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Pathologic processes that involve the central nervous system, phrenic nerve, neuromuscular junction, and skeletal muscle can impair diaphragm function. When these processes are of sufficient severity to cause diaphragm dysfunction, respiratory failure may be a consequence. This article reviews basic diaphragm anatomy and physiology and then discusses diagnostic and therapeutic approaches to disorders that result in unilateral or bilateral diaphragm dysfunction. This discussion provides a context in which disorders of the diaphragm and their implications on respiratory function can be better appreciated.

Objective: The anatomy and neurophysiology of cough has been reviewed in the preceding section. The objective of this section is to describe how the varied anatomic components of the respiratory system work in concert to produce an effective cough. Methods: This was accomplished by reviewing (1) the factors needed to produce effective cough pressures and gas velocity in the airways, and (2) the salient features of the interaction between the airflow generated during a cough and the mucus that lines the tracheobronchial tree. The MEDLINE database was searched for this review, and the search consisted of studies published in English between 1960 and April 2004. Search terms were "cough mechanics" and "cough physiology." Results: Inhaling to high lung volumes and glottic closure prior to the expiratory phase of cough facilitate the generation of high intrathoracic pressures. These high intrathoracic pressures (1) provide the driving force for airstream flow during cough and (2) dynamically compress the central airways, which further enhances the cough airstream velocity. Conclusions: High intrathoracic pressures are needed to generate the requisite cough expiratory flows and airstream velocities. However, cough may be effective in individuals with mild-to-moderate degrees of respiratory muscle weakness, as only modest increases in intrathoracic pressure are needed to dynamically compress the large intrathoracic airways and increase cough flow velocity.

Background: Airway clearance may be impaired in disorders associated with abnormal cough mechanics, altered mucus rheology, altered mucociliary clearance, or structural airway defects. A variety of interventions are used to enhance airway clearance with the goal of improving lung mechanics and gas exchange, and preventing atelectasis and infection. Method: A formal systematic review of nonpharmacologic protussive therapies was performed and constitutes the basis for this section of the guideline. In addition, the articles reviewed were found using the same methodology but were not limited to those that focused only on cough as a symptom. The MEDLINE database was searched for this review and consisted of studies published in the English language between 1960 and April 2004. The search terms used were “chest physiotherapy,” “forced expiratory technique,” “positive expiratory pressure,” “high frequency chest compression,” “insufflation,” and “exsufflation.” Results: In general, studies of nonpharmacologic methods of improving cough clearance are limited by methodological constraints, and most were conducted only in patients with cystic fibrosis. Chest physiotherapy, including postural drainage, chest wall percussion and vibration, and a forced expiration technique (called huffing), increase airway clearance as assessed by sputum characteristics (ie, volume, weight, and viscosity) and clearance of the radioaerosol from the lung, but the long-term efficacy of these techniques compared with unassisted cough alone is unknown. Other devices that allow patients to achieve the same benefits derived from chest physiotherapy without the assistance of a caregiver appear to be as effective as chest physiotherapy in increasing sputum production. Conclusions: Some nonpharmacologic therapies are effective in increasing sputum production, but their long-term efficacy in improving outcomes compared with unassisted cough alone is unknown. (CHEST 2006; 129:250S–259S)

Recognition of the importance of cough in clinical medicine was the impetus for the original evidence-based consensus panel report on “Managing Cough as a Defense Mechanism and as a Symptom,” published in 1998,1 and this updated revision. Compared to the original cough consensus statement, this revision (1) more narrowly focuses the guidelines on the diagnosis and treatment of cough, the symptom, in adult and pediatric populations, and minimizes the discussion of cough as a defense mechanism; (2) improves on the rigor of the evidence-based review and describes the methodology in a separate section; (3) updates and expands, when appropriate, all previous sections; and (4) adds new sections with topics that were not previously covered. These new sections include nonasthmatic eosinophilic bronchitis (NAEB); acute bronchitis; nonbronchiectatic suppurative airway diseases; cough due to aspiration secondary to oral/pharyngeal dysphagia; environmental/occupational causes of cough; tuberculosis (TB) and other infections; cough in the dialysis patient; uncommon causes of cough; unexplained cough, previously referred to as idiopathic cough; an empiric integrative approach to the management of cough; assessing cough severity and efficacy of therapy in clinical research; potential future therapies; and future directions for research. To mitigate future diagnostic confusion, two new diagnostic terms have been introduced to replace two older terms that may represent misnomers. The committee unanimously recommends that the term upper airway cough syndrome (UACS) be used in preference to postnasal drip syndrome (PNDS) when discussing cough that is associated with upper airway conditions because it is unclear whether the mechanism of cough is postnasal drip, direct irritation, or inflammation of the cough receptors in the upper airway. The committee also recommends using the term unexplained cough rather than idiopathic cough because it is likely that more than one unknown cause of chronic cough will be discovered. The term idiopathic implies that one is dealing with only one disease. For managing adult patients with cough, the committee recommends an empiric, integrative diagnostic approach, which is presented in the section entitled “An Empiric Integrative Approach to the Management of Cough”.3 Guidelines for managing acute, subacute, and chronic cough are presented in algorithmic form (Fig 1–3). Guidelines with algorithms for evaluating chronic cough in pediatric patients < 15 years of age are presented in the section entitled “Guidelines for Evaluating Chronic Cough in Pediatrics”2,4 [Fig 4, ​,5].5]. For a full discussion on how to use the algorithms, please refer to these sections. Figure 1 Acute cough algorithm for the management of patients ≥ 15 years of age with cough lasting < 3 weeks. For diagnosis and treatment recommendations refer to the section indicated in the algorithm. PE = pulmonary embolism; Dx = diagnosis; ... Figure 3 Chronic cough algorithm for the management of patients ≥ 15 years of age with cough lasting > 8 weeks. ACE-I = ACE inhibitor; BD = bronchodilator; LTRA = leukotriene receptor antagonist; PPI = proton pump inhibitor. See the legend of ... Figure 4 Approach to a child 6 years of age and in some children ... Figure 5 Approach to a child ≤ 14 years of age with chronic specific cough (ie, cough associated with other features suggestive of an underlying pulmonary and/or systemic abnormality). Children > 14 years of age should be managed as outlined in ...

Study objectives: To determine the accuracy of a portable magnetometer designed to measure tidal volume (VT), inspiratory time (TI), and expiratory time (TE). Participants: Fourteen healthy subjects. Design: Subjects breathed over a sixfold range of VTs while at rest (sitting and standing) and during treadmill exercise. We then compared VT ,T I, and TE measured by magnetometry (VTmag, TImag, and TEmag) with VT ,T I, and TE measured by spirometry (VTspiro, TIspiro, and TEspiro, respectively). Setting: Pulmonary function and exercise physiology laboratories. Measurements and results: The sternal-umbilical distance and the anteroposterior displacements of the rib cage and abdomen were measured with two pairs of magnetometer coils. VT was calculated from the sum of these three signals, and was simultaneously measured using a spirometer or flow meter. A total of 1,111 breaths were analyzed for the resting condition, and 1,163 breaths were analyzed for the exercise condition. We found that VTmag was highly correlated with VTspiro at rest (R 2 0.90) and during exercise (R 2 0.79) for pooled data. The slope of this relationship approached the line of identity. The mean percentage differences between VTmag and VTspiro were 10.1 6.6% at rest and 13.5 8.6% with exercise. By Bland-Altman analysis, the mean differences between VTmag and VTspiro were 38 mL at rest with changes in posture, and 182 mL during exercise. TImag and TIspiro values and TEmag and TEspiro values also were highly correlated (R 2 0.97 and R 2 0.95, respectively) for pooled data. Conclusion: A portable magnetometer system can give useful measures of VT ,T I, and TE over a wide range of VTs in sitting, standing, and exercising subjects. (CHEST 2002; 122:684 – 691)

Intermittent positive pressure ventilation (IPPB) is reported to improve lung compliance and decrease the work of breathing in subjects with kyphoscoliosis. These results suggest that IPPB may improve chest wall and lung compliance in patients with neuromuscular disease. We studied the short-term effects of IPPB on total respiratory system compliance in 14 subjects with neuromuscular disease. Seven were quadriplegics, and seven had muscular dystrophy. Vital capacity was reduced to 38±14 percent of the predicted normal values. Baseline measurements of total respiratory system compliance were 57±18 percent when compared to normal control values. After a 20 minute treatment of IPPB delivered with inspiratory pressures of 20 to 25 cm H 2 O that more than tripled resting tidal volume, there was no significant change in total respiratory system compliance in either group of patients. These findings indicate that patients with quadriplegia or muscular dystrophy do not derive immediate improvement in ventilatory mechanics from IPPB treatments.

An asymptomatic 22-year-old man was evaluated for a persistent left lower lobe infiltrate. Barium enema and upper gastrointestinal series revealed colon and small bowel freely mobile in the left thorax. CT confirmed absence of the left hemidiaphragm. This is the first reported case of total absence of a hemidiaphragm in an adult, and extends the clinical spectrum of diaphragmatic defects. Unlike the more common partial diaphragmatic defects where strangulation of hernia contents may occur, the asymptomatic presentation of complete absence of the hemidiaphragm with the unimpeded movement of abdominal contents suggests that no treatment is necessary. (Chest 1988; 94:1301-03)