Three algorithms for assessment of respiratory sinus arrhythmia (RSA) have been evaluated: cross-correlation function, histogram analysis and regression plot. The algorithms were tested experimentally in a group of 11 subjects. A cross-correlation function with a high time resolution (1 ms) was used for investigation of the time lag between instantaneous heart rate and respiration (CTL). This time lag was not affected by the breathing rate in a range of 8 to 29 breaths per minute. A mathematical model of CTL compared with experimental results indicates that respiratory sinus arrhythmia is probably modulated directly by the respiratory network in the brainstem rather than by a baroreflex in the range of breathing rate investigated. Histogram analysis reflects the impact of inspiration and expiration on respiratory sinus arrhythmia. For this purpose heart rate changes were separated into two distributions (inspiration - expiration). The result value (CI-VAL) of the Mann-Whitney (J-test reflects the impact of respiration on heart rate variability. Regression analysis of heart rate versus respiration shows that the heart rate increase is more closely coupled to inspiration than the heart rate decrease to expiration. Both, CTL and CJ-VAL are thought to be useful parameters for clinical investigation of RSA.
Ventilation related heart rate oscillations – respiratory sinus
arrhythmia (RSA) – originate in human from several mechanisms.
Two most important of them – the central mechanism (direct
communication between respiratory and cardiomotor centers),
and the peripheral mechanism (ventilation-associated blood
pressure changes transferred to heart rate via baroreflex) have
been described in previous studies. The major aim of this study
was to compare the importance of these mechanisms in the
generation of RSA non-invasively during various states by
quantifying the strength of the directed interactions between
heart rate, systolic blood pressure and respiratory volume
signals. Seventy-eight healthy volunteers (32 male, age range:
16.02-25.77 years, median age: 18.57 years) participated in this
study. The strength of mutual interconnections among the
spontaneous beat-to-beat oscillations of systolic blood pressure
(SBP), R-R interval (RR signal) and respiration (volume changes –
RESP signal) was quantified during supine rest, orthostatic
challenge (head-up tilt, HUT) and cognitive load (mental
arithmetics, MA) using bivariate and trivariate measures of
cardio-respiratory information transfer to separate baroreflex and
nonbaroreflex (central) mechanisms. Our results indicate that
both basic mechanisms take part in RSA generation in the intact
cardiorespiratory control of human subjects. During orthostatic
and mental challenges baroreflex based peripheral mechanism
becomes more important
Respiratory sinus arrhythmia (RSA), i.e. heart rate (HR) variations
during inspiration and expiration, is considered as a noninvasive
index of cardiac vagal control. Mitral valve prolapse (MVP) could
be associated with increased cardiovascular risk; however, the
studies are rare particularly at adolescent age. Therefore, we
aimed to study cardiac vagal control indexed by RSA in adolescent
patients suffering from MVP using short-term heart rate variability
(HRV) analysis. We examined 12 adolescents (girls) with MVP (age
15.9±0.5 years) and 12 age and gender matched controls. Resting
ECG was continuously recorded during 5 minutes. Evaluated HRV
indices were RR interval (ms), rMSSD (ms), pNN50 (%), log HF
(ms2
), peak HF (Hz) and respiratory rate (breaths/min). RR interval
was significantly shortened in MVP group compared to controls
(p=0.004). HRV parameters-rMSSD, pNN50 and log HF were
significantly lower in MVP compared to controls (p=0.017,
p=0.014, p= 0.015 respectively). Our study revealed reduced RSA
magnitude indicating impaired cardiac vagal control in MVP already
at adolescent age that could be crucial for early diagnosis of
cardiovascular risk in MVP.