Respiratory physical therapy has always sought to prove the efficiency of techniques,(1-3) such as chest vibration/percussion and changes in inspirato-ry/expiratory flow, in bronchial hygiene. However, this has failed to be proven be-cause of methodological differences among the studies and the fact that these techniques depend on being properly performed by the physical therapist, as well as, in many cases, on the collaboration of the patients.(4)

We believe that studies that corroborate the use of bronchial hygiene tech-niques are important, since they are necessary to prevent atelectasis and pulmo-nary infections, as well as to reduce the length of hospital stay. In this context, Chicayban et al.,(5) in the present issue of the Jornal Brasileiro de Pneumologia, contemplate us with a study comparing two bronchial hygiene techniques that can be used in clinical practice.

Postural drainage, tapotement and chest vibration, acceleration of expirato-ry flow, positive end-expiratory pressure-zero end-expiratory pressure maneu-vers,(6) bag squeezing,(7) and manual hyperinflation performed with an artificial manual breathing unit (AMBU) are among the most frequently studied tech-niques. Bag squeezing and manual hyperinflation, when compared with the stimulation of cough or tracheal aspiration without the prior use of physical thera-py maneuvers, have so far been shown not to be effectively capable of demon-strating an increase in the mobilization and in the amount of fluid.(8)

Cough depends on inspiratory and expiratory muscles being preserved; however, after prolonged ICU stays and use of mechanical ventilation, in addition to the evolution of various diseases, these muscles might become impaired and end up compromising effective coughing.(8) In this context, maneuvers that im-prove the patient's ability to perform deep and sustained inhalations are very im-portant to make coughing more effective, revert possible areas of atelectasis, and prevent other pulmonary complications due to accumulation of secretions.(8)

A recent study(8) evaluated the major bronchial hygiene techniques used by physical therapists: vibrocompression, hyperinflation, postural drainage, tracheal aspiration, and motor physical therapy. The authors found that the most frequent reason for using one or the other maneuver was the personal experience of the professional (not scientific evidence), which demonstrates the need for further studies on this topic because techniques/maneuvers have always been used and recommended in the routine of such professionals.(8) Based on these findings, interventions were started to help improve or simulate the physiological mecha-nisms of fluid clearance.

Breath stacking techniques, which include voluntary and involuntary breath stacking, have the physiological principle of increasing lung volume and elastic recoil. These techniques are intended to reexpand collapsed areas and assist coughing, which are mechanisms that can be impaired in various diseases. For this reason, we believe that the study by Chicayban et al.(5) is valuable be-cause it scientifically supports physical therapy approach using viable, compre-hensive resources in clinical practice. In addition, breath stacking techniques have demonstrated a solid scientific basis as to their effectiveness.(9-13) These techniques have been well-established in the treatment of neuromuscular dis-eases and, in practice, are aided by AMBU, which increases inspiratory volume above three liters. This acts on lung elastic recoil, and it makes coughing more effective during forced expiration, whether associated with thoracoabdominal re-striction or not. The major function of involuntary breath stacking is not related to mobilizing fluid, as is observed in conventional maneuvers. In fact, it simulates cough mechanisms, increases PEF and peak cough flow, carrying fluid to the up-per airways. Therefore, it is a technique that should applied and studied in other diseases, besides neuromuscular diseases.(12) The voluntary breath stacking technique has good results in terms of improving oxygenation in patients with ate-lectasis.(14) However, the effects of this technique on respiratory mechanics in pa-tients with severely impaired lung function should be further evaluated to contrib-ute to decision-making in clinical practice. It is of note that voluntary breath stack-ing depends more on the muscle contraction of the patient to generate tidal vol-ume, whereas involuntary breath stacking relies on the volume generated by AM-BU (bag-valve-mask).

Although both techniques can be used easily and independently,(5) invol-untary breath stacking appeared to be more effective in generating inspiratory volume and increasing static compliance when compared with voluntary breath stacking. In the study by Chicayban et al.,(5) 85% of the patients needed fluid aspi-ration due to coughing during the performance of involuntary breath stacking. Be-cause this increases elastic recoil, we can strategically think that there was an effect of "sudden decompression" that, when associated with more vigorous ex-piratory efforts, could generate a more productive and effective cough, carrying secretions more easily, which was well discussed and demonstrated by the au-thors.(5)

Regarding the safety of the maneuvers,(5) these were repeated in 4-5 con-secutive cycles, which seemed not to cause adverse effects, such as hemody-namic instability, patient discomfort, or increased airway resistance. This corrobo-rates the studies by Sarmento et al.(13) and Naue et al.,(15) who compared different bronchial hygiene techniques, combined and isolated, and concluded that the techniques were safe and that, when combined, they appeared to be more effi-cient in reducing the frequency of aspiration and the duration of mechanical ven-tilation.

Although the authors(5) do not mention the level of awareness and coopera-tion of the patients at the time that interventions were performed, we believe that more cooperative patients can benefit more from such maneuvers, especially when they receive orientation on how to perform the maneuvers themselves after hospital discharge.

In conclusion, we found that both techniques promote bronchial hygiene by increasing inspiratory volume, inspiratory capacity, and complacency, favoring a greater peak cough flow. The study by Chicayban et al.(5) helps support the use of reexpansion techniques based on evidence and applicability in an attempt to supply the absence of well-evidenced studies with proper methodology on this topic.



References

1. Peruzzi WT, Smith B. Bronchial hygiene therapy. Crit Care Clin. 1995;11(1):79-96. https://doi.org/10.1016/S0749-0704(18)30086-1
2. Varekojis SM, Douce FH, Flucke RL, Filbrum DA, Tice JS, McCoy KS, et al. A comparison of the therapeutic effectiveness of and preference for pos-tural drainage and percussion, intrapulmonary percussive ventilation, and high-frequency chest wall compression in hospitalized cystic fibrosis pa-tients. Respir Care. 2003;48(1):24-28.
3. Florêncio RB, Aliverti A, Fagundes MLLC, Batista IPDS, Nóbrega AJS, Resqueti VR, et al. Acute effects of three pulmonary reexpansion modali-ties on thoracoabdominal motion of healthy subjects: Randomized crosso-ver study. PLoS One. 2019;14(3):e0213773. https://doi.org/10.1371/journal.pone.0213773
4. Walton JR, Shapiro BA. Appropriate utilization of bronchial hygiene thera-py: development and evaluation of a cost-effective respiratory therapy pro-gram. QRB Qual Rev Bull. 1981;7(1):21-25.
5. Chicayban LM, Hemétrio AC, Azevedo LTR. Comparison of the effects of voluntary and involuntary breath stacking techniques on respiratory me-chanics and lung function patterns in tracheostomized patients: a random-ized crossover clinical trial. J Bras Pneumol. 2020;46(4):e20190295. https://doi.org/10.36416/1806-3756/e20190295
6. Santos FR, Schneider Júnior LC, Forgiarini Junior LA, Veronezi J. Effects of manual rib-cage compression versus PEEP-ZEEP maneuver on res-piratory system compliance and oxygenation in patients receiving mechan-ical ventilation. Rev Bras Ter Intensiva. 2009;21(2):155-161. https://doi.org/10.1590/S0103-507X2009000200007
7. Windsor HM, Harrison GA, Nicholson TJ. "Bag squeezing": a physiothera-peutic technique. Med J Aust. 1972;2(15):829-832. https://doi.org/10.5694/j.1326-5377.1972.tb103565.x
8. Matilde INE, Eid RAC, Nunes AF, Ambrozin ARP, Moura RH, Carnieli-Cazati D, et al. Bronchial hygiene techniques in patients on mechanical ventilation: what are used and why? Einstein (Sao Paulo). 2018;16(1):eAO3856. https://doi.org/10.1590/s1679-45082018ao3856
9. Toussaint M, Pernet K, Steens M, Haan J, Sheers N. Cough Augmentation in Subjects With Duchenne Muscular Dystrophy: Comparison of Air Stack-ing via a Resuscitator Bag Versus Mechanical Ventilation. Respir Care. 2016;61(1):61-67. https://doi.org/10.4187/respcare.04033
10. Camela F, Gallucci M, Ricci G. Cough and airway clearance in Duchenne muscular dystrophy. Paediatr Respir Rev. 2019;31:35-39. https://doi.org/10.1016/j.prrv.2018.11.001
11. Iskandar K, Sunartini, Nugrahanto AP, Ilma N, Kalim AS, Adistyawan G, et al. Use of air stacking to improve pulmonary function in Indonesian Du-chenne muscular dystrophy patients: bridging the standard of care gap in low middle income country setting. BMC Proc. 2019;13(Suppl 11):21. https://doi.org/10.1186/s12919-019-0179-4
12. Brito MF, Moreira GA, Pradella-Hallinan M, Tufik S. Air stacking and chest compression increase peak cough flow in patients with Duchenne muscu-lar dystrophy. J Bras Pneumol. 2009;35(10):973-979. https://doi.org/10.1590/S1806-37132009001000005
13. Sarmento A, de Andrade AF, Lima ÍN, Aliverti A, de Freitas Fregonezi GA, Resqueti VR. Air Stacking: A Detailed Look Into Physiological Acute Ef-fects on Cough Peak Flow and Chest Wall Volumes of Healthy Subjects. Respir Care. 2017;62(4):432-443. https://doi.org/10.4187/respcare.05189
14. Marini JJ, Rodriguez RM, Lamb VJ. Involuntary breath-stacking. An alter-native method for vital capacity estimation in poorly cooperative subjects. Am Rev Respir Dis. 1986;134(4):694-698. https://doi.org/10.1164/arrd.1986.134.5.902
15. Naue WDS, Herve BB, Vieira FN, Deponti GN, Martins LF, Dias AS, et al. Comparison of bronchial hygiene techniques in mechanically ventilated patients: a randomized clinical trial. Rev Bras Ter Intensiva. 2019;31(1):39-46. https://doi.org/10.5935/0103-507X.20190005