* 18 years of age. * person unable to give consent. * person who refuses to participate. * pregnancy and lactation * participating in other study * requirement for mechanical ventilation. * inability to maintain prolonged sitting position (at least 2 hours) * subject with contraindications to hbot (pulmonary shock, bullae, emphysema or untreated pneumothorax, severe seizures, uncontrolled hypertension, chronic obstructive disease of grade iii or iv).

* 18 years of age. * person unable to give consent. * person who refuses to participate. * pregnancy and lactation * participating in other study * requirement for mechanical ventilation. * inability to maintain prolonged sitting position (at least 2 hours) * subject with contraindications to hbot (pulmonary shock, bullae, emphysema or untreated pneumothorax, severe seizures, uncontrolled hypertension, chronic obstructive disease of grade iii or iv).

- 18 years of age. - person unable to give consent. - person who refuses to participate. - pregnancy and lactation - participating in other study - requirement for mechanical ventilation. - inability to maintain prolonged sitting position (at least 2 hours) - subject with contraindications to hbot (pulmonary shock, bullae, emphysema or untreated pneumothorax, severe seizures, uncontrolled hypertension, chronic obstructive disease of grade iii or iv).

- 18 years of age. - person unable to give consent. - person who refuses to participate. - pregnancy and lactation - participating in other study - requirement for mechanical ventilation. - inability to maintain prolonged sitting position (at least 2 hours) - subject with contraindications to hbot (pulmonary shock, bullae, emphysema or untreated pneumothorax, severe seizures, uncontrolled hypertension, chronic obstructive disease of grade iii or iv).