Abstract des Autors

The power spectrum analysis of R-R interval variability (RRV) has been estimated by means of an autoregressive method in 6 men in supine (S) and sitting (C) postures at rest and during steady-state cycle exercise at about 14, 28, 45, 67 VO2max. The total power of RRV decreased exponentially as a function of exercise intensity in a similar way in both postures. 3 components were recognized in the power spectra: 1) a high frequency peak (HF), an expression of respiratory arrhythmia, the central frequency (f-central) of which increased in both S and C from a resting value of about 0.26 Hz to 0.42 Hz at 67 VO2max; 2) a low frequency peak (LF) related to arterial pressure control, the f-central of which remained constant at 0.1 Hz in C, whereas in S above 28 VO2max decreased to 0.07 Hz; and 3) a very low frequency component (VLF; less than 0.05 Hz, no f-central). The power of the 3 components (as a of the total power) depended on the body posture and the metabolic demand. HF at rest was 30.3+-6.6 in S and 5.0+-0.8 in C. During exercise HF decreased by about 30 in S and increased to 19.7+-5.5 at 28 VO2max in C. LF was lower in S than in C at rest (31.6+-5.7 vs 44.9+-6.4), remaining constant up to 28 VO2max. At the highest intensities it increased to 54.0+-15.6 in S whereas in C it decreased to 8.5+-1.6. VLF represented the remaining power and the change was in the opposite direction to LF. Changes in power spectrum distribution of RRV during exercise depended on intensity and body posture.