Increase in mucociliary clearance in normal man induced by oral high frequency oscillation

Clinical application of intrapulmonary percussive ventilation: A scoping review

Impaired respiratory function secondary to acute or chronic respiratory disease poses a significant clinical and healthcare burden. Intrapulmonary percussive ventilation (IPV) is used in various clinical settings to treat excessive airway secretions, pulmonary atelectasis, and impaired gas exchange. Despite IPV's wide use, there is a lack of clinical guidance on IPV application which may lead to inconsistency in clinical practice. This scoping review aimed to summarise the clinical application methods and dosage of IPV used by clinicians and researchers to provide guidance. A two-staged systematic search was conducted to retrieve studies that used IPV in inpatient and outpatient settings. MEDLINE, EMBASE, CINAHL, Scopus, and Google scholar were searched from January 1979 till 2022. Studies with patients aged ≥16 years and published in any language were included. Two reviewers independently screened the title and abstract, reviewed full text articles, and extracted data. Search yielded 514 studies. After removing duplicates and irrelevant studies, 25 studies with 905 participants met the inclusion criteria. This is the first scoping review to summarise IPV application methods and dosages from the available studies in intensive care unit (ICU), acute inpatient (non-ICU), and outpatient settings. Some variations in clinical applications and prescribed dosages of IPV were noted. Despite variations, common trends in clinical application and prescription of IPV dosages were observed and summarised to assist clinicians with IPV intervention. Although an evidence-based clinical guideline could not be provided, this review provides detailed information on IPV application and dosages in order to provide clinical guidance and lays a foundation towards developing a clinical practice guideline in the future.

Effect of intrathoracic oscillations on pulmonary functions in children with cerebral palsy

Objectives

This study was aimed at investigating the effects of intrathoracic oscillations on pulmonary function in children with spastic quadriplegic cerebral palsy.

Methods

This study comprised 24 boys and girls 6-8 years of age with spastic quadriplegic cerebral palsy. According to the modified Ashworth scale, the degree of spasticity was 2 to 2+. The children were able to sit independently and follow instructions. The children were randomly divided into a study group and control group. A spirometer was used to examine each child before and after 6 weeks. Children in the control group received traditional chest physiotherapy (postural drainage and percussion), whereas children in the study group underwent quake device training. For 6 weeks, both groups received four sessions per week. After treatment, the results were collected. Paired t-test and independent-samples t-test were applied to compare the means for each group. p-values <0.05 were considered significant.

Results

The post-treatment results of forced expiratory volume at 1 s, peak expiratory flow, forced vital capacity, and the ratio of forced expiratory volume at 1 s to forced vital capacity demonstrated significant differences favoring the study group over the control group (p < 0.001, p < 0.001, p = 0.002, and p = 0.023, respectively).

Conclusion

Intrathoracic oscillations may improve pulmonary function in children with quadriplegic cerebral palsy.

Performance Characteristics of Positive Expiratory Pressure Devices

BACKGROUND

Positive expiratory pressure (PEP) therapy imposes expiratory flow resistance to increase airway diameter and enhance mucus clearance. PEP is achieved several ways. Oscillatory PEP devices (OPEP) generate repeated occlusions that are known to reduce mucus viscosity. There are many marketed devices, but comparative performance is mostly unreported. The purpose of this study was to evaluate performance characteristics of many PEP/OPEP devices. For OPEP devices, we defined an optimal performance metric by creating an oscillation index that combines the OPEP performance characteristics.

METHODS

PEP devices (TheraPEP, EzPAP, VersaPAP, Resistex, AccuPEP, AccuPAP, and Threshold PEP) and OPEP devices (Acapella DH, Acapella DM, Acapella Choice, ShurClear, Aerobika, VibraPEP, vPEP, and PocketPEP with and without the Oxyjet attachment) were tested by adjusting simulated expiratory flow from 5 L/min to 30 L/min in increments of 5 L/min using a standard flow meter.

RESULTS

All devices showed varying performance characteristics. As expiratory flow increased, mean PEP increased for most devices. The TheraPEP showed a mean PEP of 13 cm H₂O across all settings. For OPEP devices, there was a major difference between pressure and flow waveforms. The Acapella DH, ShurClear, and Aerobika showed the highest flow amplitude, flow frequency, and oscillation index.

CONCLUSIONS

PEP devices behaved similarly and as expected, with increased pressure with increased flow (flow resistors) or flow independence (threshold resistors). There was much greater variation in the performance of the OPEP devices. A higher oscillation index indicates better mechanical performance characteristics. Many devices have similar characteristics. However, the devices with the highest oscillation index have the highest flow amplitude and frequency, which may indicate better clinical performance.

Comparison of breathing patterns, pressure, volume, and flow characteristics of three breathing techniques to encourage lung inflation in healthy older people

Background: It is important to encourage lung inflation to prevent postsurgical pulmonary complications and we compared three breathing techniques that place different emphasis on inspiratory flow and breath-holding. Methods: Fourteen healthy older people (69 ± 3.6 yrs) used diaphragmatic breathing (DB), Triflo II (TF), and a water pressure threshold device (BreatheMAX; BM) in a randomized and balanced crossover design. Outcome measures were inspiratory flow and pressure, inspiratory time (Ti), tidal volume (Vt), and breathing frequency. Results: Inspiratory flow with TF was significantly faster than DB and BM (p < 0.001: 0.96 ± 0.1; 0.43 ± 0.20 and 0.28 ± 0.1 L.s^-1, respectively) and pressures greater (p < 0.001: -1.3 ± 0.6, -5.5 ± 1.2 and -2.8 ± 3.6 cm H₂O). However, Ti was shorter (TF, 1.16 ± 0.21s; DB, 3.31 ± 0.97 s, p < 0.001; BM, 5.53 ± 1.92 s, p < 0.001), resulting in smaller Vt (TF, 1.12 ± 0.29 L; DB, 1.28 ± 0.29L, p = 0.003; BM, 1.37 ± 0.43L, p = 0.016). Breathing frequency was faster with TF compared to DB and BM (p < 0.001). Conclusions: Substantial lung inflation could be achieved with any of the above-mentioned methods, although Vt was smaller with TF and the high inspiratory flow with this method may not inflate the lower lung. The high pressures and rapid breathing with TF could increase the sense of effort. Trials are needed to determine the clinical value of the different breathing exercises.

Effects of intrapulmonary percussive ventilation on airway mucus clearance: A bench model

AIM

To determine the ability of intrapulmonary percussive ventilation (IPV) to promote airway clearance in spontaneously breathing patients and those on mechanical ventilation.

METHODS

An artificial lung was used to simulate a spontaneously breathing patient (Group 1), and was then connected to a mechanical ventilator to simulate a patient on mechanical ventilation (Group 2). An 8.5 mm endotracheal tube (ETT) connected to the test lung, simulated the patient airway. Artificial mucus was instilled into the mid-portion of the ETT. A filter was attached at both ends of the ETT to collect the mucus displaced proximally (mouth-piece filter) and distally (lung filter). The IPV machine was attached to the proximal end of the ETT and was applied for 10-min each to Group 1 and 2. After each experiment, the weight of the various circuit components were determined and compared to their dry weights to calculate the weight of the displaced mucus.

RESULTS

In Group 1 (spontaneously breathing model), 26.8% ± 3.1% of the simulated mucus was displaced proximally, compared to 0% in Group 2 (the mechanically ventilated model) with a P-value of < 0.01. In fact, 17% ± 1.5% of the mucus in Group 2 remained in the mid-portion of the ETT where it was initially instilled and 80% ± 4.2% was displaced distally back towards the lung (P < 0.01). There was an overall statistically significant amount of mucus movement proximally towards the mouth-piece in the spontaneously breathing (SB) patient. There was also an overall statistically significant amount of mucus movement distally back towards the lung in the mechanically ventilated (MV) model. In the mechanically ventilated model, no mucus was observed to move towards the proximal/mouth piece section of the ETT.

CONCLUSION

This bench model suggests that IPV is associated with displacement of mucus towards the proximal mouthpiece in the SB patient, and distally in the MV model.

A new method for enhanced expectoration of sputum by vibratory stimulation of the cervical trachea

BACKGROUND

Expectoration of sputum can be difficult for patients with respiratory conditions such as chronic obstructive pulmonary disease, chronic bronchitis, or bronchiectasis because of the effects of decreased pulmonary function, respiratory muscle fatigue, altered sputum properties, and impaired ciliary function. We developed a new method for the vibratory stimulation of the cervical trachea and this study aimed to compare it with the Acapella (a current oscillation device) method.

METHODS

Patients with chronic productive cough and difficulty with expectoration were recruited for the study. The tracheal vibration and Acapella methods were applied for 4 weeks each, according to a crossover design with an intervening 4-week washout period. To perform the tracheal vibration method, an electronic artificial larynx (Yourtone®) was applied to the cervical trachea for up to 5minutes. Patient preference for the two devices was determined from the performance scores recorded for each device and by using a visual analogue scale.

RESULTS

Twelve patients were recruited in the study. According to the performance scores assigned by the subjects, the tracheal vibration method was effective in 9 patients, while the Acapella method was effective in 10 patients. Both methods were effective in 8 patients, among whom the tracheal vibration method was more effective in 5 patients. Both methods were found to be ineffective in 1 patient.

CONCLUSIONS

The tracheal vibration method may be effective at removing central airway sputum and does not require repeated forced expiratory effort, which can otherwise cause exhaustion in patients with decreased lung function. Further investigation is required to confirm its use as a new oscillation technique.

Measurement of Resonant Frequencies in the Human Chest

Measurements of resonant frequencies in the human chest, and of how resonant frequency varies with the subject's mass, height, chest size and sex, were undertaken as a pilot study on a sample of 15 volunteers. These were obtained by measuring the acceleration response of the chest when a force was applied to the back at a range of frequencies, and noting the peak response frequency. It is foreseen that mechanical stimulation of the chest at the appropriate frequency might form a useful part of physiotherapy treatment offered to patients with particular chest disorders. The results suggest that the chest resonant frequency is sensitive to the subject's mass and chest size, but is less dependent on height. Typical values found were 25 Hz for males and 33 Hz for females.

Optimizing an Internal Airway Percussion Device for Facilitating Exhalate Diagnostics of the Human Respiratory System

PURPOSE

There is an urgent need for simple, inexpensive, noninvasive, and repeatable technique for the diagnosis of pulmonary diseases. Bronchoalveolar lavage, which is the gold standard diagnostic method for pulmonary diseases, does not meet any of these criteria. This study seeks to develop and optimize a novel technique of Internal Airway Percussion (IAP) to facilitate the collection and characterization of human respiratory system exhalates.

METHODS

The IAP device transmits sound waves into the respiratory tract, thereby increasing the release of aerosolized particles within exhaled breath by vibrating both lungs. Nine combinations of sound wave frequencies and amplitudes were studied to determine optimal frequency and amplitude combination for maximum aerosol particle gain in healthy human subjects.

RESULTS

Square-shaped sound waves generated at 15 Hz and 3 cm H₂O resulted in 15 times greater total mass of collected particles in the first 2 min of sampling, and 1.2 to 1.5 times increase in count median diameter of the particles.

CONCLUSIONS

IAP, optimized at the frequency of 15 Hz and the pressure amplitude of 3 cm H₂O, increased the total mass of particles exhaled from the human respiratory system. IAP has a broad range of potential clinical applications for noninvasive diagnosis of lung diseases including asthma, cystic fibrosis, pneumonia, and lung cancer, along with improvement of mucus clearance.

Breathing exercise using a new breathing device increases airway secretion clearance in mechanically ventilated patients

OBJECTIVES

To evaluate the efficacy and safety of a new device (BreatheMAX) that humidifies and oscillates inspired air to increase secretion clearance in mechanically ventilated patients.

BACKGROUND

Poor secretion clearance is a serious problem for intubated patients leading to lung complications and delayed weaning.

METHODS

Double blinded crossover; fifteen patients, median age 60 years, range 16-75. Interventions consisted of spontaneous deep breathing with (treatment) and without (sham) humidification and oscillation of inspired air. Airway secretions were aspirated for 3 h before and after each intervention and wet weight and viscosity determined.

RESULTS

The sham intervention caused no change in secretion clearance (95% CI: -1.8, 1.8 g) but after treatment secretions increased by 4.0 g (95% CI: 1.3, 6.7; p < 0.05). Viscosity decreased 30% after treatment and was unchanged after sham. Changes in cardiopulmonary function were not clinically significant and the patients reported only mild perceptions of breathlessness.

CONCLUSIONS

Breathing exercise with a device that includes vibration and humidification of inspired air is effective for increasing secretion clearance with patients dependent on mechanical ventilation and was without any adverse effects.

Improving mucociliary clearance in chronic obstructive pulmonary disease

Patients with COPD usually experience mucus hypersecretion as a result of airway inflammation and response to noxious stimuli. These in turn lead to worsening airway resistance, impaired airflow, increased work of breathing, dyspnoea and exercise intolerance. Mucus hypersecretion may also lead to increased exacerbations and poor health related quality of life (HRQL). Institution based pulmonary rehabilitation programs incorporating airway clearance techniques have been shown to improve HRQL, reduce dyspnoea and improve exercise tolerance but are often difficult to provide due to restricted accessibility and resource implications. This review examines the current evidence base and best clinical practice in the area of airway clearance. Mechanical devices such as the flutter valves, positive end expiratory pressure and high frequency chest wall oscillation (HFCWO) may be able to provide the benefits of improved airway clearance in the patient's home potentially with reduced demands on healthcare resources.

Current devices of respiratory physiotherapy

In recent years patients with respiratory diseases use various devices, which help the removal of mucus from the airways and the improvement of pulmonary function. The aim of the present study is to determine the effectiveness of the current devices of respiratory physiotherapy, as it comes from the review of literature. The current devices of physiotherapy for patients with respiratory diseases, are presented as an alternative therapy method or a supplemental therapy and they can motivate patients to apply therapy by themselves. These devices seem to increase patients' compliance to daily treatment, because they present many benefits, as independent application, full control of therapy and easy use. These devices are the Positive Expiratory Pressure, the High Frequency Chest Wall Oscillation, the Oral High Frequency Oscillation, the Intrapulmonary Percussive Ventilation, the Incentive Spirometry the Flutter and the Acapella and the Cornet. Current devices seem to be effective in terms of mucus expectoration and pulmonary function improvement, as it is shown by published studies. The choice of the suitable device for each patient is a challenge for the physiotherapist in order to achieve better compliance in daily treatment. More controlled studies are needed due to the fact that the number of published studies is limited.

Treatment of experimental meconium aspiration syndrome with surfactant lung lavage and conventional vs. asymmetric high-frequency jet ventilation

Respiratory failure caused by meconium aspiration requires combined strategies. We hypothesized that surfactant lung lavage with asymmetric high-frequency jet ventilation (AHFJV) can increase the removal of meconium and improve lung function. During conventional ventilation (CV), a suspension of human meconium (25 mg/ml, 4 ml/kg) was instilled into the tracheal tube of anesthetized rabbits to cause respiratory failure. Animals were then divided into four groups: saline lavage + CV (Sal-CV), surfactant lavage + CV (Surf-CV), saline lavage + HFJV (Sal-HFJV), and surfactant lavage + HFJV (Surf-HFJV). Lung lavage (10 ml/kg in 3 portions) was performed with diluted surfactant (Curosurf, 100 mg of phospholipids/kg) or saline during CV (frequency (f), 30/min; inspiration time (Ti), 50%) or AHFJV (f, 300/min; Ti, 70%). Animals were ventilated for an additional hour with either CV or HFJV (Ti, 50%). Surfactant lavage with both CV and AHFJV removed more meconium than saline lavage. However, the highest removal was found in the Surf-HFJV group vs. all other groups (P < 0.05). The oxygenation index decreased after surfactant lavage in both groups compared to controls (P < 0.001), and more prominently in the Surf-CV group. Elimination of CO(2) was significantly higher in the Surf-HFJV group vs. all other groups (P < 0.05). The ventilation efficiency index increased after lavage in both surfactant groups vs. saline controls (P < 0.05). Dynamic lung-thorax compliance gradually increased, and right-to-left pulmonary shunts decreased in both surfactant groups vs. saline controls after lavage (P < 0.05). Combination of surfactant lavage with both CV and AHFJV was beneficial in rabbits with meconium aspiration syndrome. While AHFJV was more effective in the removal of meconium, CV had a more favorable effect on lung function in the postlavage period.

Effect of high-frequency oral airway and chest wall oscillation and conventional chest physical therapy on expectoration in patients with stable cystic fibrosis

STUDY OBJECTIVE

To compare the effect of high-frequency oral airway oscillation, high-frequency chest wall oscillation, and conventional chest physical therapy (CPT) on weight of expectorated sputum, pulmonary function, and oxygen saturation in outpatients with stable cystic fibrosis (CF).

DESIGN

Prospective randomized trial.

SETTING

Pediatric pulmonary division of a tertiary care center.

PATIENTS

Fourteen outpatients with stable CF recruited from the CF center.

INTERVENTIONS

Two modes of oral airway oscillation (1: frequency 8 Hz; inspiratory to expiratory [I:E] ratio 9:1; 2: frequency 14 Hz; I:E ratio 8:1), two modes of chest wall oscillation (1: frequency 3 Hz; I:E ratio 4:1; 2: frequency 16 Hz; I:E ratio 1:1, alternating with frequency 1.5 Hz, I:E ratio 6:1), and CPT (clapping, vibration, postural drainage, and encouraged coughing) were applied during the first 20 min of 4 consecutive hours.

MEASUREMENTS AND RESULTS

Sputum was collected on an hourly basis for a total of 6 consecutive hours. During the first and the last hour, patients collected sputum without having any treatment and underwent pulmonary function tests (PFTs). Oxygen saturation was measured at 30-min intervals during hours 1 to 6. For the first 20 min of the second to the fifth hour, patients received one of the treatments. To assess the effect of the intervention, the weight of expectorated sputum during hours 2 to 6 was averaged and expressed as percentage of the weight expectorated during the first hour (baseline). For the five treatment modalities, mean sputum dry and wet weights ranged between 122% and 185% of baseline. There was no statistically significant difference among the treatment modalities. As measured by sputum wet weight, all oscillatory devices tended to be less effective than CPT (p=0.15). As measured by dry weight, oral airway oscillation at 8 Hz with an I:E ratio of 9:1 and CPT tended to be more effective than the other treatment modalities (p=0.57). None of the treatment modalities had an effect on PFTs and oxygen saturation and all were well tolerated.

CONCLUSION

In outpatients with stable CF, high-frequency oscillation applied via the airway opening or via the chest wall and CPT have comparable augmenting effects on expectorated sputum weight without changing PFTs or oxygen saturation. In contrast to CPT, high-frequency oral airway and chest wall oscillations are self-administered, thereby containing health-care expenses.

Promoting meconium clearance from the lungs of the neonatal piglet with asymmetric high frequency oscillation

To investigate the role of high frequency oscillation (HFO) in promoting meconium clearance from the airway, we used a commercially available ventilator configured with maximal expiratory flow exceeding inspiratory flow (asymmetric HFO or AHFO). We hypothesized that AHFO would move meconium in an expiratory direction (toward the ventilator). We first tested our hypothesis in vitro and, later, in vivo using the neonatal piglet. In vitro experiments using a Plexiglas airway confirmed meconium movement in an expiratory direction when bias ratio was > or = 2. For in vivo experiments, each piglet received a 3 mL/kg intratracheal bolus of a 44 g/100 mL meconium mixture followed by 45 min of mechanical ventilation. Then, in part 1, the piglet was placed in a 15 degree head down tilt position and randomized to either AHFO [ratio of inspiratory time/expiratory time (I:E) of 70:30] or HFO (I:E ratio of 30:70). After 30 min of either AHFO or HFO, the piglet was crossed over to the alternate strategy for an additional 30 min. For part 2, we maintained the piglet on either AHFO or HFO continuously for 4 h. Results demonstrate that, although there was a tendency for larger volumes of meconium to be aspirated from the airway during AHFO in part 1 experiments, there was no difference found in part 2. We also found no significant differences in blood gases or hemodynamic measurements between AHFO and HFO during the prolonged observation period in part 2 of our study. We conclude that AHFO is of no benefit in the treatment of meconium aspiration syndrome.

Mechanical chest stimulation as a physiotherapy aid

In patients with lung disorders there is often a build up of mucus inside the lungs which in healthy people is normally removed by the action of cilia on the lung tissue surfaces. In the diseased lung, however, this clearance mechanism may be ineffective and so patients are offered physiotherapy in order to assist the mucus removal process. The consequences of not properly removing the mucus are impaired lung function and a much higher risk of contracting lung infections and suffering consequent permanent scarring of the lung tissues. If unchecked the latter leads ultimately to failure of the lungs and to the patient's death. The most common forms of chest physiotherapy used are percussion coupled with postural drainage and an active cycle of breathing. This requires the patient to lie head downwards on an inclined surface, so that gravity might assist the mucus removal process, whilst the physiotherapist strikes the patient's chest with the hands. The procedure is interspaced by periods of 'huffing and coughing' by the patient to remove the loosened sputum from the body. An alternative to the manual percussion described above is to use machinery to provide the stimulus to the chest. If such a procedure were found to be satisfactory then it would enable more patients to manage their own physiotherapy, may make the required duration of the physiotherapy sessions shorter, and would free much of the professional physiotherapists' time to enable them to assume more of a physiotherapy management role.(ABSTRACT TRUNCATED AT 250 WORDS)

The effects of cromolyn sodium in dogs undergoing high-frequency oscillation superimposed on conventional mechanical ventilation

The effects on gas exchange of superimposition of high-frequency oscillation (HFO) (40 Hz) on conventional mechanical ventilation were investigated in mongrel dogs with eucapnic gas exchange on conventional mechanical ventilation (CMV). The dogs were anesthetized, paralyzed, and ventilated with CMV until stable. Oscillation was then superimposed for 15 min, followed by CMV alone for a further 30 min. During HFO superimposed on CMV (CMV-HFO), the arterial carbon dioxide tension (PaCO2) increased from 43.6 +/- 1.2 mm Hg to 47.2 +/- 1.4 mm Hg (p less than 0.02), whereas the arterial oxygen tension (PaO2) did not change at all. The change was inhibited completely by administration of intravenous cromolyn sodium (CS) (6 mg/kg/min). The mean pulmonary arterial pressure (mPAP), cardiac output (CO), pulmonary capillary wedge pressure (PCWP), and pulmonary vascular resistance (PVR) did not change during the experiment. These results demonstrate that CMV-HFO appears to cause CO2 accumulation and eliminates the impaired O2 transfer, and that these effects are inhibited completely by CS administration.

Effects of pulmonary function of oral high frequency oscillation in normal and asthmatic subjects

High frequency jet devices are not only used as 'internal percussors' to aid clearance of pulmonary secretions, but are also a mode of ventilatory support. As physical stimuli can cause bronchospasm in asthmatic individuals, we hypothesized that direct airway vibration may induce bronchospasm. To ascertain whether an airway vibration jet device could cause bronchoconstriction, we exposed eight asthmatic and six normal subjects to 5 min of jet-induced airway vibration or placebo treatment with cross-over at 3 h. Subjects breathed spontaneously for 5 min through an open mouthpiece into which either jet (10 Hz, 25 psi) or sham pulsations (same device, pressure vented to room at compressor) were delivered in a double-blind, random order. A constant-volume body plethysmography measured functional residual capacity and specific airway conductance (SGAW) and a water seal spirometer measured forced expiratory volume in 1 s (FEV1) and forced vital capacity (FVC). These pulmonary function measurements were taken before and at 5, 10, 20, 30, 60, 90 and 120 min after each exposure. In the normal subjects there was no significant change in any pulmonary function. There was not statistically significant change in the pulmonary function in the asthmatic patients. However, the oral high frequency oscillator induced a clinical asthmatic attack in one asthmatic patient. In this one patient, the FEV1 fell 35% from its initial value at 5 min following exposure to a maximum of 49% decline from initial value at 1 h following exposure.(ABSTRACT TRUNCATED AT 250 WORDS)

The effect of high-frequency ventilation on non-Newtonian properties of bronchial mucus

We have investigated the changes in the non-Newtonian properties of human bronchial mucus brought about by in vitro high frequency ventilation. This type of ventilation brought about changes in viscous properties, measured during creep and oscillation of the mucus, which would be expected to reduce mucus clearance in vivo. We suggest that any beneficial effects of clinical high-frequency ventilation on respiratory mucus clearance in patients are not brought about by long-term (more than a few seconds) changes in the viscous properties of the mucus itself.

The role of chest physiotherapy in mucus hypersecretion

Review of the data shows that chest physiotherapy (CP) is effective in clearing secretions from the lungs of patients with copious secretions (i.e., daily sputum production in excess of 30 ml). Assessment of the various components of CP shows that percussion, vibratory shaking, and breathing exercises have little to offer. Although instructed cough, the back up mucus clearance mechanism, is effective in clearing secretions its effect is less than that achieved with the forced expiration technique (FET). Postural drainage (PD) is on the whole successful in helping to drain secretions in the lungs. The administration of a beta 2-agonist via a nebulizer prior to CP in addition to promoting bronchodilation may also help to alter the physical properties of secretions, rendering them more amenable for clearance by FET/cough. Technology regarding high-frequency oscillations (HFO) has yet to be improved and its efficacy in clearing excess secretions proven prior to its inclusion in a CP treatment regimen. Intermittent positive pressure breathing (IPPB) may have a role to play in those patients where conventional CP is not possible. Data with positive expiratory pressure (PEP) are encouraging and direct evaluation is awaited regarding its effect on mucus clearance. With our present knowledge it seems reasonable to recommend that physiotherapists concentrate their CP treatment on the following: administration of a nebulized beta 2-agonist followed by PD and FET.

Mobilization of mucus by airway oscillations

The effects of high frequency asymmetric airway oscillations on mucus clearance were evaluated in excised tracheas of sheep, in an animal model of excessive mucus production, and in patients with bronchiectasis. Asymmetric high frequency ventilation (15 Hz) with expiratory biased flow profiles (expiratory peak-flow greater than inspiratory peak-flow) could move mucus droplets towards the pharynx in rigid and flexible tracheas by gas-liquid interaction. In rigid tracheas the mucus was transported towards the periphery of the model lung if the oscillations were inspiratory biased. In very collapsible tracheas, however, even inspiratory biased oscillations moved the mucus cephalad. Parameters influencing direction and speed of mucus are airflow profile, peak-flow, airway compliance and lung resistance. Gamma-camera studies showed that in anesthetized dogs radiolabeled artificial mucus followed the direction of the bias during high frequency ventilation. In five human volunteers with bronchiectasis and excessive secretions the asymmetric airway oscillations were superimposed during spontaneous breathing using a mouthpiece. Airway wall vibrations following the pressure swings of the oscillator could be observed. During forced expiration inward bulging of the posterior membranes of trachea and bronchi occurred at the negative pressure phase of the oscillations. This event was associated with increased appearance of sputum in the central airways. We conclude that high frequency ventilation with asymmetric flow profiles applied via tube or mouthpiece might be an effective future treatment of mucostasis.

High frequency oscillations and mucociliary transport

Mucociliary transport is influenced by high frequency oscillation of air within the lungs. While some studies suggest that high frequency ventilation may be detrimental, with appropriate techniques, there is no doubt that this has potential as a means of improving the clearance of secretions from the lung.

Effect of chest wall oscillation on mucus clearance: comparison of two vibrators

This study was designed to investigate the effect of an experimental low-energy chest wall oscillator and of a commercial chest percussor on central airway mucociliary clearance. Five normal dogs were anesthetized, intubated, and placed supine in a trough to which the oscillator or percussor was mounted. Tracheal mucus velocity (TMV) was measured by radiopaque particle or charcoal spot movement. The commercial percussor (a fixed sinusoidal device) used at its minimum frequency of 40 Hz, produced a mean (+/- SE) maximum expiratory flow rate of 0.25 +/- 0.04 L/sec at the airway opening, and had no measurable effect on TMV. The experimental oscillator, when operated at a level sufficient to generate flows of 2-3 L/sec, and with an unbiased 13-Hz sine wave (estimated energy, 150 W), increased mean TMV to 204 +/- 13% of control (P less than 0.003); the percent increase was independent of baseline TMV. We conclude that moderate oscillatory power applied to the chest wall can enhance mucus clearance in central airways, but that currently available commercial percussors may not meet the mechanical requirements for this effect.

Chest physiotherapy: time for reappraisal

Chest physiotherapy should now be updated with attention to three important features: first, its use should be limited to those patients with actual or potential sputum production and its central aim should be to increase expectoration. Second, it should incorporate the forced expiration technique with postural drainage and omit traditional elements such as percussion and vibration. Third, the additional use of inhaled adrenergic agents and possibly oral high frequency oscillation may increase sputum clearance further.