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

NEW FINDINGS: What is the central question of this study? What is the effect of three repeated breath-hold techniques routinely used by freedivers, thought to manipulate arterial partial pressures of O2 and CO2 , on the cardiorespiratory and haematological response to breath-holding during facial immersion? What is the main finding and its importance? All three techniques increased breath-hold by a similar duration, probably owing to the similar marked increase in end-tidal O2 and decrease in end-tidal CO2 observed in all three trials before facial immersion. These were the only cardiorespiratory changes that were consistently manipulated before the maximal breath-hold. This would suggest that pronounced bradycardia and vasoconstriction of selective vascular beds are probably not obligatory for prolonging breath-hold duration. ABSTRACT: 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 (P = 0.021), increasing duration (P < 0.001) or increasing frequency (P < 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 O2 and a 13.1% decrease in end-tidal CO2 immediately before facial immersion. There were no differences in blood pressure, cardiac output, heart rate, haematocrit or haemoglobin between each BHT and control conditions (P > 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.

The "GP" mechanical thrombectomy device.

We present data concerning the extraction of clots using the newly invented "GP" mechanical thrombectomy device (MTD). Artificial and porcine clots of various lengths were used in plastic tube models of an artery. We investigate the pressures and times taken for clot extraction together with the volumes of fluid extracted. We also investigate the impact of using a funnel structure mounted on the end of the device, on clot removal times and fluid removed. Finally, we present results involving clot extraction from the posterior popliteal artery of a cadaver. Our data indicated that: The embedded GP MTD is the most effective device regarding artificial and porcine blood clot removal. This result is consistent with previous published data on this device. The GP MTD was effective in removing clots positioned in the posterior popliteal artery of a cadaver. The embedded GP device removes less fluid compared with the end-mounted GP device. This confirms previous studies. There appears to be a relationship between funnel angle and pressure. Lower extraction pressures are required for larger funnel angles mounted on the GP device. Shorter times of clot extraction are required for larger funnel angles.