Baroreceptors help maintain short term control of blood pressure. Pressure receptors called arterial baroreceptors (sensory nerve endings in the vessel walls) are located in the carotid arteries and the arch of the aorta. They monitor the pressure of the blood coming from the aorta and carotid arteries. An increase in arterial pressure triggers these receptors to send impulses to the cardiovascular control center.
A rise in blood pressure sends a message (increased discharge) from the baroreceptors to the cardiovascular control center in the brain. This leads to an increased discharge of parasympathetic nerves to the heart and a decreased discharge of the sympathetic nerves to the heart, which decreases the heart rate and stroke volume (amount of blood ejected from the heart with one contraction).
There is also a decreased discharge down the sympathetic nerves to the arterioles, producing vasodilation (widening) and thus a decrease in peripheral resistance which in turn returns blood pressure to normal.
The baroreflex is one of the most important cardiovascular control mechanisms adjusting heart rate and sympathetic output to the blood vessels on a beat-by-beat basis. Sympathetic nerves are extremely important in regulating blood pressure and blood flow.
Sympathetic hyperactivity and parasympathetic withdrawal may cause and sustain hypertension. An imbalance in this system is related to a reduced or reset arterial baroreflex sensitivity. However there is good news . . . slow breathing at six breaths per minute increases baroreflex sensitivity and reduces sympathetic activity suggesting a potentially beneficial effect in hypertension.
The study noted below indicates slow breathing is capable of modifying blood pressure and improving baroreflex sensitivity in individuals with hypertension. Twenty individuals, average age 56 with essential hypertension and twenty six individual (controls), average age 52 without hypertension were studied.
Baroreflex sensitivity was measured by autoregressive spectral analysis and "alpha angle" method. Slow breathing at six breaths per minute decreased systolic pressure in hypertensive subjects from 149.7±3.7 to 141.1±4 mm Hg and diastolic pressure from 82.7±3 to 77.8±3.7 mm Hg.
Controlled breathing at 15 breaths per minute decreased systolic to 142.8±3.9 mm Hg but not diastolic pressure and decreased RR interval without altering the baroreflex.
Slow breathing increased baroreflex sensitivity in hypertensives from 5.8±0.7 to 10.3±2.0 ms/mm Hg and controls from 10.9±1.0 to 16.0±1.5 ms/mm Hg without inducing hyperventilation.
Six breaths per minute . . . lower blood pressure, enhanced baroreflex sensitivity: something to keep in mind.
Source:
Slow Breathing Improves Arterial Baroreflex Sensitivity and Decreases Blood Pressure in Essential Hypertension
Luciano Bernardi, MD
Hypertension. 2005;46:714.
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