The normal response to prolonged passive head up tilt testing

Objective-To define the responses to head up tilt in a large group of norma l adult subjects using the most widely employed protocol for tilt testing. Methods-127 normal subjects aged 19-88 years (mean (SD), 49 (20) years) wit hout a previous history of syncope underwent tilt testing at 60 degrees for 45 minutes or until syncope intervened. Blood pressure monitoring was perf ormed with digital photoplethysmography, providing continuous, non-invasive , beat to brat heart rate and pressure measurements. Results-13% of subjects developed vasovagal syncope after a mean (SD) tilt time of 31.7 (12.4) minutes (range 8.5-44.9 minutes). Severe cardioinhibiti on during syncope was observed less often than is reported in patients inve stigated for syncope. There were no differences in the age or sex distribut ions of subjects with positive or negative outcomes, or in the proportions with cardioinhibitory and vasodepressor vasovagal syncope compared with pre viously reported patient populations. Subjects with negative outcomes showe d age related differences in heart rate and blood pressure behaviour throug hout tilt. Conclusions-False positive results with tilting appear to be common. This h as important implications for the use of diagnostic tilt testing. The magni tude of the heart rate and blood pressure changes observed during negative tilts largely invalidates previously suggested criteria for abnormal non-sy ncopal outcomes.