A restrictive lung disease is associated with a reduced total lung capacity, i.e., the lungs are unable to expand fully. It may be caused by intrinsic pulmonary disorders or thoracic pathologies.
The predominating symptom in RLD patients is dyspnea. Patients may report to suffer from breathing difficulties while under exercise, but as the underlying disease progresses, dyspnea may also be present at rest. Cyanosis and palpitations may also be noted. It is not uncommon to hear that RLD patients suffer from sleep disorders since low oxygen saturation does not allow for a restful sleep.
Additional symptoms depend on the underlying disease.
Pulmonary function tests are indicated to confirm a tentative diagnosis of RLD. Plethysmography is applied to evaluate total lung capacity, while spirometry allows for the assessment of forced vital capacity, forced expiratory volume and forced expiratory flow. Confirmation of RLD is based on the detection of a diminished total lung capacity, but a marked decrease of forced vital capacity and forced expiratory volume further support that diagnosis. Moreover, functional residual capacity and residual volume are generally reduced. In patients presenting with symptomatic RLD, diffusing capacity tests indicate an impaired gas exchange and accrdingly, blood gas analyses reveal hypoxemia and hypercarbia.
Although a patient may be diagnosed with RLD based on the aforementioned findings, neither of those tests allows to identify the underlying disease. Here, diagnostic imaging is generally applied to evaluate the overall condition of the respiratory tract, the heart and the thorax. Plain radiographic images may already provide important hints as to the extent of a possible pulmonary or thoracic disease, but anomalies are often unspecific: Both nodular and reticular patterns may be observed, and distinction of alveolar and interstitial pathologies based on radiography alone is a real challenge. Thus, computed tomography is generally indicated.
Besides imaging techniques, histopathological analyses of lung biopsies may yield diagnostic findings. Further approaches depend on anamnestic data and the clinical presentation of the particular patient and are not necessarily restricted to the respiratory tract.
In order to treat RLD-induced hypoxemia, oxygen should be supplied. Arterial oxygen saturation should be monitored and may serve as an orientation when deciding about the current need for oxygen supply. It is important to note that the partial pressure of oxygen in blood may be unaltered at rest in mild to moderate RLD and thus, such evaluations should always include measurements under exercise. Continuous respiratory assistance by means of masks or portable ventilators becomes necessary if a patient suffers from pulmonary failure.
RLD patients may also benefit from pulmonary rehabilitation to improve exercise performance. Such programs comprise exercise training, education about breathing techniques and nutrition as well as psychological support. Clinical studies have shown rehabilitation programs to improve the results of pulmonary function tests, exercise endurance and life quality . At the same time, the need for oxygen supply decreased.
Of course, the underlying disease should be treated as well. In fact, therapy should aim at remedying or at least halting the progress of the primary disorder in order to reduce the need for oxygen supply and pulmonary rehabilitation. The precise therapeutic approach depends on the particular disease and may involve medication - corticosteroids are generally administered to PF patients, and if the response is unsatisfying, immunomodulators may be applied -, and surgery, particularly in case of pleural effusion and empyema.
Although the prognosis for an individual patient depends on the disease triggering RLD in that particular case, it is generally unfavorable. This is due to the fact that PF and RLD are often complication of advanced to end-stage pulmonary and thoracic disorders. Upon diagnosis, irreversible remodeling processes often have already taken place. Currently, fibrosis is considered an intractable condition. Causal therapy is available for few diseases related with RLD and at best, disease progress may be halted. Pulmonary sarcoidosis may be self-limiting, though, and surgical interventions may be curative in case of pleural diseases or neoplasms.
Moderate to severe RLD is debilitating. The patient's tolerance to exercise is considerably reduced, and some affected individuals may be rendered unable to walk more than a few meters or to lift any weights. These persons are incapable of managing their everyday life without assistance. This situation worsens with disease progress, and life expectancy decreases. Half of all patients diagnosed with idiopathic pulmonary fibrosis die within three years after diagnosis .
RLD is not an uniform entity, but rather a condition that may result from a variety of underlying disorders. There are two main causes of RLD, namely intrinsic pulmonary disorders and thoracic anomalies. These may be further divided into alveolar and interstitial lung diseases, neuromuscular disorders, pleural and thoracic cage pathologies. In detail, the following diseases may trigger RLD:
It has been ascertained that about 5% of the population show restrictive patterns in spirometry measurements . The majority of these patients presents mild RLD, but a total of 1.5% suffers from moderate to severe illness. Here, prevalence rates are decreasing, but there are considerable differences regarding the epidemiology of distinct diseases that may underly RLD:
In general, both women and men and patients of all races may develop RLD. Gender and racial predilections may exist for determined underlying diseases, though. For instance, lymphangioleiomyomatosis is most frequently diagnosed in women, anthracosis is more common in men  . Sarcoidosis has been reported to be more common in patients of African descent .
The overall prevalence of RLD increases with age, and this observation may at least partially be explained by the fact that chronic disorders trigger most cases of RLD.
It is beyond the scope of this article to discuss the pathophysiological events causing all those diseases mentioned above, but common patterns can be identified in advanced-stage chronic lung, pleural and thoracic diseases. In general, total lung capacity may either be impaired mechanically or functionally. The former is more common and the corresponding pathomechanisms can be identified in cases of PF, pleural effusion and pleural fibrosis, as well as in thoracic malformations and neoplasms.
Fibrosis is the result of chronic inflammation, which may be induced by pathogens, inorganic compounds, immune disorders, or as of yet unknown stimuli . RLD may also be provoked by a combined action of those noxious agents, and this is the current hypothesis regarding the pathogenesis of idiopathic pulmonary fibrosis . Fibrosis is marked by differentiation of fibroblasts into myofibroblasts, proliferation of those cells, and an excess production of extracellular matrix components, mainly of collagen. Determined cytokines and growth factors are required to maintain this process active. This is how immune cells are involved in organ fibrosis. If a patient suffers from pulmonary fibrosis, their lungs lose elasticity and flexibility. Pleural fibrosis, in contrast, is often associated with pathological adhesions forming between visceral and parietal pleura, which interferes directly with lung mobility.
Tumor growth may similarly alter the elastic properties of lung tissue or cause adhesions, but neoplasms may also contribute to RLD by mere reduction of intrathoracic space. To a certain extent, the latter is comparable to obesity-induced RLD. It has been shown that a patient's body mass index inversely correlates with total lung capacity and vital capacity .
If the lungs are unable to expand fully, a ventilation-perfusion mismatch is generated. There is an insufficient gas exchange, and the partial pressure of oxygen in arterial blood remains low. Hypoxemia stimulates both the cardiovascular system and the lungs, but these organs are unable to compensate for moderate to severe RLD. The affected individual suffers from dyspnea and its consequences and may eventually die from respiratory failure.
Preventive measures can only be recommended for determined diseases provoking RLD. Certain forms of pneumonia may be prevented by vaccination, e.g., against pertussis or pneumococcal pneumonia. Furthermore, avoidance of agents and drugs toxic to the lungs should be aspired. Compliance with industrial safety measures is very helpful to that end. A healthy, balanced diet and regular exercise are most effective to avoid overweight and obesity.
Restrictive lung disease (RLD) is a general term referring to the lung's inability to expand fully. This condition is medically described as a reduced total lung capacity, and may be induced by a variety of entities: On the one hand, lung expansion may be impaired due to pathologies provoking pulmonary fibrosis (PF). PF develops as an advanced stage of chronic diseases like pneumonia and pneumoconiosis and may also be induced by radiation or drugs. On the other hand, even a healthy lung cannot expand properly if surrounding tissues mechanically hinder that process. This may be the case in patients with neoplasms, pleural diseases, particularly if associated with an effusion, or due to thoracic malformations. Rarely, neuromuscular disorders are involved in RLD pathogenesis.
Patients presenting with a restrictive lung disease (RLD) may suffer from distinct pathologies that render the lungs unable to expand fully. Consequently, the main diagnostic criterion for RLD is a reduced total lung capacity, i.e., the volume of air that can be maintained in fully inflated lungs is smaller than in healthy individuals.
In order to understand which diseases may induce RLD, it is necessary to comprehend how respiration works: Upon inspiration, the thoracic cavity expands. Its inner wall is lined with the so-called parietal pleura and is separated from the lungs only be a tiny amount of liquid. The lungs are covered with the visceral pleura and between both layers of pleura and the pleural fluid, the lungs remain loosely attached to the thoracic wall. Respiratory muscle contraction is required for inspiration and as soon as those muscles relax, the lungs recoil due to the elastic properties of pulmonary tissue. Then, expiration takes place.
Accordingly, RLD may be caused by intrinsic pulmonary disorders that alter the lung's elasticity and flexibility. Also, adhesions between both layers of pleura hinder the lung's mobility and thus may provoke RLD. Thoracic malformations or space-occupying masses like tumors or fat may also impede the lungs to expand fully.
RLD are diagnosed based on pulmonary function tests. However, additional diagnostic measures have to be applied to identify the underlying disease. Treatment and prognosis largely depend on the latter and differ widely. Pulmonary sarcoidosis, for instance, is generally self-limiting and has a good prognosis. Idiopathic pulmonary fibrosis, however, is an intractable disorder with a poor outcome.