The short-term effect of weather variables on heart rate variability in patients after open-heart surgery

Abstract

BACKGROUND: The effect of meteorological indicators may be more pronounced in more sensitive subpopulations. The aim of the study was to detect the associations between parameters of heart rate variability (HRV) and weather variables in patients who underwent coronary artery bypass grafting or valve surgery. METHODS: The study was performed in Kaunas city, Lithuania, during 2008-2012. We used data of 220 patients. HRV was assessed by electrocardiographic data collected on a continuous 5-minute electrocardiogram (ECG). Data were collected at 1.5 months, 1 year, and 2 years after the surgery. The data of 495 ECG measurements were used. To investigate the associations, a mixed linear model was used adjusting for the linear trend, the month, and sociodemographic and health variables. RESULTS: On days of a higher relative humidity (RH) (>89%), a lower mean average normal-to-normal interval between R waves (NN) was observed. Two days after RH>89%, a lower mean very low-frequency (VLF) in normalized units (n.u.) and a higher high frequency (HF) in n.u. was found; besides, the effect was stronger 1.5 months after the surgery. A lower mean value of the standard deviation of the RR intervals (SDNN, ms), VLF, a low frequency (LF), and HF powers were observed on days of air temperature (T) <-1 oC and this effect was weaker if T two days before was negative. A negative association of these HRV parameters with the daily North Atlantic Oscillation indices (NAOIs) was observed. Two days after low wind speed (<2.75 kt), a higher SDNN, VLF, and LF were found. The effect of low wind speed, the NAOI, and RH two days before was observed only in males, and the effects of changes in atmospheric pressure were stronger in females. CONCLUSION: Among patients after open-heart surgery, the HRV variables may be related to specific weather changes.