Thermoregulation is a normal process in warm blooded animals including humans that tries to maintain body temperature. Hypothalamus in brain, thermoreceptors, skin sweat glands, blood vessels, and hormones such as thyroid hormones all coordinate and function together to retain body heat or cause loss of excess body heat.
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Thermoregulation in humans
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When external temperature rises, sweat glands start producing sweat which on evaporation carries the body heat with it. Blood vessels of skin dilate and release beat to atmosphere. Thyroid hormones decreases production to reduce body metabolic rate. All this is regulated via hypothalamus and receptors. Thirst centre is also activated to cause intake of water to replenish body water loss. Urine output also falls to reduce water loss since excess water is being lost via sweat production and evaporation.
When outside temperature falls, sweat glands decrease sweat production, skin blood vessels dilate and thyroid hormones production increases to increase metabolic rate. This preserves body heat.
Certain drugs given for psychiatric and behavioral disorders and blood pressure and heart ailments can affect thermoregulation. These include:
1. SSRIs (selective serotonin reuptake inhibitors)- used as antidepressants and for other mental conditions. These include sertraline, fluoxetine, escitalopram.
2. SNRIs (serotonin and norepinephrine reuptake inhibitors)-used as antidepressants and for other mental conditions. These include venlafaxine.
3. Tricyclic antidepressants are older antidepressants with anticholinergic effect. They can decrease sweat production and heat up the body in warm temperatures.
4. Antipsychotic drugs block dopamine action and thus halper body cooling
5. Stimulant drugs such as Ritalin raise metabolic rate and simultaneously constrict skin blood vessels.
6. Diuretics used for heart and blood pressure ailments can cause water loss and dehydration
7. ACE (angiotensin-converting enzyme) inhibitors and ARBs (angiotensin II receptor blockers) used in cardiovascular conditions can cause fluid loss and interfere with thirst mechanism.
8. Beta blockers constrict skin blood vessels and reduce heat loss.
Some of these drugs such as anticholinergics are also used in bladder hyperactivity, Parkinson's disease, allergies, bronchial asthma, etc.
Therefore, due to interference of these drugs with normal body thermoregulation, a person on it cannot effectively react in hot or cold atmospheres.
This is more noticed in adults who are mostly on these drugs and are on polypharmacy.
People on these drugs, both young and old, may not feel the pinch in equable climate. But they experience problems in extreme weather conditions.
Moreover with climate change, summers start early, are more severe, and remain for a longer period. Hence, chances of complications with these drugs rise. Deaths also ensue if undiagnosed or untreated.
Even with treatment, fatality rate with heat stroke is higher.
Moreover, people above 65 years of age are more likely to be on these medications. They take multiple categories of these drugs. And they are also more susceptible to ill-effects of high temperatures and climate change. Therefore risk is higher in them.
If you are on these medications,
Avoid strenuous exercises, avoid remaining outside in sun in summers, stay dehydrated and immediately shift to cooler atmosphere if you feel uneasy.
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