Tidal volume may be the most important technical indicator for ventilation. Measuring tidal volume can be used as an indicator of how effective a patient's gas exchange is, and can also be used as a predictive indicator to indirectly predict the severity of respiratory disease. This tidal volume can be measured using spirometry and pneumotachograph, and the lung function of the patient can be assessed directly or indirectly through the respiratory volume and air flow velocity. In addition, the measurement itself can change the patient's breathing pattern, and for accurate measurement, it has to be carried out in a certain space, so there is a limitation in that it is difficult to measure in a hospital bed or in a laboratory. To overcome this limitation, various methods have been introduced. The basic principle is that the tidal volume is directly proportional to the movement of the chest and proportional to the change in the length of the circumference of the chest. Over the past decade, several studies have been conducted to measure respiratory mechanics in a non-invasive way. Methods using thoracic impedance, acoustic monitoring, strain gauges, and magnetometers have been developed. Non-invasive, non-contact imaging methods have also been developed, such as thermal image, structured light plethysmography (SLP), and optoelectronic plethysmography (OEP). Therefore, in this study, the thoracic movement due to respiration was measured with a non-invasive method (IR camera), and the accuracy was compared through the impedance change obtained through impedance tomography to evaluate the effectiveness of the non-invasive equipment.

Inclusion Criteria:

• A male aged 19 years or older
• normal BMI
• patients undergoing transurethral prostate or cystectomy under spinal anesthesia

Exclusion Criteria:

• Presenting alteration in respiratory function detected by functional analysis of lung volume and capacity- pneumonectomy patient, severe ipsilateral destroyed lung patient
• Inability to understand or perform the procedure.
• ASA class 4, 5