Attenuated cardiac autonomic function in humans with high-affinity hemoglobin and compensatory polycythemia

Area of Science:

• Cardiovascular Physiology
• Autonomic Nervous System Function
• Human Physiology

Background:

• High-affinity hemoglobin alters oxygen transport and may affect cardiovascular responses during hypoxia.
• Previous observations show blunted heart rate increases in high-affinity hemoglobin individuals under hypoxic stress.
• Autonomic control of heart rate is a potential mechanism influencing these cardiovascular differences.

Purpose of the Study:

• To investigate cardiac baroreflex sensitivity (CBS) and heart rate variability (HRV) in humans with high-affinity hemoglobin compared to controls.
• To determine if altered autonomic control underlies the blunted heart rate response to hypoxia in high-affinity hemoglobin carriers.

Main Methods:

• A comparative study involving nine individuals with high-affinity hemoglobin and 12 healthy controls.
• Participants underwent isocapnic hypoxic exposure (arterial O2 partial pressure ~50 mmHg) after a normoxic baseline.
• Beat-by-beat heart rate and blood pressure were recorded; CBS and HRV were analyzed using sequence and time/frequency domain methods.

Main Results:

• Humans with high-affinity hemoglobin demonstrated significantly lower CBS at baseline and during hypoxia compared to controls (P=0.02).
• Heart rate variability, assessed by time and frequency domain analyses, was also significantly lower in the high-affinity hemoglobin group (all P<0.05).

Conclusions:

• Individuals with high-affinity hemoglobin exhibit attenuated cardiac baroreflex sensitivity and heart rate variability.
• These findings suggest impaired cardiac autonomic function in individuals with high-affinity hemoglobin, potentially explaining their altered cardiovascular response to hypoxia.