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Continuous recordings of arterial and internal jugular blood oxygen tension, oxygen saturation, carbon dioxide tension, pH, sodium and potassium, together with PECO 2 , blood pressure, and electroencephalogram were obtained to compare the effects of inspiratory and expiratory breath-holding and the Valsalva maneuver on the cerebral circulation and cerebral oxygen availability in man. During the interval of tolerated breath-holding for 69 seconds or less, jugular venous oxygen tension was increased owing to increased cerebral blood flow resulting from an increase of arterial carbon dioxide tension. There was a statistically significant correlation between changes in JPO 2 and PaCO 2 , which proved to be more or less linear for both increases and decreases of PaCO 2 4 mm. above and below control levels. No threshold was found for changes in PaCO 2 altering effective cerebral perfusion and cerebral venous PO 2 , extremely small changes in PaCO 2 (less than 1 mm. Hg) altered cerebral oxygen availability within 10 to 20 seconds. During the Valsalva maneuver a consistent reduction of jugular oxygen tension was found associated with the sudden fall in arterial blood pressure and reduction of arterial carbon dioxide tension. The rapid changes in cerebral hemodynamics and cerebral oxygen availability during the procedure are briefly discussed.
Meyer et al. (Sun,) studied this question.