The respiratory controller in this context is considered to be the cen
tral nervous system pattern generator that produces a signal that in t
urn activates muscles of the respiratory pump, By its ''output'' vie m
ean the strength of the signal, In fact, the signal varies constantly
through the respiratory cycle in amplitude and in distribution among t
he various respiratory muscles, This review discusses advantages and l
imitations of commonly used methods of assessing output including elec
tromyograms, occlusion pressure, minute ventilation, and recruitment o
f muscles beyond the diaphragm and intercostal muscles, Principles are
reviewed for choosing and interpreting these measurements for analysi
s of clinical problems, and applied to the examples of obstructive sle
ep apnea, COPD, generalized weakness of respiratory muscles, and phren
ic nerve palsy.