Human Adaptation and Physiological Risks in Apnea Diving

Abstract

Freediving is an extreme practice that subjects the human body to progressive hypoxia, intense hemodynamic shifts, and complex autonomic responses. This review aims to synthesize the main pathophysiological mechanisms involved in deep apnea, highlighting the risks associated with cerebral hypoxia, arrhythmias due to autonomic conflict, inflammation driven by HIF-1α/NF-κB signaling, and sex-based differences in hypoxic tolerance. An integrative literature review was conducted using PubMed, Scopus, and Web of Science, covering human studies published between 2003 and 2024, with in vivo measurements including arterial blood gas analysis, near-infrared spectroscopy (NIRS), electrocardiography, and immunological assays. Twenty-four studies meeting quality and clinical relevance criteria were included. Key findings include: critical oxygen desaturation during ascent, occurrence of arrhythmias without extreme hypoxemia, synergistic activation of HIF-1α and NF-κB pathways, and cerebral congestion due to vascular and respiratory mechanisms. These factors can culminate in hypoxic syncope, also known as “blackout.” Additionally, anatomical and functional sex differences were identified as influential in apnea tolerance. The evidence gathered enhances our understanding of human adaptive limits and suggests clinical applications in critical care, hypoxic training, and comparative physiology.