1. Positron emission tomography (PET) studies were performed in six normal right-handed male volunteers (age 30 +/- 3) to investigate the relationship between cerebral activation as measured by relative regional cerebral blood flow (rCBF) and force peak exerted during right index finger flexion. The purpose was to determine in which central motor structures activity is directly correlated with force for repeatedly executed movements. 2. Twelve PET rCBF measurements were performed in each volunteer with the use of H2(15)O as a perfusion tracer. Volunteers pressed a Morse-key repetitively with their right index finger for 2 min while lying in a supine position in the PET camera. The device was fitted with strain gauges to measure the force peaks exerted upon it. Scans were collected twice each at five different levels of exerted force peak and in a resting state. Individual and group results were co-registered with anatomic magnetic resonance images (MRI). 3. Group analysis revealed four major regions with a high correlation between rCBF and different degrees of repetitively exerted force peaks. One was located in the arm area of the left lateral surface [primary somatosensory and motor cortex (SI, MI)]. The second area was situated on the left mesial surface of the brain, posterior to the anterior commissure (AC) and encompassing the first gyrus dorsal to the cingulate sulcus. This area is thought to be homologous to the posterior part of the supplementary motor area (SMA) in the monkey. The third area was the dorsal bank of the posterior cingulate sulcus. The fourth area showing a significant correlation between rCBF and force peaks was in the cerebellar vermis. 4. Individual PET data were co-registered with each individual's MRI in order to identify precisely the locations of structures demonstrating a positive correlation between rCBF and force peak. Activated areas on the mesial surface consisted of the same two distinct regions seen in the group data. In three subjects the focus on the lateral surface of the cortex appeared to extend into the caudal premotor area; in two it extended into the rostral part of the superior parietal area. In no subject did blood flow in the anterior cingulate areas and anterior SMA show a correlation with the force exerted. Cerebellar correlations were present in the vermis in all subjects.(ABSTRACT TRUNCATED AT 400 WORDS)

Summary: Local cerebral hemodynamics and oxygen metabolism were measured by positron emission tomog raphy (PET) with the oxygen-15 C50) steady-state method in baboons, immediately before (TO), 1 (Tl), and 3-4 (T2) h after permanent middle cerebral artery occlu sion (MCAO). At Tl, there was a marked fall in both cerebral blood flow (CBF) and the CBF/cerebral blood volume (CBV) ratio in the occluded territory; these changes were sustained at T2, indicating stable reduction in cerebral perfusion pressure and lack of spontaneous reperfusion within this time range. Compared with pre occlusion conditions, the oxygen extraction fraction (OEF) in the occluded territory was elevated at both Tl and T2, indicative of a persistent oligemia/ischemia for up to 3 h after MCAO. At T2, however, this OEF increase had lessened, concomitantly with a decline in cerebral metabolic rate of oxygen (CMR02). This impairment of Positron emission tomography (PET) studies in humans have provided a unique insight into the metabolic and hemodynamic events which charac terize the evolution of acutely ischemic tissue, es pecially in relation to its function and viability (Baron et aI., 1981(Baron et aI., , 1983 Lenzi et aI., 1982; Wise et aI., 1983;Powers and Raichle, 1985; Hakim et aI.,

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This study's objective was to investigate regional cerebral blood flow (rCBF) within the primary motor cortex (M1) and to compare it with thresholds of transcranial magnetic stimulation (TMS) and electromyographic recordings during exertion of different force levels with the right index finger. Quantitative electromyographic recordings, TMS, and positron emission tomography scans were performed while five and six volunteers, respectively, pressed a Morse key repetitively or with constant force with the right hand at five different force levels: 5, 10, 20, 40, and 60% of the individual's maximum voluntary contraction (MVC). Although at 5% MVC muscle activity was restricted to the first dorsal interosseus muscle, superficial finger flexors, and extensors, there was progressive involvement of proximal muscles during finger flexion with increasing force. rCBF increased logarithmically in the contralateral M1 with increasing force. In ipsilateral M1, rCBF decreased at 5% MVC and then increased logarithmically at higher force levels. TMS thresholds in the contralateral hemisphere declined logarithmically to reach a plateau at high force levels. The threshold in the ipsilateral hemisphere decreased slightly at high force levels. The logarithmic increase of rCBF and decrease of TMS thresholds in the contralateral hemisphere suggest related underlying physiological phenomena; increased cortical synaptic activity and increased excitability. It suggested that the pronounced ipsilateral rCBF alterations reflect transcallosal inhibition and are more prominent during repetitive movements (as used in the positron emission tomography study) than during the generation of a constant force (as exerted during TMS).

Testing vasoreactivity with CO2 or Diamox is a common diagnostic procedure for the study of haemodynamics in stroke patients. CO2 reactivity (CO2R) was tested in 5 baboons six hours after permanent occlusion of the left middle cerebral artery (MCA) in order to attain new insights into interpretation of vasoreactivity tests. Using the microsphere method, cerebral blood flow (CBF) was determined in the various vascular territories as well as in the centre of the ischemia, the penumbra and the remaining MCA-tissue. CBF decreased significantly in the affected MCA in all animals and in addition in the contralateral cerebellum in one animal (p < 0.05). In addition, the left anterior cerebral artery (ACA) demonstrated a similar decrease. During hypercapnia CBF increased in all areas with the exception of the left, occluded MCA territory. Thus CO2 enhanced the difference between ischaemic and non-ischaemic tissue (i.e., tissue with diaschisis). Mean CO2 R was 3.37 ml/100 g/min/mmHg in the right MCA, 0.16 in the left. While the left ACA demonstrated a decreased perfusion during normocapnia in a similar range to the MCA territory, only CO2R was able to identify precisely the territory of the occluded vessel. CO2 R was zero or negative in the ischaemic core, close to zero in the penumbra and profoundly decreased in the remaining MCA tissue. The overall CO2 R of the MCA was almost zero, suggesting vasoparalysis in response to hypercapnia in the core and penumbra and exhausted CO2 R even in non-infarcted, non-penumbral tissue. One animal displayed a negative CO2 R equivalent to an intracerebral steal-phenomenon.(ABSTRACT TRUNCATED AT 250 WORDS)

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Measurement of regional cerebral blood flow (rCBF) was performed in 6 healthy baboons during ventilation with 35% stable xenon in artificial air. rCBF was measured with the intraarterial xenon-133 method. EEG was recorded continuously. All CBF areas of interest over one hemisphere reacted in the same way. Mean flow increased during short-term exposure to stable xenon and decreased if stable xenon inhalation was continued for at least 24 minutes. EEG showed a decrease of a-and /3-wave patterns a short tune after the start of stable xenon inhalation without further changes over the period when rCBF finally decreased. CO 2 reactivity increased in most animals, and autoregulation to mild arterial hypotension was significantly unpaired with increased flow. It is concluded that 35% stable xenon in artificial air increases rCBF after short-term exposure and decreases rCBF after longer exposure. EEG changes were noted after short-term exposure. rCBF and EEG recovered rapidly after the end of stable xenon inhalation. (Stroke 1987; 18:643-648)

The proposed hypotension model is suitable to analyze tachyarrhythmia-induced hemodynamic changes and end-organ perfusion in the presence of myocardial dysfunction. It has the potential to test therapeutic strategies in the treatment of tachycardias.