Reproducibility of forced expiratory flow and volume measurements in infants with bronchiolitis

Influence of sighs in the raised volume rapid thoracic compression technique (RVRTC) in infants

The raised volume rapid thoracic compression (RVRTC) technique has shown to be very promising in the evaluation of infant's lung function. In this technique lungs are inflated several times to a preset pressure prior to the thoracic compression. Many infants made a spontaneous inspiration (sigh) at the end of these inflations. Our hypothesis was that such sighs could change the major variables derived by this technique and the objective of this study was to evaluate the influence of these sighs during lung inflation in the RVRTC technique in infants. Pairs of maneuvers with and without sighs during lung inflation were obtained in 33 of 48 consecutive tests. Curves with sighs showed significantly higher values of FVC (median: 456 x 437 ml; P < 0.001) and FEV0.5 compared to those without, whereas FEF75 and FEF85 were significantly lower (median: 417 x 439 ml/sec, P = 0.008 and 251 x 273 ml/sec, P = 0.01; respectively). The mean percent change between maneuvers for FVC, FEV0.5, FEF75, and FEF85 was respectively: 6.4%, 3.8%, -3.1%, and -3.5%. These differences represent a mean change of 0.38 z score for FVC and of 0.12 z score for FEF75 and FEF85. In conclusion, the presence of sighs during lung inflation significantly changes RVRTC values in infants. We suggest that the presence or the absence of sighs should be registered for each maneuver and that it should be considered for within and between subject comparisons.

Feasibility of repetitive lung function measurements by raised volume rapid thoracoabdominal compression during methacholine challenge in young infants

BACKGROUND

The aim of the study was to evaluate the feasibility of lung function measurements by the raised volume rapid thoracoabdominal compression (RVRTC) technique during bronchial methacholine challenge in young infants.

METHOD

Four hundred two healthy infants were tested at 1 month of age with RVRTC during repeated methacholine challenges with quadrupling doses from 0.037 to 16.674 mumol.

RESULTS

Measurement of baseline lung function was successful in 99% and the provocative dose (PD) was achieved in 79% of infants by forced expiratory volume in 0.5 s (FEV(0.5)). Additionally, the PD was successfully measured in 87% by transcutaneous oxygen pressure. No serious adverse events were observed during testing or after discharge from the clinic. The methacholine dose range was appropriate as PD could be determined in the majority of infants. FEV(0.5) values in 21% of infants dropped > 40% during the test. Short-lasting, self-limiting episodes of hypoxemia of < 80% occurred in 1% of infants and bradycardia < 90 beats/min in 19% of infants. The most common observations by parents were changes in the patterns of sleeping (95%), eating (57%), and behavior (58%) of the infant after hospital discharge. The mean acceptability rating among parents was 8 on a scale from 1 to 10, with 13% rating < or = 5. It took one operator 3 h to complete the test, with the actual lung function testing accounting for half the time.

CONCLUSION

This very comprehensive experience with standardized measurements of lung function by RVRTC during methacholine challenge in young infants in a single center leads us to conclude that the test is feasible and safe to perform in asymptomatic young infants.

Sensitivity of bronchial responsiveness measurements in young infants

OBJECTIVES

There is limited evidence on the preferred methods for evaluating lung function in infancy. The objective of this study was to compare sensitivity and repeatability of indexes of lung function in young infants during induced airway obstruction.

METHODS

The study population consisted of 402 infants (median age, 6 weeks). Forced flow-volume measurements were obtained by the raised volume rapid thoracoabdominal compression technique and were compared with indexes of tidal breathing, measurements of transcutaneous oxygen (Ptco(2)), and auscultation during methacholine challenge testing.

RESULTS

Ptco(2) was the most sensitive parameter to detect increasing airway obstruction during methacholine challenge, followed by forced expiratory volume at 0.5 s (FEV(0.5)). Both were superior to other indexes of forced spirometry as well as tidal breathing indexes and auscultation. Coefficients of variations for Ptco(2) and FEV(0.5) were 4% and 7%, respectively.

CONCLUSIONS

Ptco(2) and FEV(0.5) are the most sensitive parameters for measurement of bronchial responsiveness in young infants. Measurements of baseline lung function should preferably be made using FEV(0.5.) Measurements of bronchial responsiveness are best assessed using Ptco(2), which may be performed in nonsedated infants and improve feasibility of future studies on lung function in infancy.

Does bronchodilator responsiveness in infants with bronchiolitis depend on age?

OBJECTIVE

To assess the relation between age and bronchodilator responsiveness in infants with bronchiolitis.

STUDY DESIGN

In 41 infants (age, 2 to 18 months) with bronchiolitis, lung function was measured with the raised volume rapid thoracoabdominal compression technique before and after salbutamol inhalation. Lung function was quantified in terms of timed volumes (FEV(0.5), FEV(0.75), and FEV(1.0)). A significant change was defined as a postbronchodilator value that differed from baseline by more than twice the within-subject coefficient of variation.

RESULTS

For the group, postbronchodilator values did not differ significantly from baseline (DeltaFEV(0.5), 3.8% +/- 9.3%; DeltaFEV(0.75), 3.5% +/- 9.5%; and DeltaFEV(1.0), 4.0 +/- 9.8%). Eleven subjects showed significantly increased timed volumes; 3 presented with a decreased lung function; the remaining patients failed to show a significant change. The mean age of subjects with improved lung function did not differ significantly from the mean age of those with no or paradoxical responses (9.7 +/- 4.7 vs 8.1 +/- 4.1 months); there was no correlation of age with the size of the bronchodilator response.

CONCLUSIONS

The results of the current study indicate that bronchodilator responsiveness in infants with bronchiolitis is not age-dependent.

Variability of the raised volume rapid thoracic compression technique in infants with recurrent wheezing

Measuring forced expiratory flows from raised lung volume in infants represents a significant advance in the assessment of pulmonary function early in life. However, variability in the main parameters obtained with raised volume rapid thoracic compression (RVRTC), FVC, FEV(0.5), FEF(50), FEF(75), and FEF(25-75), has not been completely evaluated. This study was performed to determine the intra-subject variability of spirometric-like parameters in infants with recurrent wheezing obtained with RVRTC. One hundred and two infants with recurrent wheezing (mean age 62 +/- 22 weeks) who were asymptomatic at the moment of measuring lung function participated in this study. For the variability analysis, three to five technically acceptable curves at flow-limitation jacket pressure were employed. The mean coefficient of variation (95 % CI) of spirometric parameters was as follows: FVC = 2.9 % (2.6-3.2); FEV(0.5) = 2.2 % (1.9-2.5); FEF(50) = 3.7 % (3.3-4.1); FEF(75) = 5.9 % (5.2-6.6) and FEF25-75 = 3.3 % (2.9-3.7). This study demonstrates the high reproducibility of the spirometric parameters measured with the technique of raised lung volume in infants.

The response to β-agonists in wheezy infants: three methods compared

BACKGROUND

Studies into the effects of salbutamol in the treatment of wheeze in infancy have been conflicting, possibly due to differences in outcome variables. We aimed to assess the response to salbutamol using indices derived from passive and forced expiration.

METHODS

We recruited 39 infants who had a history of wheezing (mean age 43 weeks) and measured maximum flow at functional residual capacity (V'(max FRC)) by rapid thoracoabdominal compression (RTC), and forced expired volume at 0.4s (FEV0.4) using the raised-volume RTC technique (RV-RTC). We calculated passive compliance (C(rs)), resistance (R(rs)) and time constant (tau) from relaxed expirations that followed the augmented inspirations delivered during RV-RTC. Measurements were repeated after aerosol salbutamol (800 mcg).

RESULTS

Data were obtained in 32 infants for V'(max FRC), 22 for FEV0.4 and 19 for passive mechanics. There were no mean changes in any index of forced expiration after salbutamol. Some individuals showed significant changes (improvement or worsening) in one or other index. Overall, there was a small increase in C(rs) after salbutamol but no change in R(rs) or tau.

CONCLUSIONS

We found no consistent pattern of response in either index of forced expiration. Validated clinical scores or alternative physiological techniques may be preferable to respiratory mechanics in assessing bronchodilator response.

Pathophysiology and management of pulmonary infections in cystic fibrosis

This comprehensive State of the Art review summarizes the current published knowledge base regarding the pathophysiology and microbiology of pulmonary disease in cystic fibrosis (CF). The molecular basis of CF lung disease including the impact of defective cystic fibrosis transmembrane regulator (CFTR) protein function on airway physiology, mucociliary clearance, and establishment of Pseudomonas aeruginosa infection is described. An extensive review of the microbiology of CF lung disease with particular reference to infection with P. aeruginosa is provided. Other pathogens commonly associated with CF lung disease including Staphylococcal aureus, Burkholderia cepacia, Stenotrophomonas maltophilia, Achromobacter xylosoxidans and atypical mycobacteria are also described. Clinical presentation and assessment of CF lung disease including diagnostic microbiology and other measures of pulmonary health are reviewed. Current recommendations for management of CF lung disease are provided. An extensive review of antipseudomonal therapies in the settings of treatment for early P. aeruginosa infection, maintenance for patients with chronic P. aeruginosa infection, and treatment of exacerbation in pulmonary symptoms, as well as antibiotic therapies for other CF respiratory pathogens, are included. In addition, the article discusses infection control policies, therapies to optimize airway clearance and reduce inflammation, and potential future therapies.

Exploring the relationship between forced maximal flow at functional residual capacity and parameters of forced expiration from raised lung volume in healthy infants

The raised volume rapid thoraco-abdominal compression technique (RVRTC) is being increasingly used to assess airway function in infants, but as yet no consensus exists regarding the equipment, methods, or analysis of recorded data. The aim of this study was to explore the relationship between maximal flow at functional residual capacity (V'(maxFRC)) and parameters derived from raised lung volumes, and to address analytical aspects of the latter technique in an attempt to assist with future standardization initiatives. Forced vital capacity (FVC) from lung volume raised to 3 kPa, timed forced expiratory volumes (FEV(t)), and forced expiratory flow parameters at different percentages of expired FVC (FEF(%)) were measured in 98 healthy infants (1-69 weeks of age). V'(maxFRC) using the tidal rapid thoraco-abdominal compression (RTC) technique was also measured. The within-subject relationships and within-subject variability of the various parameters were assessed. Duration of forced expiration was < 0.5 sec in 5 infants, meaning that FEV(0.3) and FEV(0.4) were the only timed volume parameters that could be calculated in all infants during the first months of life, and even when it could be calculated, FEV(0.5) approached FVC in many of these infants. It is recommended that FEV(0.4) be routinely reported in infants less than 3 months of age. Contrary to previous reports, within subject variability of V'(maxFRC) was less than that of FEF(75) (mean CV = 6.3% and 8.9%, respectively).A more standardized protocol when analyzing data from the RVRTC would facilitate comparisons of results between centers in the future.

Effect of airway inflation pressure on forced expiratory maneuvers from raised lung volume in infants

The raised lung volume technique is increasingly used to measure forced expiratory maneuvers in infants. However, there is no consensus regarding the optimal airway inflation pressure (P(inf)) required for such maneuvers, or the influence of small changes in P(inf) within and between infants. The aim of this study was to assess the effect of small differences (0.2-0.3 kPa) in P(inf) on forced vital capacity (FVC), forced expired volume in 0.5 sec (FEV(0.5)), and forced expired flow at 75% of vital capacity (FEF(75)), all derived from the raised volume rapid thoraco-abdominal compression (RVRTC) technique. Randomized paired forced expiratory maneuvers were obtained in 32 healthy infants ( 3.9-39.3 weeks old, 3.8-9.9 kg) with the safety pressure relief valve for P(inf) set to 2.7 kPa or 3.0 kPa (27 or 30 cm H(2)0). When mean (SD) P(inf) was increased by 8.4 (2.8)%, there was a significant (P < 0.01) increase in mean (SD) FVC, FEV(0.5), and FEF(75) by 5.8 (5.7)%, 6.1 (6)%, and 8.3 (16.2)%, respectively. In conclusion, relatively small differences in P(inf) will result in significant differences in FVC, FEV(0.5), and FEF(75) by RVRTC technique. Precision in setting and reporting the applied P(inf) is therefore essential, particularly if data are to be compared between centers.

Bronchiolitis in infants

Bronchiolitis is a common cause of wheezing among infants. Respiratory syncytial virus (RSV) is the most common infectious agent to cause bronchiolitis, and RSV infection accounts for more than 125,000 hospitalizations per year in the United States. Beyond supportive measures, the care of infants with bronchiolitis remains controversial. Practitioners continue to treat infants with a variety of pharmacologic agents, despite limited evidence of their efficacy. Investigators continue to search for the safest and most cost-effective methods to treat infants with bronchiolitis, not only to overcome obstructive symptoms during the acute illness, but also to prevent recurrent symptoms of airway obstruction that occur in some children for years after their initial episode of bronchiolitis. Improved understanding of the pathogenesis of RSV infection and of virus-host interactions may one day lead to the development of agents that alter the initial inflammatory response and strategies that help prevent recurrent episodes of wheezing and the development of asthma after acute bronchiolitis.

Dynamic imaging of hyperpolarized (3)He distribution in rat lungs using interleaved-spiral scans

The use of spiral scan techniques is investigated for (3)He lung imaging on small animals. Dynamic series of up to 40 high temporal resolution (3)He ventilation images are obtained using a single bolus of gas. General properties of the spiral technique are discussed and compared to those of standard imaging techniques in relation to the specific case of rare gas imaging. To improve temporal resolution of the image series, the efficiency of a sliding window technique, combining data from two consecutive spiral images, is demonstrated. An example of the typical global (3)He signal variation during the (3)He breathing of the animal is shown. Pixel-by-pixel measurements of the (3)He signal derivative during the gas inspiration are performed. A corresponding lung map of the magnetization per time unit entering the lung during gas inflow is presented.