Cold shock response

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Cold shock response is a series of neurogenic cardio-respiratory responses caused by sudden immersion in cold water.

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In cold water immersions, such as by falling through thin ice, cold shock response is perhaps the most common cause of death. [1] Also, the abrupt contact with very cold water may cause involuntary inhalation, which, if underwater, can result in fatal drowning.

Death which occurs in such scenarios is complex to investigate and there are several possible causes and phenomena that can take part. The cold water can cause heart attack due to severe vasoconstriction, [2] where the heart has to work harder to pump the same volume of blood throughout the arteries. For people with pre-existing cardiovascular disease, the additional workload can result in myocardial infarction and/or acute heart failure, which ultimately may lead to a cardiac arrest. A vagal response to an extreme stimulus as this one, may, in very rare cases, render per se a cardiac arrest. Hypothermia and extreme stress can both precipitate fatal tachyarrhythmias. A more modern view suggests that an autonomic conflict — sympathetic (due to stress) and parasympathetic (due to the diving reflex) coactivation — may be responsible for some cold water immersion deaths. Gasp reflex and uncontrollable tachypnea can severely increase the risk of water inhalation and drowning. [3]

Some people are much better prepared to survive sudden exposure to very cold water due to body and mental characteristics and due to conditioning. [1] In fact, cold water swimming (also known as ice swimming or winter swimming) is a sport and an activity that reportedly can lead to several health benefits when done regularly. [4]

Physiological response

Cold water immersion syndrome — four-stage model

The physiological response to a sudden immersion in cold water may be divided in three or four discrete stages, with different risks and physiological changes, all being part of an entity labelled as Cold Water Immersion Syndrome. Although this process is a continuum, the 4 phases was initially described in the 1980s as follows: [3] [4]

PhaseTimePhysiological Changes
Initial (cold shock)First 2 – 3 minutesCooling of the skin, hyperventilation, tachycardia, gasp reflex
Short-termAfter 3 minutesSuperficial neuromuscular cooling
Long-termAfter 30 minHypothermia, later collapse
Circum-rescue collapse (afterdrop)Immediately before, during or after rescueCardiac arrythmia, hemostasis, unconsciousness

The first stage of cold water immersion syndrome, the cold shock response, includes a group of reflexes lasting under 5 min in laboratory volunteers and initiated by thermoreceptors sensing rapid skin cooling. Water has a thermal conductivity 25 times and a volume-specific heat capacity over 3000 times that of air; subsequently, surface cooling is precipitous. The primary components of the cold shock reflex include gasping, tachypnea, reduced breath-holding time, and peripheral vasoconstriction, the latter effect highlighting the presumed physiologic principle (i.e., warmth preservation via central blood shunting). The magnitude of the cold shock response parallels the cutaneous cooling rate, and its termination is likely due to reflex baroreceptor responses or thermoreceptor habituation.

Diving reflex

The diving reflex is a set of physiological responses that occur in response to cold water immersion, particularly when the face or body is exposed to cold water. It is an evolutionary adaptation that helps mammals, including humans, manage the challenges of being submerged in cold water. The diving reflex is more pronounced in aquatic mammals and is thought to have originated as a way to conserve oxygen and enhance the ability to stay underwater for longer periods.

Key components of the diving reflex include:

  1. Bradycardia: The heart rate decreases significantly when the face is exposed to cold water. This helps to conserve oxygen by slowing down the heartbeat. The degree of bradycardia can vary among individuals, but it is a common and well-documented response.
  2. Peripheral Vasoconstriction: Blood vessels in the extremities constrict, reducing blood flow to the limbs. This shunting of blood helps to redirect it to essential organs, such as the heart and brain, preserving oxygen for vital functions.
  3. Apnea: The diving reflex triggers an involuntary breath-holding response (apnea). This allows individuals to hold their breath for longer periods, enhancing their ability to stay submerged without the immediate need to breathe.
  4. Blood Redistribution: The body redistributes blood flow, prioritizing essential organs and minimizing blood flow to non-essential areas, such as the skin and muscles. This redistribution helps to conserve heat and oxygen.

While the diving reflex is more pronounced in some mammals, its presence in humans is well-documented, particularly in cold water situations. The reflex is more prominent in infants and young children but can be observed in individuals of all ages. [3]

Cardiac arrhythmias and autonomic conflict

Early models of cold water immersion syndrome focused primarily on sympathetic responses, however recent research suggests sympathetic and parasympathetic coactivation (leading to a conflict of the autonomic system response) may be responsible for some cold water immersion deaths. Although reciprocal activation between sympathetic (cold shock) and parasympathetic (diving response) systems is commonly adaptive (follow one another), simultaneous activation appears to be associated with arrythmya. Cold water induced rhythm disturbances are common, albeit frequently asymptomatic. In most humans, head-out cold-water immersion results in sympathetically driven tachycardia with variable disturbances. These cold water immersion induced arrythmias appear to be accentuated by parasympathetic stimulation resulting from facial submersion or breath holding. Even vagally dominant diving bradycardia caused by isolated cold water facial immersion frequently is interrupted by supraventricular arrhythmias or premature beats. In theory, atrioventricular blockade or sinus arrest due to profound parasympathetic dominance might result in syncope or sudden cardiac death, but these rhythms tend to be rapidly reversed by lung stretch receptor activation associated with breathing. As such, a vagally produced arrest scenario is likelier during entrapment submersion than in flush drowning. [3] [4]

Conditioning against cold shock

It is possible to undergo physiological conditioning to reduce the cold shock response, and some people are naturally better suited to swimming in very cold water. Beneficial adaptations include the following:

  1. having an insulating layer of body fat covering the limbs and torso; [1]
  2. ability to experience immersion without involuntary physical shock or mental panic; [1]
  3. ability to resist shivering; [1]
  4. ability to raise metabolism (and, in some cases, increase blood temperature slightly above the normal level);[ citation needed ]
  5. a generalized delaying of metabolic shutdown (including slipping into unconsciousness) as central and peripheral body temperatures fall.[ citation needed ]

Benefits and Risks of cold water immersion

Cold water immersion tactics are often employed by athletes to speed up muscle recovery and reduce inflammation and soreness after intense exercise or after trauma. [5]

There are several reported benefits from regular ice swimming, namely: [4]

Cold water swimming still poses a significant health risk for inexperienced and untrained swimmers. It is recommended that in order to fully benefit from the metabolic and thermogenic effects of cold water swimming, a grade and progressive acclimatization program is required and preferably done under supervisor.

Cold shock response in other organisms

Cold shock in mammals

Cold shock has been described in several species and at least part of the physiology is similar, as described above in the Diving Reflex.

Cold shock in bacteria

A cold shock is when bacteria undergo a significant reduction in temperature, likely due to their environment dropping in temperature. To constitute as a cold shock the temperature reduction needs to be both significant, for example dropping from 37 °C to 20 °C, and it needs to happen over a short period of time, traditionally in under 24 hours. [6] Both prokaryotic and eukaryotic cells are capable of undergoing a cold shock response. [7] The effects of a cold shock in bacteria include: [8]

The bacteria uses the cytoplasmic membrane, RNA/DNA, and ribosomes as cold sensors in the cell, placing them in charge of monitoring the cell's temperature. [7] Once these sensors send the signal that a cold shock is occurring, the bacteria will pause the majority of protein synthesis in order to redirect its focus to producing what are called cold shock proteins (Csp). [9] The volume of the cold shock proteins produced will depend on the severity of the temperature decrease. [10] The function of these cold shock proteins is to assist the cell in adapting to the sudden temperature change, allowing it to maintain as close to a normal level of function as possible. [7]

One way cold shock proteins are thought to function is by acting as nucleic acid chaperones. These cold shock proteins will block the formation of secondary structures in the mRNA during the cold shock, leaving the bacteria with only single strand RNA. [8] Single strand is the most efficient form of RNA for the facilitation of transcription and translation. This will help to counteract the decreased efficiency of transcription and translation brought about by the cold shock. [10] Cold shock proteins also affect the formation of hairpin structures in the RNA, blocking them from being formed. The function of these hairpin structures is to slow down or decrease the transcription of RNA. So by removing them, this will also help to increase the efficiency of transcription and translation. [10]

Once the initial shock of the temperature decrease has been dealt with, the production of cold shock proteins is slowly tapered off. [8] Instead, other proteins are synthesized in their place as the cell continues to grow at this new lower temperature. However, the rate of growth seen by these bacterial cells at colder temperatures is often lower than the rates of growth they exhibit at warmer temperatures. [6]

Transcriptional response of Escherichia coli to cold shock

Cold shocks cause the repression of several hundreds of genes in the bacterium E. coli. Many of these genes are repressed quickly after the decrease in temperature, while others are only affected several hours after this event. [11] The repression mechanism is described in. [12] Shortly, during cold-shocks, cellular energy levels decrease. This hampers the efficiency by which DNA gyrases remove positive supercoils produced by transcription events, whose accumulation eventually blocks future transcription events.

Many of the genes repressed during cold shock are involved in cell metabolism. By knowing the mechanism by which these genes respond, one can potentially tune it, in genetically modified bacteria, to modify at which temperature is the response to cold shock activated. This modification could reduce the energy costs of bioreactors. [12]

See also

Related Research Articles

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The vagus nerve, also known as the tenth cranial nerve, cranial nerve X, or simply CN X, is a cranial nerve that carries sensory fibers that create a pathway that interfaces with the parasympathetic control of the heart, lungs, and digestive tract. It comprises two nerves—the left and right vagus nerves—but they are typically referred to collectively as a single subsystem.

<span class="mw-page-title-main">Parasympathetic nervous system</span> Division of the autonomic nervous system

The parasympathetic nervous system (PSNS) is one of the three divisions of the autonomic nervous system, the others being the sympathetic nervous system and the enteric nervous system. The enteric nervous system is sometimes considered part of the autonomic nervous system, and sometimes considered an independent system.

<span class="mw-page-title-main">Sympathetic nervous system</span> Part of the autonomic nervous system which stimulates fight-or-flight responses

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Heat shock proteins (HSP) are a family of proteins produced by cells in response to exposure to stressful conditions. They were first described in relation to heat shock, but are now known to also be expressed during other stresses including exposure to cold, UV light and during wound healing or tissue remodeling. Many members of this group perform chaperone functions by stabilizing new proteins to ensure correct folding or by helping to refold proteins that were damaged by the cell stress. This increase in expression is transcriptionally regulated. The dramatic upregulation of the heat shock proteins is a key part of the heat shock response and is induced primarily by heat shock factor (HSF). HSPs are found in virtually all living organisms, from bacteria to humans.

<span class="mw-page-title-main">Diving reflex</span> The physiological responses to immersion of air-breathing vertebrates

The diving reflex, also known as the diving response and mammalian diving reflex, is a set of physiological responses to immersion that overrides the basic homeostatic reflexes, and is found in all air-breathing vertebrates studied to date. It optimizes respiration by preferentially distributing oxygen stores to the heart and brain, enabling submersion for an extended time.

<span class="mw-page-title-main">Fight-or-flight response</span> Physiological reaction to a perceived threat or harmful event

The fight-or-flight or the fight-flight-freeze-or-fawn is a physiological reaction that occurs in response to a perceived harmful event, attack, or threat to survival. It was first described by Walter Bradford Cannon. His theory states that animals react to threats with a general discharge of the sympathetic nervous system, preparing the animal for fighting or fleeing. More specifically, the adrenal medulla produces a hormonal cascade that results in the secretion of catecholamines, especially norepinephrine and epinephrine. The hormones estrogen, testosterone, and cortisol, as well as the neurotransmitters dopamine and serotonin, also affect how organisms react to stress. The hormone osteocalcin might also play a part.

<span class="mw-page-title-main">Vasodilation</span> Widening of blood vessels

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<span class="mw-page-title-main">Baroreflex</span> Homeostatic mechanism in the body

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fis E. coli gene

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<span class="mw-page-title-main">CspA mRNA 5′ UTR</span>

cspA mRNA 5' UTR is the untranslated region of the cspA gene, which is important in the cold shock response in Enterobacteriales such as E. coli. The 5' UTR element acts as an RNA thermometer, regulating the expression of cspA in response to temperature. By regulating temperature, cspA proteins carry out the vital function of homeostasis.

<span class="mw-page-title-main">RNA thermometer</span> Temperature-dependent RNA structure

An RNA thermometer is a temperature-sensitive non-coding RNA molecule which regulates gene expression. RNA thermometers often regulate genes required during either a heat shock or cold shock response, but have been implicated in other regulatory roles such as in pathogenicity and starvation.

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References

  1. 1 2 3 4 5 "Exercise in the Cold: Part II - A physiological trip through cold water exposure". The science of sport. www.sportsscientists.com. 29 January 2008. Retrieved 2010-04-23.
  2. ↑ Staff. "4 Phases of Cold Water Immersion". Beyond Cold Water Bootcamp. Canadian Safe Boating Council. Archived from the original on 3 December 2013. Retrieved 8 November 2013.
  3. 1 2 3 4 Farstad, David J.; Dunn, Julie A. (September 2019). "Cold Water Immersion Syndrome and Whitewater Recreation Fatalities". Wilderness & Environmental Medicine. 30 (3): 321–327. doi: 10.1016/j.wem.2019.03.005 . ISSN   1545-1534. PMID   31178366. S2CID   182948780.
  4. 1 2 3 4 Knechtle, Beat; Waśkiewicz, Zbigniew; Sousa, Caio Victor; Hill, Lee; Nikolaidis, Pantelis T. (December 2020). "Cold Water Swimming—Benefits and Risks: A Narrative Review". International Journal of Environmental Research and Public Health. 17 (23): 8984. doi: 10.3390/ijerph17238984 . ISSN   1661-7827. PMC   7730683 . PMID   33276648.
  5. ↑ Tipton, M. J.; Collier, N.; Massey, H.; Corbett, J.; Harper, M. (2017-11-01). "Cold water immersion: kill or cure?: Cold water immersion: kill or cure?". Experimental Physiology. 102 (11): 1335–1355. doi: 10.1113/EP086283 . PMID   28833689.
  6. 1 2 Shires, K.; Steyn, L. (2001). "The cold-shock stress response in Mycobacterium smegmatis induces the expression of a histone-like protein". Molecular Microbiology. 39 (4): 994–1009. doi: 10.1046/j.1365-2958.2001.02291.x . ISSN   1365-2958. PMID   11251819.
  7. 1 2 3 Phadtare, S., Alsina, J., & Inouye, M. (1999). “Cold-shock response and cold-shock proteins”. Current Opinion in Microbiology. 2(2), 175-180. doi:10.1016/S1369-5274(99)80031-9
  8. 1 2 3 Phadtare, Sangita (2004). "Recent developments in bacterial cold-shock response". Current Issues in Molecular Biology. 6 (2): 125–136. ISSN   1467-3037. PMID   15119823.
  9. ↑ Di Pietro, Fabio; Brandi, Anna; Dzeladini, Nadire; Fabbretti, Attilio; Carzaniga, Thomas; Piersimoni, Lolita; Pon, Cynthia L; Giuliodori, Anna Maria (2013). "Role of the ribosome-associated protein PY in the cold-shock response of Escherichia coli". MicrobiologyOpen. 2 (2): 293–307. doi:10.1002/mbo3.68. ISSN   2045-8827. PMC   3633353 . PMID   23420694.
  10. 1 2 3 Keto-Timonen, Riikka; Hietala, Nina; Palonen, Eveliina; Hakakorpi, Anna; Lindström, Miia; Korkeala, Hannu (2016). "Cold Shock Proteins: A Minireview with Special Emphasis on Csp-family of Enteropathogenic Yersinia". Frontiers in Microbiology. 7: 1151. doi: 10.3389/fmicb.2016.01151 . ISSN   1664-302X. PMC   4956666 . PMID   27499753.
  11. ↑ Phadtare, Sangita; Inouye, Masayori (October 2004). "Genome-wide transcriptional analysis of the cold shock response in wild-type and cold-sensitive, quadruple-csp-deletion strains of Escherichia coli". Journal of Bacteriology. 186 (20): 7007–7014. doi:10.1128/JB.186.20.7007-7014.2004. ISSN   0021-9193. PMC   522181 . PMID   15466053.
  12. 1 2 Dash, Suchintak; Palma, Cristina S D; Baptista, Ines S C; Almeida, Bilena L B; Bahrudeen, Mohamed N M; Chauhan, Vatsala; Jagadeesan, Rahul; Ribeiro, Andre S (2022-08-03). "Alteration of DNA supercoiling serves as a trigger of short-term cold shock repressed genes of E. coli". Nucleic Acids Research. 50 (15): 8512–8528. doi:10.1093/nar/gkac643. ISSN   0305-1048. PMC   9410904 . PMID   35920318.

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