In a manner analogous to the use of the electrocardiogram to assess cardiac function, electrophysiological tests of respiratory muscles—respiratory muscle motor latencies and elec-


Stimulation Test Normal Values (in Adults) Abnormal in:

Phrenic nerve/diaphragm latency 6-8 ms Demyelinating polyneuropathies, e.g.,

Guillain-Barre syndrome

Elicited CMAP Depends on recording electrode Phrenic nerve palsy, neuromuscular transmission defect, polyneuropathy of sepsis, myopathies

Central conduction time, total conduction time minus phrenic nerve latency ~ 4 ms Multiple sclerosis

Definition of abbreviation: CMAP = compound muscle action potential.

tromyography—can be used to assess (1) respiratory drive, respiratory muscle coordination, and the level of activation of individual muscles; (2) the presence of neural and neuromuscular pathology; and (3) the apparent efficacy of the contractile function of the muscles, when used in conjunction with measurements of contractile force. The special challenges presented by data analysis complexity and by a host of potential artifacts lead to the need for great care in the application of EMG techniques to respiratory muscles. Nevertheless, neuro-physiological tests are emerging as indispensable components of the respiratory muscle physiologist's arsenal.

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