“Prior studies have found that colder temperatures lead to an increased risk for intracerebral haemorrhage,” said Dr Rajeev Garg, an assistant professor in the Department of Neurological Sciences at Rush and principal investigator of the study. “Temperature influences barometric pressure and vice versa.”

“What we do not know is which of these two is causing the increased risk of haemorrhage. Our findings suggest that when it gets colder outside, the corresponding barometric pressure is likely the cause for the increased risk for intracerebral haemorrhage, not just temperature change alone.”

The team of researchers analyzed the impact of one of these two weather variables when the other is held constant. They found that the change in barometric pressure and average barometric pressure are independent, but the change in temperature is influenced by the average barometric pressure.

“This is the first study to look at the collective influence of temperature, barometric pressure and dew point temperature on the incidence of spontaneous intracerebral haemorrhage,” Garg said.

The study prospectively screened 603 patients who suffered a spontaneous intracerebral haemorrhage between January 2013 and December 2016. The mean age was 61 years, 56 per cent of patients were men, 59.1 per cent were black and 86.6 per cent of patients were diagnosed with high blood pressure.

Hourly temperature, sea level barometric pressure (SLP), and dew point for the three-year period were obtained from the National Oceanic Atmospheric Administration’s weather stations at Midway and O’Hare International Airports. 

Of the 603 patients, 455 (75.5 per cent) patients identified had an established date and time when they each last felt normal. Then, temperature, barometric pressure, and dew point temperature were analyzed for a six-hour period prior to each stroke incident for the patients. The date and time of the last known normal, which is the time right before haemorrhage, were prospectively ascertained from each patient during a personal interview. 

Researchers used a type of analysis called the Monte-Carlo simulation to determine whether the weather patterns prior to haemorrhage were different from the weather at a randomly selected moment in time. They found that the following three variables could be linked to a higher risk for sICH:

Change in temperature

Change in barometric pressure

Average barometric pressure

Researchers also wanted to see if specific characteristics such as age, gender, or race were more likely associated with weather patterns that increased the risk for spontaneous intracerebral haemorrhage.

“The results of the study indicate that the influence of weather on the incidence of spontaneous intracerebral haemorrhages is not a chance event,” said Garg. “We did not find any association between patient characteristics and high-risk weather patterns. This suggests that high-risk weather patterns seem to impact patients equally.

“We must monitor the effects of climate change on weather variability,” Garg added. “If weather variability increases, this may place us at an increased risk for spontaneous intracerebral haemorrhage.”