Machander, A. R. (1982). Comments on the increase of intrathoracic pressure in the practice ofpranayama. Jógová Cvicení, pp. 65-70. * [In Czechoslovakian.]
Summary: “Both intrathoracic and intraabdominal pressure can be increased during yogic practice. Abhyantara kumbhaka . . . during pranayama can increase intrathoracic pressure in different degree[s], according to the technique used. The increase of thoracic pressure elevates venous pressure with consequent venous blockade and the increase of pressure both in cerebrovascular fluid and intracranially. If the breath-holding with increased intrathoracic pressure lasts 45 seconds, it causes stagnant hypoxy of the brain with metabolic changes . . .Thanks to limited venous return, minute heart volume is decreased to one-half with consequent disturbance of cardiac rhythm. Therefore the breath-holding with increased thoracic pressure is not without danger (cerebral stroke, collapse, paroxysm of epilepsy, coronary infarction).
“Pronounced increase of thoracic pressure can be caused by [the] following conditions: 1) if tension of expiratory thoracic muscles is increased after glottis is closed, 2) if uddiyana bandha is practiced incorrectly, causing abdominal press[ure], 3) if there is relaxation of diaphragm during breath-holding and increased abdominal pressure expands over it to thoracic cavity. Increased intraabdominal pressure can have negative effect also during asanas, if they are practice with longer breath-holding and with activation of expiratory muscles (e.g., mayurasana, backward bending).
“As a consequence we can state that incorrect practicing of certain yogic exercises can endanger especially disposed persons and regular incorrect practice could negatively influence even healthy people.”