Genetic Predisposition to Breath-Hold Diving-Induced Hemoptysis, Preliminary Study
Authors: Danilo Cialoni, Claudio Marabotti, Nicola Sponsiello, Massimo Pieri, Costantino Balestra, Vittorio Lucchini, Alessandro Marroni
DOI / Source: https://pubmed.ncbi.nlm.nih.gov/26094307/
Date: 2015
Reading level: Intermediate
Why This Matters for Freedivers
Some divers can do “the same dives” as everyone else and still be the one who coughs blood or gets chest tightness. This paper suggests there may be a real biological reason for that: certain genetic variants linked to how your blood vessels regulate flow and pressure may increase the chance of post-dive respiratory symptoms and hemoptysis. It supports a safer mindset: if you’ve had lung symptoms before, treat it seriously and dive more conservatively, because it might not just be technique.
Synopsis
A surprising number of breath-hold divers report episodes of cough, chest tightness, breathlessness, and sometimes blood-streaked sputum after repetitive deep diving. This is often grouped under “lung squeeze” or suspected pulmonary edema, but not everyone is affected equally—and that’s what this study explores: could some people be genetically more prone?
The researchers studied 108 experienced breath-hold divers (mostly male, instructor-level, training regularly) and split them into two groups based on whether they had ever experienced breath-hold diving–induced hemoptysis (BH-DIH). About 22% reported at least one BH-DIH episode, while about 78% did not. They then tested three common genetic variants involved in vascular tone and blood flow regulation: two variants of endothelial nitric oxide synthase (eNOS G894T and eNOS T786C) and the ACE insertion/deletion variant (ACE I/D).
The key finding is that BH-DIH was more common in certain genotypes. Divers with the “TT” genotype in eNOS G894T and eNOS T786C were reported to have higher rates of BH-DIH, and the ACE “ID” genotype was also associated with higher prevalence compared with “II” (in this sample, none of the ACE “II” divers reported BH-DIH). When the researchers looked at combinations, people carrying two or three of the “high-risk” profiles were more likely to report BH-DIH than those with mostly “low-risk” profiles.
The proposed mechanism is simple and very freediver-relevant: if your genetics reduce nitric oxide availability or alter vascular regulation, you may vasoconstrict more strongly during dives, driving a larger central blood shift and higher pulmonary capillary pressures. That can increase “capillary stress” and make fluid leakage or bleeding more likely, especially with known triggers like cold water, deep personal-best attempts, low lung volume diving, hard equalization maneuvers, and strong diaphragm contractions.
Abstract
Introduction: Breath-hold diving-induced hemoptysis (BH-DIH) has been reported in about 25% breath-hold divers (BHD) and is characterized by dyspnea, coughing, hemoptysis and chest pain. We investigated whether eNOS G894T, eNOS T786C and ACE insertion/deletion I/D genetic variants are possible BH-DIH risk factors.
Methods: 108 experienced healthy instructor BHDs with the same minimum requirements (102 male, six female; mean age 43.90±7.49) were studied. We looked for different eNOS G894T, eNOS T786C and ACE insertion/deletion genetic variants between BH-DIH-positive and BH-DIH-negative subjects to identify the variants most frequently associated with BH-DIH.
Results: At least one BH-DIH episode was reported by 22.2% of subjects, while 77.7% never reported BH-DIH. The majority of BH-DIH-positive subjects showed eNOS G894T (p=0.001) and eNOS T786C (p=0.001) genotype “TT” (high-risk profile). Prevalence of BH-DIH was higher in subjects with eNOS G894T TT genotype (50%) than in subjects with GT (9.5%) and GG (24%) genotype (low-risk profile). Similar results were observed for eNOS T786C: BH-DIH prevalence was higher in the TT genotype (41.2%) group than in the CT (15.4%) and CC genotype (9.1%) groups. BH-DIH prevalence was significantly higher in subjects showing ACE ID genotype (34.5%) than II (0%) and DD (10.5%). Of the ACE “II” genotype group, 100% never developed BH-DIH.
Discussion: eNOS-G894T, eNOS-T786C and ACE influence NO availability and regulation of peripheral vascular tone and blood flow. Different genetic variants of eNOS-G894T, eNOS-T786C and ACE appear significantly related to the probability to develop BH-DIH (p<0.001).