Effects of exercise, blood particles and the menstrual cycle on bubbles in divers

A randomized controlled, cross-over study will be conducted with 40 participants (see figure added). Each participant will complete five identical hyperbaric chamber dives. Three of the hyperbaric exposures will be conducted without prior exercise (dives 1, 3, and 5), and two will be preceded by a form of moderate exercise (cycling or brisk walking). For each participant, these two forms of exercise will be randomly allocated to their two 'prior exercise dives’. Pre hyperbaric chamber dive visit Before the first hyperbaric chamber exposure, digital written informed consent will be obtained during a site or digital meeting. Followed by a digital questionnaire, including dive history, age, gender, ethnicity, height, weight, and for women, if and which anticonception they use and their cycle length. Moreover, the Recreational Scuba Council screening questionnaire for fitness to dive will be completed. Subsequently, all participants will attend the University of Auckland exercise laboratory prior to starting the hyperbaric measurements to undertake the Astrand exercise test, which allows for an objective evaluation of maximal heart rate. Pre-Dive Exercise Prior to dives preceded by exercise (dives 2 and 4), participants will attend the University of Auckland Exercise Laboratory. Three hours prior to the scheduled dive, they will undertake the allocated supervised exercise regimen, treadmill walking or stationary bike cycling for 40 minutes. In both settings, exercise intensity will be adjusted to sustain 70% of the participant’s maximum heart rate estimated from the Astrand test, performed prior to starting the study. Hyperbaric chamber dives Each participant will complete five identical hyperbaric chamber dives to five atmospheres (equivalent to 40 metres of sea water) for 20 minutes at depth, with at least 5 days between each hyperbaric chamber dive. On arrival at five atmospheres, participants will exercise at 90 watts on a manually braked cycle ergometer. The hyperbaric chamber dives will take place in the Slark Hyperbaric Medicine Unit at North Shore Hospital. All dives will be undertaken in dry conditions, breathing hyperbaric chamber air with the participants accompanied by a member of the study team. Depending on the visit with or without pre-dive exercise the study visit will take 4-7 hours. Participants will be asked to refrain from other diving activities five days before each measurement and to avoid exercise (meaning purposive avoidance of any exercise other than necessary activities of daily living) for 48 hours prior to each experiment. After exiting the chamber, participants will be monitored for Venous Gas Emboli (VGE) using TransThoracic Echocardiography (TTE) and standard quantitation protocols. VGE grades from the three dives without prior exercise will be used to assess VGE variability in individual participants performing identical dives. VGE grades following the dives preceded by exercise will be compared to those from the dives without prior exercise to evaluate the effect of pre-dive exercise on post-dive VGE formation. Blood samples Blood samples will be repeatedly taken for analyzing microparticles, CRP, serum cortisol and sex hormones. At the beginning of each study visit an intravenous access will be placed for blood draws. Venous blood samples will be taken immediately prior to beginning exercising, directly after exercising and immediately prior to commencement of decompression. In the study visits where people will not exercise blood draws will take place prior to beginning hyperbaric exposure and again immediately prior to commencement of decompression. Microparticles The blood specimens for analyzing microparticles will be stored prior to being sent for analysis to a collaborator in the USA for microparticle counting and typing.