Wave forms attributed to the primary respiratory mechanism (PRM), as published by Viola Frymann, DO, in JAOA June 1971, were analyzed for an undescribed parameter, cycle-to-cycle variability. Tracings from this paper were independently measured by two physicians focusing on the duration of each cycle. Consistency of the measurements and interexaminer agreement were shown. The duration of individual cycles demonstrated significant cycle-to-cycle variability ranging from 0.6 second up to 6.3 seconds. The reason for variability as well as its clinical significance is unknown. The minute rate of each tracing ranged from 6.5 to 13.8 cycles per minute (0.108 to 0.230 Hz [corrected]), mean 10.8 +/- 2.3 (0.180 +/- 0.038 Hz [corrected]). (Different minute rates attributed to the PRM have been reported in other studies.) Although variability is an innate characteristic of biologic cycles, this phenomenon has not been previously reported for the PRM. The authors suggest that this variability has likely confounded previous interexaminer reliability studies and should be considered in any future studies of this type. Determination of causes of this variability present timely and fruitful avenues of research.

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