Increased complexity of short-term heart rate variability in hyperthyroid patients during orthostatic challenge.
Hyperthyroidism is a pathological condition characterized by an altered autonomic cardiovascular control, resulting in an increase of the sympathetic and a decrease of the parasympathetic modulation of heart rate variability. Recently, the entropy-based indices derived from short-term heart period variability have been proved to be helpful in evaluating the autonomic cardiovascular modulation. The aim of our study was to evaluate the autonomic cardiovascular modulation of hyperthyroid subjects at rest and during standing using spectral parameters and corrected conditional entropy indices derived from short-term heart period variability in 12 hyperthyroid (HYPTH) and 9 normal healthy (N) females. Mean heart period was significantly decreased by standing both in N and HYPTH and the LF power expressed in normalized units was increased. The respiratory rate was faster in the HYPTH group compared to N and complexity was significantly greater in HYPTH compared to N during standing. Results suggested an enhanced complexity of cardiovascular control in HYPTH, more evident in a condition of sympathetic activation. The increased complexity of the cardiovascular regulation is probably not completely due to autonomic control but also to other influences, such as metabolic effects of thyroid hormones impinging upon respiratory control mechanisms and, therefore, on cardiorespiratory coupling.
Tobaldini
Eleonora
E
Department of Clinical Sciences, Internal Medicine II, L. Sacco Hospital, University of Milan, Italy. ele.ric@alice.it
Porta
Alberto
A
Bulgheroni
Mara
M
Pecis
Marica
M
Muratori
Milena
M
Bevilacqua
Maurizio
M
Montano
Nicola
N
D000328:Adult; D000704:Analysis of Variance; D001341:Autonomic Nervous System / Q000503:physiopathology; D001698:Biomedical Engineering; D016022:Case-Control Studies; D047630:Depsipeptides / Q000502:physiology; D005260:Female; D006339:Heart Rate / Q000502:physiology*; D006801:Humans; D006980:Hyperthyroidism / Q000503:physiopathology*; D008875:Middle Aged; D011187:Posture / Q000502:physiology
D047630:Depsipeptides; C081425:respirantin