Opening the Schrödinger Box: Short- and Long-Range Mammalian Heart Rate Variability.

Area of Science:

• Physiology
• Cardiovascular Research
• Comparative Biology

Background:

• Heart rate variability (HRV) is governed by autonomic nervous system (ANS), endocrine, and intrinsic pacemaker interactions.
• A debate exists regarding the specific mechanisms driving HRV across different time scales (short vs. long).
• Current methods often require invasive drug perturbations or organ isolation to study these mechanisms.

Purpose of the Study:

• To develop a general, non-invasive method to differentiate ANS from pacemaker contributions to HRV in mammals.
• To investigate the universality of ANS and pacemaker system contributions across different mammalian species.
• To analyze HRV mechanisms on both short (milliseconds-seconds) and long (seconds-minutes) time scales.

Main Methods:

• Utilized published electrocardiogram (ECG) data from dogs, rabbits, and mice.
• Compared ECG segments before and after autonomic nervous system blockade to isolate ANS effects.
• Applied a novel analytical approach to differentiate between ANS and pacemaker influences on HRV.

Main Results:

• Successfully differentiated ANS from extrinsic and intrinsic pacemaker mechanisms.
• In dogs, pacemaker mechanisms dominated long-range HRV, while ANS dominated short-range HRV.
• In rabbits and mice, both ANS and pacemakers influenced both time scales; anesthesia altered pacemaker contributions. Extrinsic mechanisms impacted long-range HRV in mice but not rabbits.

Conclusions:

• A novel approach for determining the relative contributions of ANS and pacemaker mechanisms to HRV was established.
• The study underscores the importance of selecting appropriate mammalian models for HRV research based on species-specific mechanisms.
• Findings provide insights into the comparative physiology of heart rate regulation across different mammals.