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Physiological effects of vibration in cystic fibrosis; implications for COVID-19 rehabilitation.

In order to facilitate the removal of secretions in cystic fibrosis patients, vibrotherapy techniques have been used for many years {this study relates to a 2006 article but the techniques described in it are still in use today; editorial note}. They can be both manual (such as vibrations and tapping) or engaging devices generating air oscillations, e.g. Flutter® or Acapella® {for comprehensive review see [Morrison and Milroy, 2017],where authors detail also the vibrating vests of cystic fibrosis clinic; editorial note}. Special attention in the presented article was given to manual vibrations. They rely on performing oscillating movements combined with pressure on the patient’s chest wall. The goal of Australian scientists from the University of Sydney was to compare the physiological effects of manual vibrations to other standard physiotherapeutic interventions used to clear the airways of patients with cystic fibrosis and to relate them to appropriate physiological mechanisms.

  • No adverse effects were reported during the interventions.
  • The average peak expiratory flow rate (PEFR) during manual vibration was:
    1.4 times higher than for Flutter® intervention;
    1.9 times higher than for tapping;
    2.7 times higher than for the intervention with Acapella®;
    3.6 times higher than for PEP intervention.
  • Disease severity did not influence PEFR while using the manual vibrations.

Prepared on the basis of:

Physiological effects of vibration in subjects with cystic fibrosis. McCarren B, Alison JA. Eur Respir J. 2006 Jun;27(6):1204-9.

Study population

A total of 18 people (seven women) diagnosed with cystic fibrosis volunteered for the study. Mean age: 28.5 ± 6.2 years; mean body mass index: 20.8 ± 2.8 kg m-2. The mean forced expiratory volume in 1 second was 55% predicted. Six patients had severe lung disease, eight had moderate lung disease, one had mild lung disease, and three patients had normal lung function.

Test procedure

All interventions were performed in one session and included: manual vibrations, tapping, PEP, Flutter® and Acapella®.

Each type of intervention was applied 3 times. The order of all interventions was random.

Use of vibration in the study

Manual vibrations given by physiotherapists consisted of oscillatory movements combined with the pressure of the patient’s chest wall. They were applied while exhaling following a slow maximum inhalation. The subjects were asked not to put any effort into the exhalation. The tapping was applied manually while breathing calmly. During both vibration and percussion, the subject was lying on the side of the body with a lung less affected by secretions exposing the more productive side to manual vibrotherapy. If there was no difference in sputum production between the left and right lungs, the exposed side of the body was randomized. Patients were sitting upright while performing PEP, Flutter® or Acapella®.

When using the Flutter®, the device was almost horizontal to maximize the oscillation amplitude, aiming to achieve an oscillation frequency of the range of 10-15 Hz. According to previous studies, this frequency range has the greatest effect on mucus mobilization. Acapella® has been used according to the manufacturer’s (DHD Healthcare) recommendations with resistance set to the minimum level; each patient could feel the vibration for 3-4 seconds while exhaling.

The vibration frequency of the physiotherapeutic interventions used was determined by frequency spectral analysis:

  • Manual vibration – 8.4 ± 0.4 (7.3-10.0)
  • Percussion – 7.3 ± 0.3 (6.5-8.0)
  • Flutter® – 11.3 ± 1.5 (7.5-13.7)
  • Acapella® – 13.5 ± 1.7 (10.0-18.3)

Results

No adverse effects were reported during the interventions. There was no significant difference in the perceived effort involved in any intervention. There was no significant effect of the order of intervention on the perceived effort.

The influence of physiotherapeutic interventions on both the flow rate and tidal volume

The mean PEFR during manual vibration was 1.4 times greater than for the Flutter® intervention (p = 0.002), 1.9 times greater than for the tapping (p <0.001), 2.7 times greater than for the intervention with Acapella® (p <0.001) and 3.6 times higher than for the PEP intervention (p <0.001). There was no significant effect of disease severity on PEFR when using manual vibrations (p = 0.17).

There was no significant difference in inhaled volumes between the manual vibration treatment and the use of PEP, Flutter® or Acapella®. The inhaled volume of air during manual vibration was greater than during tapping (p <0.001).

There was no difference in the number of coughs between the interventions (p = 0.7).

Forced expiratory strategies

The mean PEFR of cough and huffHIGH were 2.9 (p < 0.001) or 3.2 times (p < 0.001), respectively, higher than during the vibration.

Comment

The study compares the effects of different types of vibrotherapy: manual vibration, tapping, the positive expiratory pressure (PEP), techniques using oscillating PEP with Acapella® or Flutter®. As shown in previous publications, all these interventions help move pulmonary mucus to the central airways, from where it can be expectorated. Also, this form of physiotherapy has been shown to be more effective at removing mucus than no intervention, but the exact mechanisms by which these interventions assist in removing mucus in cystic fibrosis patients are unknown. Understanding the mechanism would be helpful in choosing a treatment for known symptom severity. Among the considered mechanisms, the following are proposed:

  • increasing PEFR to move mucus to the oropharynx;
  • improving the expiratory air flow to increase the annular flow of mucus towards the mouth and pharynx, which occurs when PEFR is 10% greater than the peak inspiratory flow rate (PIFR), i.e. PEFR/PIFR ratio > 1, 1;
  • increasing mucus transport by reducing the viscosity of the mucus and improving the expiratory flow due to the effects of air flow oscillations in the frequency range of 3-17 Hz;
  • induction of spontaneous coughing by mechanical stimulation of the airways.

The presented results show that manual vibrations resulted in higher expiratory flow and provided a higher PEFR/PIFR ratio than other analyzed physiotherapeutic interventions, with Flutter® and Acapella® having even higher oscillation frequencies than manual vibrations.

The PEFR of manual vibration was greater than that of other interventions. Manual vibrations applied to the chest wall can increase the pressure within the pleura and therefore can increase the expiratory flow rate. In addition, during manual vibration there is no need to deal with additional resistance in the mouth hindering the expiratory flow as it is when using PEP, Acapella® or Flutter®. Therefore, external forces applied to the chest wall in the form of vibrations can more effectively increase the peak expiratory flow rate and, if the increase in expiratory flow contributes to the mechanisms of secretion clearance, the manual vibration can be a beneficial intervention in secretion removal and more efficient than other interventions analyzed.

The mean number of spontaneous coughs during manual vibration sessions was less than 1 and did not differ significantly from other interventions. Perhaps, therefore, it is not the stimulation to cough that is responsible for the pulmonary secretions clearance.

The removal of secretions may be assisted by the oscillations (vibrations) of the air flow. All analyzed physiotherapeutic interventions, with the exception of PEP, generated oscillations in the 3-17 Hz range, which should facilitate mucociliary clearance, as shown earlier. These frequencies can work by altering the rheology of the mucus and by accelerating the rate of epithelial cells ciliary movement. The oscillation frequencies of Flutter® (11.3 Hz) and Acapella® (13.5 Hz) were close to the optimal frequency for secretion removal (which is 13 Hz, as shown in previous publications). The natural frequency of ciliary beats is 11-15 Hz, so delivering an oscillation of a similar frequency can cause the flowing air to resonate and thus increase the amplitude of respiratory epithelium cilia, what can directly increase mucus transport.

{The editors would like to correlate the presented research on cystic fibrosis with the suggestion of post-COVID-19 rehabilitation. In the era of the COVID-19 pandemic, rehabilitation of pulmonary complications seems to be particularly important. Many years of clinical practice in using vibrotherapy to facilitate the elimination of secretions in cystic fibrosis allows for a hypothesis that vibrotherapy may also be effective in post-COVID-19 rehabilitation. It is especially noteworthy as the exposure of hospital staff to possible contact with the SARS-CoV-2 must be kept at a minimum level in order not to block health care workers in quarantines. The current techniques of vibrotherapy make it possible to replace manual vibration with automated systems that do not require the constant presence of a physiotherapist next to the patient. Vibrating vests generating high-frequency chest vibrations (The Vest®, VibraVest®, SmartVest®) used for years in cystic fibrosis physiotherapy should be tested first [Hill et al., 2019; Seitz et al., 2010], as well as vibrating belts that have already been tested in one clinical trial in mechanically ventilated covid patients [Sancho i wsp., 2020]. It seems also that the potential of other available devices generating therapeutic vibrations should be tested. Especially those already used in physiotherapeutic practice of other diseases. In addition, COVID-19 symptoms often persist for weeks and months after discharge from hospital. Therefore, post-COVID-19 rehabilitation may be a long-term therapy and should be properly directed. That’s why there is an urgent need for a number of clinical trials. It seems crucial to test various forms of physiotherapy already acting in other diseases on symptoms similar to those observed in COVID-19. Therefore, it is worth looking at vibrotherapy as it already improves the quality of life in chronic obstructive pulmonary disease or fibromyalgia [Sañudo et al., 2020]. Editorial note.}

More in:

Physiological effects of vibration in subjects with cystic fibrosis. McCarren B, Alison JA. Eur Respir J. 2006 Jun;27(6):1204-9. doi: 10.1183/09031936.06.00083605. Epub 2006 Feb 2. PubMed PMID: 16455834.

Author of the coverage:
Rafal Aleksander Guzik, PhD (med. sci)

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