Background  Heart failure patients typically exhibit decreased daily activity and limited motor function, body position/physical activity information is closely related to disease severity and prognosis of patients with heart failure. Quantifying body position/physical activity information through wearable physiological monitoring systems can be used as a potential quantitative evaluation method for the severity of heart failure, and its relationship with New York Heart Association (NYHA) heart function class requires further research.

  Objective  To investigate the correlation between body position/physical activity information and NYHA class in patients with heart failure.

  Methods  This study included heart failure patients hospitalized in the Department of Cardiology, West China Hospital of Sichuan University from May 2021 to November 2022. The 24-hour continuous physiological monitoring data were collected by the wearable physiological monitoring system on the day of admission and one day before discharge, and clinical data were also collected simultaneously. Four body position/physical activity indicators were calculated by processing and analyzing the information of the three-axis acceleration sensor in the wearable physiological monitoring system, including bed rest time, activity time, step number, and the number of toss-and-turn events. Patients were grouped based on the NYHA class at admission, admission and discharge, and whether the NYHA class improved at discharge. Subsequently, the correlation between body position / physical activity indicators and NYHA class was analyzed.

  Results  A total of 69 patients with heart failure were involved, including 40 males, with an average age of (60.90 ± 14.24) years old and there are 9 patients in the NYHA class Ⅱ group, 24 patients in class Ⅲ, and 36 patients in class Ⅳ. With the increase of NYHA class, the proportion of bed rest time throughout the day gradually increased, while the proportion of activity time and the average number of steps per hour gradually decreased, the above three indicators showed significant differences between NYHA Ⅱ, Ⅲ, and Ⅳ class (P<0.05). The proportion of bed rest time (r_s =0.319, P=0.008) was positively correlated with NYHA class, while the proportion of activity time (r_s =-0.312, P=0.009) and the average number of steps per hour (r_s=-0.309, P=0.010) were negatively correlated with NYHA class. The proportion of bed rest time at discharge was significantly lower than that at admission (96.25% vs 97.63%, P=0.026), while the proportion of activity time at discharge was significantly higher than that at admission (3.32% vs 1.78%, P<0.001), the average number of steps per hour at discharge was significantly higher than at admission (97.17 steps/h vs 35.58 steps/h, P<0.001). The trend of changes in body position/physical activity indicators in the improved group was the same as above. In patients with no improvement, only the average number of steps per hour at discharge was significantly higher than that at admission, but the enlargement was greater in the NYHA-improved group (71.21 steps/h vs 21.31 steps/h, P=0.003).

  Conclusion  The wearable physiological monitoring system can objectively monitor the body position/physical activity information of patients with heart failure for a long time. The bed rest time is positively correlated with NYHA class, while activity time and step number are negatively correlated with NYHA class. These body position/physical activity indicators may be used as useful indicators for disease severity classification and state monitoring evaluation of patients with heart failure, which can be further extended to home and long-term monitoring of patients in the future.