2.3 | Monitoring of physiological parameters
During the experiment, electrocardiography, mean arterial blood pressure, and the percentage of arterial hemoglobin oxygen saturation (SpO2) were continuously measured via a monitor (M1205A Omni-Care 24/24C, Hewlett Packard, Essex, MA, USA). Respiratory flow and airway pressure were measured with a heated pneumotachograph coupled to a differential pressure transducer (MP-45-16, Validyne, Kenilworth, NJ, USA) and a pressure transducer (MP45-28, Validyne), respectively. The tidal volume was integrated from the flow signal. These signals were recorded by a recorder (TA11, Gould, Eastlake, OH, USA) and a data acquisition system (PowerLab 16/30, ADInstruments Pty Ltd, Bella Vista, NSW, Australia). Arterial blood gas levels were analyzed using an autoanalyzer (OPTIMedical, Roswell, GA, USA). Alveolar-arterial oxygen gradient (AaDO2) was calculated.