Objective: We explored the physiological background of the non-linear operating mode of cardiorespiratory oscillators as the fundamental question of cardiorespiratory homeodynamics and as a prerequisite for the understanding of neurocardiovascular diseases. We investigated 20 healthy human subjects for changes using electrocardiac RR interval (RRI) and respiratory signal (Resp) Detrended Fluctuation Analysis (DFA, α 1RRI , α 2RRI , α 1Resp , α 2Resp), Multiple Scaling Entropy (MSE RRI1−4 , MSE RRI5−10 , MSE Resp1−4 , MSE Resp5−10), spectral coherence (Coh RRI−Resp), cross DFA (ρ 1 and ρ 2) and cross MSE (X MSE1−4 and X MSE5−10) indices in four physiological conditions: supine with spontaneous breathing, standing with spontaneous breathing, supine with 0.1 Hz breathing and standing with 0.1 Hz breathing. Main results: Standing is primarily characterized by the change of RRI parameters, insensitivity to change with respiratory parameters, decrease of Coh RRI−Resp and insensitivity to change of in ρ 1 , ρ 2 , X MSE1−4 , and X MSE5−10. Slow breathing in supine position was characterized by the change of the linear and non-linear parameters of both signals, reflecting the dominant vagal RRI modulation and the impact of slow 0.1 Hz breathing on Resp parameters. Coh RRI−Resp did not change with respect to supine position, while ρ 1 increased. Slow breathing in standing reflected the qualitatively specific state of autonomic regulation with striking impact on both cardiac and respiratory parameters, with specific patterns of cardiorespiratory coupling. Significance: Our results show that cardiac and respiratory short term and long term complexity parameters have different, state dependent patterns. Sympathovagal non-linear interactions are dependent on the pattern of their activation, having different scaling properties when individually activated with respect to the state of their joint activation. All investigated states induced a change of α 1 vs. α 2 relationship, which can be accurately expressed by the proposed measure-inter-fractal angle θ. Short scale (α 1 vs. MSE 1−4) and long scale (α 2 vs. MSE 5−10) complexity measures had reciprocal interrelation in standing with 0.1 Hz breathing, with specific cardiorespiratory coupling pattern (ρ 1 vs. X MSE1−4). These results support the hypothesis of hierarchical organization Matić et al. RRI-Respiratory Complexity and Cardiorespiratory Coupling of cardiorespiratory complexity mechanisms and their recruitment in ascendant manner with respect to the increase of behavioral challenge complexity. Specific and comprehensive cardiorespiratory regulation in standing with 0.1 Hz breathing suggests this state as the potentially most beneficial maneuver for cardiorespiratory conditioning.
Objective: In this research we explored the (homeo)dynamic character of cardiorespiratory coupling (CRC) under the influence of different body posture and breathing regimes. Our tool for it was the pulse respiration quotient (PRQ), representing the number of heartbeat intervals per breathing cycle. We obtained non-integer PRQ values using our advanced Matlab® algorithm and applied it on the signals of 20 healthy subjects in four conditions: supine position with spontaneous breathing (Supin), standing with spontaneous breathing (Stand), supine position with slow (0.1 Hz) breathing (Supin01) and standing with slow (0.1 Hz) breathing (Stand01).Main results: Linear features of CRC (in PRQ signals) were dynamically very sensitive to posture and breathing rhythm perturbations. There are obvious increases in PRQ mean level and variability under the separated and joined influence of orthostasis and slow (0.1 Hz) breathing. This increase was most pronounced in Stand01 as the state of joint influences. Importantly, PRQ dynamic modification showed greater sensitivity to body posture and breathing regime changes than mean value and standard deviation of heart rhythm and breathing rhythm. In addition, as a consequence of prolonged supine position, we noticed the tendency to integer quantization of PRQ (especially after 14 min), in which the most common quantization number was 4:1 (demonstrated in other research reports as well). In orthostasis and slow breathing, quantization can also be observed, but shifted to other values. We postulate that these results manifest resonance effects induced by coupling patterns from sympathetic and parasympathetic adjustments (with the second as dominant factor).Significance: Our research confirms that cardiorespiratory coupling adaptability could be profoundly explored by precisely calculated PRQ parameter since cardiorespiratory regulation in healthy subjects is characterized by a high level of autonomic adaptability (responsiveness) to posture and breathing regime, although comparisons with pathological states has yet to be performed. We found Stand01 to be the most provoking state for the dynamic modification of PRQ (cardiorespiratory inducement). As such, Stand01 has the potential of using for PRQ tuning by conditioning the cardiorespiratory autonomic neural networks, e.g., in the cases where PRQ is disturbed by environmental (i.e., microgravity) or pathologic conditions.
Due to the fact that respiratory breath-to-breath and cardiac intervals between two successive R peaks (BBI and RRI, respectively) are not temporally concurrent, in a previous paper, we proposed a method to calculate both the integer and non-integer parts of the pulse respiration quotient (PRQ = BBI/RRI = PRQint + b1 + b2), b1 and b2 being parts of the border RRIs for each BBI. In this work, we study the correlations between BBI and PRQ, as well as those between BBI and mean RRI within each BBI (mRRI), on a group of twenty subjects in four conditions: in supine and standing positions, in combination with spontaneous and slow breathing. Results show that the BBI vs. PRQ correlations are positive; whereas the breathing regime had little or no effect on the linear regression slopes, body posture did. Two types of scatter plots were obtained with the BBI vs. mRRI correlations: one showed points aggregated around the concurrent PRQint lines, while the other showed randomly distributed points. Five out of six of the proposed aggregation measures confirmed the existence of these two cardio-respiratory coupling regimes. We also used b1 to study the positions of R pulses relative to the respiration onsets and showed that they were more synchronous with sympathetic activation. Overall, this method should be used in different pathological states.
Cardiorespiratory coupling (CRC), a set of cardiac and respiratory rhythms that optimise the body oxygenation and the adaptability of the cardiorespiratory system to the external and internal environment, is represented in the linear domain by coefficient Qpr, the number of heartbeats per respiratory cycle (1, 2). Slow 0.1Hz breathing in supine position (Supin01) and active standing (Stand) represent the states of maximal RRI vagal and sympathetic modulation, respectively, in physiological quiescence; standing with 0.1Hz breathing (stand01) is characterized by qualitatively specific pattern of CRC(3). The aim of our work was to investigate the Qpr in 4 states: supine position with spontaneous breathing (supin), stand, supin01and stand01. Methods: The ECG (RRI) and respiration signals were simultaneously recorded in 20 healthy human subjects in four conditions. Data acquisition and processing was performed as in (3). Results: Parameter Supin (mean95%CI) Stand (mean95%CI) Supin01 (mean95%CI) Stand01 (mean95%CI) RRI [s] 0.980.13 0.720.10 1.060.13 0.750.09 sd RRI [s] 0.060.02 0.040.02 0.090.03 0.070.02 BBI [s] 4.681.53 4.581.80 9.850.71 9.950.20 sdBBI [s] 1.110.69 1.351.29 1.440.94 1.060.44 Qpr 4.811.67 6.392.43 9.411.20 13.481.66 sdQpr 1.140.67 1.931.73 1.390.71 1.540.53 Table 1. Mean value and 95%CI of RRI, BBI and Qpr for 20 healthy subjects in four physiological states: Supin-supine position with spontaneous breathing, Stand- standing with spontaneous breathing, Supin01-supine position with 0.1Hz breathing, Stand01-standing with slow 0.1Hz breathing. Parameter Supin-Stand Supin-Supin01 Supin-Stand01 Supin01-Stand01 RRI 0.000 0.0 04 0.000 0.000 sd RRI 0.0 04 0.00 0 0.351 0.0 10 BBI 0.391 0.000 0.000 0.313 sdBBI 0.232 0.433 0.911 0.135 Qpr 0.0 00 0.000 0.000 0.000 sdQpr 0.0 06 0.370 0.0 33 0.191 Table 2. Probability values (p) of statistically significant differences between different physiological states. Wilcoxon test on a sample of 20 subjects. Color-indicated statistically significant changes in values (p <0.05) whose changes were related and discussed. - increase of mean value, -decrease of mean value. Our results show that Qpr is state dependent and that it increases with the behavioral task complexity. Postural change tunes Qpr by RRI modulation, while 0.1Hz breathing dominantly by the increase of BBI. Stand01 is characterized by concomitant adjustment of both RRI and BBI. These data imply that Qpr regulation is "loosely" and selectively coordinated in stand and supin01("dual control") while integrated in stand01 ("unitary control"(4)). Analogously to nonlinear CRC(3), Qpr is probably operated by hierarchically higher diencephalo-telencephalic autonomic networks. References: 1. Moser M et al, Biol Rhythm Res 1995;26(1):100-111. 2. Scholkmann F et al, Front Physiol 2019;10:371. 3. Matić Z et al, Front Physiol 2020;11:24. 4. Feldman JL et al, Annu Rev Physiol 1988;50,593606.
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