[Quality control of spirometry in workers' medical surveillance]

Spirometry plays an important role in occupational respiratory health surveillance programs. However, when not performed correctly, the values obtained can be misleading, resulting in misclassification of the workers' health status. Studies carried out in Italy have shown that spirometries recorded by occupational physicians often do not comply with quality criteria for recording FEV1 and FVC, according to joint statements on lung function testing for the American Thoracic Society and the European Respiratory Society, issued in 2005. For this reason, they are useless for the purposes of their execution. Compliance with ATS/ERS statements is essential to assure that spirometry results are beneficial for the monitoring of workers' health.

Tumor Necrosis Factor-α in Airway Secretions from Cystic Fibrosis Patients Upregulate Endothelial Adhesion Molecules and Induce Airway Epithelial Cell Apoptosis: Implications for Cystic Fibrosis Lung Disease

Airway inflammation plays a crucial role in lung damage in cystic fibrosis (CF) and is characterized by a persistent influx of neutrophils into the airways. We hypothesized that the high levels of inflammatory products that accumulate in the microenvironment of the CF lung contribute to induce the persistent neutrophil recruitment and the airway epithelial damage. Thus, we evaluated the in vitro effect of sputum sol phase (SSP) from CF patients on a) adhesion molecule expression by human microvascular endothelial cells (HMECs) and b) apoptosis of human bronchial epithelial cells (HBECs), both wild-type and CFTR-defective. SSP was obtained from 7 clinically stable adult CF patients and 8 patients with an acute exacerbation. HMECs and HBECs were cultured in the absence or presence of SSP. Cell adhesion molecule expression was assessed by flow cytometry and cell death by the detection of histone-associated DNA fragments, caspase activation, and cytochrome c release. SSP obtained from CF patients, especially at the time of an acute exacerbation, induced a) an upregulation of endothelial adhesion molecules on cultured HMECs that was associated with an increase of neutrophil adhesion to these cells, and was mediated at least in part by TNF-α and IL-1 and b) apoptosis of airway epithelial cells, mainly activated by TNF-α pathway. These results suggest that the high concentrations of inflammatory mediators in CF airways contribute both to the chronic neutrophil influx and the airway damage, and support the crucial role of early anti-inflammatory treatment in the disease.

Role of chest radiography in the diagnosis of allergic bronchopulmonary aspergillosis in adult patients with cystic fibrosis

PURPOSE

This study aimed to verify the usefulness of chest radiography in the diagnosis of allergic bronchopulmonary aspergillosis (ABPA) in adult patients with cystic fibrosis.

MATERIALS AND METHODS

Eleven patients (with a total of 14 episodes) affected by ABPA were selected from among subjects attending a Regional Cystic Fibrosis Centre. For each episode, we retrospectively reviewed the baseline chest radiographs obtained before the diagnosis of ABPA, those obtained during the course of ABPA and those obtained during follow-up. Radiographs were assessed for the presence of bronchial wall thickening, bronchiectasis, infiltrates, atelectasis, mucoid impaction, lymphadenopathy, pleural effusion and fluid levels. Radiographic findings that had appeared at the time of ABPA diagnosis and disappeared after treatment were considered related to ABPA and thus useful for a correct diagnosis of the disease. Chest radiograph abnormalities were compared with changes on the respiratory function tests [forced expiratory volume in 1 s (FEV1)] during the different stages of the disease.

RESULTS

Radiographic findings at the time of ABPA diagnosis appeared to have deteriorated in 8/14 cases when compared with the baseline films; after treatment, the radiographic findings deteriorated in 6/14 cases and improved in 6/14. The most significant among the radiographic signs considered (infiltrates and mucoid impaction) appeared at the time of ABPA diagnosis in 7/14 and 4/14 cases, respectively, and in some patients, they were also present at baseline and persisted during follow-up. FEV1 values were significantly decreased (>10%) in 9/14 cases at the time of ABPA diagnosis.

CONCLUSIONS

Our results demonstrate the limited usefulness of chest radiography in the diagnosis of ABPA in patients with cystic fibrosis. The most significant abnormalities are nonspecific and commonly seen on baseline films in cystic fibrosis without ABPA and persist after treatment in most cases.

Variation of CD8+ T-lymphocytes around the bronchial internal perimeter in chronic bronchitis

The variation of CD8+ cells has been determined around the internal perimeter of intrapulmonary bronchi in smokers with chronic bronchitis (CB), and the amount of tissue required to confidently estimate the true mean has been calculated. Lung specimens were obtained from 10 smokers with CB. Paraffin sections of intrapulmonary bronchi were immunostained and CD8+ cells counted in the epithelium and subepithelium in up to 10 sequential 1-mm segments around the internal perimeter of each airway. The percentage of counts falling between +/-20% of the final mean was 43.0% for epithelium and 40.9% for subepithelium. In 90% of subjects, the cumulative mean was stable after examination of subepithelial tissue associated with 5 mm of reticular basement membrane. There is considerable variation in the counts of CD8+ cells between adjacent 1-mm airway mucosal segments in chronic bronchitis. In order to achieve a representative count and to maximise statistical power to detect differences between study populations, subepithelial tissue including a minimum of 5 mm of reticular basement membrane length should be examined.

Mechanisms and markers of airway inflammation in cystic fibrosis

Airway inflammation is now recognized as a major factor in the pathogenesis of lung disease in cystic fibrosis (CF). Its most characteristic feature is a marked and persistent influx into the airways of neutrophils, which damage the lung by releasing noxious mediators, such as reactive oxygen species and proteolytic enzymes. Recent studies suggest that inflammation occurs very early and may even happen in the absence of infection. Furthermore, links between CF transmembrane conductance regulator dysfunction and both infection and inflammation are postulated; dysregulation of cytokine production and abnormal epithelial host defences have been regarded as causes of sustained inflammation. Bronchoalveolar lavage and the evaluation of neutrophils and inflammatory mediators provide the most accurate picture of airway inflammation. Routine bronchoscopy with bronchoalveolar lavage, however, is unpleasant for the patient and usually is of no immediate benefit to the management of individual cases. Therefore, surrogate markers collected by noninvasive procedures would be of great assistance in the follow-up of cystic fibrosis patients. Several markers have been evaluated in the sputum, serum and urine of cystic fibrosis patients and related to the degree of airway inflammation. Long-term studies are needed to confirm their potential clinical utility and specificity, and to determine which can be used clinically to monitor disease outcome and efficacy of treatment.

Interleukin-4 and interleukin-5 gene expression and inflammation in the mucus-secreting glands and subepithelial tissue of smokers with chronic bronchitis. Lack of relationship with CD8(+) cells

We wished to determine if the inflammatory cells surrounding the airway mucus-secreting glands in chronic bronchitis (CB) were associated with interleukin (IL)-4 and IL-5 mRNA expression and whether the CD8 T cell population expressed these cytokines. Digoxigenin-labeled IL-4 and IL-5 antisense RNA probes were used to detect gene expression in 11 asymptomic smokers (AS), 11 smokers with CB alone with normal lung function, and 10 smokers with chronic bronchitis and coexisting chronic obstructive pulmonary disease (CB+COPD; FEV(1)% of predicted of 43-77% and FEV(1)/ FVC of 51-68%). There were approximately three times as many IL-4 than IL-5 mRNA(+) cells. The highest number of IL-4 mRNA(+) cells were in the submucosal glands of the CB group with normal lung function (216/mm(2)), significantly higher than the values in either the AS (63/mm(2)) or the CB+COPD (87/mm(2)) groups, respectively (p < 0.01). There were similar group differences when the total numbers of inflammatory cells were compared. Accordingly, there was a positive correlation between the number of IL-4 mRNA(+) cells and the total number of inflammatory cells in both the subepithelium and glandular compartments (r = 0.60; p = 0.01 and r = 0.70; p = 0.02, respectively). There were no significant associations between the numbers of CD8(+) and IL-4 or IL-5 mRNA(+) cells. Of 1328 IL-4(+) and 1404 CD8(+) cells counted none was double labeled. Of 727 IL-5(+) and 1569 CD8(+) cells, none was double labeled. In contrast, as a positive control, 34% of tumor necrosis factor (TNF)-alpha(+) cells were also CD8(+) and 15% of CD8(+) cells were TNF-alpha positive. Thus, cells other than the CD8(+) phenotype produce IL-4 and IL-5 in CB. We conclude that there is increased inflammation and IL-4 gene expression in the mucus-secreting glands and the airway mucosa of smokers with bronchitis: both are lower in those with CB and coexisting COPD suggesting that airway inflammation in CB is reduced when airway obstruction develops.

[Usefulness of chest X-ray during cystic fibrosis exacerbation in adult patients]

PURPOSE

Verify the real usefulness of chest X-ray during clinical exacerbation of cystic fibrosis (FC).

MATERIAL AND METHODS

The study was based on a group of 46 adult patients affected by FC. For every subject we selected one or more pair of chest films, of which the first was used as reference image (To), whereas the second (T1) was selected among the following controls, either in course of clinical obvious exacerbation, or during another routine control. The 64 pairs of chest films (32 representing phases of clinical stability, 32 documenting evolution towards clinical deterioration) were subjected to evaluation by two radiologists, who were first asked to judge if stability, improvement or worsening of the overall radiographic picture could be observed; then to estimate the improvement, worsening, stability or absence of the 12 radiographic signs, selected among those more frequently correlating with the acute phase of disease.

RESULTS

The comprehensive radiological evaluation, which shows a statistically significant difference (p=0.012) between the two groups considered, weakly correlates with the patient clinical status. Among the patients with exacerbation, the radiographic picture appeared worsened in only 18/32 cases (sensibility 56%, specificity 78%), while on the contrary 7/32 clinically stable patients exhibited a radiographic deterioration. Among the considered radiographic-sings, some were exclusively observed during exacerbation (specificity 100%), but with low sensitivity (pneumothorax: 6%, increment of bronchiectasis: 9%, air space disease 22%); the most common alterations (mucoid impactions and bronchial wall thickening) were observed in both groups of patients.

DISCUSSION AND CONCLUSIONS

Our results demonstrate that there is not a precise correlation between the radiographic picture and the clinical manifestations of exacerbation and confirm the poor usefulness of chest X-ray in such a phase of disease. Chest X-ray is needed to exclude pnemothorax or extensive air space disease, rather then to accurately diagnose exacerbation.

Circulating adhesion molecules in cystic fibrosis

A marked influx of inflammatory cells occurs into the airways of patients with cystic fibrosis (CF), which may contribute to the development of lung injury. Leukocyte-endothelial adhesion molecules play a crucial role in the recruitment of inflammatory cells, and soluble forms of these molecules have been shown to increase in several inflammatory diseases. By using a capture ELISA, we determined serum levels of soluble ICAM-1 (sICAM-1), E-selectin (sE-selectin), and VCAM-1 (sVCAM-1) in patients with CF, in stable clinical conditions (n = 29, mean age: 25.8+/-1.5 yr), and healthy control subjects (n = 12, mean age: 27.6+/-1.5 yr). Clinical, spirometric, microbiological, and hematological assessments were made in all subjects. sICAM-1 and sE-selectin concentrations, but not sVCAM-1 levels were significantly increased in CF patients as compared with normal subjects (both p < 0.001). sICAM-1 levels were inversely related to FEV1 values (r = -0.519, p = 0.004) and Schwachman score (r = -0.405, p = 0.03) in CF patients. In 7 of 29 CF patients, soluble adhesion molecule levels were determined not only at the time of stable clinical conditions, but also before and after antibiotic treatment for a pulmonary exacerbation. sICAM-1 and sE-selectin levels increased in all patients at the time of the exacerbation, compared with levels at the time of stable conditions (p < 0.02 for both comparisons); antibiotic treatment induced a significant decrease of both circulating adhesion molecules (p < 0.02). The elevated serum levels of sICAM-1 and sE-selectin in CF patients, even when they are clinically stable, may reflect the marked and persistent inflammatory process in the disease.

Release of prostaglandin E2 and leukotriene B4 by alveolar macrophages from patients with sarcoidosis

BACKGROUND

Mediators released by alveolar macrophages, as well as by T cells, play an important part in modulating local immune processes in sarcoidosis. Among alveolar macrophage secretory products, arachidonic acid metabolites are known to regulate inflammatory and immune reactions. It has been suggested that cyclo-oxygenase and lipoxygenase pathway metabolites of arachidonic acid modulate the evolution of the granulomatous inflammatory response in the lung differently.

METHODS

Alveolar macrophages recovered from the bronchoalveolar lavage (BAL) fluid of 32 patients with sarcoidosis in different states of disease activity and 10 normal subjects were evaluated for their ability to release prostaglandin E2 (PGE2) and leukotriene B4 (LTB4). Alveolar macrophages were cultured in the presence or absence of opsonised zymosan (500 micrograms/ml), and PGE2 and LTB4 levels in the culture supernatants were determined by enzyme immunoassay (EIA).

RESULTS

Stimulated alveolar macrophages from patients with active sarcoidosis released higher LTB4 levels than those from normal subjects, but no differences in PGE2 release were observed between the two groups. The time course of LTB4 release by activated alveolar macrophages showed that normal cells produced similar levels of the hydroxyacid during the early and late times of culture while LTB4 release by activated cells from patients with sarcoidosis increased markedly after 60 minutes of culture, remaining elevated until 24 hours. Indomethacin (3 x 10(6) M) caused the expected inhibition of PGE2 formation without affecting LTB4 release.

CONCLUSIONS

These results suggest that alveolar macrophages from the BAL fluid of patients with active sarcoidosis are primed to release LTB4, which may contribute to the locally heightened immune response.

Are asthma-like symptoms due to bronchial or extrathoracic airway dysfunction?

Patients with asthma-like symptoms may not have asthma but obstruction of the extrathoracic airway (EA). To evaluate if dysfunction of the EA causes asthma-like symptoms, we assessed bronchial and EA responsiveness to inhaled histamine in 441 patients who presented with at least one of three key symptoms--cough, wheeze, dyspnoea--but had neither documented asthma nor bronchial obstruction. The histamine concentrations causing a 20% fall in forced expiratory volume in 1 s (PC20FEV1) and a 25% fall in maximal mid-inspiratory flow (PC25MIF50) were used as respective thresholds of bronchial and EA responsiveness. Values 8 mg/mL or less indicated bronchial (B-HR) or EA hyper-responsiveness (EA-HR). The influence of concurrent upper respiratory tract diseases, such as post-nasal drip (PND), pharyngitis, laryngitis and sinusitis, was also assessed. We found four response patterns to the histamine challenge: EA-HR in 26.5% of the patients, B-HR in 11.1%, combined EA-HR and B-HR in 40.6%, and no-HR in 21.8%. Cough was reported by 79% of the patients, wheeze by 53%, and dyspnoea by 40%. Patients with cough as the sole presenting symptom (34.2%), as compared with those with wheeze and/or dyspnoea (20%), had significantly greater probability of having EA-HR (OR 5.35, 95% CI 3.25-8.82) and lower probability of having B-HR (OR 0.45, CI 0.28-0.70); patients with cough plus wheeze and/or dyspnoea (45.8%) had significantly greater probability of having both EA-HR and B-HR than either those with cough alone (OR 2.48, CI 1.49-4.13), or those with wheeze and/or dyspnoea but not cough (OR 1.74, CI 1.36-2.22). EA-HR alone or combined with B-HR was strongly associated with EA diseases, particularly pharyngitis and PND. Cough was significantly associated with PND, either when it was the sole symptom (OR 2.16, CI 1.14-4.09) or when it was combined with wheeze and/or dyspnoea (OR 3.53, CI 1.97-6.33). Our results suggest that extrathoracic airway dysfunction may account for asthma-like symptoms, particularly chronic cough. This abnormality seems to be sustained by chronic diseases of the upper respiratory tract.

Intercellular adhesion molecule-1 is upregulated on peripheral blood T lymphocyte subsets in dual asthmatic responders

To examine the role of adhesion molecules in T cell recruitment and activation during allergen-induced late asthmatic response (LAR), we evaluated the expression of lymphocyte function-associated antigen-1 alpha (LFA-1 alpha) and intercellular adhesion molecule-1 (ICAM-1) on peripheral blood T lymphocyte subsets from atopic asthmatic patients and their changes following allergen inhalation challenge. 12 atopic asthmatic patients were studied. Six patients showed only a single early response after allergen challenge, and six developed a dual response. At baseline, dual responders (DR) had a significantly higher expression of ICAM-1 on CD4+ and CD8+ T lymphocytes as compared with both single early responders (P < 0.005 and P < 0.02, respectively) and controls (P < 0.001, both comparisons). Allergen challenge was followed by a decrease of CD8+ ICAM-1+ T lymphocytes in all DR (P < 0.05) and of CD4+ ICAM-1+ T lymphocytes in four out of six DR, at the time of the LAR. At the same time, a significant rise in serum levels of the soluble form of ICAM-1 was observed in DR. These results suggest that peripheral blood immunoregulatory T lymphocytes are in a higher state of activation in DR as compared with early responders. The upregulation of ICAM-1 on these cells may be important in enhancing airway inflammation in patients with LAR.

Imipenem in acute lung infections and bacterial re-exacerbations of chronic obstructive lung disease

The Authors examine the changes observed in the epidemiology of lower respiratory tract infections and the role of imipenem in acute lung infections as well as in bacterial re-exacerbations of chronic obstructive lung disease. Imipenem is a new beta-lactam antibiotic characterized by an unusually broad spectrum of antibacterial activity that includes most gram-positive and gram-negative aerobic and anaerobic bacteria, by a remarkable stability to both plasmid and chromosomally-mediated beta-lactamases and by good pharmacokinetic properties. These peculiar features make this drug an attractive candidate to be used in the treatment of lower respiratory tract infections. The use of imipenem, however, should be restricted to nosocomial infections due to gram-negative aerobic resistant to other antibiotics, mixed infections due to both aerobic and anaerobic flora and as initial empirical therapy of infections in immunocompromised patients.

Familial elevation of serum angiotensin converting enzyme activity

A clustering of high levels of serum angiotensin converting enzyme (S-ACE) was found in an Italian family. The elevation affected five subjects, two of whom were completely healthy and free from known causes of S-ACE increase. The values of S-ACE in hyperACEmic subjects exceeded the values found in normal relatives severalfold. HyperACEmia seemed to be inherited as an autosomal dominant trait. Immunogenetic studies were performed, but we did not find a genetic marker for this condition. The S-ACE activity was inhibited in vitro by edetic acid (EDTA) and SQ 14,225 (captopril). The S-ACE activity was also determined after 1:8 dilution and dialysis against saline of sera. From these experiments we deduced that Lieberman's intrinsic ACE inhibitor was lacking in the hyperACEmic sera. In the presence of remarkable S-ACE increase, a congenital elevation of S-ACE should be considered and it would be useful to perform a familial investigation.

Familial elevation of serum angiotensin converting enzyme activity

A clustering of high levels of serum angiotensin converting enzyme (S-ACE) was found in an Italian family. The elevation affected five subjects, two of whom were completely healthy and free from known causes of S-ACE increase. The values of S-ACE in hyperACEmic subjects exceeded the values found in normal relatives severalfold. HyperACEmia seemed to be inherited as an autosomal dominant trait. Immunogenetic studies were performed, but we did not find a genetic marker for this condition. The S-ACE activity was inhibited in vitro by edetic acid (EDTA) and SQ 14,225 (captopril). The S-ACE activity was also determined after 1:8 dilution and dialysis against saline of sera. From these experiments we deduced that Lieberman's intrinsic ACE inhibitor was lacking in the hyperACEmic sera. In the presence of remarkable S-ACE increase, a congenital elevation of S-ACE should be considered and it would be useful to perform a familial investigation.

Double-blind trial RU 41740 vs. placebo: immunological and clinical effects in a group of patients with chronic bronchitis

A double-blind trail was performed to investigate the effects of RU 41740, a glycoprotein extract from Klebsiella pneumoniae, on host defenses and its efficacy in reducing the number of exacerbation in 29 evaluable patients with chronic bronchitis, out of 36 patients who entered the study. The drug enhanced the phagocytosis indexes of both polymorphonuclear and mononuclear phagocytes. Increased candidacidal activity of monocytes was also observed. These effects, already detectable after one course of therapy and during the entire period of treatment, were no longer detectable when tested 6 months after the end of treatment. A significantly (p less than 0.05) larger number of patients in the treated group than in the placebo group had no exacerbations during drug administration (0-3 months). Moreover, patients treated with RU 41740 had significantly fewer and shorter episodes of acute exacerbation. The positive decreases in these two parameters persisted throughout the follow-up.

Evaluation of systemic host defense mechanisms in chronic bronchitis

Seventy-six chronic bronchitis patients were studied in order to determine the possible presence of disorders in their systemic defense mechanisms. No significant difference in lymphocyte subsets, in serum immunoglobulin and complement component (C3 and C4) levels was found in chronic bronchitis patients compared to normal adult controls. Skin tests for delayed hypersensitivity revealed a high frequency (39%) of hypoergic patients (with 1-2 positive reactions) in comparison to normal subjects. Altered values of many functional properties of both neutrophils and monocytes were demonstrated. The percentage of patients with intermediate (between 1 and 2 SD below the mean of controls) and defective (lower than 1.96 SD) values of chemotaxis, phagocytosis index and Candida killing was about 50%. Phagocytosis frequency and nitroblue tetrazolium reduction frequency were less frequently impaired.

Roxithromycin (RU 28965) in the treatment of respiratory tract infections

The clinical efficacy of roxithromycin, administered at the daily dosage of 300 mg (150 mg every 12 hours), was evaluated in 25 patients with respiratory tract infections, mostly infectious exacerbations of chronic bronchitis. Pathogens isolated before treatment were Staphylococcus aureus, Streptococcus pneumoniae, Streptococcus beta-haemoliticus, Haemophilus influenzae. Clinical cure or improvement was achieved in 21 out of 22 evaluable patients. The eradication rate was 91%. Tolerability was good: two patients reported gastrointestinal side effects which caused treatment discontinuation. These preliminary data suggest that roxithromycin may have a place in the treatment of respiratory infections.

The effect of teicoplanin on leukocytic activity and intraleukocytic micro-organisms

The interference of teicoplanin with certain phagocyte activities was investigated in comparison with that of vancomycin. Neither teicoplanin nor vancomycin interfered with chemotaxis, adherence, phagocytosis or nitroblue tetrazolium reduction of human neutrophils. Teicoplanin, but not vancomycin, enhanced intracellular killing by neutrophils from normal donors and from a patient with chronic granulomatous disease. Human monocytes in the absence of fresh human serum did not significantly kill Staphylococcus aureus but when pre-treated with teicoplanin 90% of phagocytozed bacteria were killed during 4 h incubation.

Evaluation of the host defense system in asthmatic patients

The efficiency of some components of the host defense system has been evaluated in 32 atopic patients with rhinitis, asthma or asthma and rhinitis. No alterations in components of complement (C3 and C4), serum immunoglobulins (IgG, IgA, and IgM) and neutrophil functional parameters were found. As expected, serum IgE values were higher than in controls. A decreased percentage of total circulating T lymphocytes, an increased percentage of Ia1-positive cells, but normal values of OKT4- and OKT8-positive T lymphocytes were demonstrated. However, a greater heterogeneity in the distribution of the suppressor-cytotoxic subset was shown in atopic patients.

Interstitial pneumopathy and low-dosage amiodarone

In a 61-year-old man receiving chronic low-dosage amiodarone an interstitial pneumopathy was observed. In the absence of other causes, we suspected an adverse reaction to amiodarone, not least because of the similarity with histologic findings of cases previously reported. Drug withdrawal and cortisone administration led to resolution of the disease.

In vivo study of xibornol on phagocyte functions

Polymorphonuclear leukocytes (PML) represent the first step of defense against bacteria and fungi. Since many antimicrobial drugs have been reported to inhibit phagocyte function, we tested the interference of xibornol, a new antimicrobial agent, on phagocyte functions, in order to evaluate its possible use in chronic respiratory diseases. In the patients treated with xibornol (500 mg every 8 h for 7 days) we did not find any modification in phagocytosis frequency (PMF), phagocytosis index (PHI), nitroblue tetrazolium (NBT), reduction frequency (NRF), microbicidal activity and neutrophil mobility of PML, before, during and after the end of therapy.

[Study of aspecific bronchial reactivity in subjects with allergic diseases and in bronchial asthma patients]

A study has been carried out on the effect of inhalatory metacholine in a series of 29 subjects, 10 of whom were normal, 11 asthmatic and 8 non-asthmatic allergopathics. Respiratory alterations were studied using 8 functional parameters designed to highlight the behaviour of the major and minor airways respectively. Metacholine at very high doses was studied in normal subjects, demonstrating its lack of effect at respiratory level. The functional behaviour of the allergopathics proved to differ from that of the asthmatics and was characterized essentially by a diminution in low expiratory flows unassociated with clinical signs or functional involvement of the main airways. The meaning of the results and their possible clinical importance are discussed.