## 3 Clinical Significance of CPF Evaluation
### Neuromuscular Disease  
In a previous study of patients over 11 years of age with Duchenne muscular dystrophy (DMD) published in 1997, [PERSON] [35] showed that CPF could be used to assess the risk of DMD patients developing acute respiratory failure because no patients with a CPF above 270 L/min developed acute respiratory distress. In addition, a recent study involving thirty-four patients with amyotrophic lateral sclerosis [36] reported that the CPF decline rate reflects the progression of bulbar and respiratory dysfunction and is an independent prognostic factor for survival as, patients exhibiting a CPF decline rate over 25% had a shorter overall survival (\(p<0.0001\)). Moreover, in adults and probably also children above 12 years of age, a CPF above 160 L/min is required to effectively clear secretions and maintain airway patency [8] because patients with an assisted CPF under 160 L/min cannot be successfully extubated or decannulated [27]. Even in patients with diseases other than neuromuscular diseases such as pneumonia, asthma, and chronic obstructive pulmonary disease exacerbations, CPF is commonly used to evaluate the cough strength to predict re-intubation in intensive care units (ICUs). Previous studies have found that the optimal cutoff value for CPF was 35 L/min as reported by [PERSON] et al. [37], 60 L/min as reported by [PERSON] et al. [7], and 62.4 L/min as reported by [PERSON] et al. [38].  
Manually mechanically assisted coughing that augments cough flow is often employed to reduce the health risk. Forced exhalation can be augmented by pushing on the upper abdomen or chest wall in synchrony with the patient's own cough effort [39]. Glososopharyngeal breathing (GPB) and air stacking can increase the lung volume and cough flow [40]. The maximum insufflation capacity (MIC) is the maximum volume of air stacked within the patient's lungs beyond the spontaneous vital capacity [8], which is one of the determinants of CPF. The application of positive pressure with a self-inflating bag and mask, an intermittent positive pressure breathing device, and a mechanical ventilator are effective techniques to increase the MIC [39]. In addition, mechanical insufflation-exsufflation (MIE) is used as a mechanical technique to assist in coughing. MIE and an oximeter are prescribed when the patient's maximum assisted CPF declines below 300 L/min [41, 42]. Recent studies have reported that MIE exsufflation (cough) flow (MIE-EF) correlates with upper airway patency [43, 44] and that a successful transition from invasive to noninvasive respiratory management requires an MIE-EF value of at least 150 to 200 L/min [44].  
To obtain an effective peak flow to expel airway secretions, we should appropriately select cough assist techniques according to the patient's condition. Generally, cough assist techniques should be used to achieve a baseline CPF above 160 L/min [8, 39]. However, several guidelines recommend that cough assist techniques should be used in patients with neuromuscular disease when their CPF is below 270 L/min [8, 39] because DMD patients are at risk of developing acute respiratory failure when their (assisted) CPF is below 270 L/min [35].