Material and methods: gas exchange and heart rate (HR) kinetics were investigated in 20 patients with cystic fibrosis (CF) by using a pseudorandom binary sequence (PRBS)-technique. Electrocardiogram was continuously recorded, and V02, VC02and ventilation/min (VE) responses to a multifrequent input signal were measured by means of breath-by-breath analysis. Lag time and peak value in the time-domain, and amplitude ratios in the frequency-domain were calculated to characterize the crosscorrelation functions between input and responses, and compared to normal ranges. Results: Time and frequency domain parameters are abnormal for V02,VC02and VE responses in moderately and severely ill patients, and for the HR response only in severely ill patients. Correlations are shown between those parameters, the severity of the illness evaluated by the Shwachman score and the level of impairment of the pulmonary function. Conclusion: The PRBS-technique is a useful tool to investigate the gas exchange and HR kinetics in CF patients, that offers many advantages: (1) no explicit mathematical models are assumed, (2) it is a walking test that may be used even in very young or severely ill patients, and (3) it challenges the ability to adapt to nonsteady state exercise and is therefore representative for daily activities.

Keywords: Cystic Fibrosis, heart rate kinetics, Spectral analysis, gas exchange kinetics, PRBS exercise