Nonlinear waves in solids with slow dynamics: an internal-variable model.

In heterogeneous solids such as rocks and concrete, the speed of sound diminishes with the strain amplitude of a dynamic loading (softening). This decrease, known as 'slow dynamics', occurs at time scales larger than the period of the forcing. Also, hysteresis is observed in the steady-state response. The phenomenological model by Vakhnenko et al. (2004 Phys. Rev. E 70, 015602. (doi:10.1103/PhysRevE.70.015602)) is based on a variable that describes the softening of the material. However, this model is one dimensional and it is not thermodynamically admissible. In the present article, a three-dimensional model is derived in the framework of the finite-strain theory. An internal variable that describes the softening of the material is introduced, as well as an expression of the specific internal energy. A mechanical constitutive law is deduced from the Clausius-Duhem inequality. Moreover, a family of evolution equations for the internal variable is proposed. Here, an evolution equation with one relaxation time is chosen. By construction, this new model of the continuum is thermodynamically admissible and dissipative (inelastic). In the case of small uniaxial deformations, it is shown analytically that the model reproduces qualitatively the main features of real experiments.

Effect of edentulism on spirometric tests.

The impact of denture wear in edentulous subjects while performing routine spirometric measurements has never been systematically investigated. We compared the values of FVC, FEV(1), PEFR, FEF(50%), FIV(1), and FIF(50%) recorded with and without dentures in three groups of edentulous subjects: 36 asymptomatic subjects with normal spirometry (N), 22 patients with chronic obstructive pulmonary disease (COPD), and 18 with interstitial lung disease (ILD). In 14 subjects retropharyngeal space with and without dentures was assessed by cephalometry. Subjects with N and ILD had significantly lower airflow rates without dentures, whereas subjects with COPD had no significant difference in spirometric values recorded with or without dentures. The retropharyngeal space was significantly decreased by removing dentures (from 1.52 +/- 0.07 to 1.16 +/- 0.09 cm, SEM, p < 0.0001). These findings indicate that in edentulous subjects with a normal or restrictive pattern, the recording of flow-volume curves with or without dentures produces small but significant differences. Although such differences do not appear to have clinical significance, the fact that when dentures are used some respiratory flows are higher would favor the use of dentures in edentulous subjects during spirometric evaluation.

Exhaled nitric oxide in systemic sclerosis: relationships with lung involvement and pulmonary hypertension.

OBJECTIVE: To measure nitric oxide (NO) concentration in exhaled air of patients with systemic sclerosis (SSc) and to investigate its relationships with lung involvement, complicated or not by pulmonary hypertension (PH). METHODS: Exhaled NO was measured by chemiluminescence in 47 patients with SSc (16 with PH) and in 30 controls. All the patients underwent Doppler echocardiography to assess pulmonary artery pressure (PAP), lung function tests, and thin section computed tomographic scans of the lung to quantify the extent of fibrosing alveolitis. RESULTS: Exhaled NO levels were higher in patients with SSc (16.6 +/- 9.1 ppb), particularly those with interstitial lung disease (ILD) (18.3 +/- 10.4 ppb), compared to controls (9.9 +/- 2.9 ppb; p < 0.0001). In patients with PH, exhaled NO was less than in patients without PH (10.7 +/- 5.9 vs 19.6 +/- 9 ppb, respectively; p < 0.001), and patients with PH without ILD had even lower exhaled NO than patients with PH and ILD (6.6 +/- 1.1 vs 12.6 +/- 6.3 ppb; p = 0.004). There was an inverse correlation between PAP and exhaled NO (r = 04).53, p = 0.004). Exhaled NO was not correlated to age, disease duration, current therapy, or form of disease (limited or diffuse). CONCLUSION: The increased concentration of exhaled NO in patients with SSc may reflect respiratory tract inflammation. The relatively low value of exhaled NO in patients with PH and the negative correlation between PAP and exhaled NO suggest the important role of NO in regulating pulmonary vascular resistance in patients with SSc.

Changes in airway responsiveness following mantle radiotherapy for Hodgkin's disease.

UNLABELLED: STUDY OBJECTIVES To investigate whether mantle radiotherapy (MRT) for the lung, through its proinflammatory effects, can induce an increase in airway responsiveness. DESIGN: Follow-up of the changes in lung function and methacholine responsiveness in patients 1, 6, 12, and 24 months after they underwent MRT. PATIENTS: Thirteen nonasthmatic patients with bulky Hodgkin's lymphoma who were scheduled for MRT. MEASUREMENTS AND RESULTS: Chest radiographs, lung function tests, methacholine thresholds of the bronchi (the provocative dose of methacholine causing a 10% fall in FEV(1) [PD(10)]) and central airway (the provocative dose of methacholine causing a 25% fall in the maximal mid-inspiratory flow [PD(25)MIF(50)]), and the provocative dose of methacholine causing five or more coughs (PDcough) were serially assessed. One month after patients underwent MRT, there were significant decreases in PD(10) (mean [+/- SEM], 2,583 +/- 414 microg to 1,512 +/- 422 microg, respectively; p < 0.05), PD(25)MIF(50) (mean 2,898 +/- 372 microg to 1,340 +/- 356 microg, respectively; p < 0.05), and PDcough (mean 3,127 +/- 415 microg to 1,751 +/- 447 microg; p < 0.05), which were independent of the decrease in FEV(1) and reversed within 6 months in all patients but three. Six months after undergoing MRT, four patients showed radiation-induced lung injury (RI) on chest radiographs, which subsequently evolved into fibrosis. These patients had greater decreases in vital capacity, FEV(1), MIF(50), and methacholine thresholds than those without RI, and this persisted up to 2 years after they had undergone MRT. One year after the patients underwent MRT, a close relationship was found overall between the change in FEV(1) and those in both PD(10) (r = 0.733; p = 0.004) and PD(25)MIF(50) (r = 0.712; p = 0.006). CONCLUSIONS: : MRT triggers an early transient increase in airway responsiveness, which reverses spontaneously. In patients with RI, the persistence of airway dysfunction long after undergoing MRT may depend on airway remodeling from radiation fibrosis.