Quantification of Cardiac Baroreflex Function at Rest and during Autonomic Stimulation

Abstract

The cardiac baroreflex constitutes an important mechanism mediating autonomic control of heart activity. Its function can be quantified by applying sequence analysis based on continuous recordings of blood pressure and heart rate. In this study, several indices derived from this method were compared regarding their suitability to estimate baroreflex function at rest and during autonomic stimulation. A cold pressor test was used to induce vagal withdrawal. Changes in the following indices evoked by this procedure were examined: baroreflex sensitivity (the extent of changes in heart period following blood pressure fluctuations), baroreflex effectiveness (the relative frequency in which the reflex responds to blood pressure fluctuations), and baroreflex power (the reflex operations in a defined period). The values of all indices decreased during autonomic stimulation. The strongest and most consistent effect, however, was observed for baroreflex sensitivity, suggesting that this parameter is the most sensitive to changes in parasympathetic tone among the three parameters. Baroreflex sensitivity also proved to differentiate between individuals with higher and lower resting blood pressure. Therefore, this index may best reflect the well-known involvement of the baroreflex in the long-term setting of blood pressure. Midrange correlations between the indices of baroreflex function suggest that they quantify similar, though not identical, aspects of baroreflex function. This study supports the use of sequence analysis as a reliable tool for the quantification of parasympathetic cardiac control. The sensitivity index must be considered the most relevant to quantify baroreflex function among the three parameters.

Cold pressor stress affects cardiac attenuation of startle

“…As mentioned above, we did not observe an effect of the CP intervention on the BRS, contrary to earlier findings (Duschek and Reyes del Paso, 2007). One reason may be the lower power in the current study compared to the work of Duschek and Reyes del Paso, based on the fact that Steptoe and Sawada (1989) also did not find CP effects on BRS with a smaller sample.…”

“…HR during both startle sessions did not differ from those during the cardiovascular measurement sessions in between, except for the pre-intervention session. BRS, whose baseline values were marginally lower in our sample than in comparable studies (Duschek and Reyes del Paso, 2007), was also reduced in both groups only in the pre-intervention session. These effects may be due to a fear response in expectation of a potentially harmful stimulus, as seen in earlier studies (e.g., Melzig et al, 2008;Virtanen et al, 2003).…”

“…Baroreflex sensitivity of heart rate control (BRS) is a measure that may serve as an indicator of the integrity of this neural circuit (Frattola et al, 1997). Exposure to mental and physical stressors has been repeatedly found to reduce BRS in healthy subjects (Duschek and Reyes del Paso, 2007;Reyes del Paso et al, 2004;Steptoe and Sawada, 1989). The decrease of BRS during autonomic stress may be explained by vagal withdrawal (Duschek and Reyes del Paso, 2007).…”

“…Exposure to mental and physical stressors has been repeatedly found to reduce BRS in healthy subjects (Duschek and Reyes del Paso, 2007;Reyes del Paso et al, 2004;Steptoe and Sawada, 1989). The decrease of BRS during autonomic stress may be explained by vagal withdrawal (Duschek and Reyes del Paso, 2007). However, the impact of stress on baro-afferent signal processing remains unclear.…”

Increased Baroreflex Sensitivity and Reduced Cardiovascular Reactivity in Individuals with Chronic Low Blood Pressure

“…Data from humans also support the role of the baroreflex in the long-term regulation of blood pressure. In addition to the well-known baroreflex-hyposensitivity in chronically elevated blood pressure (14,15), there is evidence of an inverse relationship between baroreflex sensitivity and tonic blood pressure in healthy normotensive subjects (17,31). In a recent longitudinal study, reduced baroreflex sensitivity predicted a 5-year rise in blood pressure (32).…”