Antonio Pedotti

Expiratory flow limitation detected by forced oscillation and negative expiratory pressure

The within-breath change in reactance (ΔX̄rs) measured by forced oscillation technique (FOT) at 5 Hz reliably detects expiratory flow limitation in chronic obstructive pulmonary disease (COPD). The present study compared this approach to the standard negative expiratory pressure (NEP) method. In total, 21 COPD patients were studied by applying both techniques to the same breath and in 15 patients the measurements were repeated after bronchodilator. For each patient and condition five NEP tests were performed and independently scored by three operators unaware of the FOT results. In 180 tests, FOT classified 53.3% as flow limited. On average, the operators scored 27.6% of tests flow limited and 47.6% non-flow limited, but could not score 24.8%. The methods disagreed in 7.9% of cases; in 78% of these the NEP scores differed between operators. Bronchodilation reduced NEP and ΔX̄rs scores, with only the latter achieving significance. Averaging the operators′ NEP scores, a threshold between 24.6–30.8% of tidal volume being flow limited by NEP produced 94% agreement between methods. In conclusion, when negative expiratory pressure and forced oscillation technique were both available they showed good agreement. As forced oscillation technique is automatic and can measure multiple breaths over long periods, it is suitable for monitoring expiratory flow limitation continuously and identifying patients′ breathing close to the onset of expiratory flow limitation, where intermittent sampling may be unrepresentative.

Effect of bronchodilation on expiratory flow limitation and resting lung mechanics in COPD

Bronchodilator drugs produce variable improvements in forced expiratory volume in 1 s (FEV1), but larger changes in end-expiratory lung volume (EELV) in chronic obstructive pulmonary disease (COPD), which were suggested to be related to the presence of expiratory flow limitation (EFL) at rest. We tested this concept in 42 COPD patients (FEV1 42.3±13.8% predicted) during spontaneous breathing before and after 5 mg nebulised salbutamol. EFL was detected by within-breath changes in respiratory system reactance measured by a multifrequency forced oscillation method, while changes in EELV were assessed by inspiratory capacity (IC). Bronchodilation (BD) increased IC (from 1.8±0.5 to 2.1±0.6 L, p<0.001) and reduced inspiration resistance (R̄insp) at 5 Hz (from 5.1±1.6 to 4.2±1.5 cmH2O·s·L−1, p<0.001). R̄insp identified BD responders with a discriminative power of 80.1%. In total, 20 patients were flow-limited before BD. They showed worse spirometry and higher residual volume, but significant improvements in IC were seen in all patients irrespective of flow limitation. Changes in R̄insp were confined to flow-limited patients, as were reactance changes. BD reduced the degree of heterogeneity in the respiratory system, a change best seen with inspiratory values. BD has complex effects on lung mechanics in COPD, and EFL affects both this and the response of some respiratory variables to treatment. However, changes in EELV are consistently seen, irrespective of the presence of flow limitation at rest.

Real-time three-dimensional motion analysis for patient positioning verification.

BACKGROUND AND PURPOSE This paper describes the technology and methods involved in a system for automatically checking the position of patients at radiotherapy units. This is proposed for improving the accuracy in the irradiation geometrical set-up, which is a crucial factor in radiotherapy quality control. MATERIALS AND METHODS The system is based on real-time opto-electronics and close-range photogrammetry and detects multiple passive markers placed on selected patient skin landmarks. Patient alignment and position monitoring is carried out by comparing the current three-dimensional positions of the markers with those of an initial reference position acquired during the simulation procedure and/or the first irradiation session. The system was used to measure the accuracy of conventional laser centering techniques for patient repositioning. Inaccuracies due to breathing and random movements were also taken into account. Professional technicians were asked to reposition three volunteer subjects carefully using a traditional laser centering procedure. RESULTS The results revealed significant repositioning errors even in highly controlled conditions, affecting particularly body areas relatively far from the skin reference points used for laser alignment. CONCLUSIONS The outcome of the experimental application of this technology confirms its potential as a tool for patient repositioning and automatic detection of any errors caused by breathing or other unpredictable movements. The real-time feedback on the patients position given by the system provides operators with appropriate visual indices and allows them to take suitable countermeasures in case of significant failures. In addition, the use of the system output for automatic position control is envisaged.

Opto-electronic Plethysmography

Recent developments of Opto-Electronic plethysmography allow a noninvasive and accurate measurement of the volume of the chest wall and its different thoraco-abdominal compartments, without any calibration specific on the subject under analysis. OEP provides the complete ventilatory pattern without using any device attached to the subject in any conditions and posture. Combined with pressure and airflow measurements, it can be used to study statics, dynamics and energetics of the chest wall and to estimate possible blood shifts between the thorax and the extremities.

Noninvasive detection of expiratory flow limitation in COPD patients during nasal CPAP

The difference between mean inspiratory and expiratory respiratory reactance (ΔX̄rs) measured with forced oscillation technique (FOT) at 5 Hz allows the detection of expiratory flow limitation (EFL) in chronic obstructive pulmonary disease (COPD) patients breathing spontaneously. This aim of this study was to evaluate whether this approach can be applied to COPD patients during noninvasive pressure support. ΔX̄rs was measured in seven COPD patients subjected to nasal continuous positive airway pressure (CPAP) at 0, 4, 8 and 12 cmH2O in sitting and supine positions. Simultaneous recording of oesophageal pressure and the Mead and Whittenberger (M–W) method provided a reference for scoring each breath as flow-limited (FL), non-flow-limited (NFL) or indeterminate (I). For each patient, six consecutive breaths were analysed for each posture and CPAP level. According to M–W scoring, 47 breaths were FL, 166 NFL and 51 I. EFL scoring using FOT coincided with M–W in 94.8% of the breaths. In the four patients who were FL in at least one condition, ΔX̄rs was reduced with increasing CPAP. These data suggest that the forced oscillation technique may be useful in chronic obstructive pulmonary disease patients on nasal pressure support by identifying continuous positive airway pressure levels that support breathing without increasing lung volume, which in turn increase the work of breathing and reduce muscle effectiveness and efficiency.