Elevated humidity in the atmosphere is an associated cause for accelerated heart rate, a condition called cardiovascular strain, a research reports. The study was undertaken by the researchers at Pennsylvania State University and was reported in the Journal of Applied Physiology.
Even with air temperatures as low as 34oC, people could experience uneasiness when humidity encapsulates us. The study observes the build-up of cardiovascular strain even before the body’s internal temperature begins to rise up.
The Hot-humid Conditional Study
The study by Rachel Cottle and colleagues to determine the exact point at which heart risk occurs, was made possible by voluntary support of 51 young and healthy participants. They were asked to partake in mild physical activity within a controlled environmental chamber. The temperature or humidity of the chamber went up every 5 minutes as a part of the controlled setting of the experiment.
The team of researchers closely observed the core temperature of each participant, which represents the internal organ temperature, by utilizing sensors contained within capsules that were ingested by the participants. Additionally, the researchers recorded the heart rates of the individuals as part of the study.
The steady increase in temperature inside the chamber, recorded increased heart rate in the volunteers, which eventually reached a plateau. However, as the temperatures continued to go up, the heart rates of the volunteers began to climb up again and were still ascending when the experimentation concluded. This observation signaled cardiovascular strain.
When compared to humid-conditions studies, the participants started experiencing cardiovascular strain at temperatures around 34oC, with slow-paced walking as a part of minimal physical activity. On the other hand, the threshold for cardiovascular strain was recorded around 41oC in dry conditions. Furthermore, the study also confirmed that cardiovascular strain always began at least 20 minutes prior to the rise in participant’s core temperatures.
Heart rate can serve as a valuable indicator since it can be easily measurable. An abrupt and gradual increase in heart rate may signal an upcoming rise in core temperature, prompting the need for precautionary actions, according to Cottle. However, as per Craig Crandall, director of The Thermal and Vascular Physiology Laboratory, Texas Health Presbyterian Hospital, one should exercise caution. He suggests that the team’s observation of heart rate elevation preceding core temperature rise could be attributed to delays in measuring core temperature within the gut.
Heart at Rest
Another aspect of a related study suggests that a heart at rest is actually not resting in hot and humid conditions. A research study by Lewis Halsey, University of Roehampton, London and his team, it was evaluated that when exposed to a temperature of 50 °C, participants experienced an average increase of 64% in their resting heart rate compared to when exposed to a temperature of 28 °C, while maintaining a humidity level of 50%. This implies that even during periods of rest, such as being outdoors on a sunny beach, individuals can still expect their heart rate to rise.
Barrak Alahmad, expert in climate change and health at the Harvard T.H.Chan School of Public Health, Massachusetts, explains that the human body signals two main mechanisms to activate during periods of high temperatures- sweating and increasing the flow of blood from the core to the skin. This in turn demands high metabolic activity and high pulsating heart rates. This results in an extreme strain on the heart, all the same directing blood flow away from it.
While this may be relatively harmless for healthy young adults, it can be potentially dangerous for older individuals or those with pre-existing heart conditions. This highlights the increased vulnerability of certain populations to the adverse effects of heat, in short climate change on cardiovascular health.