Biorhythms (cont.)
Can the "body clock" affect diagnostic testing?
The body clock's powerful influence can also be seen in the way it affects
diagnostic test results. These results can vary significantly, possibly
producing inaccurate readings, depending on the time of day when a test is done.
Consider how the body clock affects blood pressure. Blood pressure isn't
constant throughout the day and night; it normally rises in the morning, remains
elevated during the day and early evening, and decreases to its lowest level
during sleep. So a single reading taken during the day may not give a true
picture of whether blood pressure is within the normal range or requires
treatment. Some doctors now ask patients to wear special monitoring devices that
provide a complete 24-hour blood pressure pattern by recording blood pressures a
number of times during the day.
The body clock also affects skin testing for allergies. Results are lower in
the morning, considerably higher in the evening, and greatest just before
bedtime.
The body clock may complicate testing for asthma
severity. Airway patency, or
degree of openness, is poorest during the night and best during midday and
evening. The same is generally true for forced expiratory volume and peak
expiratory flow readings, which can be up to 50% higher at midday and in the
afternoon than overnight or when the patient wakes up. Unless these circadian
rhythms are taken into account, daytime evaluation of asthma patients could
result in underestimating the severity of the disease.
What's being done to help doctors obtain the most accurate results from
diagnostic tests likely to be affected by the body clock?
Just heightening their
awareness of the problem helps. In addition, medical chronobiologists are
working to develop test interpretation guidelines for doctors that take
circadian rhythms into account.
Next: Can drug therapy be matched to the "body clock?" »
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