Using the amount of sputum as the outcome measurement of HFCWO is not strongly recommended. However, immediate cardiopulmonary changes in HFCWO have not been studied in patients receiving mechanical ventilation, although this measurement is more explicit than lung function and BODE score, as they are impractical in these patients. Changes in ventilator settings caused by HFCWO are a concern when the patients receive both treatments simultaneously. The aim of this study was to investigate the effect of HFCWO on pneumonic subjects with acute respiratory failure receiving mechanical ventilation by evaluating immediate cardiopulmonary changes and changes in the initial ventilator settings.