Indications
Tests of cardiac parasympathetic and sympathetic damage.
Procedure
Tests of cardiac parasympathetic damage require the following equipment: a sphygmomanometer, a 5 ml syringe and an ECG machine.
1. Heart rate response to the Valsalva manoeuvre.
Start ECG machine (limb leads only, use lead II). Patient blows (hard) into the nozzle end of the 5 ml syringe for 15 seconds, continue recording for 30 seconds after release of pressure.
Start ECG machine. Ask patient to breathe quietly at a rate of six breaths over one minute (5 seconds in and 5 seconds out). Mark ECG at start of each inspiration and expiration.
Measure maximum and minimum R-R interval for each cycle and convert to beats/min. Result is the mean difference (max - min) for heart rate during deep breathing.
1. Blood pressure response to standing.
Measure blood pressure lying and then 2 minutes after standing. Record postural difference.
Interpretation
Tests |
Normal |
Borderline |
Abnormal |
Valsalva ratio |
1.21 |
1.11-1.20 |
1.10 |
(max-min) HR |
>15 |
11-14 |
<10 |
(30th:15th ratio) |
>1.04 |
1.01-1.03 |
1.00 |
Fall in BP |
10 |
11-29 |
30 |
These tests can be used to determine the degree of abnormality present: if two or more of the parasympathetic tests plus the sympathetic tests are clearly abnormal then this indicates significant autonomic damage.
Earlier damage is signified by abnormalities in at least two parasympathetic tests.
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