05:45am Sunday 07 June 2020

Blood pressure medication may cause fainting when used for other ailments

Nia Lewis, a Canada Heart and Stroke Foundation funded post-doctoral research fellow with the Centre for Heart, Lung and Vascular Health in the School of Health and Exercise Sciences at the Okanagan campus, completed the study recently published in the American Journal of Physiology – Regulatory, Integrative and Comparative Physiology.

Lewis studied patients with normal blood pressure who took the drug prazosin, commonly used to treat hypertension, or high blood pressure. The drug treats other conditions, such as post-traumatic stress syndrome, anxiety or prostate problems, but shows potential negative effects.

Investigators found 11 of 12 participants who took the medication experienced temporary dizziness or lightheadedness upon standing.

“We were able to determine that, because prazosin shuts down a pathway that is critical to regulate blood pressure, the capacity to safely control blood flow to the brain was also reduced to a level that could induce fainting,” says Lewis.

Part of the research show that the actions of the sympathetic nervous system that would normally prevent the big drop in blood pressure on standing, and consequently prevents an unnecessary fall in brain blood flow, is prevented by the drug, which has sympathetic receptor-blocking properties. The physiological response can prove dangerous for those patients with normal blood pressure who use prazosin for treating other ailments.

The senior author Philip Ainslie, co-director of the new Centre for Heart Lung and Vascular Health and Canada Research Chair in Cerebrovascular Function in Health and Disease, says Lewis’s project plays an important role in understanding the mechanisms involved in human brain blood flow regulation during periods of low blood pressure.


The randomized controlled study, entitled Initial orthostatic hypotension and cerebral blood flow regulation: effect of a1-adrenorreceptor activity, was conducted on eight male and four female patients, average age 25, with normal blood pressure, using both placebo and the blood pressure drug.

The research team included Ainslie of UBC; Greg Atkinson of Teesside University of the UK; Helen Jones of Liverpool John Moores University; and Emily J.M. Grant and Samuel J.E. Lucas of the University of Otago, New Zealand.

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