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Related Experiment Videos

Closed-loop analysis of the reflex function in orthostatic hypotension.

H I Chen1, L H Chow, D J Wang

  • 1Department of Physiology, National Defense Medical Center, Taiwan, Republic of China.

The Chinese Journal of Physiology
|January 1, 1988
PubMed
Summary

The baroreflex loop gain, crucial for blood pressure control during orthostatic stress, decreases with greater head-up tilt angles. This indicates less efficient baroreflex compensation as blood pressure perturbations increase.

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Area of Science:

  • Cardiovascular Physiology
  • Autonomic Nervous System Regulation
  • Hemodynamics

Background:

  • Arterial baroreceptors and cardiopulmonary receptors are vital for regulating blood pressure, especially during orthostatic stress.
  • Understanding baroreflex function is key to comprehending the body's response to changes in posture and potential hypotension.

Purpose of the Study:

  • To quantitatively assess the baroreflex loop gain in arterial pressure compensation during orthostatic hypotension.
  • To investigate how different degrees of head-up tilt (45 and 90 degrees) affect baroreflex efficiency.

Main Methods:

  • Utilized pentobarbital-anesthetized, gallamine-paralyzed dogs subjected to head-up tilt.
  • Measured orthostatic hypotension before and after sinus denervation and cervical vagotomy (D' and D).

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  • Calculated baroreflex loop gain (G) using closed-loop analysis: G = (D/D')-1.

    • Main Results:

    • Baroreflex loop gain was significantly lower at 90 degrees tilt (1.64 +/- 0.24) compared to 45 degrees tilt (2.73 +/- 0.26).
    • Orthostatic hypotension (D') increased from 17.2 mmHg at 45 degrees to 30.6 mmHg at 90 degrees.
    • Atropine sulfate did not alter the mean arterial pressure response to tilt, suggesting vagal efferents are not primarily responsible for the observed changes.

    Conclusions:

    • Baroreflex loop gain is not constant and decreases with increasing orthostatic stress (higher tilt angles).
    • The baroreflex operates as a nonlinear control system, becoming less efficient in compensating for larger blood pressure perturbations.
    • Cervical vagotomy's effect on hypotension is likely due to interruption of aortic nerves and vagal afferents.