The Implications of the Diving Response in Reducing Panic Symptoms

Increased CO2 sensitivity is common in panic disorder (PD) patients. Free divers who are known for their exceptional breathing control have lower CO2 sensitivity due to training effects. This study aimed to investigate the immediate effects of cold facial immersion (CFI), breath holding and CO2 challenges on panic symptoms. Healthy participants and patients with PD were subjected to four experimental conditions in a randomly assigned order. The four conditions were (a) breath-holding (BH), (b) CFI for 30 s, (c) CO2 challenge, and (d) CO2 challenge followed by CFI. Participants completed a battery of psychological measures, and physiological data (heart rate and respiration rate) were collected following each experimental condition. Participants with PD were unable to hold their breath for as long as normal controls; however, this finding was not significant, potentially due to a small sample size. Significant reductions in both physiological and cognitive symptoms of panic were noted in the clinical group following the CFI task. As hypothesized, the CFI task exerted demonstrable anxiolytic effects in the clinical group in this study by reducing heart rate significantly and lessening self-reported symptoms of anxiety and panic. This outcome demonstrates the promise of the CFI task for clinical applications.

Use of Vagus Nerve Stimulation and Vagal Maneuvers as Adjuvant Therapy for COVID-19 Patients

At present there is no effective specific antiviral drug to treat the ongoing COVID-19 pandemic that has already infected millions of individual and caused hundreds of thousand deaths worldwide. There is strong indication that a cytokine storm is responsible for the severity of COVID-19 patients. Pilot studies using IL-6 receptor inhibitors such as Tolicizumab have shown promising results. However, since the cytokine storm is a complex systemic inflammatory response involving multiple cytokines it can be hypothesized that a “paninhibition” of cytokines and/or cytokine receptors will be more effective. However, at the same time this strategy may cause more adverse effects. In this article, we propose the application of Vagus Nerve Stimulation (NVS) and/or some forms of vagal maneuvers as adjuvant therapies to prevent and/or mitigate the cytokine response in COVID-19 patients. This proposal is based on the ability of NVS and to decrease the production of IL-6 and other cytokines. The potential application of the diving response (one form of vagal maneuver), that has been shown to confer intrinsic resistance to inflammation in the blood of diving mammals, is also discussed as adjuvant therapy for COVID-19 patients. Doi: 10.28991/SciMedJ-2021-03-SI-2 Full Text: PDF

Using Underwater Pulse Oximetry in Freediving to Extreme Depths to Study Risk of Hypoxic Blackout and Diving Response Phases

Deep freediving exposes humans to hypoxia and dramatic changes in pressure. The effect of depth on gas exchange may enhance risk of hypoxic blackout (BO) during the last part of the ascent. Our aim was to investigate arterial oxygen saturation (SpO2) and heart rate (HR) in shallow and deep freedives, central variables, which have rarely been studied underwater in deep freediving. Four male elite competitive freedivers volunteered to wear a newly developed underwater pulse oximeter for continuous monitoring of SpO2 and HR during self-initiated training in the sea. Two probes were placed on the temples, connected to a recording unit on the back of the freediver. Divers performed one “shallow” and one “deep” constant weight dive with fins. Plethysmograms were recorded at 30 Hz, and SpO2 and HR were extracted. Mean ± SD depth of shallow dives was 19 ± 3 m, and 73 ± 12 m for deep dives. Duration was 82 ± 36 s in shallow and 150 ± 27 s in deep dives. All divers desaturated more during deeper dives (nadir 55 ± 10%) compared to shallow dives (nadir 80 ± 22%) with a lowest SpO2 of 44% in one deep dive. HR showed a “diving response,” with similar lowest HR of 42 bpm in shallow and deep dives; the lowest value (28 bpm) was observed in one shallow dive. HR increased before dives, followed by a decline, and upon resurfacing a peak after which HR normalized. During deep dives, HR was influenced by the level of exertion across different diving phases; after an initial drop, a second HR decline occurred during the passive “free fall” phase. The underwater pulse oximeter allowed successful SpO2 and HR monitoring in freedives to 82 m depth – deeper than ever recorded before. Divers’ enhanced desaturation during deep dives was likely related to increased exertion and extended duration, but the rapid extreme desaturation to below 50% near surfacing could result from the diminishing pressure, in line with the hypothesis that risk of hypoxic BO may increase during ascent. Recordings also indicated that the diving response is not powerful enough to fully override the exercise-induced tachycardia during active swimming. Pulse oximetry monitoring of essential variables underwater may be an important step to increase freediving safety.

Physiology, pathophysiology and (mal)adaptations to chronic apnoeic training: a state-of-the-art review

Breath-hold diving is an activity that humans have engaged in since antiquity to forage for resources, provide sustenance and to support military campaigns. In modern times, breath-hold diving continues to gain popularity and recognition as both a competitive and recreational sport. The continued progression of world records is somewhat remarkable, particularly given the extreme hypoxaemic and hypercapnic conditions, and hydrostatic pressures these athletes endure. However, there is abundant literature to suggest a large inter-individual variation in the apnoeic capabilities that is thus far not fully understood. In this review, we explore developments in apnoea physiology and delineate the traits and mechanisms that potentially underpin this variation. In addition, we sought to highlight the physiological (mal)adaptations associated with consistent breath-hold training. Breath-hold divers (BHDs) are evidenced to exhibit a more pronounced diving-response than non-divers, while elite BHDs (EBHDs) also display beneficial adaptations in both blood and skeletal muscle. Importantly, these physiological characteristics are documented to be primarily influenced by training-induced stimuli. BHDs are exposed to unique physiological and environmental stressors, and as such possess an ability to withstand acute cerebrovascular and neuronal strains. Whether these characteristics are also a result of training-induced adaptations or genetic predisposition is less certain. Although the long-term effects of regular breath-hold diving activity are yet to be holistically established, preliminary evidence has posed considerations for cognitive, neurological, renal and bone health in BHDs. These areas should be explored further in longitudinal studies to more confidently ascertain the long-term health implications of extreme breath-holding activity.

Genes lost during the transition from land to water in cetaceans highlight genomic changes associated with aquatic adaptations

The transition from land to water in whales and dolphins (cetaceans) was accompanied by remarkable adaptations. To reveal genomic changes that occurred during this transition, we screened for protein-coding genes that were inactivated in the ancestral cetacean lineage. We found 85 gene losses. Some of these were likely beneficial for cetaceans, for example, by reducing the risk of thrombus formation during diving (F12 and KLKB1), erroneous DNA damage repair (POLM), and oxidative stress–induced lung inflammation (MAP3K19). Additional gene losses may reflect other diving-related adaptations, such as enhanced vasoconstriction during the diving response (mediated by SLC6A18) and altered pulmonary surfactant composition (SEC14L3), while loss of SLC4A9 relates to a reduced need for saliva. Last, loss of melatonin synthesis and receptor genes (AANAT, ASMT, and MTNR1A/B) may have been a precondition for adopting unihemispheric sleep. Our findings suggest that some genes lost in ancestral cetaceans were likely involved in adapting to a fully aquatic lifestyle.