Physiological effects of vibration in subjects with cystic fibrosis

Subjects

Subjects diagnosed with CF were recruited for the study. The exclusion criteria were the presence of two or more of any of the five signs or symptoms of an acute infection within the previous 2 weeks, i.e. fever >37.5°C, acute increase in secretion production, increase in shortness of breath, feeling unwell and an increased use of antibiotics.

Procedure

All testing was carried out during one session. The subjects were asked to refrain from performing any respiratory physiotherapy treatment and taking hypertonic saline or pulmonzyme for ≥4 h prior to the study 11. In addition, subjects were asked not to take any other medication (bronchodilators, etc.) that they would routinely take prior to respiratory physiotherapy. Such medication was administered 15 min prior to dynamic spirometry (Vitalograph Compact; Vitalograph Ltd, Buckingham, UK) and the testing session.

All interventions were carried out by the same physiotherapist, who instructed the subjects in the various interventions to ensure their consistent application. Each intervention was implemented to replicate current clinical practice and was applied or performed three times by each subject. The order for all interventions was randomised using a computer-generated list.

The physiotherapy interventions were vibration, percussion, PEP device (hereafter referred to as PEP; Astra Tech, Molndal, Sweden), Flutter VRP1 valve® (hereafter referred to as Flutter®; Desitin/Scandipharm VarioRaw SA, Birmingham, AL, USA) and Acapella PEP® therapy DH (hereafter referred to as Acapella®; DHD Healthcare, Wampsville, NY, USA). The forced expiratory manoeuvres were voluntary cough and huff from high lung volumes (huff_HIGH). The subjects also performed an inspiration to total lung capacity (TLC) followed by passive expiration (TLC_relax) to act as a control manoeuvre to account for the effects of lung recoil on expiratory flow.

Vibration was applied manually to the chest wall during expiration after a slow maximal inspiration described to the subject as a “big” breath in. The subjects were asked not to actively expire. Percussion was applied manually during tidal breathing for ≥30 s per application. During both vibration and percussion the position of the subject was side-lying, with the reported most productive side uppermost. If there was no difference in reported sputum production between the left and right lungs, then the side-lying position was randomised. The forces applied to the subject's chest wall during both percussion and vibration were at the greatest tolerated level of comfort.

The breathing manoeuvre during the use of the devices of PEP, Flutter® and Acapella® was an inspiration slightly deeper than a normal tidal breath with an end-inspiratory pause of 2–3 s. Expiration was slightly active but not forceful, lasting for ∼5 s. During the use of PEP, the resistor selected was one which allowed a positive expiratory pressure between 15–20 cmH₂O 11 for 5 s to be achieved by each subject. During the use of Flutter®, the device was in almost neutral position (i.e. horizontal) to maximise the oscillation amplitude and to target the mid-frequency range of oscillation of 10–15 Hz 12. This mid-frequency range is proposed to have maximal effect on mucus transport 4, 13. The Acapella® was used according to manufacturer's recommendations (DHD Healthcare) with the resistance set by adjusting the numerical dial to the minimal level at which each subject could exhale for 3–4 s while feeling the vibratory effects.

During huff_HIGH and cough the subjects were instructed to inspire maximally, followed by either a forced expiration with the glottis open for huff_HIGH or a cough. For TLC_relax subjects were instructed to inspire to TLC and expire passively.

Subjects were instructed to inspire as slowly as possible for all interventions (except percussion) to maximise an expiratory bias to airflow. They were sitting upright for all of the interventions with the exception of vibration and percussion. Between repetitions of an intervention and between each intervention, subjects were encouraged to rest and perform relaxed tidal breathing until they had returned to the baseline effort of breathing.

Ethical approval for the study was obtained from the Central Sydney Area Health Service Ethics Committee and The University of Sydney's Human Research Ethics Committee (both located in Camperdown, New South Wales, Australia) and informed consent was obtained from each subject.

Measurements

The inspiratory and expiratory flow rates during all interventions were measured via a mouthpiece with a heated pneumotachograph (Hans Rudolph Model 3813; Hans Rudolph Inc., Kansas City, MO, USA). Flow signals were integrated to provide volume measurements 14. The devices of PEP, Flutter® and Acapella® were attached to the expiratory port of a two-way non-rebreathing valve (2700 series; Hans Rudolph Inc.), which was connected to the pneumotachograph. This enabled inspiration through the pneumotachograph and expiration through the pneumotachograph and the devices. The pneumotachograph was calibrated and used according to recommended guidelines 15. Data was collected at a sampling frequency of 100 Hz. The subjects were asked to score perceived breathing effort of each intervention using the modified Borg scale for breathlessness 16. During each intervention the number of spontaneous coughs elicited was recorded with an audiotape for later analysis.

Data analysis

The oscillation frequency of the interventions that had a proposed oscillation component (i.e. vibration, percussion, Flutter® and Acapella®) was determined via frequency spectral analysis (Fourier Transform of the auto-correlation function) 17 of the flow data. Analysis of oscillation frequency of cough and huff_HIGH was not performed. After each session the number of spontaneous coughs stimulated during each intervention was recorded from the audiotape.

To calculate sample size, a power analysis was performed on the data of the first 14 subjects, to detect a 25% difference in PEFRs between vibration and one of the other interventions of Flutter®, Acapella®, percussion or PEP. A sample size of 12 subjects was required for this repeated measure study to have 80% power with α of 0.05.

In order to minimise the risk of a type-one error due to too many statistical tests, only the inspiratory volume (V_I), PEFR, cough frequency and oscillation frequency of vibration were compared with the other physiotherapy interventions of percussion, PEP, Flutter® and Acapella®. An additional analysis, comparing V_I and PEFR of vibration with cough and huff_HIGH, was performed. A repeated measures ANOVA and a post hoc Dunnett's test were used. A Friedman ANOVA for repeated measures was used to compare the subject's reported breathing effort during vibration with the physiotherapy interventions of Acapella®, Flutter®, PEP and percussion as the data were not normally distributed. A one-way ANOVA was used to compare the effect of disease severity on the PEFR of vibration. Disease severity was based on forced expiratory volume in one second (FEV₁) % predicted, where severe lung disease was FEV₁ ≤40% pred, moderate lung disease was FEV₁ >40%– ≤70% pred, mild lung disease was FEV₁ >70%– <90% pred and normal lung function was FEV₁ ≥90% pred 18. The results report the mean±sd of the subjects' data and mean±sd of means of the triplicate measures of each intervention of each subject. Significance was set at the p<0.05 level.

Subjects

A total of 18 subjects (seven female) diagnosed with CF volunteered for the study. The mean±sd age of these subjects was 28.5±6.2 yrs with a body mass index of 20.8±2.8 kg·m⁻². The mean FEV₁ was 55% pred, with a FEV₁/forced vital capacity ratio of 58%. Six subjects had severe lung disease, eight had a moderate lung disease, one had mild lung disease and three subjects had normal lung function.

Effects of physiotherapy interventions on respiratory flow rates and volumes

The mean PEFR of vibration was 1.4 times greater than Flutter® (p = 0.002), 1.9 times greater than percussion (p<0.001), 2.7 times greater than Acapella® (p<0.001) and 3.6 times greater than PEP (p<0.001; table 1⇓, fig. 1⇓). Figure 2⇓ shows the time course of expiratory flow of the interventions of one subject. There was no significant effect of disease severity on the PEFR of vibration (p = 0.17).

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Fig. 1—

The peak expiratory flow rate (PEFR) of physiotherapy interventions. Data are presented as mean±sd of means of each subject. PEP: positive expiratory pressure. p-values are significantly different from vibration. ***: p<0.001; ^#: p = 0.002.

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Fig. 2—

The time course of the expiratory flow of the interventions in one subject. The eight traces have been separated vertically for clarity. Huff_HIGH: huff from high lung volumes; TLC_relax: total lung capacity passive expiration; PEP: positive expiratory pressure.

There was no significant difference in inspired volumes between vibration and those of PEP, Flutter® and Acapella® (table 1⇑). The inspired volume of vibration was greater than percussion (p<0.001). There was no difference in the number of coughs stimulated between vibration, percussion, Flutter®, Acapella® and PEP (p = 0.7).

Frequency of oscillation of physiotherapy interventions

Table 2⇓ shows the frequency of oscillation of airflow for vibration, percussion, Flutter® and Acapella®.

Forced expiratory manoeuvres

The mean PEFR of cough and huff_HIGH were 2.9 (p<0.001) and 3.2 (p<0.001) times greater than vibration, respectively. The mean inspired volumes of vibration, cough and huff_HIGH were similar (table 3⇓).

There were no reported adverse effects during any of the interventions during this study. There was no significant difference in the perceived effort between the interventions and no significant effect of the order of the interventions on perceived effort was noted.

Limitations

The principle aim of this study was to measure expiratory flow rates and oscillation frequencies of vibration and other physiotherapy interventions, not to measure the effects of these interventions on secretion clearance. Thus, it was not determined whether the subjects had excessive secretions, nor was secretion clearance measured. However, all subjects performed physiotherapy for airway clearance at least daily, implying that they perceived they had excessive secretions. Secondly, the PEFR does not reflect flow in the peripheral airways from which the physiotherapy interventions are proposed to clear secretions. A measure of interest would have been the maximal expiratory flow rates during the latter half of expiration as an indication of peripheral airflow. However, in order to compare this measure between interventions, the flow rates at similar lung volumes are required. The physiotherapy interventions were performed at different lung volumes, reflecting current clinical practice and thus precluding such a comparison.

Conclusions

This study provided physiological evidence to suggest that in subjects with cystic fibrosis and stable lung function, vibration may be effective in secretion clearance by assisting with the movement of secretions according to the theoretical rationale of increasing absolute expiratory flow rates, peak expiratory flow rate/peak inspiratory flow rate ratio >1.1 and oscillation frequency. The effects of vibration on secretion clearance are still unknown. However, the data from the present study have provided some evidence to enable inferences to be drawn about the possible effects of these physiotherapy interventions on secretion clearance based on theoretical rationale.