Cardio-ventilatory responses to poikilocapnic hypoxia and hypercapnia in trained breath-hold divers.
Level 4 - case-series / case-control
Cross-sectional comparative physiological study with a small sample size
PubMed 24341998 · doi:10.1016/j.resp.2013.12.005
What was done
Researchers assessed hypercapnic ventilatory responses (HCVR) and hypoxic ventilatory responses at rest (HVRr) and during exercise (HVRe) in 7 trained breath-hold divers (BHDs) compared to 7 non-diver controls (NDs). Cardiac output, stroke volume, and heart rate were also measured during testing.
What was found
Carbon dioxide sensitivity did not differ significantly between BHDs and NDs (2.85 ± 1.41 vs. 1.85 ± 0.93 L·min⁻¹·mmHg⁻¹, p > 0.05). However, hypoxic ventilatory response was increased in BHDs at rest (+68%) and during exercise (+31%). During the hypoxic exercise test, cardiac output and heart rate reached lower values in BHDs than in NDs.
Why it matters
The study indicates that repeated bouts of intermittent hypoxia and hypercapnia in breath-hold divers are associated with enhanced chemo-responsiveness to poikilocapnic hypoxia without blunting hypercapnic response.
Limits
The study is limited by a very small sample size (n=7 per group) and a cross-sectional design that cannot determine whether these responses represent acquired training adaptations or baseline self-selection traits. Exact numerical values for hemodynamic outcomes and baseline characteristics were not reported in the abstract.
Cited by
- contradicts The brainstem's ventilatory sensitivity and tolerance to elevated carbon dioxide levels can be trained and adapted through intentional breath-holding exercises.