Autonomic adaptation to repeated cold water ingestion: time-resolved HRV analysis

Area of Science:

• Physiology
• Autonomic Nervous System Research
• Cardiovascular Regulation

Background:

• Heart rate variability (HRV) serves as a non-invasive indicator of autonomic nervous system (ANS) function.
• Cold-water ingestion is a known method for modulating HRV.
• Previous research lacked a unified framework to analyze repeated HRV stimulation effects.

Purpose of the Study:

• To develop and validate a time-resolved modeling framework for analyzing HRV changes.
• To differentiate between residual and stimulus-specific autonomic responses to repeated cold-water ingestion.
• To quantify the physiological adaptation and additive effects of sequential HRV stimuli.

Main Methods:

• Analysis of electrocardiograms from 39 healthy participants undergoing two cold-water ingestion trials.
• Segmentation of recordings into 5-minute windows for HRV variable extraction (time, frequency, fractal domains).
• Application of linear mixed-effects models with time components to characterize transient and sustained autonomic responses.

Main Results:

• The first cold-water stimulus significantly altered HRV, with maximum effects observed within 17-30 minutes and recovery up to 60 minutes.
• The second stimulus produced attenuated yet additive responses, indicating partial physiological adaptation and shorter recovery times.
• Frequency domain analysis showed additive effects, while fractal analysis indicated changes in short-term but not long-term dynamics.

Conclusions:

• The developed time-resolved modeling framework successfully distinguishes residual from stimulus-specific HRV effects.
• This framework enables precise quantification of autonomic responses to repeated stimuli.
• It establishes a standardized methodology for future studies involving repeated HRV stimulation paradigms.