Poincaré plot in obstructive sleep apnoea patients before and after CPAP treatment

To the Editors: Adults with obstructive sleep apnoea (OSA) display substantial heart rate changes during sleep, associated with obstructive respiratory events 1, 2. These heart rate changes are significantly attenuated or abolished with effective continuous positive airway pressure (CPAP) treatment 3. Heart rate variability (HRV) refers to the regulation of the sinoatrial node by the sympathetic and parasympathetic branches of the autonomic nervous system. Evaluation of autonomic heart rate control by means of HRV measures has been widely accepted as an important source of information on cardiovascular function 4, 5. HRV is important because it provides a window to observe the heart's ability to respond to normal or abnormal regulatory impulses that affect its rate and rhythm. Several sophisticated methodologies were developed for measuring HRV, notably those using the heart rate power spectrum and nonlinear dynamics analysis 6. However, based on the literature, no simple methodology is available for comprehensive use in daily medical practice. However, a Poincare or Lorenz plot is a simple semi-quantitative method for visualising and calculating HRV 7–10. It has been previously shown that the length and width of a Poincare plot are a weighted combination of low- and high-frequency powers, so it provides a theoretical link between …