Cardiovascular effects of static carotid baroreceptor stimulation during water immersion in humans

The effects of cold exposure (cold water immersion, whole- and partial- body cryostimulation) on cardiovascular and cardiac autonomic control responses in healthy individuals: A systematic review, meta-analysis and meta-regression

BACKGROUND

Cryostimulation and cold-water immersion (CWI) have recently gained widespread attention due to their association with changes in cardiovascular and cardiac autonomic control responses. Therefore, the aim of the present systematic review and meta-analysis was to identify the global impact of such cold exposures on cardiovascular and cardiac autonomic activity.

METHODS

Three databases (PubMed, Embase, Web-of-Science) were used. Studies were eligible for inclusion if they were conducted on healthy participants using cryostimulation and/or CWI. The outcomes included measurements of blood pressure (BP), heart rate (HR), and heart rate variability (HRV) indices: RR interval (RR), Root mean square of successive RR interval differences (RMSSD), low frequency band (LF), high frequency band (HF), and LF/HF ratio.

RESULTS

Among the 27 articles included in our systematic literature review, only 24 were incorporated into the meta-analysis. Our results reveal a significant increase in HRV indices: RMSSD (Standardized mean difference (SMD) = 0.61, p < 0.001), RR (SMD = 0.77, p < 0.001), and HF (SMD = 0.46, p < 0.001), as well as significantly reduced LF (SMD = -0.41, p < 0.001) and LF/HF ratio (SMD = -0.25, p < 0.01), which persisted up to 15 min following cold exposure. Significantly decreased heart rate (SMD = -0.16, p < 0.05), accompanied by slightly increased mean BP (SMD = 0.28, p < 0.001), was also observed. These results seem to depend on individual characteristics and the cooling techniques.

CONCLUSION

Our meta-analysis suggests that cryostimulation and/or CWI exposure enhance parasympathetic nervous activity. There is scarce scientific literature regarding the effect of individual characteristics on cold-induced physiological responses.

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.

Statin Use Improves Cardiometabolic Protection Promoted By Physical Training in an Aquatic Environment: A Randomized Clinical Trial

BACKGROUND

Statin use is highlighted as the most commonly utilized therapy for the treatment of dyslipidemias and can be considered as the most efficient pharmacological intervention for low-density lipoprotein (LDL) reduction. On the other hand, physical training can be considered an efficient and safe non-pharmacological strategy to promote improvements in lipid profile. However, the influence of statins on lipid adaptations arising from water-based training in populations with dyslipidemia is not known.

OBJECTIVES

To analyze the influence of simvastatin use on lipid adaptations arising from water-based aerobics and resistance training in elderly women with dyslipidemia.

METHODS

Sixty-nine elderly (66.13 ± 5.13 years), sedentary, and dyslipidemic women, both non-users and users of simvastatin (20 mg and 40 mg), were randomized into the following 3 groups: water-based aerobic training (WA), water-based resistance training (WR), and control group (CG). Total duration of interventions, for all experimental groups consisted of 10 weeks, with 2 weekly sessions. Biochemical analyses were performed before the beginning of the interventions and repeated after the end of the trial. Generalized estimating equations were used to compare these data, setting α = 0.05.

RESULTS

In intention-to-treat analysis, the medicated participants obtained a greater magnitude of decrease in total cholesterol (TC) (-3.41 to -25.89 mg.dl-1; p = 0.038), LDL (-5.58 to -25.18 mg.dl-1; p = 0.007) and TC/HDL ratio (-0.37 to -0.61; p = 0.022) when compared to the non-medicated participants, and this decrease was statistically significant only in the WR group.

CONCLUSIONS

Statin use enhances the adaptations promoted by water-based physical training in CT, LDL levels, and CT/HDL ratio, and it is more pronounced after WR.

"The immediate effect of neutral spinal compress on heart rate variability in hypertensive individuals"

OBJECTIVES

Hypertension (HTN) is considered as chronic medical condition. Because of the increased complications associated with the conventional medicine, the effects of naturopathic modalities were emphasized to prevent and minimize those adverse effects. This study was done to assess the immediate effect of neutral spinal compress on heart rate variability and blood pressure and thereby to substantiate the clinical understanding of its effect in hypertensive individuals.

METHODS

Hundred hypertensive individuals were recruited for the study. Subjects were assessed for Blood Pressure (BP) and Heart Rate Variability (HRV) before and immediately after the intervention of 20 min.

RESULTS

Result shows significant reduction in mean Heart Rate (HR) (p<0.001), Low Frequency (LF) (p<0.001), Low Frequency/High Frequency (LF/HF) (p<0.001), Systolic blood pressure (SBP) (p<0.001) and Diastolic blood pressure (DBP) (p<0.001) and significant increase in mean R-R interval (Mean RR) (p<0.001) and High frequency (HF) (p<0.001) components of Heart Rate Variability after neutral spinal compress intervention.

CONCLUSIONS

The results of the study reported that full neutral spinal compress reduces the sympathetic tone and shifts the Sympatho-vagal balance in favor of parasympathetic dominance and hence it can be concluded that neutral spinal compress can be effectively used in the management of hypertension.

TRIAL REGISTRATION

Clinical Trial Registry- India (CTRI); CTRI Reg. No- CTRI/2020/01/022639.

Post-exercise Body Cooling: Skin Blood Flow, Venous Pooling, and Orthostatic Intolerance

Athletes and certain occupations (e.g., military, firefighters) must navigate unique heat challenges as they perform physical tasks during prolonged heat stress, at times while wearing protective clothing that hinders heat dissipation. Such environments and activities elicit physiological adjustments that prioritize thermoregulatory skin perfusion at the expense of arterial blood pressure and may result in decreases in cerebral blood flow. High levels of skin blood flow combined with an upright body position augment venous pooling and transcapillary fluid shifts in the lower extremities. Combined with sweat-driven reductions in plasma volume, these cardiovascular alterations result in levels of cardiac output that do not meet requirements for brain blood flow, which can lead to orthostatic intolerance and occasionally syncope. Skin surface cooling countermeasures appear to be a promising means of improving orthostatic tolerance via autonomic mechanisms. Increases in transduction of sympathetic activity into vascular resistance, and an increased baroreflex set-point have been shown to be induced by surface cooling implemented after passive heating and other arterial pressure challenges. Considering the further contribution of exercise thermogenesis to orthostatic intolerance risk, our goal in this review is to provide an overview of post-exercise cooling strategies as they are capable of improving autonomic control of the circulation to optimize orthostatic tolerance. We aim to synthesize both basic and applied physiology knowledge available regarding real-world application of cooling strategies to reduce the likelihood of experiencing symptomatic orthostatic intolerance after exercise in the heat.

An Ice Vest, but Not Single-Hand Cooling, Is Effective at Reducing Thermo-Physiological Strain During Exercise Recovery in the Heat

Sports limit the length of breaks between halves or periods, placing substantial time constraints on cooling effectiveness. This study investigated the effect of active cooling during both time-limited and prolonged post-exercise recovery in the heat. Ten recreationally-active adults (VO2peak 43.6 ± 7.5 ml·kg-1·min-1) were exposed to thermally-challenging conditions (36°C air temperature, 45% RH) while passively seated for 30 min, cycling for 60 min at 51% VO2peak, and during a seated recovery for 60 min that was broken into two epochs: first 15 min (REC0-15) and total 60 min (REC0-60). Three different cooling techniques were implemented during independent recovery trials: (a) negative-pressure single hand-cooling (~17°C); (b) ice vest; and (c) non-cooling control. Change in rectal temperature (T re), mean skin temperature (T ¯ sk ), heart rate (HR), and thermal sensation (TS), as well as mean body temperature (T ¯ b ), and heat storage (S) were calculated for exercise, REC0-15 and REC0-60. During REC0-15, HR was lowered more with the ice vest (-9 [-15 to -3] bts·min-1, p = 0.002) and single hand-cooling (-7 [-13 to -1] bts·min-1, p = 0.021) compared to a non-cooling control. The ice vest caused a greater change inT ¯ sk compared to no cooling (-1.07 [-2.00 to -0.13]°C, p = 0.021) and single-hand cooling (-1.07 [-2.01 to -0.14]°C, p = 0.020), as well as a greater change in S compared to no cooling (-84 [-132 to -37] W, p < 0.0001) and single-hand cooling (-74 [-125 to -24] W, p = 0.002). Across REC0-60, changes inT ¯ b (-0.38 [-0.69 to -0.07]°C, p = 0.012) andT ¯ sk (-1.62 [-2.56 to -0.68]°C, p < 0.0001) were greater with ice vest compared to no cooling. Furthermore, changes in inT ¯ b (-0.39 [-0.70 to -0.08]°C, p = 0.010) andT ¯ sk (-1.68 [-2.61 to -0.74]°C, p < 0.0001) were greater with the ice vest compared to single-hand cooling. Using an ice vest during time-limited and prolonged recovery in the heat aided in a more effective reduction in thermo-physiological strain compared to both passive cooling as well as a single-hand cooling device.

Post-exercise Heart Rate Variability: Whole-body Cryotherapy vs. Contrast Water Therapy

High-intensity training sessions are known to alter cardiac autonomic modulation. The purpose of this study was to compare the effects of whole-body cryotherapy, contrast water therapy and passive recovery on the time course of cardiac autonomic markers following a standardized HIT session. Eleven runners completed a high intensity session followed by one of the following recovery interventions: whole-body cryotherapy, contrast water therapy or passive recovery. Changes in cardiac autonomic modulation were assessed in supine and standing positions during an active tilt test at pre-, post-14 h and post-38 h. In supine, high-frequency power increased from pre- to post-14 h following whole-body cryotherapy (1661.1±914.5 vs. 2799.0±948.4 ms², respectively; p=0.023) and contrast water therapy (1906.1±1327.9 vs. 4174.3±2762.9 ms², respectively; p=0.004) whereas high frequency power decreased in response to passive recovery (p=0.009). In standing, low-frequency power increased from pre-to post-38 h (1784.3 ± 953.7 vs. 3339.8±1862.7 ms², respectively; p=0.017) leading to an increase in total power from pre- to post-38 h (1990.8 ± 1089.4 vs. 3606.1±1992.0 ms², respectively; p=0.017). Spectral analysis revealed that contrast water therapy appears to be a more efficient recovery strategy than whole-body cryotherapy in restoring cardiac autonomic homeostasis.

The beneficial effects of a water-based aerobic exercise session on the blood lipids of women with dyslipidemia are independent of their training status

OBJECTIVES

To evaluate the acute effects of a session of water-based aerobic exercise on the blood lipid levels of women with dyslipidemia and to compare these results according to their training status.

METHOD

Fourteen premenopausal women with dyslipidemia, aged 40-50 years, participated in two water-based aerobic exercise sessions, the first when they were generally sedentary and the second after they were trained with a water-based aerobic training program for 12 weeks. Both experimental sessions were performed using the same protocol, lasted 45 min, and incorporated an interval method, alternating 3 min at a rating of perceived exertion (RPE) of 13 and 2 min at an RPE of 9. Total cholesterol (TC), triglycerides (TG), low-density lipoprotein (LDL), high-density lipoprotein (HDL), and lipoprotein lipase enzyme (LPL) were obtained through venous blood collection before and immediately after each session. A generalized estimating equation method and Bonferroni tests were conducted (with time and training status as factors) for statistical analyses.

RESULTS

At enrollment, the mean age of the participants was 46.57 years (95% confidence interval [CI] 44.81-48.34). The statistical analyses showed a significant time effect for all variables (TC: p=0.008; TG: p=0.012; HDL: p<0.001; LPL: p<0.001) except for LDL (p=0.307). However, the training status effect was not significant for any variable (TC: p=0.527; TG: p=0.899; HDL: p=0.938; LDL: p=0.522; LPL: p=0.737). These results indicate that the TC and TG levels reduced and the HDL and LPL concentrations increased from pre- to post-session in similar magnitudes in both sedentary and trained women.

CONCLUSIONS

A single water-based aerobic exercise session is sufficient and effective to beneficially modify the lipid profile of women with dyslipidemia, regardless of their training status.

Water-Based Aerobic and Resistance Training as a Treatment to Improve the Lipid Profile of Women With Dyslipidemia: A Randomized Controlled Trial

Background: Regular exercise is recommended for the treatment of dyslipidemia. The aquatic environment presents some beneficial characteristics for patients suffering from dyslipidemia. However, it is unknown which modality promotes better results. This study aims to compare the effects of water-based aerobic training (WA) and water-based resistance training (WR) on lipid profile of dyslipidemic elderly women. Methods: Sixty-nine dyslipidemic elderly women participated in this 3-arm randomized controlled clinical trial with groups in parallel. The interventions were WA, WR, and control group, with 2 weekly sessions for 10 weeks. Total cholesterol (TC), triglycerides, low-density lipoprotein, high-density lipoprotein (HDL) levels, and TC/HDL ratio, were determined before and after interventions. Results: Intention-to-treat analysis showed that WA and WR participants obtained similar decreases in TC (-10.0% and -9.6%, respectively), triglycerides (-13.4% and -15.7%, respectively), low-density lipoprotein (-16.1% and -16.9%, respectively), TC/HDL (-16.9% and -23.4%, respectively) and increases in HDL (7.6% and 16.9%, respectively). The control group maintained their TC and low-density lipoprotein levels unchanged, whereas triglycerides and TC/HDL were increased (3.6% and 11.3%, respectively), and HDL decreases 4.8%. Conclusions: WA and WR improve similarly the lipid profile of dyslipidemic elderly women, representing interesting nonpharmacological tools in the treatment of dyslipidemia.

Post-Exercise Whole Body Cryotherapy (-140 °C) Increases Energy Intake in Athletes

PURPOSE

The purpose of the present study was to investigate the effect of whole-body cryotherapy (WBC) treatment after exercise on appetite regulation and energy intake.

METHODS

Twelve male athletes participated in two trials on different days. In both trials, participants performed high-intensity intermittent exercise. After 10 min following the completion of the exercise, they were exposed to a 3-min WBC treatment (-140 °C, WBC trial) or underwent a rest period (CON trial). Blood samples were collected to assess plasma acylated ghrelin, serum leptin, and other metabolic hormone concentrations. Respiratory gas parameters, skin temperature, and ratings of subjective variables were also measured after exercise. At 30 min post-exercise, energy and macronutrient intake were evaluated during an ad libitum buffet meal test.

RESULTS

Although appetite-regulating hormones (acylated ghrelin and leptin) significantly changed with exercise (p = 0.047 for acylated ghrelin and p < 0.001 for leptin), no significant differences were observed between the trials. Energy intake during the buffet meal test was significantly higher in the WBC trial (1371 ± 481 kcal) than the CON trial (1106 ± 452 kcal, p = 0.007).

CONCLUSION

Cold exposure using WBC following strenuous exercise increased energy intake in male athletes.

Thermoneutral immersion exercise accelerates heart rate recovery: A potential novel training modality

This study compared heart rate recovery (HRR) after incremental maximal exercise performed at the same external power output (P_ext) on dry land ergocycle (DE) vs. immersible ergocycle (IE). Fifteen young healthy participants (30 ± 7 years, 13 men and 2 women) performed incremental maximal exercise tests on DE and on IE. The initial P_ext on DE was 25 W and was increased by 25 W/min at a pedalling cadence between 60 and 80 rpm, while during IE immersion at chest level in thermoneutral water (30°C), the initial P_ext deployment was at a cadence of 40 rpm which was increased by 10 rpm until 70 rpm and thereafter by 5 rpm until exhaustion. Gas exchange and heart rate (HR) were measured continuously during exercise and recovery for 5 min. Maximal HR (DE: 176 ± 15 vs. IE 169 ± 12 bpm) reached by the subjects in the two conditions did not differ (P > .05). Parasympathetic reactivation parameters (ΔHR from 10 to 300 s) were compared during the DE and IE HR recovery recordings. During the IE recovery, parasympathetic reactivation in the early phase was more predominant (HRR at Δ10-Δ60 s, P < .05), but similar in the late phase (HRR at Δ120-Δ300 s, P > .05) when compared to the DE condition. In conclusion, incremental maximal IE exercise at chest level immersion in thermoneutral water accelerates the early phase parasympathetic reactivation compared to DE in healthy young participants.

Head Exposure to Cold during Whole-Body Cryostimulation: Influence on Thermal Response and Autonomic Modulation

Recent research on whole-body cryotherapy has hypothesized a major responsibility of head cooling in the physiological changes classically reported after a cryostimulation session. The aim of this experiment was to verify this hypothesis by studying the influence of exposing the head to cold during whole-body cryostimulation sessions, on the thermal response and the autonomic nervous system (ANS). Over five consecutive days, two groups of 10 participants performed one whole-body cryostimulation session daily, in one of two different systems; one exposing the whole-body to cold (whole-body cryostimulation, WBC), and the other exposing the whole-body except the head (partial-body cryostimulation, PBC).10 participants constituted a control group (CON) not receiving any cryostimulation. In order to isolate the head-cooling effect on recorded variables, it was ensured that the WBC and PBC systems induced the same decrease in skin temperature for all body regions (mean decrease over the 5 exposures: -8.6°C±1.3°C and -8.3±0.7°C for WBC and PBC, respectively), which persisted up to 20-min after the sessions (P20). The WBC sessions caused an almost certain decrease in tympanic temperature from Pre to P20 (-0.28 ±0.11°C), while it only decreased at P20 (-0.14±0.05°C) after PBC sessions. Heart rate almost certainly decreased after PBC (-8.6%) and WBC (-12.3%) sessions. Resting vagal-related heart rate variability indices (the root-mean square difference of successive normal R-R intervals, RMSSD, and high frequency band, HF) were very likely to almost certainly increased after PBC (RMSSD:+49.1%, HF: +123.3%) and WBC (RMSSD: +38.8%, HF:+70.3%). Plasma norepinephrine concentration was likely increased in similar proportions after PBC and WBC, but only after the first session. Both cryostimulation techniques stimulated the ANS with a predominance of parasympathetic tone activation from the first to the fifth session and in slightly greater proportion with WBC than PBC. The main result of this study indicates that the head exposure to cold during whole-body cryostimulation may not be the main factor responsible for the effects of cryostimulation on the ANS.

The effect of different water immersion temperatures on post-exercise parasympathetic reactivation

Purpose

We evaluated the effect of different water immersion (WI) temperatures on post-exercise cardiac parasympathetic reactivation.

Methods

Eight young, physically active men participated in four experimental conditions composed of resting (REST), exercise session (resistance and endurance exercises), post-exercise recovery strategies, including 15 min of WI at 15°C (CWI), 28°C (TWI), 38°C (HWI) or control (CTRL, seated at room temperature), followed by passive resting. The following indices were assessed before and during WI, 30 min post-WI and 4 hours post-exercise: mean R-R (mR-R), the natural logarithm (ln) of the square root of the mean of the sum of the squares of differences between adjacent normal R–R (ln rMSSD) and the ln of instantaneous beat-to-beat variability (ln SD1).

Results

The results showed that during WI mRR was reduced for CTRL, TWI and HWI versus REST, and ln rMSSD and ln SD1 were reduced for TWI and HWI versus REST. During post-WI, mRR, ln rMSSD and ln SD1 were reduced for HWI versus REST, and mRR values for CWI were higher versus CTRL. Four hours post exercise, mRR was reduced for HWI versus REST, although no difference was observed among conditions.

Conclusions

We conclude that CWI accelerates, while HWI blunts post-exercise parasympathetic reactivation, but these recovery strategies are short-lasting and not evident 4 hours after the exercise session.

Whole-body cryotherapy: empirical evidence and theoretical perspectives

Whole-body cryotherapy (WBC) involves short exposures to air temperatures below −100°C. WBC is increasingly accessible to athletes, and is purported to enhance recovery after exercise and facilitate rehabilitation postinjury. Our objective was to review the efficacy and effectiveness of WBC using empirical evidence from controlled trials. We found ten relevant reports; the majority were based on small numbers of active athletes aged less than 35 years. Although WBC produces a large temperature gradient for tissue cooling, the relatively poor thermal conductivity of air prevents significant subcutaneous and core body cooling. There is weak evidence from controlled studies that WBC enhances antioxidant capacity and parasympathetic reactivation, and alters inflammatory pathways relevant to sports recovery. A series of small randomized studies found WBC offers improvements in subjective recovery and muscle soreness following metabolic or mechanical overload, but little benefit towards functional recovery. There is evidence from one study only that WBC may assist rehabilitation for adhesive capsulitis of the shoulder. There were no adverse events associated with WBC; however, studies did not seem to undertake active surveillance of predefined adverse events. Until further research is available, athletes should remain cognizant that less expensive modes of cryotherapy, such as local ice-pack application or cold-water immersion, offer comparable physiological and clinical effects to WBC.

Blood pressure regulation IV: adaptive responses to weightlessness

During weightlessness, blood and fluids are immediately shifted from the lower to the upper body segments, and within the initial 2 weeks of spaceflight, brachial diastolic arterial pressure is reduced by 5 mmHg and even more so by some 10 mmHg from the first to the sixth month of flight. Blood pressure thus adapts in space to a level very similar to that of being supine on the ground. At the same time, stroke volume and cardiac output are increased and systemic vascular resistance decreased, whereas sympathetic nerve activity is kept surprisingly high and similar to when ground-based upright seated. This was not predicted from simulation models and indicates that dilatation of the arteriolar resistance vessels is caused by mechanisms other than a baroreflex-induced decrease in sympathetic nervous activity. Results of baroreflex studies in space indicate that compared to being ground-based supine, the carotid (vagal)-cardiac interaction is reduced and sympathetic nerve activity, heart rate and systemic vascular resistance response more pronounced during baroreflex inhibition by lower body negative pressure. The future challenge is to identify which spaceflight mechanism induces peripheral arteriolar dilatation, which could explain the decrease in blood pressure, the high sympathetic nerve activity and associated cardiovascular changes. It is also a challenge to determine the cardiovascular risk profile of astronauts during future long-duration deep space missions.

Parasympathetic activity and blood catecholamine responses following a single partial-body cryostimulation and a whole-body cryostimulation

The aim of this study was to compare the effects of a single whole-body cryostimulation (WBC) and a partial-body cryostimulation (PBC) (i.e., not exposing the head to cold) on indices of parasympathetic activity and blood catecholamines. Two groups of 15 participants were assigned either to a 3-min WBC or PBC session, while 10 participants constituted a control group (CON) not receiving any cryostimulation. Changes in thermal, physiological and subjective variables were recorded before and during the 20-min after each cryostimulation. According to a qualitative statistical analysis, an almost certain decrease in skin temperature was reported for all body regions immediately after the WBC (mean decrease±90% CL, -13.7±0.7°C) and PBC (-8.3±0.3°C), which persisted up to 20-min after the session. The tympanic temperature almost certainly decreased only after the WBC session (-0.32±0.04°C). Systolic and diastolic blood pressures were very likely increased after the WBC session, whereas these changes were trivial in the other groups. In addition, heart rate almost certainly decreased after PBC (-10.9%) and WBC (-15.2%) sessions, in a likely greater proportion for WBC compared to PBC. Resting vagal-related heart rate variability indices (the root-mean square difference of successive normal R-R intervals, RMSSD, and high frequency band, HF) were very likely increased after PBC (RMSSD: +54.4%, HF: +138%) and WBC (RMSSD: +85.2%, HF: +632%) sessions without any marked difference between groups. Plasma norepinephrine concentrations were likely to very likely increased after PBC (+57.4%) and WBC (+76.2%), respectively. Finally, cold and comfort sensations were almost certainly altered after WBC and PBC, sensation of discomfort being likely more pronounced after WBC than PBC. Both acute cryostimulation techniques effectively stimulated the autonomic nervous system (ANS), with a predominance of parasympathetic tone activation. The results of this study also suggest that a whole-body cold exposure induced a larger stimulation of the ANS compared to partial-body cold exposure.

Effect of recovery mode on postexercise vagal reactivation in elite synchronized swimmers

This study investigated the effect of whole-body cryostimulation (WBC), contrast-water therapy (CWT), active recovery (ACT), and passive condition (PAS) protocols on the parasympathetic reactivation and metabolic parameters of recovery in elite synchronized swimmers who performed 2 simulated competition ballets (B1 and B2) separated by 70 min. After determining maximal oxygen consumption (V̇O(2max400)) and blood lactate concentrations ([La(-)](b400)) during a 400-m swim trial, 11 swimmers performed 1 protocol per week in randomized order. Heart rate variability (HRV) was measured at rest (PreB1), 5 min after B1 (PostB1), before B2 (PreB2), and 5 min after B2 (PostB2). V̇O(2peak) was measured at PostB1 and PostB2, and [La(-)](b) was measured at PostB1, PreB2, and PostB2. PostB1 V̇O(2peak) and V̇O(2max400) were similar, but PostB1 [La(-)](b) was higher than [La(-)](b400) (p = 0.004). Each ballet caused significant decreases in HRV indices. At PreB2, all HRV indices had returned to PreB1 levels in the CWT, PAS, and ACT protocols, whereas the WBC protocol yielded a 2- to 4-fold increase in vagal-related HRV indices, compared with PreB1. WBC and ACT both increased [La(-)](b) recovery, compared with PAS (p = 0.06 and p = 0.04, respectively), and yielded an increased V̇O(2peak) from B1 to B2; however, it decreased after PAS (+5.4%, +3.4%, and -3.6%; p < 0.01). This study describes the physiological response to repeated maximal work bouts that are highly specific to elite synchronized swimming. In the context of short-term recovery, WBC yields a strong parasympathetic reactivation, and shows similar effectiveness to ACT on the metabolic parameters of recovery and subsequent exercise capacity.

Effect of cold or thermoneutral water immersion on post-exercise heart rate recovery and heart rate variability indices

This study aimed to investigate the effect of cold and thermoneutral water immersion on post-exercise parasympathetic reactivation, inferred from heart rate (HR) recovery (HRR) and HR variability (HRV) indices. Twelve men performed, on three separate occasions, an intermittent exercise bout (all-out 30-s Wingate test, 5 min seated recovery, followed by 5 min of submaximal running exercise), randomly followed by 5 min of passive (seated) recovery under either cold (CWI), thermoneutral water immersion (TWI) or control (CON) conditions. HRR indices (e.g., heart beats recovered in the first minute after exercise cessation, HRR(60)(s)) and vagal-related HRV indices (i.e., natural logarithm of the square root of the mean of the sum of the squares of differences between adjacent normal R-R intervals (Ln rMSSD)) were calculated for the three recovery conditions. HRR(60)(s) was faster in water immersion compared with CON conditions [30+/-9 beats min(-)(1) for CON vs. 43+/- 10 beats min(-)(1) for TWI (P=0.003) and 40+/-13 beats min(-)(1) for CWI (P=0.017)], while no difference was found between CWI and TWI (P=0.763). Ln rMSSD was higher in CWI (2.32+/-0.67 ms) compared with CON (1.98+/-0.74 ms, P=0.05) and TWI (2.01+/-0.61 ms, P=0.08; aES=1.07) conditions, with no difference between CON and TWI (P=0.964). Water immersion is a simple and efficient means of immediately triggering post-exercise parasympathetic activity, with colder immersion temperatures likely to be more effective at increasing parasympathetic activity.

Effects of musical cadence in the acute physiologic adaptations to head-out aquatic exercises

The purpose of this study was to analyze the relationships between musical cadence and the physiologic adaptations to basic head-out aquatic exercises. Fifteen young and clinically healthy women performed, immersed to the breast, a cardiovascular aquatic exercise called the "rocking horse." The study design included an intermittent and progressive protocol starting at a 90 b.min(-1) rhythm and increasing every 6 minutes, by 15 b.min(-1), up to 195 b.min(-1) or exhaustion. The rating of perceived effort (RPE) at the maximal heart rate achieved during each bout (HRmax), the percentage of the maximal theoretical heart rate estimated (%HRmax), and the blood lactate concentration ([La-]) were evaluated. The musical cadence was also calculated at 4 mmol.L(-1) of blood lactate (R4), the RPE at R4 (RPE@R4), the HR at R4 (HR@R4), and the %HRmax at R4 (%HRmax@R4). Strong relationships were verified between the musical cadence and the RPE (R2 = 0.85; p < 0.01), the HRmax (R2 = 0.66; p < 0.01), the %HRmax (R = 0.61; p < 0.01), and the [La-] (R2 = 0.54; p < 0.01). The R4 was 148.13 +/- 17.53 b.min, the RPE@R4 was 14.53 +/- 2.53, the HR@R4 was 169.33 +/- 12.06 b.min, and the %HRmax@R4 was 85.53 +/- 5.72%. The main conclusion is that increasing musical cadence created an increase in the physiologic response. Therefore, instructors must choose musical cadences according to the goals of the session they are conducting to achieve the desired intensity.

Effect of cold water immersion on postexercise parasympathetic reactivation

The aim of the present study was to assess the effect of cold water immersion (CWI) on postexercise parasympathetic reactivation. Ten male cyclists (age, 29 +/- 6 yr) performed two repeated supramaximal cycling exercises (SE(1) and SE(2)) interspersed with a 20-min passive recovery period, during which they were randomly assigned to either 5 min of CWI in 14 degrees C or a control (N) condition where they sat in an environmental chamber (35.0 +/- 0.3 degrees C and 40.0 +/- 3.0% relative humidity). Rectal temperature (T(re)) and beat-to-beat heart rate (HR) were recorded continuously. The time constant of HR recovery (HRRtau) and a time (30-s) varying vagal-related HR variability (HRV) index (rMSSD(30s)) were assessed during the 6-min period immediately following exercise. Resting vagal-related HRV indexes were calculated during 3-min periods 2 min before and 3 min after SE(1) and SE(2). Results showed no effect of CWI on T(re) (P = 0.29), SE performance (P = 0.76), and HRRtau (P = 0.61). In contrast, all vagal-related HRV indexes were decreased after SE(1) (P < 0.001) and tended to decrease even further after SE(2) under N condition but not with CWI. When compared with the N condition, CWI increased HRV indexes before (P < 0.05) and rMSSD(30s) after (P < 0.05) SE(2). Our study shows that CWI can significantly restore the impaired vagal-related HRV indexes observed after supramaximal exercise. CWI may serve as a simple and effective means to accelerate parasympathetic reactivation during the immediate period following supramaximal exercise.

Spinal cord transection inhibits HR reduction in anesthetized rats immersed in an artificial CO2-hot spring bath

Like humans, the heart rate (HR) of anesthetized rats immersed in CO(2)-water is lower than that when immersed in tap water at the same temperature. To investigate the afferent signal pathway in the mechanism of HR reduction, Wistar rats were anesthetized with urethane and then the spinal cord was transected between T(4) and T(5). The animals were immersed up to the axilla in a bathtub of tap-water (CO(2) contents: 10-20 mg.l(-1)) or of CO(2)-water (965-1,400 mg.l(-1)) at 35 degrees C while recording HR, arterial blood pressure, and arterial blood gas parameters (PaCO(2), PaO(2), pH). Arterial blood gas parameters did not change during immersion, irrespective of CO(2) concentration of the bath water, whereas the HR was reduced in the CO(2)-water bath. The inhalation of CO(2)-mixed gas (5% CO(2), 20% O(2), 75% N(2)) resulted in increased levels of blood gases and an increased HR during immersion in all types of water tested. The HR reduction observed in sham transected control animals immersed in CO(2)-water disappeared after subsequent spinal cord transection. These results show that the dominant afferent signal pathway to the brain, which is involved in inducing the reduced HR during immersion in CO(2)-water, is located in the neuronal route and not in the bloodstream.

Immersion in warm water induces improvement in cardiac function in patients with chronic heart failure

BACKGROUND

The effects of immersion and training of patients with chronic heart failure (CHF) in warm water has not been thoroughly investigated. The aim of this study was to assess the acute hemodynamic response of immersion and peripheral muscle training in elderly patients with CHF.

METHODS

Thirteen CHF patients and 13 healthy subjects underwent echocardiography on land and in a temperature-controlled swimming pool (33-34 degrees C).

RESULTS

Rest. Heart rate decreased (CHF, p=0.01; control, p=0.001) and stroke volume increased (CHF, p=0.01; control, p=0.001) during water immersion in both groups, with no change in systolic or diastolic blood pressure. Ejection fraction (p<0.05) and transmitral Doppler E/A ratio (p=0.01) increased in the CHF group, with no changes in left ventricular volumes. The healthy subjects had similar responses, but also displayed an increase in cardiac output (p<0.01) and left ventricular volumes (p<0.001). Exercise. Cardiac output and systolic blood pressure increased significantly in water, in both groups.

CONCLUSION

A general increase in early diastolic filling was accompanied by a decrease in heart rate, leading to an increase in stroke volume and ejection fraction in most patients with CHF during warm water immersion. These beneficial hemodynamic effects might be the reason for the previously observed good tolerability of this exercise regime.

Atrial distension, arterial pulsation, and vasopressin release during negative pressure breathing in humans

During an antiorthostatic posture change, left atrial (LA) diameter and arterial pulse pressure (PP) increase, and plasma arginine vasopressin (AVP) is suppressed. By comparing the effects of a 15-min posture change from seated to supine with those of 15-min seated negative pressure breathing in eight healthy males, we tested the hypothesis that with similar increases in LA diameter, suppression of AVP release is dependent on the degree of increase in PP. LA diameter increased similarly during the posture change and negative pressure breathing (-9 to -24 mmHg) from between 30 and 31 +/- 1 to 34 +/- 1 mm (P < 0.05). The increase in PP from 38 +/- 2 to 44 +/- 2 mmHg (P < 0.05) was sustained during the posture change but only increased during the initial 5 min of negative pressure breathing from 36 +/- 3 to 42 +/- 3 mmHg (P < 0.05). Aortic transmural pressure decreased during the posture change and increased during negative pressure breathing. Plasma AVP was suppressed to a lower value during the posture change (from 1.5 +/- 0.3 to 1.2 +/- 0.2 pg/ml, P < 0.05) than during negative pressure breathing (from 1.5 +/- 0.3 to 1.4 +/- 0.3 pg/ml). Plasma norepinephrine was decreased similarly during the posture change and negative pressure breathing compared with seated control. In conclusion, the results are in compliance with the hypothesis that during maneuvers with similar cardiac distension, suppression of AVP release is dependent on the increase in PP and, furthermore, probably unaffected by static aortic baroreceptor stimulation.

Central volume expansion is pivotal for sustained decrease in heart rate during seated to supine posture change

During prolonged, static carotid baroreceptor stimulation by neck suction (NS) in seated humans, heart rate (HR) decreases acutely and thereafter gradually increases. This increase has been explained by carotid baroreceptor adaptation and/or buffering by aortic reflexes. During a posture change from seated to supine (Sup) with similar carotid stimulation, however, the decrease in HR is sustained. To investigate whether this discrepancy is caused by changes in central blood volume, we compared (n = 10 subjects) the effects of 10 min of seated NS (adjusted to simulate carotid stimulation of a posture change), a posture change from seated to Sup, and the same posture change with left atrial (LA) diameter maintained unchanged by lower body negative pressure (Sup + LBNP). During Sup, the prompt decreases in HR and mean arterial pressure (MAP) were sustained. HR decreased similarly within 30 s of NS (65 +/- 2 to 59 +/- 2 beats/min) and Sup + LBNP (65 +/- 2 to 58 +/- 2 beats/min) and thereafter gradually increased to values of seated. MAP decreased similarly within 5 min during Sup + LBNP and NS (by 7 +/- 1 to 9 +/- 1 mmHg) and thereafter tended to increase toward values of seated subjects. Arterial pulse pressure was increased the most by Sup, less so by Sup + LBNP, and was unchanged by NS. LA diameter was only increased by Sup. In conclusion, static carotid baroreceptor stimulation per se causes the acute (<30 s) decrease in HR during a posture change from seated to Sup, whereas the central volume expansion (increased LA diameter and/or arterial pulse pressure) is pivotal to sustain this decrease. Thus the effects of central volume expansion override adaptation of the carotid baroreceptors and/or buffering of aortic reflexes.