Baroreflex

The baroreflex is the fastest mechanism to regulate acute blood pressure changes via controlling heart rate, contractility, and peripheral resistance.  The baroreflex or baroreceptor sensitivity (BRS) index is a measurement to quantify how much control the baroreflex has on the heart rate.  BRS can be valuable in assessing the development and progression of cardiovascular diseases.


Reduced BRS can indicate:

  • Neurological Disorders
  • Cardiovascular Disease
    • Hypertension
    • Coronary artery disease
    • Myocardial infarction
    • Heart failure
  • End-organ damage
  • Progression of underlying disease
  • Increased cardiovascular risk in post MI and heart failure patients

Physiology of Baroreceptors

Baroreceptors are mechanoreceptors located in the carotid sinus and in the aortic arch.  Their function is to sense pressure changes by responding to change in the tension of the arterial wall.  The baroreflex mechanism is a fast response to changes in blood pressure.  Impulses sent from the mechanoreceptors are relayed to the nucleus of the tractus solitarius and ultimately to the vasomotor center of the brain.  A sudden increase in blood pressure stretches the baroreceptors and the increased firing results in the vasomotor center inhibiting sympathetic drive and increasing vagal tone on the SA node of the heart. The SA node is slowed by the acetylcholine and heart rate slows to correct the increase in pressure.  When a person has a sudden drop in blood pressure, for example standing up, the decreased blood pressure is sensed by baroreceptors as a decrease in tension therefore will decrease in the firing of impulses.  This causes the vasomotor center to uninhibit sympathetic activity in the heart and blood vessels and decrease vagal tone (parasympathetic influence on the cardiac SA node) causing an increase in heart rate.  The baroreflex responds to acute changes in blood pressure.  If the hypertension/hypotension is still present after approximately one day, the baroreceptors will reset to the new blood pressure levels.

BRS requires beat-to-beat information from both blood pressure and RR interval.  The systolic blood pressure is typically derived from systemic arterial pressure, whereas the RR interval is derived from the electrocardiogram.  The spectral analysis method to assess baroreceptor sensitivity, outputs the gain and phase of the transfer function.  The gain corresponds to the effectiveness with which the baroreflex is able to maintain constant conditions.  The phase is the time lag between the systolic blood pressure and RR interval.

 
Figure 1  Shows the data manipulation workflow to output BRS

DSI Scientific Services has developed an analysis tool to help researchers quantify and report baroreceptor sensitivity. Contact Scientific Services for more information.

 

DSI offers several technologies to record ECG or blood pressure signals including implantable telemetry, external telemetry and hardwired options.

Implantable Telemetry

DSI’s PhysioTelTM, PhysioTelTM HD and PhysioTelTM Digital implants are designed for monitoring and collecting data from conscious, freely moving animals.  Implants are offered in different sizes to support a variety of animal species including mice, rats, dogs and non-human primates.  Several telemetry models are capable of monitoring ECG and blood pressure.

 Telemetry Systems include


Small Animal Telemetry System

 

Large Animal Telemetry System
 

Jacketed External Telemetry (JET)

ECG and blood pressure signals are collected from conscious, freely moving animals wearing a jacket which contains and protects a small JET device capable of monitoring cardiovascular data and transmitting data to an acquisition and analysis computer system.

ECG is collected via the placement of electrodes on the exterior of the animal which are connected to the JET Device.
 

Blood pressure is collected via the placement of a Minimally Invasive Blood Pressure (MIBP) implant in an artery of the animal.  This implant then transmits to a nearby antenna in the animal’s jacket, which is connected to the JET Device.

 JET Systems include:

 JET system


Hardwired Instrumentation

Short durations of data are collected from chemically or physically restrained animals which are connected to external devices capable of monitoring ECG and recording directly into an acquisition and analysis computer system.  DSI offers two hardwired ECG options, the Multi-lead ECG Pod and Isolated/Defibrillation Protected ECG and General Purpose Probes.

 

 

Multi-Lead ECG Pod Systems include:

Isolated/Defibrillation Protected ECG and General Purpose Probes Systems include:

 



Andriessen, P. (2003). Cardiovascular Fluctuations and Transfer Function Analysis in Stable Preterm Infants. Pediatric Research, 53(1), 89–97. doi:10.1203/01.PDR.0000041514.73559.7D

Gross, V. (2002). Heart Rate Variability and Baroreflex Function in AT2 Receptor-Disrupted Mice. Hypertension, 40(2), 207–213. doi:10.1161/01.HYP.0000027279.69240.75

Robbe, H. W., Mulder, L. J., Ruddel, H., Langewitz, W. a., Veldman, J. B., & Mulder, G. (1987). Assessment of baroreceptor reflex sensitivity by means of spectral analysis. Hypertension, 10(5), 538–543. doi:10.1161/01.HYP.10.5.538