LONG-TERM WITHIN-SUBJECT VARIABILITY OF INSPIRATORY NEURAL DRIVE RESPONSE TO HYPOXIA

Study objective: We analyze the within-subject variation of mouth occl usion pressure (P-0.1) response to progressive isocapnic hypoxic stimu lation over long time periods in normal subjects. Patients and interve ntions: We studied 21 healthy subjects (14 male and 7 female; aged 40/-12 yrs) (mean+/-SD). Lung volumes, basal P-0.1, and P-0.1 response t o hypoxia were measured on two separate occasions 2 months apart, unde r similar ambient and clinical conditions. Results: There was no signi ficant change in clinical condition, FVC, FEV1, arterial oxygenation s aturation, end-tidal and mixed venous PCO2 levels, or P-0.1 between th e two visits. The mean P-0.1 responses to hypoxia in the two explorati ons were 0.032+/-0.022 and 0.034+/-0.022 kPa/%, respectively. There wa s a moderate intrasubject variability of P-0.1 response to hypoxia, wi th a coefficient of reproducibility of 0.01 kPa/%. Power calculations to establish the optimal sample size required for hypoxic stimulation are presented. Conclusion: Long term within-subject variability of P-0 .1 response to hypoxia is moderate. This intrinsic variability needs t o be emphasized when interpreting the effects of experimental interven tions on hypoxic sensitivity.