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A Model of Blood Pressure, Heart Rate, and Vaso-Vagal Responses Produced by Vestibulo-Sympathetic Activation.

Raphan T, Cohen B, Xiang Y, Yakushin SB - Front Neurosci (2016)

Bottom Line: Stochastic changes in threshold maintained the compensatory Baroreflex Sensitivity.Sudden decreases in Desired BP elicited non-compensatory VVRs with smaller pulse pressures, consistent with experimental data.It also shows that a VVR is generated when the vestibular input triggers a marked reduction in Desired BP.

View Article: PubMed Central - PubMed

Affiliation: Department of Computer and Information Science, Institute for Neural and Intelligent Systems, Brooklyn College, City University of New York New York, NY, USA.

ABSTRACT
Blood Pressure (BP), comprised of recurrent systoles and diastoles, is controlled by central mechanisms to maintain blood flow. Periodic behavior of BP was modeled to study how peak amplitudes and frequencies of the systoles are modulated by vestibular activation. The model was implemented as a relaxation oscillator, driven by a central signal related to Desired BP. Relaxation oscillations were maintained by a second order system comprising two integrators and a threshold element in the feedback loop. The output signal related to BP was generated as a nonlinear function of the derivative of the first state variable, which is a summation of an input related to Desired BP, feedback from the states, and an input from the vestibular system into one of the feedback loops. This nonlinear function was structured to best simulate the shapes of systoles and diastoles, the relationship between BP and Heart Rate (HR) as well as the amplitude modulations of BP and Pulse Pressure. Increases in threshold in one of the feedback loops produced lower frequencies of HR, but generated large pulse pressures to maintain orthostasis, without generating a VasoVagal Response (VVR). Pulse pressures were considerably smaller in the anesthetized rats than during the simulations, but simulated pulse pressures were lowered by including saturation in the feedback loop. Stochastic changes in threshold maintained the compensatory Baroreflex Sensitivity. Sudden decreases in Desired BP elicited non-compensatory VVRs with smaller pulse pressures, consistent with experimental data. The model suggests that the Vestibular Sympathetic Reflex (VSR) modulates BP and HR of an oscillating system by manipulating parameters of the baroreflex feedback and the signals that maintain the oscillations. It also shows that a VVR is generated when the vestibular input triggers a marked reduction in Desired BP.

No MeSH data available.


Related in: MedlinePlus

BP, HR, and Pulse Pressure in response to 3 mA, 0.025 Hz sGVS. (A) sGVS stimulus. (B) BP response showing a VVR and oscillations in response to sGVS. (C) Systolic BP as a function of time, before, during, and after sGVS. BP transiently fell, was sustained during stimulation and then rose back to steady state level. HR also fell, but not synchronously with BP. (D) Pulse pressure averaged over 25 s interval rose and fell in synchrony with BP.
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Figure 7: BP, HR, and Pulse Pressure in response to 3 mA, 0.025 Hz sGVS. (A) sGVS stimulus. (B) BP response showing a VVR and oscillations in response to sGVS. (C) Systolic BP as a function of time, before, during, and after sGVS. BP transiently fell, was sustained during stimulation and then rose back to steady state level. HR also fell, but not synchronously with BP. (D) Pulse pressure averaged over 25 s interval rose and fell in synchrony with BP.

Mentions: If Pulse Pressure were to be predicted by the simulations, it would be an independent test of the underlying concept. Pulse Pressure, which is the difference between systolic and diastolic levels, approximately represents the force that the heart generates each time it contracts (Franklin et al., 1999; Vaccarino et al., 2001). In response to sGVS during a typical experiment (Figure 7A), BP generally rose and then dropped dramatically during a VVR (Figure 7B) and then rose again slowly to steady state levels. For this particular experiment, systolic levels rose slightly prior to initiating the sGVS (Figure 7B), although HR remained level (Figure 7C). The rise in BP prior to sGVS was variable and did not always occur. At the initiation of sGVS, systolic BP dropped transiently while HR slowly declined at a later time (Figure 7C). Both Systolic BP and HR then returned to steady state levels. Pulse Pressure followed the trend of systolic BP, although the drops in pulse pressure were somewhat slower (Figure 7D). A key prediction of the model was that Pulse Pressure would be approximately proportional to systolic BP, which is approximately proportional to Desired BP. This prediction compared favorably with the experimental data. When simulations were run with different levels of Desired BP, the model predicted an approximately linear increase in pulse pressure with Desired BP (Figure 8A). The data also showed that pulse pressure rose approximately linearly with Average BP (Figure 8B), when average BP was computed over a 25 s window. The differences could be because in the model the Desired BP could be precisely controlled, whereas the data were lumped with those observed during VVR to expand the range over which Average BP could be plotted. There are also probably nonlinearities in the processing that were not considered. Despite small differences, this simple model predicted the experimental data on pulse pressure, and demonstrated the predictive capability of the model. This result also suggests that pulse pressure might be an important parameter when considering cardiovascular function.


A Model of Blood Pressure, Heart Rate, and Vaso-Vagal Responses Produced by Vestibulo-Sympathetic Activation.

Raphan T, Cohen B, Xiang Y, Yakushin SB - Front Neurosci (2016)

BP, HR, and Pulse Pressure in response to 3 mA, 0.025 Hz sGVS. (A) sGVS stimulus. (B) BP response showing a VVR and oscillations in response to sGVS. (C) Systolic BP as a function of time, before, during, and after sGVS. BP transiently fell, was sustained during stimulation and then rose back to steady state level. HR also fell, but not synchronously with BP. (D) Pulse pressure averaged over 25 s interval rose and fell in synchrony with BP.
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4814511&req=5

Figure 7: BP, HR, and Pulse Pressure in response to 3 mA, 0.025 Hz sGVS. (A) sGVS stimulus. (B) BP response showing a VVR and oscillations in response to sGVS. (C) Systolic BP as a function of time, before, during, and after sGVS. BP transiently fell, was sustained during stimulation and then rose back to steady state level. HR also fell, but not synchronously with BP. (D) Pulse pressure averaged over 25 s interval rose and fell in synchrony with BP.
Mentions: If Pulse Pressure were to be predicted by the simulations, it would be an independent test of the underlying concept. Pulse Pressure, which is the difference between systolic and diastolic levels, approximately represents the force that the heart generates each time it contracts (Franklin et al., 1999; Vaccarino et al., 2001). In response to sGVS during a typical experiment (Figure 7A), BP generally rose and then dropped dramatically during a VVR (Figure 7B) and then rose again slowly to steady state levels. For this particular experiment, systolic levels rose slightly prior to initiating the sGVS (Figure 7B), although HR remained level (Figure 7C). The rise in BP prior to sGVS was variable and did not always occur. At the initiation of sGVS, systolic BP dropped transiently while HR slowly declined at a later time (Figure 7C). Both Systolic BP and HR then returned to steady state levels. Pulse Pressure followed the trend of systolic BP, although the drops in pulse pressure were somewhat slower (Figure 7D). A key prediction of the model was that Pulse Pressure would be approximately proportional to systolic BP, which is approximately proportional to Desired BP. This prediction compared favorably with the experimental data. When simulations were run with different levels of Desired BP, the model predicted an approximately linear increase in pulse pressure with Desired BP (Figure 8A). The data also showed that pulse pressure rose approximately linearly with Average BP (Figure 8B), when average BP was computed over a 25 s window. The differences could be because in the model the Desired BP could be precisely controlled, whereas the data were lumped with those observed during VVR to expand the range over which Average BP could be plotted. There are also probably nonlinearities in the processing that were not considered. Despite small differences, this simple model predicted the experimental data on pulse pressure, and demonstrated the predictive capability of the model. This result also suggests that pulse pressure might be an important parameter when considering cardiovascular function.

Bottom Line: Stochastic changes in threshold maintained the compensatory Baroreflex Sensitivity.Sudden decreases in Desired BP elicited non-compensatory VVRs with smaller pulse pressures, consistent with experimental data.It also shows that a VVR is generated when the vestibular input triggers a marked reduction in Desired BP.

View Article: PubMed Central - PubMed

Affiliation: Department of Computer and Information Science, Institute for Neural and Intelligent Systems, Brooklyn College, City University of New York New York, NY, USA.

ABSTRACT
Blood Pressure (BP), comprised of recurrent systoles and diastoles, is controlled by central mechanisms to maintain blood flow. Periodic behavior of BP was modeled to study how peak amplitudes and frequencies of the systoles are modulated by vestibular activation. The model was implemented as a relaxation oscillator, driven by a central signal related to Desired BP. Relaxation oscillations were maintained by a second order system comprising two integrators and a threshold element in the feedback loop. The output signal related to BP was generated as a nonlinear function of the derivative of the first state variable, which is a summation of an input related to Desired BP, feedback from the states, and an input from the vestibular system into one of the feedback loops. This nonlinear function was structured to best simulate the shapes of systoles and diastoles, the relationship between BP and Heart Rate (HR) as well as the amplitude modulations of BP and Pulse Pressure. Increases in threshold in one of the feedback loops produced lower frequencies of HR, but generated large pulse pressures to maintain orthostasis, without generating a VasoVagal Response (VVR). Pulse pressures were considerably smaller in the anesthetized rats than during the simulations, but simulated pulse pressures were lowered by including saturation in the feedback loop. Stochastic changes in threshold maintained the compensatory Baroreflex Sensitivity. Sudden decreases in Desired BP elicited non-compensatory VVRs with smaller pulse pressures, consistent with experimental data. The model suggests that the Vestibular Sympathetic Reflex (VSR) modulates BP and HR of an oscillating system by manipulating parameters of the baroreflex feedback and the signals that maintain the oscillations. It also shows that a VVR is generated when the vestibular input triggers a marked reduction in Desired BP.

No MeSH data available.


Related in: MedlinePlus