Materials
Prior to the first ABPM, a Microlife watchBP Office BP device (Microlife, AG Widnau, Switzerland) was used for bilateral BP measurements. If the inter-arm difference was larger than 10/5 mmHg (SBP/DBP) the ABPM device was fitted to the arm with the highest BP. If not, patients were given the option to choose which arm the cuff was fitted on. The same arm was used for both ABPMs.Spacelabs Ontrak and Spacelabs 90217A (Spacelabs Healthcare, Snoqualmie, Washington, USA) were used for the ABPMs. Both devices are validated according to internationally recognized standards [During high frequency ABPM (HF-ABPM), daytime was predefined as 07:00–23:00 and BP was measured every 20 min in this time interval and every 30 min for the remaining eight hours. Low frequency ABPM (LF-ABPM) measured BP once every hour during all 24 h. Patients reported individual bed- and rising times after each ABPM, and these were used to define awake and sleep measurements post hoc. If a planned measurement failed, the device was programmed to perform one extra measurement within two minutes. Initially, four measurements were made during fitting to ensure that the device worked correctly. These initial measurements and measurements performed after 24 h of recording, were removed from our analysis.