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Muscle chemoreflex-induced increases in right atrial pressure
D D Sheriff1, R A Augustyniak, D S O'Leary
1Flight Motion Effects Branch, Air Force Research Laboratory, Brooks Air Force Base, San Antonio, Texas 78235. USA.
The American Journal of Physiology
|September 2, 1998
Summary
The muscle chemoreflex, activated by low oxygen in muscles, helps maintain right atrial pressure (RAP) during exercise. This reflex causes vascular adjustments that prevent a drop in RAP, which is crucial for adequate blood flow.
Area of Science:
- Cardiovascular Physiology
- Exercise Physiology
- Autonomic Nervous System
Background:
- The muscle chemoreflex is triggered by metabolic byproducts in active muscles when oxygen delivery is insufficient.
- Previous research has mainly explored the reflex's impact on arterial pressure and nerve activity.
- Cardiac output (CO) increases are vital for distributing blood flow during exercise, but heart rate and contractility have limitations in raising CO due to the inverse relationship with right atrial pressure (RAP).
Purpose of the Study:
- To investigate whether activating the muscle chemoreflex can induce peripheral vascular changes that increase right atrial pressure (RAP).
- To determine if the muscle chemoreflex can defend RAP against decreases typically associated with increased cardiac output and arterial pressure during exercise.
Main Methods:
- Graded reductions in hindlimb blood flow were used to activate the muscle chemoreflex in conscious dogs during treadmill exercise.
- Cardiac output was maintained constant using ventricular pacing combined with beta1-adrenergic blockade (atenolol) in some experiments to isolate the reflex's effect on RAP.
- Measurements included arterial pressure, cardiac output, and right atrial pressure during reflex activation under varying exercise intensities.
Main Results:
- The muscle chemoreflex activation successfully maintained or increased RAP during exercise, counteracting the expected drop due to increased CO and arterial pressure.
- Even when CO was artificially held constant, activating the muscle chemoreflex led to a significant rise in RAP (from 5.1 to 7.4 mmHg).
- During heavier exercise with normal cardiac function, the reflex also caused a significant increase in RAP (from 5.7 to 6.6 mmHg).
Conclusions:
- The muscle chemoreflex plays a significant role in regulating cardiovascular function during exercise.
- Peripheral vascular adjustments mediated by the muscle chemoreflex are effective in increasing right atrial pressure (RAP).
- This reflex mechanism is crucial for maintaining adequate venous return and cardiac filling pressures during conditions of metabolic stress in active muscles.