Blood pressure in rats selectively bred for their resistance to decompression sickness.

INTRODUCTION: Susceptibility to decompression sickness (DCS) is characterised by a wide inter-individual variability whose origins are still poorly understood. This hampers reliable prediction of DCS by decompression algorithms. We previously selectively bred rats with a 3-fold greater resistance to DCS than standard rats. Based on its previously reported relation with decompression outcomes, we assessed whether modification in vascular function is associated with resistance to DCS. METHODS: The arterial pressure response to intravenous administration of acetylcholine (ACh, 5 µg.kg-1) and adrenaline (5 and 10 µg.kg-1) was compared in anaesthetised DCS-resistant rats (seven females, seven males) and standard Wistar rats (seven females, 10 males) aged 14-15 weeks. None of these rats had previously undergone hyperbaric exposure. RESULTS: There was a non-significant tendency for a lower diastolic (DBP) and mean blood pressure (MBP) in DCS-resistant rats. After ACh administration, MBP was significantly lower in resistant rats, for both males (P = 0.007) and females (P = 0.034). After administration of adrenaline 10 µg.kg-1, DCS-resistant rats exhibited lower maximal DBP (P = 0.016) and MBP (P = 0.038). Systolic and pulse blood pressure changes did not differ between groups in any of the experiments. CONCLUSIONS: Resistance to DCS in rats is associated to a trend towards a lower vascular tone but not blood pressure reactivity. Whether these differences are a component of the susceptibility to DCS remains to be confirmed.

Pulmonary Effects of One Week of Repeated Recreational Closed-Circuit Rebreather Dives in Cold Water.

Background and Objectives: The use of closed-circuit rebreathers (CCRs) in recreational diving is gaining interest. However, data regarding its physiological effects are still scarce. Immersion, cold water, hyperoxia, exercise or the equipment itself could challenge the cardiopulmonary system. The purpose of this study was to examine the impact of CCR diving on lung function and autonomous cardiac activity after a series of CCR dives in cold water. Materials and Methods: Eight CCR divers performed a diving trip (one week) in the Baltic Sea. Spirometry parameters, SpO2, and the lung ultrasonography score (LUS) associated with hydration monitoring by bioelectrical impedance were assessed at the end of the week. Heart rate variability (HRV) was recorded during the dives. Results: No diver declared pulmonary symptoms. The LUS increased after dives combined with a slight non-pathological decrease in SpO2. Spirometry was not altered, and all body water compartments were increased. Global HRV decreased during diving with a predominant increase in sympathetic tone while the parasympathetic tone decreased. All parameters returned to baseline 24 h after the last dive. Conclusions: The lung aeration disorders observed seem to be transient and not associated with functional spirometry alteration. The HRV dynamics highlighted physiological constraints during the dive as well as environmental-stress-related stimulation that may influence pulmonary changes. The impact of these impairments is unknown but should be taken into account, especially when considering long and repetitive CCR dives.