The control group (I): The participants will follow the traditional pulmonary rehabilitation program including (active cycle of breathing technique, breathing control, deep breathing exercises, huffing). The session duration will be between 30 min twice/day for 15 days as guided by subject fatigue and comfort. (According to Borg scale of dyspnea for monitoring).

The study group (II): The participants will receive active cycle of breathing technique, breathing control, deep breathing exercises (15 min) in addition to (HFCWO); the patient position will be in a semi-recline position, with wrapped vest around the chest. The (HFCWO) protocol included 3-5 cycles, with a pressure range of +10 to +40 IP cmH2O and will be adjusted according to the patient age, number of secretions, tolerance of patients, and chest auscultation every session. The numbers of total sets will be 3-5 with a duration of 15 min, daily, for two sessions / day , time range according to the ability of the patient. (Çelik et al., 2021).

The HFCWO device used a triangular wave form which increases the airflow velocity more than other devices. Therefore, clearing sticky airway mucus and alveolar exudates and maintaining airway patency has become currently the most urgent issue in the ventilatory management of patients with severe COVID-19.

Arterial blood gas analysis is a common investigation in emergency departments and intensive care units for monitoring patients with acute respiratory failure. ABG also has some applications in general practice, such as assessing the need for domiciliary oxygen therapy in patients with chronic obstructive pulmonary disease. An arterial blood gas result can help in the assessment of a patient's gas exchange, ventilator control and acid-base balance. (Verma et al., 2010)

The neutrophil-to-lymphocyte ratio (NLR) is an inflammatory marker derived from combining the absolute blood neutrophil and lymphocyte counts, two routinely performed parameters in clinical settings. Recently, studies have reported that NLR levels were higher in more severe patients and were suggested to confer a prognostic value in COVID-19 patients (Lagunas et al.,2020).

Earlier diagnosis of COVID-19 may be facilitated by heart rate (HR) and heart rate variability (HRV) monitoring. HR and HRV parameters could not only help to detect COVID-19 in a timely manner but could also help to identify patients at risk for cardiovascular/pulmonary complications. Additionally, HRV and HR parameters may help to assess the course of the disease. (Buchhorn et al., 2020).

The World Health Organization indicates that a resting value of RR > 30 breaths/min is a critical sign for the diagnosis of severe pneumonia in adults, while the cut-off value for children varies according to age (World Health Organization, 2020).

Resting RR values also contribute to the prognosis of COVID-19 patients as ICU admission and mortality are associated with significantly higher RR values compared to non-ICU patients and survivors (Huang et al., 2020 & Zhou et al., 2020).

The Dyspnea-12 (D-12) Questionnaire is a convenient patient-reported scale for measuring the severity of breathlessness. Breathlessness is quantified by using 12 descriptors to cover both the physical and the psychological dimensions. The D-12 has established its validity and reliability in COPD, asthma, interstitial lung disease, and pulmonary hypertension. (Yorke et al., 2010).