Among CFS patients, α-gain LF actually increased during LBNP.
During LBNP, compared to controls, α-gain HF decreased more, and α-gain LF and the ratio of α-gain LF/α-gain HF increased more in CFS patients, all suggesting greater shift from parasympathetic to sympathetic baroreflex control.
However, during LBNP, α-gain HF tended to decrease more, and α-gain LF tended to increase more among CFS patients than controls, leading to a marked increase in the ratio of α-gain LF/α-gain HF in the CFS-patients which was not present in the controls.
Furthermore, in adults, both sedentary and gravitational deconditionings seem to be associated with attenuated sympathetic responsiveness during orthostatic stress (Levine et al. 1991; Sun et al. 2003), and endurance training in sedentary individuals tends to increase LF baroreflex gain at rest (Iwasaki et al. 2003).
There were no differences in the baroreflex function, as estimated by the cross-spectral LF gain (data not shown).
Contrasting these results, we found equal LF baroreflex gain among controls and CFS patients at rest and increased LF baroreflex gain in CFS patients during orthostatic stress, making hypovolemia an unlikely explanation.
Moreover, an attenuation of LF baroreflex gain has been demonstrated during experimentally induced hypovolemia by LBNP (Barbieri et al. 2002).
However, detailed studies of baroreflex function with techniques similar to ours have revealed a reduced LF baroreflex gain at rest following blood donation (Triedman et al. 1993) and furosemide treatment (Iwasaki et al. 2000) and a further attenuation of LF baroreflex gain in hypovolemic individuals during orthostatic stress (Triedman et al. 1993).
(F ) H3K23me3 localization in loss-of-function and gain-of-function mutants (lf or gf, respectively) of the Notch-like receptor GLP-1.
Previous studies applying the same bivariate technique used here have demonstrated that during upright posture the α-gain decreases in both LF and HF ranges (Barbieri et al. 2002), presumably secondary to parasympathetic withdrawal.
However, the sequential method adopted in the latter study does not allow separate estimation of LF and HF gain, making it most sensitive for parasympathetic heart rate control.
