Dry, warm air increases the risk of stroke

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 complex interdependence with air temperature and humidity

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.

Such a complex interdependence with so many cases and subtypes has never been investigated to date

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.

Large numbers of cases at the University Hospital of Augsburg

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.

Figures, data, facts

The figure of exactly 17,989 cases examined is not identical to the number of patients taken into account. Although most cases are new cases, a few of the patients included in the study had al-ready had a second or third stroke. Of the cases, 27 percent were under the age of 65, 73 percent were older than 65. 52 percent were men, 48 percent were women.

Prof. Naumann and his colleague Ertl and their team at the UKA treat nearly 2,000 stroke patients each year. This makes the Department of Neurology and Clinical Neurophysiology of the University Hospital of Augsburg one of the largest stroke care providers in Germany. Through the cooperation project TESAURUS, a total of seven smaller clinics in the region are connected to the UKA and receive support in the form of consultations, so that they can provide their patients, as far as medically acceptable, with local care.

The climate researchers at the Institute of Geography of the University of Augsburg have been involved for many years within the framework of national and international research collaborations in the investigation of the relationships between atmospheric processes and various environmental parameters.

The severity of each stroke was not considered in the study. With the large number of study participants, the research team of neurologists, climate and environmental scientists, epidemiologists and environmental physicians of the University Hospital and the University of Augsburg, as well as the Helmholtz Zentrum Munich and the Augsburg University Centre for Health Sciences UNIKA-T, had to focus on the indicators described.

The Augsburg University Medical School …

… includes the Faculty of Medicine of the University of Augsburg, the University Hospital of Augsburg and – as a cooperation partner – the Augsburg District Hospital – Department of Psychiatry, Psychotherapy and Psychosomatic Medicine of the University of Augsburg. The main research areas of the Faculty of Medicine are medical informatics as well as environment and health. Around 100 professors will ultimately be involved in biomedical and human medical research and teaching. Since the winter semester of 2019/20, the Faculty of Medicine has offered a model study programme in human medicine that integrates pre-clinical and clinical content and attaches particular importance to the scientific education of ultimately 1,500 students.

The University Hospital of Augsburg (UKA), which has been under the auspices of the Free State of Bavaria since 2019, offers optimal medical care to the population of the city and the region through its involvement in university medical research and teaching at the Faculty of Medicine at the University of Augsburg. Including the day hospital beds, there are 1,740 beds available at the UKA. 24 clinics, three institutes and 19 centres assure diagnosis and treatment at the highest level in all medical disciplines. Around 250,000 outpatients and inpatients are cared for annually at the UKA. With approximately 80,000 patients per year, the emergency department of the UKA is the second largest emergency department in the Federal Republic. Every year more than 2,450 children come into the world at the UKA. With 560 training places, the UKA-affiliated Academy of Health Professions is one of the largest training providers in the region.

contact for scientific information:
PD Dr. med. Michael Ertl, michael.ertl@uk-augsburg.de, University Hospital Augsburg
Dr Christoph Beck, Department of Physical Geography, University Augsburg

original publication:
Ertl M., Beck C., Kühlbach B., Hartmann J., Hammel G., Straub A., Giemsa E., Seubert S., Philipp A., Traidl-Hoffmann C., Soentgen J., Jacobeit J., Naumann M.: New Insights into Weather and Stroke: Influences of Specific Air Masses and Temperature Changes on Stroke Incidence. In: Cerebrovasc Diseases 2019;47:275–284, https://doi.org/10.1159/000501843

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