Measurements
HEART, COMPLICATIONS
Heart rate variability during head‐up tilt was assessed during a single head‐up tilt session, which was performed before randomization. Two types of electrocardiography (ECG) devices were used for short‐ and long‐term recordings. Short‐term measurements of 5 min were done in supine position and during head‐up tilt at the baseline timepoint using a three‐lead ECG and a bio‐amplifier (FE132 Bio Amp, ADInstruments) at a sample rate of 1 kHz. The data from the device was stored using Labchart (Labchart ver. 8.0, ADInstruments). This allowed us to obtain data that were synchronized with the head‐up tilt procedure. Recordings that were shorter than 5 min because of complications or interference were later excluded from analysis.Additionally, long‐term recordings were performed on all patients with a device for measuring two‐lead ECG (ePatch‐Biotelemetry, Inc.) at baseline before randomization. The ePatch was placed with an adhesive electrode patch ventrally of the sternum before the first head‐up tilt and recorded continuous ECG for up to 5 days (120 h) at a sample rate of 256 Hz.In the patient group, the head‐up tilt was performed before randomization and before any of the trial interventions.Although we did collect arterial blood samples before and during head‐up tilt, we did not measure plasma catecholamines.