Beyond freezing: unveiling physiological transformations triggered by a cryochamber exposure
CC BY-NC-SA 4.0
Beyond freezing: unveiling physiological transformations triggered by a cryochamber exposure
CC BY-NC-SA 4.0
Introduction
Cryotherapy is mainly used to relieve symptoms of musculoskeletal injuries and during recovery in athletes. Cryotherapy aims to improve various symptoms, such as pain and swelling.1 The popularity of cold therapy has been constantly rising and it has been widely recommended as treatment for numerous medical afflictions, such as arthritis, fibromyalgia, or cutaneous lesions.2
Cryotherapy aims to cool the body for therapeutic reasons. Even though there are a few variations of cryotherapy, the most popular one is whole‑body cryotherapy (WBC), which takes place in a special chamber. A cryochamber session typically involves entering a specially designed chamber with dry air, with temperature lowered to subzero levels (with usual range of temperature from –110 °C to –140 °C) for about 2 to 3 minutes. The exposure to extreme cold is believed to stimulate various physiological responses.3
As any other medical procedure, WBC has its indications and contraindications. The contraindications to WBC include, for example, Raynaud’s disease, hypothyroidism, acute respiratory disorders, cardiovascular diseases (unstable angina, cardiac failure stages III and IV according to the New York Heart Association [NYHA]), or sympathetic nervous system neuropathies.1 When conducted in suitable and controlled conditions, WBC is a safe procedure, as evidenced by studies showing no harmful effects on lung4 or heart function.5 Nonetheless, it is worth noting that there have been rare instances of a minor and clinically insignificant rise in systolic blood pressure, warranting caution in patients with cardiovascular conditions.6 Despite extensive utilization of cryotherapy in sports medicine, a limited number of studies have focused on investigating its impact on cardiovascular performance and autonomic regulation among nonathletes.
This study aimed to investigate safety and comprehensive physiological effects of exposure to extremely low temperatures, with a focus on cardiovascular performance and autonomic regulation.
Patients and methods
The study was approved by the bioethics committee at the Jan Kochanowski University in Kielce, Poland (42/2019). All participants provided their written consent after being informed about potential risks and benefits associated with the study.
The study involved 108 adults who did not have any contraindications to cryotherapy, including a history of cardiovascular disease. Before enrollment, medical history was taken and physical examination performed. The exclusion criteria consisted of the main contraindications to cryochamber therapy. The primary indications for cryotherapy in our study group included chronic spinal pain, osteoarthritis, neuralgia, and post‑traumatic conditions of the musculoskeletal system, such as sprains and strains. Our patients exhibited a few cardiovascular risk factors, namely cigarette smoking (n = 31; 28.7%), overweight (n = 45; 41.7%), and obesity (n = 21; 19.4%). All eligible patients from the surrounding region were included in the study.
To acclimate and perform necessary qualification for the procedure, the patients were advised to arrive at the cryotherapy center 30 minutes before their session. During the session, the participants were instructed to wear minimal clothing that included a tank top, shorts, a surgical mask, a cap, woolen gloves, socks, and wooden clogs. They spent a total of 3 minutes inside the cryochamber. The first 30 seconds they remained adapting in an antechamber, where the temperature was around –60 °C. Afterward, they moved into the main chamber, where the temperature ranged between –100 °C and –140 °C. All tests were performed before and immediately after the cryostimulation sessions (before physical exercises), and did not exceed 2 minutes.
The following parameters with recognized prognostic and arrhythmogenic significance were included in the study: 1) electrocardiographic (ECG) parameters such as heart rate (HR), the QTc interval, and the QRS duration; 2) spatial QRS‑T angle as a predictor of cardiac disease risk, including sudden cardiac death (SCD); 3) index of cardiac electrophysiological balance (iCEB) as a predictor of ventricular arrhythmia; and 4) subendocardial viability ratio (SEVR) as a reflection of subendocardial perfusion. A simplified equation used to determine the SEVR is presented below,
where DD denotes diastole duration; dPTI, diastolic pressure time index; LVEDP, left ventricular end‑diastolic pressure; LVET, left ventricular ejection time; MdBP, mean diastolic blood pressure; MsBP, mean systolic blood pressure; sPTI, systolic pressure time index; and SEVR, subendocardial viability ratio.
Cardiac device (IMED Co Ltd., Budapest, Hungary) was used to assess the ECG parameters. The Kors method was employed to estimate the spatial QRS‑T angle. Additionally, we included other cardiovascular parameters, such as brachial systolic pressure, brachial diastolic pressure, central systolic pressure, central diastolic pressure, central pulse pressure, central mean pressure, central augmentation pressure, central augmentation index, ejection duration, and systolic and diastolic mean arterial pressure, which were estimated using an AtCor SphygmoCor XCEL device (SphygmoCor, AtCor Medical, Sydney, Australia). Masimo Root system with a SEDLine monitor (Irvine, California, United States) was used to measure oxygen saturation.
Statistical analysis
Descriptive statistics were used to summarize the data. Continuous variables are presented as mean and SD for normally distributed data, or as median with interquartile range (IQR) for non‑normally distributed data. The distribution of the variables was tested with the Shapiro–Wilk test. Only the distribution of SEVR changes was normal; therefore, in this case, the dependent group t test was used. For all other comparisons, the Wilcoxon signed‑rank test was performed. A P value below 0.05 was considered significant. All analyses were performed using TIBCO (2017) and Statistica software version 13 (TIBCO Software Inc., Palo Alto, California, United States). We calculated the minimum sample size required to ensure a test power of 80%, assuming a specific effect size (delta) and a significance level of 5%. Assuming delta equal to or above 0.28, the sample size obtained for the 2‑sided Wilcoxon test and the paired t test was 107 and 103 participants, respectively. For the majority of parameters (15 out of 18), the desired test power was guaranteed, as the study sample consisted of 108 patients. For 3 parameters (spatial QRS‑T angle, iCEB, and QRS duration), the test power was below 80% for this sample size. The minimum sample size and a posteriori test power were calculated using G*Power 3.1.9.4 package (Heinrich‑Heine‑Universität Düsseldorf, Düsseldorf, Germany).
Results
The study included 72 women (66.67%) and 36 men (33.33%). Mean (SD) age of the participants was 50.83 (11.29) years. The youngest participant was 31, and the oldest 78 years old.
We observed significant changes in 4 of the measured parameters. However, there were no significant differences between men and women. SEVR (P <0.001) and the QRS time (P = 0.003) increased after treatment in the whole group. The parameters, whose values decreased after the cryochamber session were iCEB (P <0.001) and QTc interval (P <0.001). All results before and after the cryochamber session are shown in Table 1.
Parameter | Before a cryochamber session | After a cryochamber session | Difference (∆) | P value |
Data are presented as mean (SD) or median (IQR).
Delta represents differences between pre- and postcryochamber session values.
Abbreviations: iCEB, index of cardioelectrophysiological balance; IQR, interquartile range, MAP, mean arterial pressure; SEVR, subendocardial viability ratio | ||||
Oxygen saturation, % | 96 (95.5–98) | 97 (96–99) | 1 (–1 to 1) | <0.001 |
Brachial systolic pressure, mm Hg | 137.5 (128.5–154) | 141 (127.5–155.5) | 2.5 (–6.5 to 8) | 0.17 |
Brachial diastolic pressure, mm Hg | 86 (77–90.5) | 83.5 (77–89) | –1 (–6 to 3.5) | 0.09 |
Heart rate, bpm | 70.5 (66–81) | 67 (62–78.5) | –4 (–7 to –1) | <0.001 |
Central systolic pressure, mm Hg | 127 (116–141) | 128.5 (115.5–141.5) | 1 (–5 to 6) | 0.19 |
Central diastolic pressure, mm Hg | 86 (78–94) | 85 (79–90) | –1 (–5 to 3) | 0.28 |
Central pulse pressure, mm Hg | 39 (34–52) | 43.5 (37–52.5) | 2 (–4.5 to 7) | 0.02 |
Central mean pressure, mm Hg | 104 (94.5–113) | 101.5 (95–110) | –0.5 (–5 to 3.5) | 0.19 |
Central augmentation pressure, mm Hg | 13.5 (9–21) | 15 (9–24) | 7 (–6.5 to 15.5) | 0.006 |
Central augmentation index, mm Hg | 34 (24.5–39.5) | 32 (24–40) | 1 (–3.5 to 5) | 0.11 |
MAP systole, mm Hg | 117 (107.5–127) | 117.5 (105.5–127.5) | 1.5 (–5 to 4.5) | 0.29 |
MAP diastole, mm Hg | 97 (86.5–105) | 93.5 (88.5–100.5) | –0.5 (–4 to 3) | 0.61 |
QRS duration, ms | 96 (90–102) | 96 (92–105) | 0 (–2 to 4) | 0.003 |
QTc interval, ms | 432.5 (420–443) | 427.5 (411–437.5) | –6 (–17 to 1) | <0.001 |
Ejection duration, ms | 319.5 (307–347) | 332 (314–344) | 8 (–5 to 14.5) | 0.002 |
SEVR, % | 126.11 (23.7) | 133.97 (23.05) | 7.86 (23.81) | <0.001 |
Spatial QRS‑T angle, ° | 15 (10.23–23.94) | 17.26 (10.34–24.77) | 0.08 (–3.5 to 5.6) | 0.07 |
iCEB | 4.44 (4.18–4.9) | 4.35 (4.02–4.72) | –0.1 (–0.25 to 0.04) | <0.001 |
Discussion
To the best of our knowledge, this is the first study to comprehensively show the effects of cold exposure in a cryochamber on the cardiovascular system, especially the vascular changes of the myocardium itself. Our study brought about 2 major findings. Firstly, we observed a significant increase in the SEVR, and secondly, we confirmed safety of a cryochamber session for healthy participants due to its lack of effects on the ECG‑derived markers.
SEVR is a noninvasive measure of myocardial perfusion calculated using pulse wave analysis. SEVR reflects the balance between myocardial oxygen supply and demand, and indicates the efficiency and effectiveness of the heart’s pumping action.7 A lower SEVR value indicates reduced subendocardial perfusion, and is associated with impaired myocardial performance, suggesting reduced cardiac output and potential dysfunction.8 Conversely, a higher SEVR value suggests an improvement in myocardial function and cardiac performance.9
Surprisingly, we noted an increase in the SEVR after the cold exposure. This finding is particularly interesting, as cold is a well‑known trigger for symptoms indicative of ischemia in patients with cardiovascular diseases (CVDs), such as coronary artery disease.10 This pathomechanism is associated with an increase in blood pressure, which is a component of afterload. As is well known, an increase in afterload increases the heart’s workload and oxygen demand, which can trigger the symptoms of myocardial ischemia. This is why CVDs (eg, unstable angina, cardiac failure of NYHA stage III and IV) are contraindications to cryotherapy.1 Transport of blood, supplying the heart with nutrients and oxygen, takes place during diastole. Prolongation in the ejection duration suggests an improvement in cardiac performance after a cryochamber session. This finding may indicate enhancement in ventricular contractility, arterial compliance, and vascular resistance as a result of cryotherapy. Complete understanding of this dependency mechanism and determining its potential clinical relevance require further investigation. It is crucial to note that the results of our study conducted in healthy individuals cannot be directly extrapolated to other populations, especially those afflicted with various diseases, particularly cardiac conditions.
The session in the cryochamber did not significantly affect the parameters assessed on the ECG. We noted an elongation of the QRS duration time (P = 0.003) after the cryochamber session. Its maximum value reached approximately 99.11 mm. However, the QRS elongation did not exceed the pathologic value, so this may not be a clinically relevant increase. Additionally, we did not observe a significant change in the spatial QRS‑T angle. It is a measure of myocardial inhomogeneity, and is thought to be an independent and significant predictor of CVDs and all‑cause mortality, including SCD, as confirmed by numerous studies.11-18 Our study showed that the cryochamber session did not affect the QRS‑T angle, which indirectly proves the safety of this procedure in terms of SCD in healthy individuals.
iCEB is a relatively new noninvasive marker of ventricular arrhythmias, and it is measured by dividing the QT interval by the QRS duration. iCEB reflects the balance between the repolarization and depolarization, and is thought to be a prognostic factor of cardiac wavelength. A high iCEB value indicates a relatively longer QT interval, as compared with the QRS duration, which may suggest an increased risk of torsades de pointes (TdP). Reduced iCEB value may indicate a non‑TdP mediated ventricular tachycardia (VT) or ventricular fibrillation. In our study, we noticed a decrease in the iCEB values after the cryochamber session. However, they remained within the range of reference (3.14–5.35).19 Consequently, we observed a decrease in the values of QTc after the cryochamber session, which indirectly suggests a reduced risk for polymorphic VT, also known as TdP.20
Moreover, it is worth noting that our results may identify the potential effects of cryochamber exposure on autonomic regulation. The decrease in HR and changes in the abovementioned parameters suggest a modulation of the sympathetic‑parasympathetic balance. Based on the study by Mäkinen et al,21 a short whole‑body exposure to cold may lead to increased parasympathetic activity and, consequently, blunted sympathetic response, resulting in improved cardiac efficiency.21 Additionally, Chiang et al22 stated that consumption of cold liquids may also activate the parasympathetic nervous system in healthy individuals.
We observed a significant increase in oxygen saturation following the cryochamber session. This suggests that a cryochamber exposure may enhance oxygen delivery to tissues. The improvement in oxygen saturation could be attributed to various factors, such as increased blood flow or enhanced microcirculation. It can also be caused by the physical conditions of the cryochamber and the specific composition of the air used during the procedure. It should also be noted that cold air can expand in the lungs under the influence of body heat and that gases dissolve better in a cold environment.4
Limitations
Our study has some limitations. The relatively small sample size and the short‑term nature of the intervention are 2 limitations that must be considered. Moreover, we focused only on selected examinations with a relatively short execution time due to the upcoming exercises after the cryochamber session. Additionally, we acknowledge that some of the estimated parameters are not widely used in clinical practice; however, there is a growing interest in scientific research on these variables. Further studies in larger groups and longer follow‑up would be beneficial to validate and expand our findings.
Conclusions
Our study confirmed that a single cryochamber session does not affect ECG‑related parameters associated with adverse cardiovascular events. Thus, a cryochamber session seems to be a safe procedure in healthy individuals. However, the surprising improvement in the SEVR induced by cold exposure requires further studies to confirm the pathomechanism and clinical significance of this finding.
- Lombardi G, Ziemann E, Banfi G. Whole‑body cryotherapy in athletes: from therapy to stimulation. An updated review of the literature. Front Physiol. 2017; 8: 1‑16. | Crossref
- Coppi F, Pinti M, Selleri V, et al. Cardiovascular effects of whole‑body cryotherapy in non‑professional athletes. Front Cardiovasc Med. 2022; 9: 1‑8. | Crossref
- Bleakley C, Bieuzen F, Davison G, Costello J. Whole‑body cryotherapy: empirical evidence and theoretical perspectives. Open Access J Sport Med. 2014; 5: 25‑26. | Crossref
- Smolander J, Westerlund T, Uusitalo A, et al. Lung function after acute and repeated exposures to extremely cold air (−110 °C) during whole‐body cryotherapy. Clin Physiol Funct Imaging. 2006; 26: 232‑234. | Crossref
- Banfi G, Melegati G, Barassi A, D’Eril GM. Effects of the whole‑body cryotherapy on NTproBNP, hsCRP and troponin I in athletes. J Sci Med Sport. 2009; 12: 609‑610. | Crossref
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