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phase
angle
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Phase angle is an indicator of cellular health and integrity.
Research in humans has shown that the relationship between phase
angle and cellular health is increasing and nearly linear (1,2,3).
A low phase angle is consistent with an inability of cells to store
energy and an indication of breakdown in the selective permeability
of cellular membranes. A high phase angle is consistent with large
quantities of intact cell membranes and body cell mass.
Phase angle reflects the ratio of body cell mass to fat-free mass.
Phase angle is proportional to the ratio of reactance and resistance.
Therefore, phase angle is proportional to the ratio of body cell
mass to fat-free mass.
| What causes the phase angle to
increase? |
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An increase in body cell mass relative
to fat-free mass. |
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An increase in fat-free mass relative
to body weight. |
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Improving hydration of fat-free mass. |
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Phase angle is useful when comparing individuals.
Reactance along with the patient's weight indicates an absolute amount
of body cell mass (BCM). Therefore, reactance is best applied when
comparing test results in a single patient at different times. It
is possible for two patients with exactly the same reactance (X)
to have differing amounts of BCM in kilograms, depending upon the
patient's weight.
However, since the phase angle indicates a proportion of BCM to FFM, any
patient with a higher phase angle will always have a higher proportion
of BCM than any other patient with a lower phase angle.
Phase angle does not include the effect of statistical regression.
Like body cell mass (BCM), the phase angle indicates the number of intact
cell membranes. However, phase angle does not include the effect of statistical
regression analysis. As a result, phase angle is a direct measurement of
relative amounts of intact cellular membranes.
What exactly is the phase angle, anyway?
A bioimpedance analyzer applies a small 50 kilohertz alternating current
to the body. If an oscilloscope were connected to the body, the phase angle
appears as a small delay between the voltage waveform and the current waveform.
The period of each wave at 50 kilohertz is 20 microseconds. If, for example,
the time delay is ten percent of the period, then the time delay is 2 microseconds.
When expressed in units of time, it is said that the phase delay is
2 microseconds.
Another way of expressing this time delay is as a percentage of the entire
wave period in degrees. Each complete wave period consists of 360 degrees.
If the time delay is one-tenth the total period of the wave, it is equivalent
to 36 degrees. When the time delay is expressed this way (in degrees of
the total wave period), it is called the phase angle.
When electrical potential and current are illustrated sweeping around a
circle instead of moving over time, the relationship between reactance,
resistance, and phase angle is easier to see. This is shown below.
The range of phase angle in the human body is 1 to 20 degrees. The phase
angle is the arctangent of (X/R).
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