For some people, a needle is just a quick pinch. For others, it’s a one-way ticket to the floor.
In this episode of Curious People, we explore the strange biology behind vasovagal syncope - the reflex that causes some people to become lightheaded, nauseous, even sometimes briefly unconscious.
The story begins in a pre-procedure room at my workplace, where my husband passed out before his colonoscopy even started… on an extremely urgent trip to the bathroom. I use this story to unpack what’s actually happening in the body when your nervous system gives bad advice to cardiovascular system.
If you’ve ever gotten woozy during a blood draw - or watched someone turn white as a ghost at the sight of a needle - this episode will explain why.
You can read the full written article on Substack here.
About the Show
Curious People is a science storytelling podcast about the strange, fascinating science hiding just below the surface of everyday life.
Hosted by nurse anesthetist Kayla McClanahan.
References
- Andresen MC, Mendelowitz D. Autonomic nervous system: central cardiovascular control. Encyclopedia of Neuroscience. 2009;863-869. doi:https://doi.org/10.1016/B978-008045046-9.00648-3
- Jeanmonod R, Sahni D, Silberman M. Vasovagal Episode. StatPearls. 17 July, 2023. Retrieved from https://www.ncbi.nlm.nih.gov/books/NBK470277/
- Niehues LJ, Klovenski V. Vagal maneuver. StatPearls. 3 July, 2023. Retrieved from https://www.ncbi.nlm.nih.gov/books/NBK551575/
- Verhulst J. Effect of Gravity and Upright Posture on Circulation. Thoracic Key. 2003. Retrieved from https://thoracickey.com/effect-of-gravity-and-upright-posture-on-circulation/
- Silva C, Marcos P. Intravenous fluid therapy: essential components and key considerations. Porto Biomed J. 2025;10(4):e296. doi: 10.1097/j.pbj.0000000000000296
- Schweitzer K. IV Hydration Spas Are Gaining Popularity, but Are They Safe? JAMA. 2025;334(18):1609–1610. doi:10.1001/jama.2025.18832
van Dijk, N, Quartieri, F, Blanc, J. et al. Effectiveness of Physical Counterpressure Maneuvers in Preventing Vasovagal Syncope: The Physical Counterpressure Manoeuvres Trial (PC-Trial). JACC. 2006;48(8):1652–1657. https://doi.org/10.1016/j.jacc.2006.06.059