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The loop gain of autonomic reflex function in orthostatic hypotension
1Clinical Research Center, Triservice General Hospital, Taipei, Taiwan, Republic of China.
The Japanese Journal of Physiology
|January 1, 1989
Summary
Autonomic reflex function during orthostatic stress was measured in dogs. The study found that reflexes from arterial baroreceptors and cardiopulmonary receptors significantly compensate for orthostatic hypotension, with system gain decreasing at higher tilt angles.
Area of Science:
- Physiology
- Autonomic Nervous System
- Cardiovascular Regulation
Background:
- Orthostatic stress, such as head-up tilt, can lead to a drop in blood pressure (orthostatic hypotension).
- The autonomic nervous system plays a crucial role in maintaining blood pressure during postural changes.
- Quantifying the effectiveness of autonomic reflex compensation is essential for understanding cardiovascular control.
Purpose of the Study:
- To quantitatively assess the loop gain (G) of the autonomic reflex function during orthostatic stress in anesthetized dogs.
- To investigate the contribution of baroreceptor and cardiopulmonary reflexes to orthostatic compensation.
- To determine if the autonomic control system operates linearly or non-linearly under varying degrees of orthostatic stress.
Main Methods:
- Anesthetized dogs were subjected to 45 and 90 degrees head-up tilt.
- Orthostatic hypotension was measured before and after interruption of autonomic reflex pathways via sinus denervation and vagotomy (SDVT) or ganglionic blockade (GB).
- Loop gain (G) was calculated using closed-loop analysis: G = (D/E) - 1, where E and D represent arterial pressure decreases before and after autonomic interruption, respectively.
Main Results:
- In SDVT experiments, average G values were 2.36 for 45 degrees tilt and 1.63 for 90 degrees tilt.
- G values from SDVT and GB experiments were not significantly different, indicating similar contributions from both reflex pathways.
- A lower G value was observed at 90 degrees tilt compared to 45 degrees tilt in all experiments.
Conclusions:
- The findings provide a quantitative measure of autonomic reflex function in orthostatic hypotension.
- Reflexes originating from arterial baroreceptors and cardiopulmonary receptors are major contributors to autonomic compensation during orthostatic stress.
- The autonomic control system for blood pressure regulation exhibits non-linear behavior, with reduced gain at higher degrees of orthostatic stress.