We have determined whether changes in PCO(2) above and below eucapnia modulate the precision of the voluntary control of breathing. Twelve trained subjects performed a compensatory tracking task in which they had to maintain the position of a cursor (perturbed by a variable triangular forcing function) on a fixed target by breathing in and out of a spirometer (ventilatory tracking; at 10 l/min)...

The cerebral effects of sevoflurane were compared in dogs with those of enflurane and isoflurane. Initially, the minimum alveolar concentrations (MAC) of sevoflurane and enflurane were determined and the electroencephalographic (EEG) responses to increasing doses of sevoflurane (1.5, 2.0 and 2.5 MAC) or enflurane (1.5 and 2.0 MAC) in unparalysed animals were examined. Administration of sevoflur...

By grouping patients who had carotid angiograms under unusually carefully monitored conditions it has been shown that hypocapnia is associated with vasodilation at low blood pressure but not at high blood pressure. The mechanism is discussed in general terms and it is suggested that the hypocapnic vasodilation may be a response to cerebral hypoxia and may be transmitted via an intracerebral aut...

Blood gas abnormalities in patients with idiopathic pulmonary arterial hypertension (IPAH) may be related to disease severity and prognosis. The present authors performed a 12-yr retrospective analysis assessing arterialised capillary blood gases, haemodynamics, exercise variables and survival in 101 patients with IPAH. At baseline, arterial oxygen tension (P(a,O(2))) and carbon dioxide arteria...

This study examined the relationship between cerebral blood flow (CBF) and end-tidal PCO2 (PETCO2) in humans. We used transcranial Doppler ultrasound to determine middle cerebral artery peak blood velocity responses to 14 levels of PETCO2 in a range of 22 to 50 Torr with a constant end-tidal PO2 (100 Torr) in eight subjects. PETCO2 and end-tidal PO2 were controlled by using the technique of dyn...

BACKGROUND No noninvasive technique is currently capable of "real-time" assessment and monitoring of cerebral blood flow (CBF). We hypothesized that cerebral perfusion could be accurately measured and monitored in "real time" with contrast-enhanced ultrasound (CEU). METHODS AND RESULTS Cerebral perfusion was assessed in 9 dogs through a craniotomy with CEU at baseline and during hypercapnia a...

Regional cerebral blood flow was simultaneously determined using the stable xenon computed tomographic and the radioactive microsphere techniques over a wide range of blood flow rates (less than 10-greater than 300 ml/100 g/min) in 12 baboons under conditions of normocapnia, hypocapnia, and hypercapnia. A total of 31 pairs of determinations were made. After anesthetic and surgical preparation o...