Impact of the prolonged slow expiratory maneuver on respiratory mechanics in wheezing infants.

OBJECTIVE: To evaluate changes in respiratory mechanics and tidal volume (V T) in wheezing infants in spontaneous ventilation after performing the technique known as the prolonged, slow expiratory (PSE) maneuver.
METHODS: We included infants with a history of recurrent wheezing and who had had no exacerbations in the previous 15 days. For the assessment of the pulmonary function, the infants were sedated and placed in the supine position, and a face mask was used and connected to a pneumotachograph. The variables of tidal breathing (V T and RR) as well as those of respiratory mechanics-respiratory system compliance (Crs), respiratory system resistance (Rrs), and the respiratory system time constant (prs)-were measured before and after three consecutive PSE maneuvers.
RESULTS: We evaluated 18 infants. The mean age was 32 ± 11 weeks. After PSE, there was a significant increase in V T (79.3 ± 15.6 mL vs. 85.7 ± 17.2 mL; p = 0.009) and a significant decrease in RR (40.6 ± 6.9 breaths/min vs. 38.8 ± 0,9 breaths/min; p = 0.042). However, no significant differences were found in the variables of respiratory mechanics (Crs: 11.0 ± 3.1 mL/cmH2O vs. 11.3 ± 2.7 mL/cmH2O; Rrs: 29.9 ± 6.2 cmH2O • mL-1 • s-1 vs. 30.8 ± 7.1 cmH2O • mL-1 • s-1; and prs: 0.32 ± 0.11 s vs. 0.34 ±0.12 s; p > 0.05 for all).
CONCLUSIONS: This respiratory therapy technique is able to induce significant changes in V T and RR in infants with recurrent wheezing, even in the absence of exacerbations. The fact that the variables related to respiratory mechanics remained unchanged indicates that the technique is safe to apply in this group of patients. Studies involving symptomatic infants are needed in order to quantify the functional effects of the technique.

Introduction

The prolonged, slow expiratory (PSE) maneuver is a respiratory therapy technique applied in infants with airway obstruction and accumulation of secretion.( , ) The benefits of different physiotherapy techniques have been described,( ) and the same occurs with the PSE maneuver. During the use of this technique, it was possible to quantify the expiratory reserve volume mobilized, the induction of sighs and maintenance of peak expiratory flow was confirmed and a decreased respiratory distress was observed after application.( , )

The evaluation of passive respiratory mechanics - respiratory system compliance (Crs), resistance (Rrs) and its time constant (prs) - has been used in studies of various segments in infants, because in addition to obtaining reproducible measurements, it assists in longitudinal monitoring of lung function and evaluation of therapeutic interventions.( ) Crs and Rrs can also help confirm the benefits of respiratory physiotherapy due to altered pulmonary flow and lung volume after the elimination of secretion.( , )Several studies on respiratory therapy in patients under mechanical ventilation in ICU used the evaluation of Crs and Rrs.( , - ) However, studies on patients breathing spontaneously are scarce. Evaluation of airway resistance can also help detect bronchospasm induced by respiratory therapy techniques. The application of chest vibration and "tapotement" (percussive tapping) in individuals with lung disease and hypersecretion resulted in no alteration in lung function, proving that this technique is safe and can be applied in subjects with bronchial hyperreactivity.( , ) This evaluation was not performed in patients undergoing PSE maneuver.

Evaluation of tidal volume (VT) is one of the oldest and most simple techniques to measure lung function in infants.( ) VT has been studied as an outcome for evaluating the efficacy of unconventional techniques of respiratory therapy. The results so far, however, are controversial, with reports of increased VT in some studies, and of maintenance in others.( , - )

The evaluation of respiratory mechanics and VT in infants breathing spontaneously is not routinely measured in the clinical practice. These functional variables, however, can be studied in specialized laboratories, and we believe that these consist of objective outcomes and important factors in evaluating the effectiveness of respiratory therapy. The objective of this study was to evaluate changes in respiratory mechanics and VT in wheezing infants in spontaneous ventilation after the application of PSE maneuver.

Methods

We conducted a cross-sectional study evaluation wheezing infants referred for pulmonary function evaluation in the Infant Pulmonary Function Laboratory at the Allergy, Clinical Immunology, and Rheumatology Section of the Department of Pediatrics, Federal University of Sao Paulo, in São Paulo, Brazil. The study was approved by the local research ethics committee (Ruling no. 1054/07). Written informed consent was given by the parents or legal guardians. Data was collected between January 2008 and February 2009.

We included infants (between 4 and 24 months of age) with a history of recurrent wheezing (at least three episodes), without acute respiratory disease manifested in the preceding 15 days. Absence of acute respiratory disease was inferred from the absence of corresponding clinical symptoms (such as cough, wheezing and difficulty in breathing) and from the lack of consistent findings in the physical examination. We excluded those with upper airway obstruction, preterm infants (less than 37 weeks of gestational age), infants with gastroesophageal reflux disease, infants who underwent thoracic and/or abdominal surgery or who have been diagnosed with heart disease or neuropathy.

To perform the pulmonary function test, infants should be fasting for at least three hours. Chloral hydrate was administered (60-80 mg/kg), according to the laboratory routine and existing standardization.( - ) The infants were monitored using a pulse oximeter (DX 2405; Dixtal Biomedica, Manaus, Brazil) and SpO2 and HR were evaluated. The infants were in the supine position with subtle cervical spine extension, using a small pad in the scapular region, without lateralization of the head. A face mask connected to a pneumotachograph (Hans Rudolph, Kansas City, MO, USA) was attached to the infants' face.

In technical phase, the PSE maneuver was performed with the infant in the supine position, with the hypothenar region of one of the therapist's hands positioned on the chest, precisely below the suprasternal notch, and the hypothenar region of the other hand placed on the abdomen above the umbilicus. At the end of the expiratory phase, the compression of both hands was made, the hand on the chest being moved in craniocaudal direction and the hand on the abdomen and hand in the caudocranial direction. The next three or four inhalations subsequent to compression were restricted and squeezing motion in the expiratory phase was continued in accordance with the technical description.( ) There were three sequences of PSE maneuver (named A, B and C) in a continuous period of 120 s (Figure 1). The interval between the sequences was 30 s. The technique was always performed by the same evaluator, trained and qualified to do so. The PSE maneuver was performed during the evaluation of VT, so the flow-volume curve was recorded constantly, allowing measurement of the VT and its derivations-RR, PEF and the ratio between the time to reach the PEF (Tme) and expiratory time (Te).

Figure 1

Representation of the acceptability criteria of the expiratory curve obtained in the evaluation of passive mechanics of the respiratory system by the technique of single occlusion. In A, flow-volume curve: segment AD - extrapolation for calculation of the time constant of the respiratory system; segment BC - linear portion of the curve ≥ 60% of the total, meaning the relaxation of respiratory muscles during expiration. In B, the pressure-time: 100 ms plateau in the expiratory phase. These are the eligibility criteria for the evaluation of respiratory mechanics.

Crs, Rrs and prs were the analyzed variables of respiratory mechanics using the airway occlusion technique, according to existing recommendations.( , ) For these measurements, the respiratory system is considered a one-compartment and linear model. The complete relaxation of the respiratory muscles in infants, necessary for the evaluation of the passive respiratory mechanics, is achieved by inducing the Hering-Breuer reflex, triggered by the rapid airway obstruction (1 s) at the end of normal inhalation. The presence of the linear segment of at least 60% of the expiratory loop was inspected visually, as well as the lack of muscular activity by the plateau in the pressure-time curve with a standard deviation < 0.1 at 100 ms (Figure 1).( , ) At least three acceptable maneuvers were performed as recommended,( ) and the average value was recorded.

All phases of the protocol were carried out during the measurement of VT. Different variables can be obtained from the analysis of VT, such as inspiratory time, Te, total respiratory time, PEF, Tme, RR and the Tme/Te ratio. For this group of patients, the evaluation was restricted to VT, RR, PEF and the Tme/Te ratio, as these are variables that can be influenced by respiratory therapy techniques. The Tme/Te ratio is one of the most studied variables in VT, as it may reflect airway obstruction.( )

The protocol comprised three phases. The first phase (pre-technique) consisted of measuring the VT and its derivations (RR, PEF and Tme/Te ratio) for 60 s. After the evaluation of the VT, the measurement of respiratory mechanics was carried out. The second phase (technique phase) consisted of applying the PSE maneuver in three sequences of compression (A, B and C) for a period of 120 s. The technique was performed during the measurement of VT (Figure 2). The third phase (post-technique) consisted of the revaluation of the VT for 60 s immediately after the application of the PSE maneuver, followed by the evaluation of the respiratory mechanics.

Figure 2

Representation of three sequences (A, B, and C) of the technique prolonged, slow expiratory (PSE) maneuver.

All continuous variables analyzed presented normal distribution and were evaluated using the Shapiro-Wilk test and therefore are presented as mean and standard deviation. The mean of the 60 s of evaluation of the VT and the three measurements of respiratory mechanics were used for pre-and post-technique comparison. We used the Student t test for dependent samples for the analysis of the tidal breathing (VT and RR) and respiratory mechanics (Crs, Rrs and prs) variables between the pre and post technique phases. The rejection level for the null hypothesis was set at 5%. The program used for the analysis was the Statistical Package for the Social Sciences, version 14.0 (SPSS Inc., Chicago, IL, USA).

Results

Of the 22 infants who started the protocol, 4 did not complete the study: one by coughing during the examination and 3 by technical difficulties (early awakening and insufficient sedation). The mean age of the infants who completed the study was 32.2 ± 11.4 weeks. Nine were female. The initial data of the population are described in Table 1.

Table 1

Demographic characteristics of infants studied (n = 18).

Variables	Results
Age, weeks	32.2 ± 11.4
Height, cm	68.0 ± 4.3
Weight, kg	8.3 ± 1.0
Number of wheezing attacks	4.8 ± 1.9
Sex male/female, n/n	9/9

Values expressed as mean ± SD, except where otherwise indicated

During the protocol, no infant showed signs of respiratory distress or expiratory grunting. The SpO2 remained over 93% throughout the tests, and HR remained between 110 and 150 bpm in all infants evaluated.

When comparing the pre and post technique phases, we observed a statistically significant mean increase in VT (p = 0.009, Figure 3) and VT corrected by height (p = 0.01, Table 2). A reduction was observed in RR from 40.6 ± 6.9 breaths/min to 38.8 ± 5.9 breaths/min after the technique (p = 0.04, Table 2). We also observed a significant increase in the Tme/Te ratio (p = 0.007). There was no significant change in the mean value of PEF when compared to the pre and post-technique phases (Table 2). Regarding respiratory mechanics, there was no statistically significant changes in Crs, Rrs and prs (Table 2).

Figure 3

Graphical representation of the variation in tidal volume before (pre-technique) and after (posttechnique) applying the slow and progressive expiration.

Table 2

Variables derived from tidal breathing and respiratory mechanics observed in the pre-and posttechnique protocol.

Variables	Phases	p
Pre-technique	Post-technique
PEF, mL/s	140.5 ± 19.2	143.5 ± 20.6	0.3
VT, mL	79.3 ± 15.6	85.7 ± 17.2	0.009
VT, % previsto	111.6 ± 18.7	120.1 ± 17.7	0.013
VT, mL/cm	1.16 ± 0.20	1.21± 0. 22	0.010
Tme/Te ratio	0.33 ± 0.11	0.35 ± 0.11	0.007
RR, breaths/min	40.6 ± 6.9	38.8 ± 5.9	0.04
Crs, mL/cmH2O	11.0 ± 3.1	11.3 ± 2.7	0.4
Rrs, cmH2O • mL−1 • s−1	29.9 ± 6.2	30.8 ± 7.1	0.4
prs, s	0.32 ± 0.11	0.34 ± 0.12	0.3

: Tidal volume

: time to reach PEF

: expiratory time

: Respiratory system compliance

: respiratory system resistance

: time constant of the respiratory system

Values expressed as mean ± SD.

Discussion

The PSE maneuver is a respiratory therapy technique described to promote bronchial clearance in infants.( , ) The scientific arguments that prove the effectiveness of the PSE maneuver were based, for a long time, on the evaluation of indirect variables, such as HR and SpO2.( , , , ) Only recently has the variation in expiratory reserve volume during PSE maneuver been described more objectively using the evaluation of pulmonary function variables.( ) However, there are still questions about variations in VT and passive respiratory mechanics immediately after the application of the PSE maneuver in subjects breathing spontaneously. After having studied the variations in volume and respiratory wheezing in infants breathing spontaneously, we observed a significant increase in VT and maintenance of the variables Crs and Rrs and after application of the PSE maneuver.

One possible explanation for the increase in VT is the reduction of airway obstruction. It has been described that the reduction in the Tme/Te ratio is an indirect form to determine airway obstruction.( ) Thus, we infer that there was a decrease in bronchial obstruction in the patients studied by the increase in the Tme/Te ratio (> 0.30) after the PSE maneuver . This reduction in the obstructive process is due to the thoracoabdominal compression performed during the PSE maneuvers, where the aim is to prolong the expiratory phase and eliminate the trapped air. If this process is successful, the reduction of the expiratory reserve volume is expected, and it is able to allow an increase in VT. In addition to finding an increase in the Tme/Te ratio, our group has previously described that the PSE maneuver contributes in removing over 50% of the expiratory reserve volume,( ) confirming the results of the decrease in obstruction.

Another factor that would justify the increase in VT in the infants studied here is the induction of sighs, characterized as breaths in which there is an increase greater than 100% in VT. Recently, we have shown that the PSE maneuver favors the induction of sighs,( ) and that it is already known that sighs act by recruiting alveoli and increasing the VT.( , )It is important to point out that the variation observed in our study in the values of VT, albeit small, is probably clinically relevant. The instability of the rib cage, routinely observed in infants, makes those more susceptible to lung volume reduction, and maneuvers that increase VT become clinically relevant.( , ) We observed an increase of nearly 10% in VT after applying three sequences of the PSE maneuver. In the clinical practice, however, physical therapists, when using the PSE maneuver technique, perform a greater number of maneuvers, basing the number of repetitions on the improvement in pulmonary auscultation.( ) Thus, it is unlikely that the actual increase of VT determined by the PSE maneuver technique in the daily practice be much more expressive than the one found in our study.

Rrs in our study was maintained after the application of the PSE maneuver, in disagreement with studies in patients on mechanical ventilation.( , , ) This finding can be explained by evaluating patients breathing spontaneously, without hypersecretion and therefore without change in the Rrs at the beginning of the protocol.

Another benefit of measuring Rrs is the detection of bronchospasm. It is described that techniques with intense mechanical vibrations in the chest, such as "tapotement" (percussive tapping) and vibration, can aggravate bronchospasm, evidenced by the reduction in FEV1 and PEF.( - ) There is no description of the unconventional techniques of physiotherapy favoring bronchospasm, due to the fact that these techniques cause no abrupt mechanical vibrations in the chest. In our study, we observed no change in either Rrs or PEF, confirming that PSE maneuver did not induce bronchospasm in this group of wheezing infants, and we consider it a safe technique to perform even in individuals prone to bronchospasm. A group of authors, when evaluating unconventional techniques of respiratory therapy similar to that applied in this study, observed no significant changes in PEF.( )

The maintenance of the values of Crs in this study can be justified due to fact that the initial values were within normal limits,( , ) and to the lack of pulmonary hypersecretion. Authors who observed that variation in respiratory function after physical therapy in mechanically ventilated patients described the secretion clearance as the main reason.( , , , )

Our study was limited by the fact that patients are not in exacerbation or presented hypersecretion. Individuals with hypersecretion were not selected, due to the fact that, in addition to the interference of this condition in the variables analyzed, the secretion could also compromise the safety of the infant, since the sedation associated with hypersecretion aggravates airway obstruction in patients breathing spontaneously. The short application time of PSE maneuver (three sequences) and functional revaluation soon after its completion are other limitations to our study. This, however, could hardly be altered due to the short time of sedation induced by chloral hydrate. Even with a small evaluation time, we observed significant changes in VT and we can speculate that the performance of a greater number of sequences of the PSE maneuver could increase the differences found. We conclude that the application of PSE maneuver in wheezing infants is able to induce changes in pulmonary function with increased VT and reduced RR. These facts are probably secondary to the reduced bronchial obstruction. The maintenance of the airway resistance values demonstrates that the PSE maneuver technique is safe for application in infants with propensity to bronchospasm.