Ventilatory Effects

The FDA has approved high frequency chest compression (HFCC) to promote secretion clearance and currently it is marketed solely for that purpose. Several research studies suggest that HFCC may provide clinically beneficial ventilatory effects. Although this potential has not been fully evaluated, encouraging data suggest that further evaluation is merited.

  1. al-Saady NM, Fernando SS, Petros AJ, Cummin AR, Sidhu VS, Bennett ED. External high-frequency oscillation in normal subjects and in patients with acute respiratory failure. Anaesthesia 1995; 50:1031-1035.

    Twenty healthy volunteers treated with an external chest wall oscillation (ECWO) device (the Hayek Oscillator) demonstrated significant improvement in lung ventilation. Effective ventilation was measured in terms of the fall in alveolar PCO2 immediately after oscillation. In the same study, ECWO was compared with intrapulmonary positive pressure ventilation (IPPV) in five patients with respiratory failure. After a 30 minute treatment with IPPV, therapy was replaced with 30 minutes of ECWO. Oxygenation improved by 16% and PCO2 decreased by 6%, indicating that ECWO can maintain adequate ventilation is this group of patients.
  2. Calverley PMA, Chang HK, Vartian V, Zidulka A. High-frequency chest wall oscillation: assistance to ventilation in spontaneously breathing subjects. Chest 1986; 89:218-223.

    Five normal spontaneously breathing supine-positioned subjects received high frequency chest  wall oscillation (HFCWO) at frequencies of 3, 5 and 8 Hz for fifteen minute sessions at both maximal and half-maximal peak tolerable cuff pressures. Each session was separated by 15 minutes of control spontaneous ventilation. A significant decrease with HFCWO in spontaneous minute ventilation at maximal and half-maximal pressures by 35 and 40 per cent respectively; at 3 Hz and by 25 and 35 percent respectively at 5 Hz and with little change at 8 Hz suggests a potential role as an aid to ventilation in spontaneously breathing patients without requiring an endotracheal tube.
  3. Dolmage TE, Eisenberg HA, Davis LL, Goldstein RS. Chest wall oscillation at 1 Hz reduces spontaneous ventilation in healthy subjects during sleep. Chest 1996; 110:128-135.

    To determine whether external chest wall oscillation (ECWO) during sleep 1) reduces spontaneous ventilation while maintaining adequate gas exchange over several hours; 2) influences the quality and distribution of sleep and; 3) increases the number of respiratory events, 7 healthy volunteers received one night of ECWO at 1 Hz and a night during which the cuirass was applied without ECWO. ECWO resulted in 1) a significant decrease in spontaneous minute ventilation (VE) in all stages of sleep; 2) was associated with a reduction in the total sleep time and; 3) a reduction in rapid eye movement (REM) sleep. Mean PCO2 was similar between the control and cuirass nights (44 to 46 mm Hg) and mean arterial oxygen saturation (SaO2) was maintained at 96 to 97% throughout sleep during the control, cuirass, and ECWO nights. Results suggest that ECWO can be tolerated for several hours and will assist ventilation while maintaining normal mean PCO2 and mean SaO2 during sleep.
  4. George RJ, Winter RJ, Flockton SJ, Geddes DM. Ventilatory saving by external chest wall compression or oral high-frequency oscillation in normal subjects and those with chronic airflow obstruction. Clin Sci (Lond). 1985; 69:349-359.
    
Oscillation of the air within the lungs at high frequency is associated with an increased clearance of CO2. In this study, high-frequency oscillations were superimposed upon tidal breathing by using a loudspeaker attached to a mouthpiece to produce oral high-frequency oscillation (OHFO) or by external chest wall compression (ECWC). Changes in ventilation and breathlessness using OHFO and ECWC in normal subjects were compared with those in patients with chronic airflow obstruction (CAO). The pattern of breath conservation was then related to the resonant frequencies of the respiratory system as a whole (5-10 Hz in normal subjects, 16-26 Hz in CAO) and those of the ribcage (70 Hz). OHFO reduced minute ventilation (VE) by up to 46% in normal subjects (P = < 0.01) and 29% in CAO (P = < 0.01) without any rise in CO2. ECWC reduced VE by 27% in normal subjects (p = < 0.01) and 16% in CAO (p = < 0.01) without a rise in CO2. High-frequency oscillation by either method relieved breathlessness in those with CAO, was comfortable and well tolerated and may have value as a supplement to ventilation.
  5. Hamel D, Gupta V, Craig D, Kotani T, Quick G, Gentile M, Cheifetz I. High frequency chest wall oscillation improves oxygenation in a pediatric swine model of acute lung injury. Duke Children’s Hospital, Durham, NC (publication pending)

    In a study to determine whether high frequency chest wall oscillation (HFCWO) improves oxygenation in acute lung injury, nine swine (12-20 kg) with a surfactant depletion model were conventionally ventilated at settings maintained constant throughout the data collection. High frequency chest wall oscillation (HFCWO) was applied to each animal at various combinations of pressure (0.5, 3, and 5) and frequency (5, 10, and 15 Hz) in random order. For each combination of HFCWO settings, an arterial blood gas was obtained after a 10-minute stabilization period without HFCWO and at the end of a 10-minute period with HFCWO. Results showed that HFCWO effectively improves oxygenation at a low (0.5) HFCWO pressure setting (p<0.04). Investigators speculate HFCWO may be a useful technique as an adjunct therapy to conventional ventilation to achieve a more optimal mean lung volume.
  6. Harf A, Zidulka A, Chang HK. Nitrogen washout during tidal breathing with superimposed high-frequency chest-wall oscillation. Am Rev Respir Dis 1985; 132:350-353.
    
To assess the efficacy of high-frequency chest wall oscillation (HFCWO) superimposed on tidal ventilation, multiple-breath nitrogen washout curves were obtained in 7 normal seated subjects. HFCWO at 5 Hz was superimposed on the regulated tidal breathing; the magnitude of the oscillatory tidal volume measured at the airway opening was 20 ml in one phase of the trial and 40 ml for a second phase. Results of analysis of the washout curve suggested that during inspiration HFCWO enhances gas mixing in the lung periphery and that during expiration HFCWO improves gas mixing in the airways.
  7. Isabey D, Piquet J. The ventilatory effect of external oscillation. Acta Anaesthesiol Scand 1989; 33 (Suppl 90):87-92.
    
External oscillation applied around the chest wall [EOCW] may provide non-invasive high frequency ventilation in large animals and humans. Results obtained with EOCW in both normal and bronchoconstricted subjects showed beneficial effects in bronchoconstricted rabbits in terms of a slight improvement in gas exchange and a potentially positive effect on inspiratory muscle fatigue. Data support the concept that HFCC may assist ventilation in bronchoconstricted subjects with high lung compliance, such as babies, neonates and normal adults.
  8. Khoo M, Gelmont D, Howell S, Johnson R, Yang F, Chang HK. Effects of high-frequency chest-wall oscillation on respiratory control in humans. Am Rev Respir Dis 1989; 139:1223-1230.
    
An investigation of spontaneous breathing patterns of 10 normal adults during high-frequency chest wall oscillation (HFCWO) showed that HFCWO increased the breath-to-breath variability of spontaneous respiration in all subjects; some subjects experienced short apneas. PACO2 decreased significantly (p = <0.05). The effects on minute ventilation, tidal volume, and inspiratory and expiratory durations remained variable across subjects although average expiratory duration increased by a non-significant 29%. Ventilatory responses to CO2 with and without HFCWO showed normocapnic (PACO2 = 40 mm Hg) ventilatory drive increased significantly (p = < 0.05) in six subjects and decreased substantially in the others. With hypercapnia, the changes in drive were attenuated in all subjects.
  9. Piquet J, Isabey D, Chang HK, Harf A. High-frequency transthoracic ventilation improves gas exchange during experimental bronchoconstriction in rabbits. Am Rev Respir Dis 1986; 133:605-608.
    
To evaluate the efficacy of ventilation by high frequency transthoracic oscillation (HFTO) in obstructive lung disease, 10 anesthetized and paralyzed rabbits with experimentally induced bronchoconstriction were placed in a body-box connected to a piston pump and in random order administered frequencies of 1 Hz ( representing “conventional” ventilation), and 5 Hz (for high frequency ventilation). Several oscillation rates were used. Data showed improved gas exchange at 5 Hz and only a minor increase in lung volume. No significant hemodynamic changes occurred.

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