Air pollution raises blood pressure 'in near real time'

Hypertension is a chronic disease that is one of the first cardiovascular risk factors. It is one of the leading causes of premature death in the world. According to the WHO, more than 10 million annual deaths are attributable to this pathology. In France, nearly 30% of adults suffer from it. Although the influence of air pollution on hypertension has long been suspected, researchers from Inserm and Sorbonne University have shown that transient increases in blood pressure over the course of a day are directly linked to the inhalation of polluting species in the inhaled air.

Specifically, the researchers characterized the effects of daily exposure to a mixture of 5 air pollutants – carbon soot, nitrogen dioxide (NO2), nitric oxide (NO), carbon monoxide (CO) and ozone ( O3) – on blood pressure (or blood pressure), that is, the force exerted by blood on the walls of blood vessels. These measurements were carried out in the very short term, in the space of a day, whereas previous work has rather focused on the long-term consequences of this exposure. They also took into account a "cocktail" of pollutant rather than an isolated species because, in everyday life, we are exposed to several components simultaneously. “This study is the first to take this aspect into consideration,” explains its manager, Basile Chaix, Inserm research director at the Pierre Louis Institute of Epidemiology and Public Health.

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In order to determine the effects of this mixture of compounds, 221 participants in the Paris region wore, for 24 hours, a blood pressure measuring device, two sensors continuously measuring the concentrations of pollutants in the ambient air in the area. of breathing, a GPS tracker and an accelerometer allowing to apprehend the respiratory rate (the volume of air inspired or expired per unit of time) via the measurement of physical activity. The people's blood pressure was measured at 30-minute intervals in order to determine very precisely its fluctuations according to variations in the concentration of pollutants in the ambient air as well as the quantity of pollutants inhaled.

The researchers were thus able to demonstrate an increase in blood pressure when the concentrations of pollutants and/or the quantity of pollutants inhaled increased in the 5 minutes preceding the blood pressure measurement. In other words, the tension tended to increase “in spurts” during the day almost immediately after a high exposure to the mixture of pollutants. Soot carbon, primarily produced by city gasoline engines (mainly diesel), and ozone were the two largest contributors to this transient increase in blood pressure. “The link between air pollution and increased blood pressure is weaker over exposure windows longer than 5 minutes, for example 15 or 30 minutes, which testifies to an almost real-time rise in blood pressure. in response to an increase in the concentrations of airborne pollutants in the mixture studied,” adds Basile Chaix.

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Thus, these results provide new evidence for the causal link between air pollution and hypertension. “In the short term, we cannot really speak of hypertension”, nuance Basile Chaix. “Nevertheless, we can put forward the hypothesis that these repeated surges in blood pressure can lead, year after year, to alterations in the circulatory system and therefore lead to chronic increases in blood pressure. ". This mechanism would explain the associations observed between exposure to pollutants and the risk of developing hypertension in a more permanent way.

However, the researchers remain cautious because, at present, they do not have the possibility of comparing their results with other work, the method used having been specifically developed for this study. Future analyzes will therefore be necessary to confirm these results and clarify the underlying mechanisms. Remember, however, that the causes of hypertension are multiple, and that pollution is not the only risk factor. Being overweight remains quite largely the leading cause of hypertension highlighted by scientists. "This does not prevent, from today, raising awareness of the risks induced by air pollution on the tension", concludes Basile Chaix. The authors hope that their results will encourage reflection on the place of motorized transport in our cities, and the exposure of pedestrians or cyclists to this pollution.