Buprenorphine decreased overall (long-term) variability of minute ventilation. Changes in variability of the SD of breath-to-breath intervals (SDBB) are plotted as means ± SD. These histograms correspond to the variability along the line x = y in fig. 3. B6 = C57BL/6J; db/db = B6.BKS(D)-Lepr^db/J; DIO = B6 with diet-induced obesity; ob/ob = B6.Cg-Lep^ob/J.