Healthy Fear of Heights

Home page Description: 
Brain ‘microbleeds’ seen in certain type of altitude sickness also experienced by ICU patients.
Image Caption: 
Blood oxygen levels can be lowered for prolonged periods of time during respiratory failure (as in ICU patient, pictured right), and also at high altitudes (pictured left).

For mountaineers who push themselves too far, too fast, a particular type of chronic mountain sickness, known as high-altitude cerebral edema, can develop.

A recent study, led by Krembil Clinician Investigator Dr. Daniel Mandell, revealed an unlikely link between mountaineers suffering from this condition and patients in the intensive care unit (ICU).

Dr. Mandell comments, “Our study showed that critically ill patients displayed extremely small, yet extensive points of bleeding in the brain known as microbleeds—a phenomenon that is also experienced by those suffering from this type of altitude sickness.”

The impetus for the study was to help explore unexplained intellectual decline experienced by some ICU patients. While the ICU provides a vital lifeline to those recovering from conditions such as major surgery, serious infections or organ failure, these patients often experience lingering memory problems and trouble concentrating.

In the study, the research team used magnetic resonance imaging (MRI) to look at the brains of 12 ICU patients. Discussing the approach, Dr. Mandell comments, “We used a type of MRI called ‘susceptibility weighted imaging’, which provides exquisite detail of blood flow in the brain.”

The cause of the microbleeds observed in ICU patients is still unknown. “While microbleeds are known to result from prolonged exposure to high altitudes, chronic high blood pressure or diseases of the blood vessels, the majority of our study participants did not have any of these conditions. This suggests that the microbleeds that we observed are a new phenomenon—one that warrants further study,” says Dr. Mandell.

One potential explanation for the observed microbleeds could be that they are caused by low blood oxygen levels. This is a particularly attractive idea because, similar to mountaineers at high altitudes, low blood oxygen levels are experienced by ICU patients with respiratory failure. In fact, in the study, most of the 12 ICU patients exhibited respiratory failure and all but one of them required mechanical ventilation.

While it is still not clear whether microbleeds account for the unexplained intellectual symptoms experienced by ICU patients, these findings lay the groundwork for future studies that will explore this link and develop approaches to prevent microbleeds.

This work was supported by Remmert Adriaan Laan Fonds (Dr. Coutinho) and the Toronto General & Western Hospital Foundation.

Fanou EM, Coutinho JM, Shannon P, Kiehl TR, Levi MM, Wilcox ME, Aviv RI, Mandell DM. Critical Illness-Associated Cerebral Microbleeds. Stroke. 2017 Apr;48(4):1085-1087. doi: 10.1161/STROKEAHA.116.016289. Epub 2017 Feb 24.