The cardiovascular helix: a three-dimensional view of blood pressure and heart rate over time

BACKGROUND: The baroreflex system plays an important role in the fast regulation of blood pressure. Conventional determination of baroreflex sensitivity either by pharmacological or by physical methods has proven cumbersome. Alternative approaches are based on continuously recording data of systolic arterial blood pressure (SAP) and heart rate, with evaluation by regression assessment or spectral analysis. Data selection for both methods results in various conflicts. We therefore developed a non-invasive method to evaluate baroreceptor functioning on the basis of a visual representation that would be independent of the restrictions related to regression and spectral analysis.METHODS: By plotting SAP and heart rate (measured by using a Finapres device) of 33 young men against time in a three-dimensional space, a helical structure could be visualized for subjects at rest as well as under stress. The shape of the helix was determined by the phase lag between SAP and heart rate and by the amplitude ratio. On the basis of this helix a model using two sinusoidal representations of SAP and heart rate parameterized the interaction between blood pressure and heart rate. The transfer function analysis was studied by means of a curve-fitting method similar to the Monte Carlo method. RESULTS: We found baroreceptor gain mode to be 9 ms/mmHg for subjects under stress and 11 ms/mmHg for subjects at rest. The values of phase lag between SAP and heart rate tended to gather around approximately 90 degrees. CONCLUSION: This method can be applied using even small sets of data over random periods of time.