Researchers from Russia and the U.S. investigated the effects of Sirshasana (headstand) on the flow of blood to the brain. Their findings were published in The Journal of Alternative and Complementary Medicine.
Most yoga practitioners believe that Sirshasana can increase blood flow to the brain, but this is not consistent with autoregulation of cerebral blood flow.
To demonstrate the truth about Sirshasana and its purported benefit, the researchers examined blood flow to the internal carotid artery (ICA) using ultrasound.
They recruited 20 men and women aged 10 to 59 years and measured ICA blood flow with a pulsed Doppler while the participants were performing Sirshasana.
Seventeen of the 20 subjects were examined in Spain in 2018 at an altitude of 2,000 meters, while the remaining three -- all females -- were studied at sea level.
The researchers found that the diameter of the participants' respective ICA remained almost unchanged during Sirshasana.
They also noted a decrease in peak flow velocities in both systole and diastole that caused a significant decrease in arterial blood flow to the brain.
This decrease was followed by the return to baseline values immediately after the antiorthostatic postural effect, which the researchers attributed to the autoregulation of cerebral blood flow and intracranial pressure.
Based on these findings, the researchers concluded that, contrary to popular belief, Sirshasana does not increase blood flow to the brain. Instead, it causes a reduction in cerebral blood delivery because of the autoregulation of cerebral blood flow. Their results also suggest that increased ICA blood flow is likely to be a contraindication of Sirshasana.
Minvaleev RS, Bogdanov RR, Bahner DP, Levitov AB. HEADSTAND (SIRSHASANA) DOES NOT INCREASE THE BLOOD FLOW TO THE BRAIN. The Journal of Alternative and Complementary Medicine. 15 August 2019;25(8):827–832. DOI: 10.1089/acm.2019.0060