The effect of various breath‐hold techniques on the cardiorespiratory response to facial immersion in humans

<jats:title>Abstract</jats:title><jats:p>Repeated maximal breath‐holds have been demonstrated to induce bradycardia, increase haematocrit and haemoglobin and prolong subsequent breath‐hold duration by 20%. Freedivers use non‐maximal breath‐hold techniques (BHTs) to improve breath‐hold duration. The aim of this study was to investigate the cardiorespiratory and haematological responses to various BHTs. Ten healthy men (34.5 ± 1.9 years) attended five randomized experimental trials and performed a 40 min period of quiet rest or one of three BHTs followed by a maximal breath‐hold challenge during facial immersion in water at 30 or 10°C. Cardiovascular and respiratory parameters were measured continuously using finger plethysmography and breath‐by‐breath gas analysis, respectively, and venous blood samples were collected throughout. Facial immersion in cold water caused marked bradycardia (74.1 vs. 50.2 beats/min after 40 s) but did not increase breath‐hold duration compared with warm water control conditions. Facial immersion breath‐hold duration was 30.8–43.3% greater than the control duration when preceded by BHTs that involved repeated breath‐holds of constant duration (<jats:italic>P</jats:italic> = 0.021), increasing duration (<jats:italic>P</jats:italic> &lt; 0.001) or increasing frequency (<jats:italic>P</jats:italic> &lt; 0.001), with no difference observed between BHTs. The increased duration of apnoea across all three BHT protocols was associated with a 6.8% increase in end‐tidal O<jats:sub>2</jats:sub> and a 13.1% decrease in end‐tidal CO<jats:sub>2</jats:sub> immediately before facial immersion. There were no differences in blood pressure, cardiac output, heart rate, haematocrit or haemoglobin between each BHT and control conditions (<jats:italic>P</jats:italic> &gt; 0.05). In conclusion, the duration of apnoea can be extended by manipulating blood gases through repeated prior breath‐holds, but changes in cardiac output and red blood cell mass do not appear essential.</jats:p>