disease (COPD) and healthy individuals using traditional measurement techniques. This feasibility study examined whether structured light plethysmography (SLP) - a noncontact, light-based technique - could also detect differences in tidal breathing patterns between patients with COPD and healthy subjects.

PATIENTS AND METHODS

A 5 min period of tidal (quiet) breathing was recorded in each patient with COPD (n=31) and each healthy subject (n=31), matched for age, body mass index, and sex. For every participant, the median and interquartile range (IQR; denoting within-subject variability) of 12 tidal breathing parameters were calculated. Individual data were then combined by cohort and summarized by its median and IQR.

RESULTS

After correction for multiple comparisons, inspiratory time (median tI) and its variability (IQR of tI) were lower in patients with COPD (p<0.001 and p<0.01, respectively) as were ratios derived from tI (tI/tE and tI/tTot, both p<0.01) and their variability (p<0.01 and p<0.05, respectively). IE50SLP (the ratio of inspiratory to expiratory flow at 50% tidal volume calculated from the SLP signal) was higher (p<0.001) in COPD while SLP-derived time to reach peak tidal expiratory flow over expiratory time (median tPTEFSLP/tE) was shorter (p<0.01) and considerably less variable (p<0.001). Thoraco-abdominal asynchrony was increased (p<0.05) in COPD.

CONCLUSION

These early observations suggest that, like traditional techniques, SLP is able to detect different breathing patterns in COPD patients compared with subjects with no respiratory disease. This provides support for further investigation into the potential uses of SLP in assessing clinical conditions and interventions.

Reliability of breath by breath spirometry and relative flow-time indices for pulmonary function testing in horses

Background

Respiratory problems are common in horses, and are often diagnosed as a cause of poor athletic performance. Reliable, accurate and sensitive spirometric tests of airway function in resting horses would assist with the diagnosis of limitations to breathing and facilitate investigations of the effects of various treatments on breathing capacity. The evaluation of respiratory function in horses is challenging and suitable procedures are not widely available to equine practitioners. The determination of relative flow or flow-time measures is used in paediatric patients where compliance may limit conventional pulmonary function techniques. The aim of the current study was to characterise absolute and relative indices of respiratory function in healthy horses during eupnoea (tidal breathing) and carbon dioxide (CO₂)-induced hyperpnoea (rebreathing) using a modified mask pneumotrachographic technique well suited to equine practice, and to evaluate the reliability of this technique over three consecutive days. Coefficients of variation, intra-class correlations, mean differences and 95% confidence intervals across all days of testing were established for each parameter.

Results

The technique provided absolute measures of respiratory function (respiratory rate, tidal volume, peak inspiratory and expiratory flows, time to peak flow) consistent with previous studies and there was no significant effect of day on any measure of respiratory function. Variability of measurements was decreased during hyperpnea caused by rebreathing CO₂, but a number of relative flow-time variables demonstrated good agreement during eupnoeic respiration.

Conclusions

The technique was well tolerated by horses and study findings suggest the technique is suitable for evaluation of respiratory function in horses. The use of relative flow-time variables provided reproducible (consistent) results, suggesting the technique may be of use for repeated measures studies in horses during tidal breathing or rebreathing.

Electronic supplementary material

The online version of this article (doi:10.1186/s12917-016-0893-3) contains supplementary material, which is available to authorized users.

Tidal breathing flow measurement in awake young children by using impedance pneumography

Characteristics of tidal breathing (TB) relate to lung function and may be assessed even in young children. Thus far, the accuracy of impedance pneumography (IP) in recording TB flows in young children with or without bronchial obstruction has not been evaluated. The aim of this study was to evaluate the agreement between IP and direct flow measurement with pneumotachograph (PNT) in assessing TB flow and flow-derived indices relating to airway obstruction in young children. Tidal flow was recorded for 1 min simultaneously with IP and PNT during different phases of a bronchial challenge test with methacholine in 21 wheezy children aged 3 to 7 years. The agreement of IP with PNT was found to be excellent in direct flow signal comparison, the mean deviation from linearity ranging from 2.4 to 3.1% of tidal peak inspiratory flow. Methacholine-induced bronchoconstriction or consecutive bronchodilation induced only minor changes in the agreement. Between IP and PNT, the obstruction-related tidal flow indices were equally repeatable, and agreement was found to be high, with intraclass correlation coefficients for T PTEF/T E, V PTEF/V E, and parameter S being 0.94, 0.91, and 0.68, respectively. Methacholine-induced changes in tidal flow indices showed significant associations with changes in mechanical impedance of the respiratory system assessed by the oscillometric technique, with the highest correlation found in V PTEF/V E (r = -0.54; P < 0.005 and r = -0.55; P < 0.005 by using IP or PNT, respectively). The results indicate that IP can be considered as a valid method for recording tidal airflow profiles in young children with wheezing disorders.

Reducing the airflow waveform distortions from breathing style and body position with improved calibration of respiratory effort belts

Background

Respiratory effort belt measurement is a widely used method to monitor respiration. Signal waveforms of respiratory volume and flow may indicate pathological signs of several diseases and, thus, it would be highly desirable to predict them accurately. Calibrated effort belts are sufficiently accurate for estimating respiratory rate, but the respiratory volume and flow prediction accuracies degrade considerably with changes in the subject’s body position and breathing style.

Methods

An improved calibration method of respiratory effort belts is presented in this paper. It is based on an optimally trained FIR (Finite Impulse Response) filter bank constructed as a MISO system (Multiple-Input Single-Output) between respiratory effort belt signals and the spirometer in order to reduce waveform errors. Ten healthy adult volunteers were recruited. Breathing was varied between the following styles: metronome-guided controlled breathing rate of 0.1 Hz, 0.15 Hz, 0.25 Hz and 0.33 Hz, and a free rate that was felt normal by each subject. Body position was varied between supine, sitting and standing. The proposed calibration method was tested against these variations and compared with the state-of-the-art methods from the literature.

Results

Relative waveform error decreased 60-70% when predicting airflow under changing breathing styles. The coefficient of determination R² varied between 0.88-0.95 and 0.65-0.79 with the proposed and the standard method, respectively. Standard deviation of respiratory volume error decreased even 80%. The proposed method outperformed other methods.

Conclusions

Results show that not only the respiratory volume can be computed more precisely from the predicted airflow, but also the flow waveforms are very accurate with the proposed method. The method is robust to breathing style changes and body position changes improving greatly the accuracy of the calibration of respiratory effort belts over the standard method. The enhanced accuracy of the belt calibration offers interesting opportunities, e.g. in pulmonary and critical care medicine when objective measurements are required.

A pilot study quantifying the shape of tidal breathing waveforms using centroids in health and COPD

During resting tidal breathing the shape of the expiratory airflow waveform differs with age and respiratory disease. While most studies quantifying these changes report time or volume specific metrics, few have concentrated on waveform shape or area parameters. The aim of this study was to derive and compare the centroid co-ordinates (the geometric centre) of inspiratory and expiratory flow-time and flow-volume waveforms collected from participants with or without COPD. The study does not aim to test the diagnostic potential of these metrics as an age matched control group would be required. Twenty-four participants with COPD and thirteen healthy participants who underwent spirometry had their resting tidal breathing recorded. The flow-time data was analysed using a Monte Carlo simulation to derive the inspiratory and expiratory flow-time and flow-volume centroid for each breath. A comparison of airflow waveforms show that in COPD, the breathing rate is faster (17 ± 4 vs 14 ± 3 min(-1)) and the time to reach peak expiratory flow shorter (0.6 ± 0.2 and 1.0 ± 0.4 s). The expiratory flow-time and flow-volume centroid is left-shifted with the increasing asymmetry of the expired airflow pattern induced by airway obstruction. This study shows that the degree of skew in expiratory airflow waveforms can be quantified using centroids.

FEV(6) as screening tool in spirometric diagnosis of obstructive airway disease

Context:

The use of spirometry is currently limited to the diagnosis of obstructive airway disease for tertiary centers mainly because of the unmet need for technical expertise and funding. Use in primary care asks for a simpler and cost-effective screening tool for obstructive airway disease.

Aim:

To estimate the efficacy of FEV₆ against the current standard of FVC in the spirometric diagnosis of obstructive airway disease.

Setting and Design:

The Pulmonary Function Laboratory of a tertiary care hospital in Coastal South India. It was a descriptive study.

Materials and Methods:

We analyzed 150 serial patients on ATS standardized spirometers. The patients were classified into normal subjects and those with airway obstruction, further categorized as mild, moderate and severe and those with mixed defect. Those with obstruction were also classified as having reversible and irreversible defects.

Statistical Analysis:

Data was analyzed using SPSS Software (v.11.5), statistical test ANOVA and Pearson correlation was done and P less than 0.05 considered statistically significant.

Results:

FVC and FEV₆ showed a linear correlation in all subjects. The difference in means was statistically significant in all subjects. The sensitivity and specificity of FEV₁/FEV₆ in comparison to FEV₁/FVC were both found to be 100%.

Conclusion:

FEV₆ is an excellent screening tool in the diagnosis of airway obstruction but, there is a necessity for further research to confirm our findings. There is also a need for reference values in an Indian setting to find out the efficiency of this new parameter. Our sample size is relatively small and comprises of a very high proportion (70%) of subjects with airway obstruction and so our results may not be applicable for use in general population.

High tidal end expiratory flow--an index of dynamic hyperinflation?

Dynamic hyperinflation is considered an important mechanism behind shortness of breath and reduced exercise capacity in chronic obstructive pulmonary disease (COPD) patients. Prevailing methods to assess dynamic hyperinflation are crude because of the large normal variation of both functional residual capacity and inspiratory capacity (IC). In the present study, we hypothesized that expiratory flow on a relatively high level near the end of tidal expiration is an indication of dynamic hyperinflation. A method to measure tidal end expiratory flow (TEEF), i.e. the flow between 0.6 s and 0.04 s before start of inspiration is presented and evaluated in 15 healthy subjects and 16 COPD patients. The COPD patients had more than twice as high TEEF values compared with the healthy subjects (45.4 +/- 23.8 and 20.4 +/- 7.3 ml s(-1) respectively; mean +/- SD; P = 0.0002, for TEEF at 0.4 s before start of inspiration). TEEF values correlated to IC, e.g. TEEF at 0.4 s before start of inspiration expressed as a fraction of mean expiratory flow, correlated to IC (% pred.) (r = 0.74; P<0.0001). These results justifies further testing of the relationship between TEEF and dynamic hyperinflation.

Changes in lung function and tidal airflow patterns after increasing extrathoracic airway resistance

OBJECTIVE

The aim of this study was to determine what changes occur in previously described tidal expiratory flow patterns when extrathoracic resistance is added.

METHODOLOGY

A total of 16 subjects with normal lung function and 15 patients with chronic COPD, were studied. The following measurements were made before and after the addition of an extrathoracic expiratory resistance (EER; 0.89 kPa/L s at a flow of 0.5 L/s) during uncoached tidal breathing: expiratory time (tE), frequency (f), expiratory time to maximum flow/total expiratory time (tPTEF/tE), tidal maximum expiratory flow (PEF(TIDAL)), and time constant of the respiratory system calculated from the passive portion of tidal expiration (trs(TIDAL)). Post peak profiles were categorized as convex, linear or concave and time for flow to fall to 80% and 20% of maximum (t80 and t20) were measured.

RESULTS

Tidal indices tE, f and PEF(TIDAL), were similar in the two groups, but tPTEF/tE was greater and trs(TIDAL) was less in the normal subjects than in the COPD patients. Addition of EER in both groups caused PEF(TIDAL) to decrease and trs(TIDAL), t80 and the percentage of convex profiles to increase. tPTEF/tE increased in the COPD patients but was unchanged in the control group.

CONCLUSION

After addition of EER during tidal breathing, expiratory flow in COPD patients resembled that seen in normal subjects.

Analysis of tidal breathing profiles in cystic fibrosis and COPD

STUDY OBJECTIVES

To explore the flow and time domain characteristics of resting tidal airflow profiles in the presence of obstructive airway disease.

METHODS

Spirometry was performed on 81 adults and 46 juveniles in the lung function laboratory. All the juveniles had cystic fibrosis (CF), as did some of the adults (n = 25), with the remainder having either healthy lungs or COPD. Resting breathing profiles were recorded using a pneumotachograph. Thirteen flow and time domain parameters were extracted from each profile. Two new indexes were derived that are influenced by the shape of the post-peak expiratory flow portion of the expirogram. In this expirogram, the first index (change in post-peak expiratory flow at time 20% [TPPEF(20)]) describes early changes in post-peak flow, while the second index (change in post-peak expiratory flow at time 80% [TPPEF(80)]) describes later changes in flow. Multiple linear regression techniques were used to define the relationship between body size, flow and time domain parameters, and FEV(1), a measure of obstructive airway disease.

RESULTS

In juvenile subjects with CF, body weight and the time to reach peak expiratory flow are the main correlates with FEV(1) (adjusted r(2) = 0.74). The adult CF group are different with the expiratory flow index (TPPEF(20)) being the major correlate with FEV(1) (adjusted r(2) = 0.77). In the COPD group, the second expiratory flow index (TPPEF(80)) is the major correlate instead (adjusted r(2) = 0.6).

CONCLUSIONS

Using multiple linear regression techniques has allowed the description of the interrelationships between body size, age, and tidal breathing profile in obstructive airway disease. The relationship between the flow indexes TPPEF(20) and TPPEF(80) show that in adults with CF, the loss of expiratory flow braking is an important adaptation to disease, while in COPD pulmonary hyperinflation is the predominant factor.

Inhaled nebulized adrenaline improves lung function in infants with acute bronchiolitis

Beta2-agonists have questionable symptomatic effect in infants with acute bronchiolitis, whereas inhaled, nebulized racemic adrenaline, commonly used in Norway, appears (clinically) to be effective. Limited lung function observations during acute bronchiolitis exists, and less for assessing possible effects inhaled adrenaline. In this preliminary study, tidal flow-volume loops were measured in 16 infants with acute bronchiolitis and seven healthy controls (mean age 7.9 and 4.4 months, respectively), with repeated measurements 15 min after inhaled nebulized racemic adrenaline (4 mg diluted in 2 ml saline) in nine bronchiolitis patients. The ratio of time to reach peak tidal expiratory flow to total expiratory time (tPTEF/tE) was significantly reduced in children with acute bronchiolitis (mean, 95% CI) (0.08, 0.05-0.10) compared to controls (0.31, 0.18-0.43), with significant improvement after inhaled racemic adrenaline 0.19 (0.13-0.25), parallel with significant clinical improvement. Lung function (tPTEF/tE) was reduced in infants with acute bronchiolitis and improved significantly after inhaled racemic adrenaline. Inhaled racemic adrenaline is potentially an important alternative for treating infants with acute bronchiolitis.

Expiratory airflow patterns in children and adults with cystic fibrosis

STUDY OBJECTIVE

To determine whether tidal expiratory airflow patterns change with increasing airways obstruction in patients with cystic fibrosis.

DESIGN

An observational study.

SETTING

Lung function laboratory.

PATIENTS

Sixty-four children and young adults with cystic fibrosis.

MEASUREMENTS

After measuring FEV(1) and airways resistance using body plethysmography, each subject was seated and asked to mouth breathe through a pneumotachograph for 2 min. The collected data were analyzed, and three expiratory airflow pattern-sensitive indexes were computed. The first index was derived from the ratio of the time to reach peak expiratory flow to the total expiratory time (tPTEF/tE). The second index, Trs, was an estimate of the time constant of the passive portion of expiration. The third index, f1.gif" BORDER="0">, describes the slope of the whole post-peak expiratory flow pattern after scaling.

RESULTS

Compared with FEV(1), the index tPTEF/tE was a poor indicator of airways obstruction (r(2) = 0.15, p = 0.002). Trs showed a strong relationship with the severity of airways obstruction (r(2) = 0.46, p < 0.001). Using f1.gif" BORDER="0">, the postexpiratory profile could be categorized into three shapes, and provided a good indicator of airways obstruction when linear and concave-shaped profiles occurred (r(2) = 0.42, p < 0.001). Convex-shaped flow profiles had to be treated separately and were indicative of normal lung function.

CONCLUSIONS

In a cross-sectional study of patients with cystic fibrosis, increase in airways resistance above normal is reflected by quantifiable changes in the expiratory airflow pattern.