Based on almost 18,000 cases collected over a period of ten years, an Augsburg study shows that the risk of certain types of stroke increases in dry and warm air masses. This is the first time such complex interactions with so many cases and subtypes have been investigated. The aim of the study was to contribute to both patients and health care institutions taking appropriate and timely preventive and treatment measures. Strokes are one of the most frequent causes of death and a reason for needing long-term care throughout Germany and the world.
Dry, warm summers - no longer a rarity. But the climate has consequences, also for health. Researchers at the University of Augsburg have now confirmed a feeling on the part of neurologists that certain strokes become particularly frequent on certain days during the course of the year.
At first it was just a feeling on the part of the neurologists at the University Hospital of Augsburg (UKA) that "certain strokes were more frequent on some days in the course of the year," says private lecturer Dr Michael Ertl, one of the two leading authors of the study. "These accumulation phenomena are familiar to many stroke neurologists, so we suspected that might also be related to weather effects." And in fact, after ten years and 17,989 cases examined - most of them new cases, but also patients with recurrent strokes - the study comes to the concrete conclusion that there is a connection between certain weather conditions and strokes in the Augsburg region. For example, the risk for some stroke subtypes in dry, warm air masses increases, whereas dry, cold air masses were associated with a significantly lower incidence of cerebral haemorrhage.
The search for the causal relationships turned out to be very complex. "The interplay of different meteorological factors - such as air temperature, air pressure and humidity - and short-term temperature changes is very complex," explains private lecturer Dr Christoph Beck from the Department of Physical Geography with focus on climate research at the University of Augsburg, who, alongside Ertl, was also the leading author of the study. Looking at the temperature development in the period of a few days before the stroke event, there are also differentiated influences on the incidence of strokes or haemorrhage, which, however, have not yet been fully clarified pathophysiologically. The interdisciplinary research team was also able to show that weather changes affect the two stroke subtypes of cerebral infarction and cerebral haemorrhage differently. For example, dry, warm air masses bring about an increased risk of certain cerebral infarction types, which account for over 80 percent of all strokes, but a lower risk for cerebral haemorrhage. The opposite is the case in dry, cool air masses: these promote cerebral haemorrhage, but involve a rarer occurrence of cerebral infarction. In the case of humid air masses, too, a reduced incidence of cerebral infarctions could be detected.
Ertl stresses "that we are not the first to see climate and stroke rates in association". According to Ertl, however, most of the studies examined only a few meteorological parameters such as air pressure and temperature as well as the stroke, without any further definition at a specific time. The study by the research team of medical scientists from the UKA and climate researchers from the Geographic Institute of the University goes much further here. "In addition to the consideration of local meteorological conditions, the air mass classifications used also include large-scale synoptic conditions such as the distribution of ground air pressure across Europe in the allocation to specific weather conditions," explains Beck. "In addition, we subdivided what is called the ischaemic stroke, in which there is a vascular occlusion of the cerebral arteries, accounting for about 85 percent of all strokes, into five other subtypes," explains Ertl. The study also took into account the air mass situation two to five days before the stroke. Classical risk factors of all patients examined, such as hypertension, obesity, diabetes, cholesterol and lifestyle, were taken from their medical reports and also noted.
An excellent starting point for the study was, on the one hand, the comprehensive database of strokes (around 2,000 patients per year) available at the UKA, as it seamlessly records stroke patients throughout the region. This provides a very large number of patients: for the study period from 2006 to 2017, there were about 18,000 strokes. On the other hand, the University of
Augsburg has had outstanding expertise in environmental and climate research at the Institute of Geography for over twenty years. Both could be successfully combined - for the benefit of better precautions and better care. After all, strokes are one of the leading causes of death in Germany and around the world and are a reason for long-term care. "With the aid of our study, we want to help ensure that both patients and healthcare providers can take appropriate and timely preventive and treatment measures. However, intensive further research will be needed in the future. The aim is to confirm and concretise the retrospectively evaluated data with further prospective investigations, "emphasises Prof. Dr Markus Naumann, Director of the Department of Neurology and Clinical Neurophysiology at the UKA.