The effects of respiratory frequency on noninvasive parameters of baroreceptor-cardiac reflex sensitivity

Abstract

EGG, blood pressure and respiration were recorded during paced breathing in eighteen young normotensive subjects in order to elucidate the effects of varying respiratory frequency on spectral and sequence parameters of baroreceptor-cardiac reflex sensitivity. Indices of baroreflex sensitivity obtained from spectral and cross-spectral analysis of systolic pressures and heart periods were modulus and weighted coherence.

Sequence analysis yielded mean regression slopes and numbers of progressively rising or declining sequences of systolic pressures and heart periods. Paced respiratory periods were 4s, 5s, 7s, 10s, and 15s.

Significant effects of respiratory frequency were observed for modulus, weighted coherence and the mean regression slope of ascending sequences. Maximum values of baroreceptor-cardiac sensitivity were found for paced respiratory periods of 10s.

There were no differences in most of these parameters between pacing frequencies in the eupneic range (T=4s, T=5s) except the number of sequences differing even between two eupneic frequencies. Ascending sequences were formed in expiration only.

Our results suggest preferential use of modulus, weighted coherence and ascending mean regression slope parameters as noninvasive indices of baroreflex sensitivity while the number of sequences give unreliable results with changes in respiratory frequency.