Face immersion increases vagal activity as assessed by heart rate variability

Influence of physical post-exercise recovery techniques on vagally-mediated heart rate variability: A systematic review and meta-analysis

In sports, physical recovery following exercise-induced fatigue is mediated via the reactivation of the parasympathetic nervous system (PNS). A noninvasive way to quantify the reactivation of the PNS is to assess vagally-mediated heart rate variability (vmHRV), which can then be used as an index of physical recovery. This systematic review and meta-analysis investigated the effects of physical recovery techniques following exercise-induced fatigue on vmHRV, specifically via the root mean square of successive differences (RMSSD). Randomized controlled trials from the databases PubMed, WebOfScience, and SportDiscus were included. Twenty-four studies were part of the systematic review and 17 were included in the meta-analysis. Using physical post-exercise recovery techniques displayed a small to moderate positive effect on RMSSD (k = 22, Hedges' g = 0.40, 95% confidence interval [CI] = 0.20-0.61, p = 0.04) with moderate heterogeneity. In the subgroup analyses, cold water immersion displayed a moderate to large positive effect (g = 0.75, 95% CI: 0.42-1.07) compared with none for other techniques. For exercise type, physical recovery techniques performed after resistance exercise (g = 0.69, 95% CI: 0.48-0.89) demonstrated a larger positive effect than after cardiovascular intermittent (g = 0.52, 95% CI: 0.06-0.97), while physical recovery techniques performed after cardiovascular continuous exercise had no effect. No significant subgroup differences for training status and exercise intensity were observed. Overall, physical post-exercise recovery techniques can accelerate PNS reactivation as indexed by vmHRV, but the effectiveness varies with the technique and exercise type.

Cardiovascular and mood responses to an acute bout of cold water immersion

Cold water immersion (CWI) may provide benefits for physical and mental health. Our purpose was to investigate the effects of an acute bout of CWI on vascular shear stress and affect (positive and negative). Sixteen healthy adults (age: 23 ± 4 y; (9 self-reported men and 7 self-reported women) completed one 15-min bout of CWI (10 °C). Self-reported affect (positive and negative) was assessed at pre-CWI (Pre), 30-min post-immersion, and 180-min post-immersion in all participants. Brachial artery diameter and blood velocity were measured (Doppler ultrasound) at Pre, after 1-min and 15-min of CWI, and 30-min post-immersion (n = 8). Total, antegrade, and retrograde shear stress, oscillatory shear index (OSI), and forearm vascular conductance (FVC) were calculated. Venous blood samples were collected at Pre, after 1-min and 15-min of CWI, 30-min post-immersion, and 180-min post-immersion (n = 8) to quantify serum β-endorphins and cortisol. Data were analyzed using a one-way ANOVA with Fisher's least significance difference and compared to Pre. Positive affect did not change (ANOVA p = 0.450) but negative affect was lower at 180-min post-immersion (p < 0.001). FVC was reduced at 15-min of CWI and 30-min post-immersion (p < 0.020). Total and antegrade shear and OSI were reduced at 30-min post-immersion (p < 0.040) but there were no differences in retrograde shear (ANOVA p = 0.134). β-endorphins did not change throughout the trial (ANOVA p = 0.321). Cortisol was lower at 180-min post-immersion (p = 0.014). An acute bout of CWI minimally affects shear stress patterns but may benefit mental health by reducing negative feelings and cortisol levels.

Whole-body cryotherapy as a treatment for chronic medical conditions?

INTRODUCTION

Whole-body cryotherapy (WBC) is a controlled exposure of the whole body to cold to gain health benefits. In recent years, data on potential applications of WBC in multiple clinical settings have emerged.

SOURCES OF DATA

PubMed, EBSCO and Clinical Key search using keywords including terms 'whole body', 'cryotherapy' and 'cryostimulation'.

AREAS OF AGREEMENT

WBC could be applied as adjuvant therapy in multiple conditions involving chronic inflammation because of its potent anti-inflammatory effects. Those might include systemic inflammation as in rheumatoid arthritis. In addition, WBC could serve as adjuvant therapy for chronic inflammation in some patients with obesity.

AREAS OF CONTROVERSY

WBC probably might be applied as an adjuvant treatment in patients with chronic brain disorders including mild cognitive impairment and general anxiety disorder and in patients with depressive episodes and neuroinflammation reduction as in multiple sclerosis. WBC effects in metabolic disorder treatment are yet to be determined. WBC presumably exerts pleiotropic effects and therefore might serve as adjuvant therapy in multi-systemic disorders, including myalgic encephalomyelitis/chronic fatigue syndrome (ME/CFS).

GROWING POINTS

The quality of studies on the effects of WBC in the clinical setting is in general low; hence, randomized controlled trials with adequate sample size and longer follow-up periods are needed.

AREAS ARE TIMELY FOR DEVELOPING RESEARCH

Further studies should examine the mechanism underlying the clinical efficacy of WBC. Multiple conditions might involve chronic inflammation, which in turn could be a potential target of WBC. Further research on the application of WBC in neurodegenerative disorders, neuropsychiatric disorders and ME/CFS should be conducted.

Enhancing Safety in Hyperbaric Environments through Analysis of Autonomic Nervous System Responses: A Comparison of Dry and Humid Conditions

Diving can have significant cardiovascular effects on the human body and increase the risk of developing cardiac health issues. This study aimed to investigate the autonomic nervous system (ANS) responses of healthy individuals during simulated dives in hyperbaric chambers and explore the effects of the humid environment on these responses. Electrocardiographic- and heart-rate-variability (HRV)-derived indices were analyzed, and their statistical ranges were compared at different depths during simulated immersions under dry and humid conditions. The results showed that humidity significantly affected the ANS responses of the subjects, leading to reduced parasympathetic activity and increased sympathetic dominance. The power of the high-frequency band of the HRV after removing the influence of respiration, PHF⟂¯, and the number of pairs of successive normal-to-normal intervals that differ by more than 50 ms divided by the total number of normal-to-normal intervals, pNN50¯, indices were found to be the most informative in distinguishing the ANS responses of subjects between the two datasets. Additionally, the statistical ranges of the HRV indices were calculated, and the classification of subjects as "normal" or "abnormal" was determined based on these ranges. The results showed that the ranges were effective at identifying abnormal ANS responses, indicating the potential use of these ranges as a reference for monitoring the activity of divers and avoiding future immersions if many indices are out of the normal ranges. The bagging method was also used to include some variability in the datasets' ranges, and the classification results showed that the ranges computed without proper bagging represent reality and its associated variability. Overall, this study provides valuable insights into the ANS responses of healthy individuals during simulated dives in hyperbaric chambers and the effects of humidity on these responses.

The diving response and cardiac vagal activity: A systematic review and meta-analysis

This article aimed to synthesize the various triggers of the diving response and to perform a meta-analysis assessing their effects on cardiac vagal activity. The protocol was preregistered on PROSPERO (CRD42021231419; 01.07.2021). A systematic and meta-analytic review of cardiac vagal activity was conducted, indexed with the root mean square of successive differences (RMSSD) in the context of the diving response. The search on MEDLINE (via PubMed), Web of Science, ProQuest and PsycNet was finalized on November 6th, 2021. Studies with human participants were considered, measuring RMSSD pre- and during and/or post-exposure to at least one trigger of the diving response. Seventeen papers (n = 311) met inclusion criteria. Triggers examined include face immersion or cooling, SCUBA diving, and total body immersion into water. Compared to resting conditions, a significant moderate to large positive effect was found for RMSSD during exposure (Hedges' g = 0.59, 95% CI 0.36 to 0.82, p < .001), but not post-exposure (g = 0.11, 95% CI -0.14 to 0.36, p = .34). Among the considered moderators, total body immersion had a significantly larger effect than forehead cooling (Q_M  = 23.46, df = 1, p < .001). No further differences were detected. Limitations were the small number of studies included, heterogenous triggers, few participants and low quality of evidence. Further research is needed to investigate the role of cardiac sympathetic activity and of the moderators.

Effects of lung volume and trigeminal nerve stimulation on diving response in breath-hold divers and non-divers

PURPOSE

This study investigated the effects of lung volume and trigeminal nerve stimulation (TS) on diving responses in breath-hold divers (BHDs) and non-divers (NDs).

METHODS

Eight BHDs and nine NDs performed four breath-hold trials at different lung volumes, with or without TS, and one trial of TS. Haemodynamic parameters and electrocardiograms were measured for each trial.

RESULTS

During the TS trial, the total peripheral resistance increased more in BHDs. Breath-hold performed at total lung capacity showed a more pronounced decrease in stroke volume and cardiac output in BHDs. The decrease in heart rate and increase in total peripheral resistance were more pronounced in BHDs when breath-holding was performed with TS.

CONCLUSION

The more pronounced diving response in BHDs was attributed to the greater increase in total peripheral resistance caused by TS. Furthermore, the lower stroke volume and cardiac output in BH performed at total lung capacity could also cause a more pronounced diving response in BHDs.

Acute Cardiovascular and Metabolic Effects of Different Warm-Up Protocols on Dynamic Apnea

The aim of this study was to evaluate the acute physiological response to different warm-up protocols on the dynamic apnea performance. The traditional approach, including a series of short-mid dives in water (WET warm-up), was compared to a more recent strategy, consisting in exercises performed outside the water (DRY warm-up). Nine athletes were tested in two different sessions, in which the only difference was the warm-up executed before 75m of dynamic apnea. Heart rate variability, baroreflex sensitivity, hemoglobin, blood lactate and the rate of perceived exertion were recorded and analyzed. With respect to WET condition, DRY showed lower lactate level before the dive (1.93 vs. 2.60 mmol/L, p = 0.006), higher autonomic indices and lower heart rate during the subsequent dynamic apnea. A significant correlation between lactate produced during WET with the duration of the subsequent dynamic apnea, suggests that higher lactate levels could affect the dive performance (72 vs. 70 sec, p = 0.028). The hemoglobin concentration and the rate of perceived exertion did not show significant differences between conditions. The present findings partially support the claims of freediving athletes who adopt the DRY warm-up, since it induces a more pronounced diving response, avoiding higher lactate levels and reducing the dive time of a dynamic apnea.

The Human Dive Reflex During Consecutive Apnoeas in Dry and Immersive Environments: Magnitude and Synchronicity

Introduction: The human dive reflex (HDR), an O₂ conserving reflex, is characterised by an interplay of central parasympathetic and peripheral sympathetic reactions, which are presumed to operate independently of each other. The HDR is fully activated during apnoea with facial immersion in water and complete immersion in water is thought to increase the magnitude of HDR during consecutive apnoeas. A comparison of HDR activity between consecutive apnoeas in full-body immersion with consecutive apnoeas in dry conditions has not been fully explored. Also, the interplay between parasympathetic and sympathetic reactions involved in the HDR has not been thoroughly analysed. Methods: 11 human volunteers performed 3 consecutive 60 s apnoeas with facial immersion in dry conditions (FIDC) and 3 consecutive apnoeas with facial immersion in full immersion (FIFI). Heart rate (HR), R-R interval (RRI), finger pulse amplitude (FPA), splenic width (SW) and SpO₂ were all measured before, during and after apnoeas. A one-way ANOVA using Dunn's post hoc test was performed to assess HDR activity, and a Pearson's correlation test was performed to assess HDR synchronisation between physiological parameters during both conditions. Results: Although HDR activity was not significantly different between both conditions, HR and RRI showed progressively greater changes during FIFI compared with FIDC, while SW and FPA changes were relatively equivalent. During FIDC, significant correlations were found between SW & SpO₂ and FPA & SpO₂. During FIFI, significant correlations were found between RRI & FPA, SW & FPA, HR & SpO₂ and FPA & SpO₂. Discussion: While there was no significant difference found between HDR activity during FIDC and FIFI, consecutive apnoeas during FIFI triggered a greater magnitude of cardiac activity. Furthermore, significant correlations between RRI and SW with FPA indicate a crosstalk between parasympathetic tone with splenic contraction and increased peripheral sympathetic outflow during FIFI compared to FIDC. In conclusion, HDR activity during consecutive apnoeas does not differ between FIDC and FIFI. There appears to be however a greater level of synchronicity during apnoeas in FIFI compared to FIDC and that this is most likely due to the physiological effects of immersion, which could induce neural recruitment and increased cross talk of HDR pathways.

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.

The Occurrence of Arrhythmias and Heart Rate Variability During Diving in Recreational Divers Using Continuous Electrocardiographic Holter Monitoring

The aim of the research was to evaluate the occurrence of arrhythmias and heart rate variability during diving in recreational divers. Continuous electrocardiographic (ECG) Holter monitoring was conducted in a group of 50 divers (age 36,8 ± 8,7). The recorded data included the duration of the dive, including a period of 60 minutes before the dive and 60 minutes after the dive. Moreover, divers filled in a questionnaire that had been prepared for the purpose of the study and the psychological tests State-Trait Anxiety Inventory (STAI). The ECG recordings were synchronised with dive computers to correlate the ECG changes with diving events and analysed for the heart rate, arrhythmias and conduction disorders. The average heart rate was the highest (M=107.34 beats/minute) before diving, and the lowest after diving (M = 102.00 beats/minute). Supraventricular arrhythmias were recorded in nineteen (38%) of the participants of the study. The number of arrhythmias during diving (M = 14,45) is significantly higher than before (M = 9,93, p < 0,01) and after dive (M = 6,02, p < 0,05). All results were obtained from the continuous ECG Holter monitoring. It seems that using continuous ECG monitoring in conditions similar to diving (physical and psychological stress), brings more benefits than traditional, resting electrocardiogram.

Autonomic cardiovascular adaptations to acute head-out water immersion, head-down tilt and supine position

PURPOSE

Thermoneutral head-out water immersion (WI) and 6° head-down tilt (HDT) have been considered as suitable models to increase central blood volume and simulate autonomic cardiovascular adaptations to microgravity, swimming or scuba diving. However, any differences in autonomic cardiovascular adaptations are still unclear. In this study, we hypothesized that WI induces a higher activation of arterial baroreceptors and the parasympathetic system.

METHODS

Ten healthy men underwent 30 min of WI, HDT, and a supine position (SP). RR intervals (RRI) and blood pressure (BP) were continuously monitored. High frequency power (HF), low frequency power (LF) and LF/HF ratio were calculated to study sympathetic and parasympathetic activities, and a spontaneous baroreflex method was used to study arterial baroreflex sensitivity (aBRS). Lung transfer of nitric oxide and carbon monoxide (TLNO/TLCO), vital capacity and alveolar volume (Vc/VA) were measured to study central blood redistribution.

RESULTS

We observed (1) a similar increase in RRI and decrease in BP; (2) a similar increase in HF power during all experimental conditions, whereas LF increased after; (3) a similar rise in aBRS; (4) a similar increase in Vc/VA and decrease in TLNO/TLCO in all experimental conditions.

CONCLUSIONS

These results showed a cardiac parasympathetic dominance to the same extent, underpinned by a similar arterial baroreflex activation during WI and HDT as well as control SP. Future studies may address their association with cold or hyperoxia to assess their ability to replicate autonomic cardiovascular adaptations to microgravity, swimming or scuba diving.

Cold Water Immersion Syndrome and Whitewater Recreation Fatalities

Sudden death during whitewater recreation often occurs through understandable mechanisms such as underwater entrapment or trauma, but poorly defined events are common, particularly in colder water. These uncharacterized tragedies are frequently called flush drownings by whitewater enthusiasts. We believe the condition referred to as cold water immersion syndrome may be responsible for some of these deaths. Given this assumption, the physiologic alterations contributing to cold water immersion syndrome are reviewed with an emphasis on those factors pertinent to flush drowning.

Face cooling exposes cardiac parasympathetic and sympathetic dysfunction in recently concussed college athletes

We tested the hypothesis that concussed college athletes (CA) have attenuated parasympathetic and sympathetic responses to face cooling (FC). Eleven symptomatic CA (age: 20 ± 2 years, 5 women) who were within 10 days of concussion diagnosis and 10 healthy controls (HC; age: 24 ± 4 years, 5 women) participated. During FC, a plastic bag filled with ice water (~0°C) was placed on the forehead, eyes, and cheeks for 3 min. Heart rate (ECG) and blood pressure (photoplethysmography) were averaged at baseline and every 60 sec during FC. High‐frequency (HF) power was obtained from spectral analysis of the R‐R interval. Data are presented as a change from baseline. Baseline heart rate (HC: 61 ± 12, CA: 57 ± 12 bpm; P = 0.69), mean arterial pressure (MAP) (HC: 94 ± 10, CA: 96 ± 13 mmHg; P = 0.74), and HF (HC: 2294 ± 2314, CA: 2459 ± 2058 msec²; P = 0.86) were not different between groups. Heart rate in HC decreased at 2 min (−7 ± 11 bpm; P = 0.02) but did not change in CA (P > 0.43). MAP increased at 1 min (HC: 12 ± 6, CA: 6 ± 6 mmHg), 2 min (HC: 21 ± 7, CA: 11 ± 7 mmHg), and 3 min (HC: 20 ± 6, CA: 13 ± 7 mmHg) in both groups (P < 0.01 for all) but the increase was greater at each interval in HC (P < 0.02). HF increased at 1 min (12354 ± 11489 msec²; P < 0.01) and 2 min (5832 ± 8002 msec²; P = 0.02) in HC but did not change in CA (P > 0.58). The increase in HF at 1 min was greater in HC versus CA (P < 0.01). These data indicate that symptomatic concussed patients have impaired cardiac parasympathetic and sympathetic activation.

Effects of Cold Stimulation on Cardiac-Vagal Activation in Healthy Participants: Randomized Controlled Trial

Background

The experience of psychological stress has not yet been adequately tackled with digital technology by catering to healthy individuals who wish to reduce their acute stress levels. For the design of digitally mediated solutions, physiological mechanisms need to be investigated that have the potential to induce relaxation with the help of technology. Research has shown that physiological mechanisms embodied in the face and neck regions are effective for diminishing stress-related symptoms. Our study expands on these areas with the design for a wearable in mind. As this study charts new territory in research, it also is a first evaluation of the viability for a wearables concept to reduce stress.

Objective

The objectives of this study were to assess whether (1) heart rate variability would increase and (2) heart rate would decrease during cold stimulation using a thermode device compared with a (nonstimulated) control condition. We expected effects in particular in the neck and cheek regions and less in the forearm area.

Methods

The study was a fully randomized, within-participant design. Volunteer participants were seated in a laboratory chair and tested with cold stimulation on the right side of the body. A thermode was placed on the neck, cheek, and forearm. We recorded and subsequently analyzed participants’ electrocardiogram. The cold stimulation was applied in 16-second intervals over 4 trials per testing location. The control condition proceeded exactly like the cold condition, except we manipulated the temperature variable to remain at the baseline temperature. We measured heart rate as interbeat intervals in milliseconds and analyzed root mean square of successive differences to index heart rate variability. We analyzed data using a repeated-measures ANOVA (analysis of variance) approach with 2 repeated-measures factors: body location (neck, cheek, forearm) and condition (cold, control).

Results

Data analysis of 61 participants (after exclusion of outliers) showed a main effect and an interaction effect for body location and for condition, for both heart rate and heart rate variability. The results demonstrate a pattern of cardiovascular reactivity to cold stimulation, suggesting an increase in cardiac-vagal activation. The effect was significant for cold stimulation in the lateral neck area.

Conclusions

The results confirmed our main hypothesis that cold stimulation at the lateral neck region would result in higher heart rate variability and lower heart rate than in the control condition. This sets the stage for further investigations of stress reduction potential in the neck region by developing a wearable prototype that can be used for cold application. Future studies should include a stress condition, test for a range of temperatures and durations, and collect self-report data on perceived stress levels to advance findings.

Physiology Of Drowning: A Review

Drowning physiology relates to two different events: immersion (upper airway above water) and submersion (upper airway under water). Immersion involves integrated cardiorespiratory responses to skin and deep body temperature, including cold shock, physical incapacitation, and hypovolemia, as precursors of collapse and submersion. The physiology of submersion includes fear of drowning, diving response, autonomic conflict, upper airway reflexes, water aspiration and swallowing, emesis, and electrolyte disorders. Submersion outcome is determined by cardiac, pulmonary, and neurological injury. Knowledge of drowning physiology is scarce. Better understanding may identify methods to improve survival, particularly related to hot-water immersion, cold shock, cold-induced physical incapacitation, and fear of drowning.

Is V̇O2 suppressed during nonapnoeic facial submersion?

The mammalian dive response (DR) is described as oxygen-conserving based on measures of bradycardia, peripheral vasoconstriction, and decreased ventilation (V̇_E). Using a model of simulated diving, this study examined the effect of nonapnoeic facial submersions (NAFS) on oxygen consumption (V̇O₂). 19 participants performed four 2-min NAFS with 8 min of rest between each. Two submersions were performed in 5 °C water, 2 in 25 °C water. Heart rate (HR) was collected using chest strap monitors. A tube connected to the inspired port of a non-rebreathing valve allowed participants to breathe during facial submersion. Expired air was directed to a metabolic cart to determine V̇O₂ and V̇_E. Baseline (BL) HR, V̇O₂, and V̇_E values were determined by the average during the 2 min prior to facial submersion; cold shock response (CSR) values were the maximum during the first 30 s of facial submersion; and NAFS values were the minimum during the last 90 s of facial submersion. A 2-way repeated-measures ANOVA indicated that both HR and V̇_E were greater during the CSR (92.5 ± 3.6 beats/min, 16.3 ± 0.8 L/min) compared with BL (78.9 ± 3.2 beats/min, 8.7 ± 0.4 L/min), while both were decreased from BL during the NAFS (60.0 ± 4.0 beats/min, 6.0 ± 0.4 L/min) (all, p < 0.05). HR_CSR was higher and HR_NAFS lower in 5 °C versus 25 °C water (p < 0.05), while V̇_E was greater in 5 °C conditions (p < 0.05). V̇O₂ exceeded BL during the CSR and decreased below BL during the NAFS (BL: 5.3 ± 0.1, CSR: 9.8 ± 0.4, NAFS: 3.1 ± 0.2 mL·kg^-1·min^-1, p < 0.05). The data illustrate that NAFS alone contributes to the oxygen conservation associated with the human DR.

Cold Face Test-Induced Increases in Heart Rate Variability Are Abolished by Engagement in a Social Cognition Task

Abstract. The vagus nerve is a major constituent in the bidirectional relationship between the heart and the prefrontal cortex. This study investigated the role of the vagus in social cognition using the cold face test (facial cooling) to stimulate the vagus nerve and increase prefrontal inhibitory control. Heart Rate Variability (HRV) was measured to index parasympathetic outflow while social cognition ability was tested using the Reading the Mind in the Eyes Test (RMET). Healthy males (n = 25) completed the RMET under two conditions: with and without facial cooling. Results indicated that although facial cooling increased HRV at rest, there was no improvement in the RMET during the facial cooling condition. Interestingly, completing the RMET with facial cooling abolished this increase in HRV, suggesting interference along the vagal reflex arc. These results are consistent with the involvement of a common cortico-subcortical circuit in autonomic and cognitive processes, important for emotion recognition.

Using stimulation of the diving reflex in humans to teach integrative physiology

During underwater submersion, the body responds by conserving O2 and prioritizing blood flow to the brain and heart. These physiological adjustments, which involve the nervous, cardiovascular, and respiratory systems, are known as the diving response and provide an ideal example of integrative physiology. The diving reflex can be stimulated in the practical laboratory setting using breath holding and facial immersion in water. Our undergraduate physiology students complete a laboratory class in which they investigate the effects of stimulating the diving reflex on cardiovascular variables, which are recorded and calculated with a Finapres finger cuff. These variables include heart rate, cardiac output, stroke volume, total peripheral resistance, and arterial pressures (mean, diastolic, and systolic). Components of the diving reflex are stimulated by 1) facial immersion in cold water (15°C), 2) breathing with a snorkel in cold water (15°C), 3) facial immersion in warm water (30°C), and 4) breath holding in air. Statistical analysis of the data generated for each of these four maneuvers allows the students to consider the factors that contribute to the diving response, such as the temperature of the water and the location of the sensory receptors that initiate the response. In addition to providing specific details about the equipment, protocols, and learning outcomes, this report describes how we assess this practical exercise and summarizes some common student misunderstandings of the essential physiological concepts underlying the diving response.

Sympathetic nerve activity and simulated diving in healthy humans

The goal of our study was to develop a simple and practical method for simulating diving in humans using facial cold exposure and apnea stimuli to measure neural and circulatory responses during the stimulated diving reflex. We hypothesized that responses to simultaneous facial cold exposure and apnea (simulated diving) would be synergistic, exceeding the sum of responses to individual stimuli. We studied 56 volunteers (24 female and 32 male), average age of 39 years. All subjects were healthy, free of cardiovascular and other diseases, and on no medications. Although muscle sympathetic nerve activity (MSNA), blood pressure, and vascular resistance increased markedly during both early and late phases of simulated diving, significant reductions in heart rate were observed only during the late phase. Total MSNA during simulated diving was greater than combined MSNA responses to the individual stimuli. We found that simulated diving is a powerful stimulus to sympathetic nerve traffic with significant bradycardia evident in the late phase of diving and eliciting synergistic sympathetic and parasympathetic responses. Our data provide insight into autonomic triggers that could help explain catastrophic cardiovascular events that may occur during asphyxia or swimming, such as in patients with obstructive sleep apnea or congenital long QT syndrome.

Dominance in cardiac parasympathetic activity during real recreational SCUBA diving

It was already established that exposure to hyperbaric conditions induces vagal-depended bradycardia but field study on autonomic nervous system (ANS) activity during self-contained underwater breathing apparatus (SCUBA) diving is lacking. The aim of the present study was to evaluate ANS modifications during real recreational SCUBA diving using heart rate variability analysis (timedomain, frequency-domain and Poincaré plot) in 10 experienced and volunteers recreational divers. Mean RR, root mean square of successive differences of interval (rMSSD), high frequency of spectral analysis and standard deviation 1 of Poincaré Plot increased (P < 0.05) during dive. Low frequency/high frequency ratio decreased during dive (P < 0.05) but increased after (P < 0.05). Recreational SCUBA diving induced a rise in vagal activity and a decrease in cardiac sympathetic activity. Conversely, sympathetic activity increases (P < 0.05) during the recovery.

Effects of head and body cooling on hemodynamics during immersed prone exercise at 1 ATA

Immersion pulmonary edema (IPE) is a condition with sudden onset in divers and swimmers suspected to be due to pulmonary arterial or venous hypertension induced by exercise in cold water, although it does occur even with adequate thermal protection. We tested the hypothesis that cold head immersion could facilitate IPE via a reflex rise in pulmonary vascular pressure due solely to cooling of the head. Ten volunteers were instrumented with ECG and radial and pulmonary artery catheters and studied at 1 atm absolute (ATA) during dry and immersed rest and exercise in thermoneutral (29-31 degrees C) and cold (18-20 degrees C) water. A head tent varied the temperature of the water surrounding the head independently of the trunk and limbs. Heart rate, Fick cardiac output (CO), mean arterial pressure (MAP), mean pulmonary artery pressure (MPAP), pulmonary artery wedge pressure (PAWP), and central venous pressure (CVP) were measured. MPAP, PAWP, and CO were significantly higher in cold pool water (P < or = 0.004). Resting MPAP and PAWP values (means +/- SD) were 20 +/- 2.9/13 +/- 3.9 (cold body/cold head), 21 +/- 3.1/14 +/- 5.2 (cold/warm), 14 +/- 1.5/10 +/- 2.2 (warm/warm), and 15 +/- 1.6/10 +/- 2.6 mmHg (warm/cold). Exercise values were higher; cold body immersion augmented the rise in MPAP during exercise. MAP increased during immersion, especially in cold water (P < 0.0001). Except for a transient additive effect on MAP and MPAP during rapid head cooling, cold water on the head had no effect on vascular pressures. The results support a hemodynamic cause for IPE mediated in part by cooling of the trunk and extremities. This does not support the use of increased head insulation to prevent IPE.

Drowning

PURPOSE OF REVIEW

To summarize current knowledge on pathophysiology and treatment of drowning accidents. Studies and case reports were searched using the keywords drowning, near-drowning, asphyxia, hypoxia and hypothermia in conjunction with organ systems and specific treatment options.

RECENT FINDINGS

Drowning is defined as death by suffocation in a liquid. In contrast, near-drowning is defined as survival beyond 24 h after a drowning accident. Drowning is a frequent preventable accident with a significant morbidity and mortality in a mostly healthy population. In the majority of patients the primary injury is pulmonary, resulting in severe arterial hypoxemia and secondary damage to other organs. Damage to the central nervous system is most critical in terms of patient survival and subsequent quality of life. Therefore, prompt resuscitation and aggressive respiratory and cardiovascular treatment are crucial for optimal survival. Immediate interruption of hypoxia, aggressive treatment of hypothermia and cardiovascular failure are the cornerstones of correct medical treatment. Unfortunately, accurate neurologic prognosis cannot be predicted from initial clinical presentation, laboratory, radiological or electrophysiological examinations.

SUMMARY

Several case studies have convincingly demonstrated that drowning victims may survive neurologically intact even after prolonged submersion times, in particular in cold water. Therefore, aggressive initial therapeutic efforts are indicated in most near-drowning victims.

Cold-Water Face Immersion Per Se Elicits Cardiac Parasympathetic Activity

BACKGROUND

Cold-water face immersion (FI) is known to produce physiological changes, including bradycardia, by stimulating the parasympathetic system. However, other factors such as sympathetic activity, intrapleural pressures, and changes in chemical mediators may also contribute to these changes.

METHODS AND RESULTS

Eight healthy volunteers underwent a series of experiments designed to observe the effects of FI on heart rate and its variability, as detected using wavelet transformation. Each subject was instructed to bend over and put the entire face into an empty basin with and without breathing (protocols 1 and 2, respectively), and then perform FI in warm-water (protocols 3 and 4, respectively) and cold-water (protocols 5 and 6, respectively) while breathing and breath holding. Change in the R-R interval with FI was only significantly greater for protocol 6 than for the control procedure (protocol 1). Also, changes in the natural logarithm of high-frequency power with FI were significantly greater for protocols 5 and 6 than the protocol 1.

CONCLUSIONS

Bradycardia associated with cold-water FI is mainly attributed to cardiac vagal activity, which is independent of both the change in body position caused by bending over a basin and breath holding.

Comportamento de variáveis fisiológicas em atletas de nado sincronizado durante uma sessão de treinamento na fase de preparação para as Olimpíadas de Atenas 2004

O objetivo do presente estudo foi avaliar o comportamento de variáveis fisiológicas durante uma sessão de treino de nado sincronizado realizada na fase de preparação para as Olimpíadas de Atenas 2004. MATERIAIS E MÉTODOS: A amostra utilizada foi constituída pelo dueto (24 ± 0 anos) representante do Brasil em Atenas 2004. A coleta de dados foi realizada durante uma sessão de treinamento com duração de 198 minutos. O treino se iniciou com a parte física, seguida da parte técnica. Para a determinação da glicemia e da concentração de beta-hidroxibutirato foi utilizado o monitor Optium® com suas respectivas tiras. As concentrações de cortisol e das enzimas lactato desidrogenase (LDH) e creatina quinase (CK) foram determinadas por radioimunoensaio (DPC©) e kits comerciais (CELM®), respectivamente. O acompanhamento da freqüência cardíaca (FC) foi realizado com o freqüêncimetro Advantage Polar®. RESULTADOS: Foi observada redução (~2%) do peso corporal. A glicemia também apresentou queda (~30%) em comparação ao valor obtido no início do treino. Em contrapartida, foi observada elevação na concentração de cortisol (salivar 22% e plasmática 29%) e de beta-hidroxibutirato (~340%). Não foi observada alteração significativa na concentração plasmática de CK e de LDH. O acompanhamento da FC demonstrou que dos 198 minutos que constituíram a sessão de treino, 36,5 ± 0,7 minutos foram realizados em intensidade leve; 103,5 ± 0,7 minutos em intensidade moderada, 54,0 ± 2,1 minutos em intensidade alta e 4,0 ± 0,0 minutos em intensidade muito alta. CONCLUSÕES: A perda de peso indica que a reposição hídrica não foi adequada. A redução na glicemia e o aumento na concentração de corpos cetônicos e de cortisol reforçam a importância da suplementação de carboidrato durante o treino de longa duração. O comportamento da FC demonstra que a sessão de treinamento foi realizada em uma intensidade moderada, porém com breves momentos de intensidade alta, nos quais foram realizadas as rotinas.

The human diving response, its function, and its control

The purpose of this review is to outline the physiological responses associated with the diving response, its functional significance, and its cardiorespiratory control. This review is separated into four major sections. Section one outlines the diving response and its physiology. Section two provides support for the hypothesis that the primary role of the diving response is the conservation of oxygen. The third section describes how the diving response is controlled and provides a model that illustrates the cardiorespiratory interaction. Finally, the fourth section illustrates potential adaptations that result after regular exposure to an asphyxic environment. The cardiovascular and endocrine responses associated with the diving response and apnea are bradycardia, vasoconstriction, and an increase in secretion of suprarenal catecholamines. These responses require the integration of both the cardiovascular system and the respiratory system. The primary role of the diving response is likely to conserve oxygen for sensitive brain and heart tissue and to lengthen the time before the onset of serious hypoxic damage. We suggest that future research should be focused towards understanding the role of altered ventilatory responses in human breath-hold athletes as well as in patients suffering from sleep-disordered breathing.

Drowning

Recent epidemiologic data have shown that the burden of drowning is much greater than expected. Prevention and timely rescue are the most effective means of reducing the number of persons at risk. Early bystander cardiopulmonary resuscitation is the most important factor for survival after submersion. Cerebral damage is a serious threat when the hypoxic period is too long. In most situations, low body temperature is an indication of the severity of the drowning incident. Sometimes hypothermia that occurs during the submersion period can be brain protective. There is also new evidence to support the strategy of inducing mild hypothermia for a period of 12 to 24 hours in comatose drowning victims. In immersed patients, hypothermia should be treated. The most appropriate technique will depend on the available means in the hospital and the condition of the patient. Treatment of pulmonary complications depends on the lung injury that occurred during aspiration and the bacteria involved in aspiration. Understanding the pathophysiology of drowning may help us to understand lung injuries and ischemic brain injuries.

Heart rate indication using musical data

Heart rate data reflects various physiological states such as biological workload, stress at work and concentration on tasks, drowsiness and the active state of the autonomic nervous system. This paper proposes system to indicate heart rate using musical data. Music changes physiological states for the better by relaxing people, or contributing to patient treatment through music therapy. Information in the form of music is advantageous because it does not hinder work as does verbal information and it contains more information than warning noises. We introduce and evaluate a prototype heart rate indication system and describe evaluation results of biofeedback effects on the worker during mental workload. The prototype system sequentially inputs the instantaneous heart rate into the computer, converts the data into musical instrument digital interface, the digital music format, and outputs it from the sound source.

Face immersion in cold water induces prolongation of the QT interval and T-wave changes in children with nonfamilial long QT syndrome

We investigated the relation between heart rate and the QT interval using face immersion in cold water in children with long QT syndrome (LQTS) without a family history of this condition, and in control children. The face immersion test revealed that all children with high probability of LQTS had a significantly longer QT interval than control children during face immersion, and that the test could induce T-wave alternans or a notched T-wave in all children with a high probability of LQTS.

Delayed vagal withdrawal slows circulatory but not oxygen uptake responses at work increase

The effect of delayed vagal activity withdrawal on cardiorespiratory responses at an increase in workload was examined. Eleven volunteers (21 +/- 3 yr, 66 +/- 4 kg) performed cycle ergometer exercise at a work rate corresponding to 80% of ventilatory threshold after 3 min of unloaded cycling. Facial stimulation was given by applying a vinyl bag filled with cold water (3-5 degrees C) to the face 1 min before to 1 min after the increase in workload (S2 trial) or no stimulation was given (Nr trial). Oxygen uptake (VO2), heart rate (HR), and cardiac output (Q) were continuously recorded in four transitions for each trial. Data were averaged for each subject and trial. Mean response time (MRT, sum of delay and time constant) was calculated with monoexponential fitting. Facial stimulation induced acute bradycardia (-10 +/- 5 beats/min in S2 trial). The MRT of HR and Q was significantly longer in the S2 trials (46 +/- 35 and 37 +/- 23 s) than in the Nr trials (26 +/- 18 and 28 +/- 19 s, respectively), but no significant change in VO2 MRT was shown (36 +/- vs. 38 +/- 12 s). These findings suggest that increased vagal activity delays the central circulatory responses, which does not alter the VO2 kinetics at the onset of stepwise increase in workload. The maintenance of VO2 kinetics during acute bradycardia may either reflect the fact that some intramuscular processes (such as oxidative enzyme inertia) limit VO2 kinetics or alternatively that increased sympathetic vasoconstriction at some remote site defends exercising muscle blood flow.