When the temperature rises, the heart rate also increases, indicating that the heat puts an overstrain on the heart, according to a study from the State University of Pennsylvania (USA) that has analyzed how the body adapts to hot and humid conditions.
For healthy young people the increase in heart rate due to heat is irrelevant and usually imperceptible. But for older people with heart disease, the additional stress placed on the heart contributes to its greater vulnerability to heat waves.
“The body dissipates excess heat with perspiration and with the dilation of peripheral blood vessels. In order for more blood to reach the skin and evacuate internal heat, the heart must work harder”, explains Enric Subirats, a specialist in internal medicine and emeritus professor at the University of Girona.
The study involved 51 people from the US, 27 of whom were women, between the ages of 19 and 27. They have lent themselves to having their body temperature and heart activity monitored as ambient temperature and/or humidity increased.
According to the results presented in the Journal of Applied Physiology, in situations of high humidity the heart rate began to increase from 34 degrees. In situations of low humidity, the increase in heart rate was observed from 41 degrees. During the measurements the volunteers were walking at a slow pace that by itself did not justify their heart racing.
The temperature thresholds from which the heart rate accelerates may be lower in people with heart disease, in the same way that their physical activity thresholds are also lower, points out Bárbara Vidal, a cardiologist at the Hospital Clínic in Barcelona. Vidal warns that no studies have been done to find out from what temperature the heart rate increases in vulnerable people.
Shortly after the increase in heart rate, the study participants experienced an elevation in their body temperature. To accurately record the temperature of their internal organs, the researchers had asked them to ingest small capsules fitted with thermal sensors.
Since heart rate is easy to measure, it can be useful for monitoring vulnerable people during heat waves, the researchers say. “If the heart rate suddenly increases rapidly and progressively, it could mean that the body temperature will start to rise. It is the moment when it is necessary to take preventive measures ”, Rachel Cottle, first author of the research, has declared to the journal Nature, which she has reported on the results.
The heat caused more than 11,000 deaths in Spain last summer, 81% of them in people over 80 years of age, according to another investigation published this week in Nature Medicine.
Good hydration relieves the overexertion that the heart must do during heat waves, points out Bárbara Vidal. “When liquids are ingested, the amount of fluid in the blood vessels increases,” explains the hospital Clínic cardiologist. "This prevents blood pressure from being too low," a situation that would force the heart to exert itself so that blood reaches the entire body.
