The aim of our study was to study regional lung function by standard computed tomography (CT) and characterise regional variations of density and specific gas volume (SVg) between different lung volumes.We studied 10 healthy and 10 severely emphysematous subjects. Corresponding CT images taken at high and low lung volumes were registered by optical flow to obtain two-dimensional maps of pixel-by-pixel differences of density (DHU) and SVg (DSVg) at slice levels near the aortic arch, carina and top diaphragm.In healthy subjects, DHU was higher at all levels (p,0.001) with higher variability expressed as interquartile range (p,0.001), largely due to its differences between dorsal and ventral regions. In patients, median DSVg values were 3.2 times lower than healthy volunteers (p,0.001), while heterogeneity of DSVg maps, expressed as quartile coefficient of variation, was 5.4 times higher (p,0.001). In all patients, there were areas with negative values of DSVg.In conclusion, DSVg is uniform in healthy lungs and minimally influenced by gravity. The significant DSVg heterogeneity observed in emphysema allows identification of areas of alveolar destruction and gas trapping and suggests that DSVg maps provide useful information for evaluation and planning of emerging treatments that target trapped gas for removal.

This paper describes an integrated chest wearable apparatus for continuous blood pressure (BP) measurements exploiting the heart-rate (HR) and the pulse arrival time (PAT) in a modified Moens-Korteweg model. The device embeds a miniaturized gas pressure sensor to record the phonocardiogram (PCG) of the heart sounds, a LED-photodiode pair to detect the photoplethysmogram (PPG) of the blood flow wave, a µcontroller, a wireless communication module and the power supply. With the proposed device no active participation would be required from human subjects for BP measurements, since the HR and the PAT are continuously extracted from the PCG and PPG signals. Dedicated signal processing algorithms were developed and implemented off-line to extract both HR and PAT. A subject-specific calibration protocol of the BP model was designed and implemented. The calibration and validation of the apparatus were performed on a cohort of 20 healthy subjects. A GIMA ABPM pressure Holter was chosen as reference device, and 8 measurements points, evenly distributed over a 10-minute interval, were used for model calibration for each subject. The range of DBP and SBP measurements were 52-85 mmHg and 90-141 mmHg, respectively. The results from Bland-Altman analysis showed that the mean±1.96SD for the estimated diastolic, systolic, and mean BP with the proposed method against reference were 0.01±7.55, 1.47±3.76, 0.74±4.38 mmHg, respectively. The corresponding mean absolute differences (MAD) were 3.06, 1.83, and 1.80 mmHg. These results demonstrates that the acquisition apparatus is able to continuously estimate the BP with an accuracy comparable to traditional cuff-based devices. INDEX TERMS Wearable device, blood pressure measurement, pulse transit time (PTT), pulse arrival time (PAT), integrated system.

No abstract

In six male anesthetized, tracheotomized, and mechanically ventilated rabbits we derived indications on alveolar mechanics from in vivo imaging, using a "pleural window" technique (pleural space intact) that allows unrestrained movement of the same subpleural alveoli (N=60) on increasing alveolar pressure from 4 to 8 cmH2O. Absolute compliance (C(abs), ratio of change in alveolar surface area to the change in alveolar pressure) was significantly lower in smaller compared to larger alveoli. Specific compliance, C(sp), obtained by normalizing C(abs) to alveolar surface area, was essentially independent of alveolar size. Both C(abs) and C(sp) were affected by large variability likely reflecting the complex matching between elastic and surface forces. We hypothesize that the relative constancy of C(sp) might contribute to reduce interregional differences in parenchymal and surface forces in the lung tissue by contributing to assure a uniform stretching in a model of mechanically inter-dependent alveoli.

In six male anesthetized, tracheotomized, and mechanically ventilated rabbits, we imaged subpleural alveoli under microscopic view (60×) through a “pleural window” obtained by stripping the endothoracic fascia and leaving the parietal pleura intact. Three different imaging scale levels were identified for the analysis on increasing stepwise local distending pressure (Pld) up to 16.5 cmH2O: alveoli, alveolar cluster, and whole image field. Alveolar profiles were manually traced, clusters of alveoli of similar size were identified through a contiguity‐constrained hierarchical agglomerative clustering analysis and alveolar surface density (ASD) was estimated as the percentage of air on the whole image field. Alveolar area distributions were remarkably right‐skewed and showed an increase in median value with a large topology‐independent heterogeneity on increasing Pld. Modeling of alveolar area distributions on increasing Pld led to hypothesize that absolute alveolar compliance (change in surface area over change in Pld) increases fairly linearly with increasing initial alveolar size, the corollary of this assumption being a constant specific compliance. Clusters were reciprocally interweaved due to their highly variable complex shapes. ASD was found to increase with a small coefficient of variation (CV <25%) with increasing Pld. The CV of lung volume at each transpulmonary pressure was further decreased (about 6%). The results of the study suggest that the considerable heterogeneity of alveolar size and of the corresponding alveolar mechanical behavior are homogenously distributed, resulting in a substantially homogenous mechanical behavior of lung units and whole organ.