Brochard, L. | Search bioRxiv

bioRxiv2023

A combined frequency domain near infrared spectroscopy and diffuse correlation spectroscopy system for comprehensive metabolic monitoring of inspiratory muscles during loading

SignificanceMechanical ventilation (MV) is a cornerstone technology in the intensive care unit as it assists with the delivery of oxygen in critical ill patients. The process of weaning patients from MV can be long, and arduous and can lead to serious complications for many patients. Despite the known importance of inspiratory muscle function in the success of weaning, current clinical standards do not include direct monitoring of these muscles. AimThe goal of this project was to develop and validate a combined frequency domain near infrared spectroscopy (FD-NIRS) and diffuse correlation spectroscopy (DCS) system for the noninvasive characterization of inspiratory muscle response to a load. ApproachThe system was fabricated by combining a custom digital FD-NIRS and DCS system. It was validated via liquid phantom titrations and a healthy volunteer study. The sternocleidomastoid (SCM), an accessory muscle of inspiration, was monitored during a short loading period in fourteen young healthy volunteer. Volunteers performed two different respiratory exercises, a moderate and high load, which consisted of a one-minute baseline, a one-minute load, and a six-minute recovery period. ResultsThe system has low crosstalk between absorption, reduced scattering, and flow when tested in a set of liquid titrations. Faster dynamics were observed for changes in blood flow index (BFi), and metabolic rate of oxygen (MRO2) compared to hemoglobin + myoglobin (Hb+Mb) based parameters after the onset of loads in males. Additionally, larger percent changes in BFi, and MRO2 were observed compared to Hb+Mb parameters in both males and females. There were also sex differences in baseline values of oxygenated Hb+Mb, total Hb+Mb, and tissue saturation. ConclusionThe dynamic characteristics of Hb+Mb concentration and blood flow were distinct during loading of the SCM, suggesting that the combination of FD-NIRS and DCS may provide a more complete picture of inspiratory muscle dynamics.

bioengineering↗

bioRxiv2017

Inflammatory Cellular Response To Mechanical Ventilation In Elastase-Induced Experimental Emphysema: Role Of Pre-Existing Alveolar Macrophages Infiltration

BackgroundAn excessive pulmonary inflammatory response could explain the poor prognosis of chronic obstructive pulmonary disease (COPD) patients submitted to invasive mechanical ventilation. The aim of this study was to evaluate the response to normal tidal volume (Vt) mechanical ventilation in a murine model of pulmonary emphysema, which represents the alveolar component of COPD. In this model, two time points associated with different levels of lung inflammation but similar lung destruction, were analyzed.\n\nMethodsC57BL/6 mice received a tracheal instillation of 5 IU of porcine pancreatic elastase (Elastase mice) or the same volume of saline (Saline mice). Fourteen (D14) and 21 (D21) days after instillation, mice were anesthetized, intubated, and either mechanically ventilated (MV) with a normal Vt (8 mL/kg) or maintained on spontaneous ventilation (SV) during two hours. We analyzed respiratory mechanics, emphysema degree (mean chord length by lung histological analysis), and lung inflammation (bronchoalveolar lavage (BAL) cellularity, proportion and activation of total lung inflammatory cells by flow cytometry).\n\nResultsAs compared with Saline mice, Elastase mice showed a similarly increased mean chord length and pulmonary compliance at D14 and D21, while BAL cellularity was comparable between groups. Lung mechanics was similarly altered during mechanical ventilation in Elastase and Saline mice. Activated alveolar macrophages CD11bmid were present in lung parenchyma in both Elastase SV mice and Elastase MV mice at D14 but were absent at D21 and in Saline mice, indicating an inflammatory state with elastase at D14 only. At D14, Elastase MV mice showed a significant increase in percentage of neutrophils concomitant with a decrease in percentage of alveolar macrophages in total lung, as compared with Elastase SV mice. Furthermore, alveolar macrophages of Elastase MV mice at D14 overexpressed Gr1, and monocytes showed a trend to overexpression of CD62L, compared with Elastase SV mice.\n\nConclusionsIn an elastase-induced model of pulmonary emphysema, normal Vt mechanical ventilation produced an increase in the proportion of pulmonary neutrophils, and an activation of alveolar macrophages and pulmonary monocytes. This response was observed only when the emphysema model showed an underlying inflammation (D14), reflected by the presence of activated alveolar macrophages CD11bmid.

cell biology↗