Consistency and signal strength of respiratory neuronal activity.

The concerns of this study are taxonomic. We demonstrate a defining characteristic of respiratory neuronal activity. This characteristic is the degree or size of the respiratory component in the activity of a respiratory cell. The essential feature of respiratory activity is that it occurs in phase with some portion of the respiratory cycle. Therefore, neuronal activity can be arranged within a matrix in which the columns are fractions of the respiratory cycle and the rows are breaths and, as Netick and Orem (10) have shown, this matrix can be analyzed with an analysis of variance to determine whether the activity contains a respiratory component. However, the analysis of variance indicates nothing about the size of a statistically significant respiratory component. We hypothesized that the size of the respiratory component in the activity of different respiratory cells differed among cells but was a stable characteristic of any given cell. The index used to quantify the degree of respiratory activity was eta 2, the proportion of the total variance of the activity of a respiratory neuron consisting of the variance occurring across fractions of the respiratory cycle. This index theoretically depends on a) the range of activity levels across a respiratory cycle and the dispersion of activity levels over this range (parameters signifying the strength of the respiratory signal) and b) the variability in the activity of the cell across breaths (a parameter signifying the consistency of the respiratory activity). Theoretically, eta 2 values can vary from 0.0 to 1.0 indicating, respectively, that none or all of the variability in the activity of a cell across breaths is accounted for by a respiratory effect. eta 2 was used to analyze the size of the respiratory component in the activity of 32 medullary respiratory neurons recorded during nonrapid eye movement (NREM) sleep in chronic cats. These different respiratory cells had activity patterns with eta 2 values ranging from 0.1 to 0.9. However, the activity of a given cell produced eta 2 values that were consistent from sample to sample. Therefore, the eta 2 value of the activity of a cell was a defining, stable characteristic of that cell. The eta 2 values of the activity of the cells were strongly correlated with the consistency of their discharge pattern from breath to breath (r x,y = 0.975).(ABSTRACT TRUNCATED AT 400 WORDS)