Mechanical airway clearance secretions therapies are key in the treatment of patients with various forms of acute or chronic respiratory failure (disorders such as obstructive, cystic fibrosis, neuromuscular, etc) under mechanical ventilatory support (weaning mechanical ventilation or prolonged mechanical ventilation) in Critical Care Units. High Frequency Chest Wall Oscillation (HFCWO) therapies are based on the physical effects of high oscillatory pressure-flow on bronchial secretions that are commonly difficult to control by conventional endotracheal aspiration techniques or manual chest physiotherapy. This book analyzes the the physical principles and rationales for the best patient-mechanical ventilator interactions (invasive, non-invasive, tracheostomies, weaning from mechanical ventilation, extubation failure, etc.) in a wide spectrum of respiratory disorders that require mechanical ventilation. It explores high-frequency oscillation devices and how to understand the basic monitoring (waveforms, flow, and pressure analysis), patterns of response, and outcomes in mechanically ventilated ill patients. This book represents a scientific and practical reference for a wide spectrum of health professionals in pulmonary critical care and chest physiotherapy.