The perception of difficulty in breathing is normally measured clinically using the Borg modification scale ( BurdoQ.eLa/ 1982). This scale categorizes words describing increasing degrees of breathlessness, relating them to scores between zero and 10. When asked to score breathlessness, the patient chooses the number which most appropriately describes the sensation that he or she experiences.
A different approach to the quantification of breathlessness is related to measurement of the principal mechanisms involved, increased demands, and decreased reserves. The ratio of minute ventilation to maximum voluntary ventilation is a good indicator of the relationship between the patient's needs and his maximum capacity. Breathlessness can be estimated from the ratio of the inspiratory pressure needed for the actual tidal volume to the maximum inspiratory pressure that can be generated by the patient (.KilJian.. .aQd.. ..Ca.mPbe.!,! 1995). We can also estimate respiratory demands by measuring the airway occlusion pressure at 0.1 s, and maximum capacities by determining the maximum inspiratory pressure. Finally, the forced expiratory volume at 1 s (FEV-,) is also considered a good indicator of breathlessness.
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