Summary: Panic-induced hyperventilation can reduce our ability to respond to environmental threats as it desensitizes body temperature to change.
Source: University of Tsukuba
The fight-or-flight response evolved to keep us safe from predators, but it can sometimes cause us to overreact in modern life when we don’t face the same dangers we once did.
Now, researchers from Japan have found that a common panic response may actually reduce our ability to deal with environmental threats.
In a study published this month in the American Journal of Physiology-Regulatory, Integrative and Comparative Physiology, researchers from the University of Tsukuba and Niigata University of Health and Welfare have revealed that a change in blood gas caused by intense breathing can desensitize the body to temperature changes.
When we encounter unexpected stressors in daily life, such as acute pain or fear, a common response is to begin breathing rapidly. This response, called hyperventilation, often involves breathing more quickly than the body really needs in order to deal with the perceived threat or danger.
“The purpose of hyperventilation during stress is not well understood, although it is thought to reduce sensitivity to the stressful stimulus,” says lead author of the study, Dr. Tomomi Fujimoto.
“However, whether and how hyperventilation reduces sensitivity to temperature changes is still unclear.”
To explore this, the researchers first tested sensitivity to temperature changes in young adults while breathing normally. Then, they were asked to breathe rapidly (hyperventilate), with or without the addition of carbon dioxide to their inspired air, to simulate hypocapnia, which is the normal decrease in carbon dioxide that occurs with hyperventilation, or normocapnia, which is a normal carbon dioxide level.
“The results were striking,” explains Professor Takeshi Nishiyasu, corresponding author. “Local detection of warm and cool stimuli was blunted when subjects hyperventilated with hypocapnia, but did not differ when they hyperventilated with normocapnia.”
In addition, less blood flow to the brain was observed during hyperventilation with hypocapnia than during hyperventilation with normocapnia. Although the reduced sensitivity to warm and cold stimuli was comparable on the forehead, the detection of warm stimuli was unchanged on the forearm.
“These findings suggest that hyperventilation-induced hypocapnia, not hyperventilation per se, attenuates local skin thermal perception, though changes in responses to warm stimuli may not be clearly perceived at some skin areas,” says Dr. Fujimoto.
Given that hyperventilation with hypnocapnia reduces blood flow to the part of the brain that receives signals about thermal stimulation, it is plausible that this is the reason for blunted thermal perception.
The findings from this study suggest that hypocapnia may be a mechanism by which hyperventilation reduces sensitivity to stress, while paradoxically dampening thermoregulatory behavior in severe hot and cold environments, which may contribute to heat stroke and accidental hypothermia.
Hypocapnia attenuates local skin thermal perception to innocuous warm and cool stimuli in normothermic resting humans
When one is exposed to a stressful situation in their daily life, a common response is hyperventilation. Although the physiological significance of stress-induced hyperventilation remains uncertain, this response may blunt perception of the stress-inducing stimulus.
This study examined the effects of voluntary hyperventilation and resultant hypocapnia on the local skin thermal detection threshold in normothermic resting humans.
Local skin thermal detection thresholds were measured in 15 young adults (three females) under three breathing conditions: 1) spontaneous breathing (Control trial), 2) voluntary hypocapnic hyperventilation (HH trial), and 3) voluntary normocapnic hyperventilation (NH trial). Local skin thermal detection thresholds were measured using thermostimulators containing a Peltier element that were attached to the forearm and forehead.
The temperature of the probe was initially equilibrated to the skin temperature, then gradually increased or decreased at a constant rate (±0.1 °C/s) until the participants felt warmth or coolness.
The difference between the initial skin temperature and the local skin temperature at which the participant noticed warmth/coolness was assessed as an index of the local skin warm/cool detection threshold. Local detection of warm and cool stimuli did not differ between the Control and NH trials, but it was blunted in the HH trial as compared with the Control and NH trials, except for detection of warm stimuli on the forearm.
These findings suggest that hyperventilation-induced hypocapnia, not hyperventilation per se, attenuates local skin thermal perception, though changes in responses to warm stimuli may not be clearly perceived at some skin areas (e.g., forearm).