A dministration of supplementary O2 is considered to be safe, as exemplified by one editorial comment1: “Oxygen should be used as soon as possible, in as near 100% as possible in all resuscitation situations, and for the early management of injury and illness. Its use will never disadvantage [our emphasis] a patient under these circumstances.” We believe this claim merits examination. The ratio...

The rCBF response to hypocapnia induced by active short-term hyperventilation was determined in the contralateral hemispheres of ten patients with acute unilateral cerebral infarction. Overall rCBF reduction occurred in only two patients. Regional or widespread abnormal responses to Paco2 reduction manifested as either no change or a paradoxical increase in the rCBF were observed in eight patie...

BACKGROUND AND PURPOSE Orthostatic and other stresses trigger tachycardia associated with symptoms of tremulousness, shortness of breath, dizziness, blurred vision, and, often, syncope. It has been suggested that paradoxical cerebral vasoconstriction during head-up tilt might be present in patients with orthostatic intolerance. We chose to study middle cerebral artery (MCA) blood flow velocity ...

The purpose of this study was to investigate changes in total retinal blood flow (RBF) using Doppler Fourier Domain Optical Coherence Tomography (Doppler FD-OCT) in response to the manipulation of systemic partial pressure of CO2 (PETCO2). Double circular Doppler blood flow scans were captured in nine healthy individuals (mean age ± standard deviation: 27.1 ± 4.1, six males) using the RTVue(™) ...

We studied the response of cerebral blood flow to acute step decreases in arterial blood pressure noninvasively and nonpharmacologically in 10 normal volunteers during normocapnia, hypocapnia, and hypercapnia. The step (approximately 20 mm Hg) was induced by rapidly deflating thigh blood pressure cuffs following a 2-minute inflation above systolic blood pressure. Instantaneous arterial blood pr...