MANUAL SINGLE NATIONAL DISABILITY (PART I OF II) CHAPTER IV 4. RESPIRATORY 4.1 General The purpose of this chapter is to conduct the evaluation of permanent impairment of the respiratory system and its effects on individual performance. It must be remembered that this type of chronic dysfunction is not static, but it may instead be a manifestation of changing processes, so that should make periodic assessments as the natural history of the disease diagnosed. The quantified lung dysfunction does not correlate directly with the extent, severity or anatomical tissue injury or the symptoms. Therefore, the classification of the deficiency be made based on the criteria in this chapter. Chronic respiratory failure is considered when the barometric  pressure of arterial oxygen  (PO2) is less than 60mm Hg, with or without elevated blood barometric pressure of carbon dioxide (PCO2) greater than 45 mm Hg. In this case, it is an advanced co...