Autonomic nervous system tests depend on resting heart rate and blood pressure

In order to study the effects of baseline blood pressure and heart frequency on autonomic function tests, 75 normal subjects (aged 8-96 years) were investigated. Heart rate variability was studied at rest, during deep breathing, following standing up and during a Valsalva manoeuvre. Blood pressure changes were recorded during standing up and during sustained handgrip. Responses were described as ratios and as differences to study the efficacy of both methods. Multiple regression analysis showed that significant relationships with the resting heart rate existed for ratios but not for differences. The blood pressure rise in the sustained handgrip test showed a significant relationship with resting blood pressure regardless of the description method. As expected, relationships with age existed for all four heart rate tests regardless of the description method. The blood pressure responses were not significantly related to age. We advise that heart rate test results should be presented as differences, as this avoids the need for correction for the resting heart rate. Correction for the resting blood pressure improves the accuracy of the standing up blood pressure test. Correction for age remains necessary for heart rate tests but not for blood pressure tests.