A study out of Binghamton University in New York suggests heart rate (HR) and blood pressure (BP) respond to environmental demands by undergoing allostasis rather than homeostasis, adding further evidence to a hypothesis scientists have mulled for years.
Corresponding author Gary D. James, an anthropology professor at Binghamton, said his team’s work provides strong evidence that a person’s heart rate and blood pressure shift throughout the day to meet the demands of that person’s external environment, both physical and social.
“This principle is in juxtaposition to the concept of homeostasis, which states that biological functions try to maintain a setpoint,” James said in a news release. “Blood pressure and heart rate are thought to undergo allostasis. So, if that is true, then someone who goes through the same routine day after day should have a reproducible pattern of circadian variation in their blood pressure and heart rate that corresponds to changing daily demands.”
James and his colleagues explored that premise in their study of 157 healthy women who worked in similar sedentary positions at one of two major medical centers in New York. The women, on average 38 years old, wore ambulatory BP monitors over the course of three midweek work days around a month apart.
The researchers said the women’s occupations were important for the study, since it’s hard to produce real-world results in a lab.
“The reason why their job matters is that it is highly likely that the subjects are going to be doing the same things pretty much every day, so you can set up a hypothesis that similar activities give you the same results,” James said. “If the participants had an occupation that required varied activities from day to day, it wouldn’t be possible to essentially mimic in real life what happens in the lab.”
The team calculated subjects’ hourly BPs and HRs from 9 a.m. to 6 a.m. the following morning, comparing those stats among the three days the women wore their monitors. The results clearly showed there were “virtually no differences” in the average levels of blood pressure or heart rate over the three separate days of study, suggesting those parameters adjusted daily—and consistently—to meet the demands of the women’s workplaces.
The only outlier in the data was a significant drop in hourly systolic BP levels between 12 p.m. and 4 a.m. on the third day of assessment compared to the first.
“Because BP and HR respond to environmental demands in an allostatic fashion, the consistency in the waking patterns of BP and HR variation suggest that the patterns of demands on a workday are reasonably stable in this sample of women,” James and colleagues wrote in the study, published in the American Journal of Human Biology. “The decline in systolic pressures from 12 p.m. to 4 a.m. over the three assessments may indicate an improving ability to sleep with the monitor over time.”