Blowing out with lips and nostrils closed, causing the ears to pop – such as we might do as an aeroplane descends from a height. We do this to drive air into the middle ear, in order to relieve the increasing cabin pressure that is bearing down upon the outside of the eardrums. If performed more vigorously, against a closed larynx (voice-box), a Valsalva manoeuvre will impede the return of blood to the heart, in the veins. The veins engorge and this back pressure is transmitted into the head and the spinal canalThe individual bones that comprise the spinal column are made up of a weight-bearing “body” and other components which, together, form a ring of bone, behind the body. These individual vertebrae, joined together as the spinal column, therefore, create a canal running down the entire length of the spine. and, in turn, this pressure is transferred into the cerebrospinal fluidThis clear, water-like fluid forms, for the most part, within the brain, more specifically inside the ventricles of the brain. Blood flows through structures inside the ventricles, called the choroid plexuses, and clear fluid is produced as a result, passing into the ventricle. This process is akin to blood flowing through the kidneys and urine being produced as a result. An important difference is that, unlike urine, the cerebrospinal fluid is not passed out of the body periodically. Instead, the fluid is re-absorbed back into the blood stream, mostly via the arachnoid granulations, into the cerebral venous sinuses. In the course of a 24-hour period, most healthy adults will produce about 500mls (or a pint) of cerebrospinal fluid, although at... channels. Coughing, sneezing, laughing, shouting or bending over are examples of every-day actions which are accompanied by brief periods during which we involuntarily squeeze air out of our lungs with the voice-box closed.
Menu