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Background The American Thoracic Society (ATS) has set the acceptable resistance for spirometers at less than 1.5 cm H ₂O/l/s over the flow range 0-14 l/s and for monitoring devices at less than 2.5 cm H ₂O/l/s (0-14 l/s). The aims of this study were to determine the resistance characteristics of commonly used spirometers and monitoring devices and the effect of resistance on ventilatory function. Methods The resistance of five spirometers (Vitalograph wedge bellows, Morgan rolling seal, Stead Wells water sealed, Fleisch pneumotachograph, Lilly pneumotachograph) and three monitoring devices (Spiro 1, Ferraris, mini-Wright) was measured from the back pressure developed over a range of known flows (1.6-13.1 l/s). Peak expiratory flow (PEF), forced expiratory flow in one second (FEV ₁), forced vital capacity (FVC), and mid forced expiratory flow (FEF _25-75%) were measured on six subjects with normal lung function and 13 subjects with respiratory disorders using a pneumotachograph. Ventilatory function was then repeated with four different sized resistors (approximately 1-11 cmH ₂O/l/s) inserted between the mouthpiece and pneumotachograph. Results All five diagnostic spirometers and two of the three monitoring devices passed the ATS upper limit for resistance. PEF, FEV ₁ and FVC showed significant (p<0.05) inverse correlations with added resistance with no significant difference between the normal and patient groups. At a resistance of 1.5 cm H ₂O/l/s the mean percentage falls (95% confidence interval) were: PEF 6.9% (5.4 to 8.3); FEV ₁ 1.9% (1.0 to 2.8), and FVC 1.5% (0.8 to 2.3). Conclusions The ATS resistance specification for diagnostic spirometers appears to be appropriate. However, the specification for monitoring devices may be too conservative. PEF was found to be the most sensitive index to added resistance.

BackgroundBronchial hyperresponsiveness (BHR) to methacholine has been reported to occur in most lung transplant recipients. BHR to physical stimuli such as exercise and non-isotonic aerosols has not been as extensively studied in this subject population. This report aims to assess the presence and degree of BHR to methacholine and hypertonic saline in stable lung transplant recipients and to relate it to the presence of airway inflammation.MethodsTen patients undergoing bilateral sequential lung transplantation and six heart-lung transplant recipients, all with stable lung function, were recruited 66-1167 days following transplantation. Subjects underwent a methacholine challenge and bronchoscopy for sampling of bronchoalveolar lavage fluid, transbronchial and endobronchial biopsy tissues. Hypertonic saline challenge was performed six days later.ResultsNine of the 16 transplant recipients had positive methacholine challenges (geometric mean PD₂₀0.18 mg, interquartile range 0.058-0.509) and three of these subjects also had positive hypertonic saline challenges (PD₁₅=2.3, 33.0, and 51.5 ml). No clear relationship was found between BHR to either methacholine or hypertonic saline and levels of mast cells, eosinophils or lymphocytes in samples of biopsy tissue or lavage fluid.ConclusionsMost of the lung transplant recipients studied were responsive to methacholine and unresponsive to hypertonic saline. BHR was not clearly related to airway inflammation, suggesting an alternative mechanism for BHR following lung transplantation from that usually assumed in asthma.

A new node is presented for frequency-domain TLM (TLM-FD). The new node has the advantage of being much less dispersive than previous TLM-FD nodes.

A new steady-state technique is presented for the 3-D symmetrical condensed TLM node. A waveguide problem is modelled to test the theory and an electromagnetic diffusion problem is modelled as a case where steady-state TLM is more efficient than time-domain TLM

A new 3-D graded TLM model for thin radiating wires is presented. The model differs from previous TLM models because the wire is modelled at the interfaces between cells, rather than through the centre of the node. The connection between the TLM symmetrical condensed-node link lines and the wire line forms a ‘wire interface’. The scattering algorithm for the interface and simulation results are given.

The dispersion characteristics of 3-D frequency-domain TLM are analysed for a regular mesh, a graded mesh and dielectric problem.

The 3-D steady state TLM technique (SS-TLM) is extended to provide TLM models for lossy materials and thin lossy films in the frequency domain. The models are evaluated by comparing with time domain TLM (TD-TLM) and analytic solutions.