Baroreflex Sensitivity Assessed by Complex Demodulation of Cardiovascular Variability

Kim, Shin Y.; Euler, David E.

doi:10.1161/01.hyp.29.5.1119

Cited by 28 publications

(17 citation statements)

References 22 publications

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“…A known drawback of the Butterworth filter is that filtered series are phase shifted. This effect was minimized by extension of the original series at the beginning and end with its own reversed array and back-to-back filtering (25,35). The filtered signal was superimposed on the raw signal and manually examined to ensure satisfactory removal of any signal artifacts.…”

Section: Discussionmentioning

confidence: 99%

Mechanism of cardioventilatory coupling: insights from cardiac pacing, vagotomy, and sinoaortic denervation in the anesthetized rat

Tzeng¹,

Larsen²,

Galletly³

2007

American Journal of Physiology-Heart and Circulatory Physiology

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Cardioventilatory coupling (CVC), a temporal alignment between the heartbeat and inspiratory activity, is a major determinant of breath-to-breath variation in observed respiratory rate (fo). The cardiac-trigger hypothesis attributes this to adjustments of respiratory timing by baroreceptor afferent impulses to the central respiratory pattern generator. A mathematical model of this hypothesis indicates that apparent CVC in graphical plots of ECG R wave vs. inspiratory time is dependent on the heart rate (HR), the rate of the intrinsic respiratory oscillator (f i), and the strength of the hypothetical cardiovascular afferent impulse. Failure to account for HR and fi may explain the inconsistent results from previous attempts to identify the neural pathways involved in CVC. Cognizant of these interactions, we factored in the HR-to-fi ratio in our examination of the role of the vagus nerve and arterial baroreceptors in CVC by cardiac pacing 29 anesthetized Sprague-Dawley rats and incrementally changing the HR. With the assumption of a relatively constant fi, CVC could be examined across a range of HR-to-fo ratios before and after vagotomy, sinoaortic denervation, and vagotomy ϩ sinoaortic denervation. We confirmed the relation between CVC, HR-to-f o ratio, and breath-to-breath respiratory period variability and demonstrated the loss of these relations after baroreceptor elimination. Sham experiments (n ϭ 8) showed that these changes were not due to surgical stress. Our data support the notion that inspiratory timing can be influenced by cardiac afferent activity. We conclude that the putative cardiovascular input arises from the arterial baroreceptors and that the vagus nerve is not critical for CVC. respiratory period variability; respiratory rhythm; arterial baroreceptors; cardiorespiratory synchronization CARDIOVENTILATORY COUPLING (CVC) is a temporal alignment between the heartbeat and inspiratory activity (11-14, 28 -30, 34, 42). Clinical studies show that CVC is a major determinant of breath-to-breath respiratory period variability, and a "cardiactrigger hypothesis" has been proposed to explain the experimental data. It has been hypothesized that CVC reflects breathto-breath adjustments of respiratory timing by afferent impulses to the central respiratory pattern generator arising from the arterial baroreceptors (12,13,26). This hypothesis is supported by modeling studies (13,26,34), as well as experimental observations of CVC under conditions where heart rate (HR) is largely independent of efferent neural modulation, for example, during fixed-rate cardiac pacing (21), in the presence of an artificial pulsatile circulation (1), and during atrial fibrillation (28). It has also been shown that the most consistent relation between inspiration and the heartbeat is the interval between inspiratory onset (I) and the immediately preceding ECG R wave (RI Ϫ1 interval) (28,42). Taken together, these observations suggest that CVC most likely reflects a "triggering" of inspiration by the heartbeat and accounts for the us...

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Section: Discussionmentioning

confidence: 99%

Mechanism of cardioventilatory coupling: insights from cardiac pacing, vagotomy, and sinoaortic denervation in the anesthetized rat

Tzeng¹,

Larsen²,

Galletly³

2007

American Journal of Physiology-Heart and Circulatory Physiology

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“…49 The relation of the resultant bradycardia and/or tachycardia to pressure changes has been overwhelmingly supported as an appropriate measure of the sensitivity, or gain, of the cardiac vagal baroreflex. 3 Considering that baroreflex gain has prognostic value for individuals with hypertension, coronary disease, and diabetes, [5][6][7][8]18 validity of the measurement is paramount. The work presented herein is a logically reasoned evaluation of 5 spontaneous indices to determine their relation to baroreflex physiology.…”

Section: Discussionmentioning

confidence: 99%

“…1,16 In recent years, investigators have exploited spontaneous fluctuations in blood pressure and heart period to index cardiovascular control 17 and have proposed that these spontaneous oscillations provide a less-invasive route to assess baroreflex gain. 18 However, it is unclear whether cardiovascular variabilities arise from fluctuations in central neural activity, extracardiovascular inputs (eg, mechanical and neural effects of respiration), and/or baroreflex engagement. 19 Although spontaneous indices for baroreflex gain might have some prognostic utility, 20,21 it remains unclear whether they broadly represent arterial baroreflex function or merely recapitulate vagally mediated heart rate variability.…”

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confidence: 99%

Spontaneous Indices Are Inconsistent With Arterial Baroreflex Gain

2003

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Abstract-Spontaneously occurring, parallel fluctuations in arterial pressure and heart period are frequently used as indices of baroreflex function. Despite the convenience of spontaneous indices, their relation to the arterial baroreflex remains unclear. Therefore, in 97 volunteers, we derived 5 proposed indices (sequence method, ␣-index, transfer function, low-frequency transfer function, and impulse response function), compared them with arterial baroreflex gain (by the modified Oxford pharmacologic technique), and examined their relation to carotid distensibility and respiratory sinus arrhythmia. The subjects comprised men and women (nϭ41) aged 25 to 86 years, 30% of whom had established coronary artery disease. Generally, the indices were correlated with each other (except ␣-index and low-frequency transfer function) and with baroreflex gain. However, the Bland-Altman method demonstrated that the spontaneous indices had limits of agreement as large as the baroreflex gain itself. Even in individuals within the lowest tertile of baroreflex gain for whom baroreflex gain appears to be the most clinically relevant, spontaneous indices failed to relate to baroreflex gain. In fact, for these individuals, there was no correlation between any index and baroreflex gain. Forward stepwise linear regression showed that all spontaneous indices and baroreflex gain were related to respiratory sinus arrhythmia, but only baroreflex gain was related to carotid distensibility. Therefore, these data suggest that spontaneous indices are inadequate estimates of gain and are inconsistent with arterial baroreflex function. Key Words: baroreceptors Ⅲ carotid sinus Ⅲ elasticity Ⅲ arrhythmia Ⅲ baroreflex T he arterial baroreflex is a key mechanism for blood pressure homeostasis, is clinically relevant as a predictor of cardiovascular mortality, 1 and is physiologically relevant as an indicator of autonomic control. 2 The sensitivity, or gain, of the arterial baroreflex is calculated routinely from the relation of bradycardic and/or tachycardic responses to increases and/or decreases in systemic arterial pressure. 3 These responses encompass both mechanical and neural aspects of the system. Changes in pressure result in stretch of the aortic arch and the carotid sinus, wherein stretch-sensitive receptors reside. These afferent baroreceptive neurons terminate in the dorsomedial medulla, which in turn signals the neurons composing the efferent autonomic limb of the baroreflex. The resultant cardiac vagal adjustments appropriately regulate heart period to buffer against pressure rises and falls. 2 Arterial baroreflex physiology dictates that both barosensory vessel distensibility and cardiac vagal function critically determine reflex sensitivity. Indeed, a relation between baroreflex gain and carotid stiffness has been shown in healthy young and middle-aged subjects, 4 as well as in hypertensive individuals. 5 Additionally, in patients with coronary disease 6,7 and diabetes, 8,9 both gain and carotid distensibility are prognostically rele...

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“…BRS was estimated as the mean value of the ratio of the smoothed amplitude oscillations in RR interval and systolic pressure (Kim and Euler 1997), for each frequency band. The smoothing was done using a moving average filter with a 5 s window.…”

Section: Complex Demodulationmentioning

confidence: 99%

Baroreflex sensitivity assessment and heart rate variability: relation to maneuver and technique

et al. 2005

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In the present study, we examined two baroreflex sensitivity (BRS) issues that remain uncertain: the differences among diverse BRS assessment techniques and the association between BRS and vagal outflow. Accordingly, the electrocardiogram and non-invasive arterial pressure were recorded in 27 healthy subjects, during supine with and without controlled breathing, standing, exercise, and recovery conditions. Vagal outflow was estimated by heart rate variability indexes, whereas BRS was computed by alpha-coefficient, transfer function, complex demodulation in low- and high-frequency bands, and by sequence technique. Our results indicated that only supine maneuvers showed significantly greater BRS values over the high frequency than in the low-frequency band. For maneuvers at the same frequency region, supine conditions presented a larger number of significant differences among techniques. The plots between BRS and vagal measures depicted a funnel-shaped relationship with significant log-log correlations (r=0.880-0.958). Very short latencies between systolic pressure and RR interval series in high-frequency band and strong log-log correlations between frequency bands were found. Higher variability among different baroreflex measurements was associated with higher level of vagal outflow. Methodological assumptions for each technique seem affected by non-baroreflex variation sources, and a modified responsiveness of vagal motoneurons due to distinct stimulation levels for each maneuver was suggested. Thus, highest vagal outflows corresponded to greatest BRS values, with maximum respiratory effect for the high-frequency band values. In conclusion, BRS values and differences across the tested techniques were strongly related to the vagal outflow induced by the maneuvers.

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Baroreflex Sensitivity Assessed by Complex Demodulation of Cardiovascular Variability

Cited by 28 publications

References 22 publications

Mechanism of cardioventilatory coupling: insights from cardiac pacing, vagotomy, and sinoaortic denervation in the anesthetized rat

Mechanism of cardioventilatory coupling: insights from cardiac pacing, vagotomy, and sinoaortic denervation in the anesthetized rat

Spontaneous Indices Are Inconsistent With Arterial Baroreflex Gain

Baroreflex sensitivity assessment and heart rate variability: relation to maneuver and technique

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