Phototoxicity induced in living HeLa cells by focused femtosecond laser pulses: a data-driven approach.

Nonlinear optical microscopy is a powerful label-free imaging technology, providing biochemical and structural information in living cells and tissues. A possible drawback is photodamage induced by high-power ultrashort laser pulses. Here we present an experimental study on thousands of HeLa cells, to characterize the damage induced by focused femtosecond near-infrared laser pulses as a function of laser power, scanning speed and exposure time, in both wide-field and point-scanning illumination configurations. Our data-driven approach offers an interpretation of the underlying damage mechanisms and provides a predictive model that estimates its probability and extension and a safety limit for the working conditions in nonlinear optical microscopy. In particular, we demonstrate that cells can withstand high temperatures for a short amount of time, while they die if exposed for longer times to mild temperatures. It is thus better to illuminate the samples with high irradiances: thanks to the nonlinear imaging mechanism, much stronger signals will be generated, enabling fast imaging and thus avoiding sample photodamage.

Non-invasive CPAP in mild and moderate ARDS secondary to SARS-CoV-2.

BACKGROUND: During the COVID-19 outbreak, a very high number of infected patients developed pneumonia and many of them complicated with acute respiratory distress syndrome. The optimal management of respiratory failure and the role of lung ultrasound imaging in the evaluation of efficacy of treatment are unknown. METHODS: In March 2020 we treated 18 patients with mild and moderate ARDS secondary to SARS-CoV-2 with non-invasive continuous positive airway pressure therapy (NI-CPAP). All patients underwent lung ultrasound imaging to verify the entity of lung recruitment after NI-CPAP initiation. RESULTS: After one hour of treatment we observed a significant improvement in PaO2/FiO2 ratio in 10 patients. Notably, only 50 % of them reached an effective improvement in lung aeration detectable with lung ultrasound. In the other 50 % or patients the improvement in PaO2/FiO2 might be related to blood redistribution and reverse of hypoxic vasoconstriction. CONCLUSION: NI- CPAP is a valid therapeutic option in mild and moderate ARDS secondary SARS-CoV-2. Lung recruitment detected by means of lung ultrasound is a relevant but not the exclusive mechanism that underlies the therapeutic efficacy of NI-CPAP in this clinical setting.