Delta plot analysis of cardiovascular and cardiorespiratory interactions in young women with orthostatic intolerance

Abstract

ObjectiveTemporal dynamics of cardiovascular and cardiorespiratory interactions during a head-up tilt test (HUTT) were investigated using a new method called delta plot analysis (DPA) that deals with the intrinsic nonstationarity feature of time series. MethodsTwenty-one young female patients (28 ± 7 years) with orthostatic intolerance (OI) and 13 age-matched female controls (26 ± 5 years) were investigated during a 70° HUTT. Analyses were performed on bivariate time series including beat-to-beat intervals (BBI), respiratory amplitude (RESP) at BBI onset as well as systolic (SYS) and diastolic (DIA) blood pressure at simultaneous and shifted beats. DPA was used to characterize cardiovascular interactions as SYS→BBI and BBI→DIA, as well as cardiorespiratory interactions as RESP→BBI and RESP→DIA. ResultsOccurrence of simultaneous BBI increases due to SYS increases (bradycardic baroreflex) was significantly reduced during orthostatic phase in patients (28.54 ± 6.32% versus 36.35 ± 4.77%, p < 0.01). Considering the magnitude of consecutive changes, patients revealed an increased amount of points characterized by low heart rate variability combined with high blood pressure variability for SYS→BBI at tau = 0, BBI→SYS at tau = 2 and BBI→DIA at tau = 1. Interaction analysis for SYS→BBI showed highly significant differences already in supine position (10.08±5.90% versus 4.78±2.42%, p < 0.01), during tilt-up (12.32±5.00% versus 5.51±3.07%, p < 0.0001) and during early orthostatic phase (14.55±6.00% versus 5.71±3.14%, p < 0.001). ConclusionTemporal dynamic analysis by DPA revealed impaired autonomic control in patients compared to healthy subjects during supine position, transition and orthostatic phase. SignificanceDPA is a promising graphical tool to demonstrate impaired autonomic regulation.