Physiological effects of mixed-gas deep sea dives using a closed-circuit rebreather: a field pilot study

Abstract

Purpose Deep diving using mixed gas with closed-circuit rebreathers (CCRs) is increasingly common. However, data regarding the effects of these dives are still scarce. This preliminary field study aimed at evaluating the acute effects of deep (90-120 msw) mixed-gas CCR bounce dives on lung function in relation with other physiological parameters. Methods Seven divers performed a total of sixteen open-sea CCR dives breathing gas mixture of helium, nitrogen and oxygen (trimix) within four days at 2 depths (90 and 120 msw). Spirometric parameters, SpO 2 , body mass, hematocrit, short term heart rate variability (HRV) and critical flicker fusion frequency (CFFF) were measured at rest 60 min before the dive and 120 min after surfacing. ResultsThe median [1st-3rd quartile] of the forced vital capacity was lower (84% [76-93] vs 91% [74-107] of predicted values; p = 0.029), whereas FEV1/FVC was higher (98% [95-99] vs 95% [89-99]; p = 0.019) after than before the dives. The other spirometry values and SpO 2 were unchanged. Body mass decreased from 73.5 kg (72.0-89.6) before the dives to 70.0 kg (69.2-85.8) after surfacing (p = 0.001), with no change of hematocrit or CFFT. HRV was increased as indicated by the higher SDNN, RMSSD and pNN50 after than before dives. ConclusionThe present observation represents the first original data regarding the effects of deep repeated CCR dives. The body mass loss and decrease of FVC after bounce dives at depth of about 100 msw may possibly impose an important physiological stress for the divers.

Endocannabinoids and Heart Rate Variability Alterations after Exposure to Prolonged Intensive Physical Exercise of the Hellenic Navy SEALs

“…In particular, brain imaging studies showed that HRV is correlated with brain networks that are responsible for the judgment of stressful situations (e.g., the ventromedial prefrontal cortex). This perspective supports the utilization of HRV for the objective investigation of stress-induced events [ 12 ]. In confirmation of this view, increased occupational stress was associated with reduced HRV [ 15 ].…”

“…The observed positive association between the mean HRV and AEA at baseline could be better understood by considering the biological meaning of both HRV and AEA. Indeed, high HRV is linked with controlling and homeostatic autonomic nervous system operations, which increase the body’s aptitude to manage the distress conditions [ 12 ], whereas stress-induced events reduce AEA levels [ 6 ]. Though there is evidence indicating a negative association between AEA and stress, the principal processes eliciting this phenomenon are debatable.…”

“…The negative association between low-frequency LF and PEA ligands at baseline might be considered both in the overall autonomic context and in association with the endocannabinoid signaling induced by environmental challenges. Indeed, increased LF of HRV indicates a low parasympathetic activity of HRV, which is interrelated with the reduction in the threat perception mediated by the brain networks responsible for the evaluation of stressful events [ 12 ]. On the other hand, PEA is believed to be implicated in endogenous protecting processes that are mobilized by the stimulation of inflammatory or nociceptive procedures [ 35 ].…”

“…As mentioned above, the ligands of the eCB are present not only in the nervous system (central and autonomous) but also in the periphery such as the myocardium and vasculature [ 5 ]. In addition, it has been shown that the administration of exogenous eCB (i.e., phytocannabinoids) in studies of humans and animals, exerts a chronotropic influence on heart rate [ 10 , 11 , 12 ]. At this point, it is useful to bring into mind that heart rate variability (HRV) is sensitive to changes in autonomic nervous system (ANS) activity (i.e., changes in the sympathetic nervous system (SNS) and parasympathetic nervous system (PNS)) associated with stress [ 12 , 13 , 14 ].…”

“…In addition, it has been shown that the administration of exogenous eCB (i.e., phytocannabinoids) in studies of humans and animals, exerts a chronotropic influence on heart rate [ 10 , 11 , 12 ]. At this point, it is useful to bring into mind that heart rate variability (HRV) is sensitive to changes in autonomic nervous system (ANS) activity (i.e., changes in the sympathetic nervous system (SNS) and parasympathetic nervous system (PNS)) associated with stress [ 12 , 13 , 14 ]. Neuroimaging studies suggested that HRV may be linked to cortical regions (e.g., the ventromedial prefrontal cortex) that are involved in stressful situation appraisal.…”