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Query: UMLS:C0085383 (hypocapnia)
 1,697 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

We performed Fourier analysis of the middle cerebral artery blood flow velocity waveform envelope in 14 normal subjects (group A) and 15 patients, of whom five had arteriovenous malformations (group B), five had cerebral vasospasm (group C), and five had arterial hypertension (group D). Measurements were obtained under conditions of normocapnia, hypercapnia, and hypocapnia. The Fourier coefficients measured in the first five harmonics of the Doppler waveforms of group A were used as the reference baseline and were compared with the coefficients found in the other three groups. Group B showed significantly lower Fourier coefficients, while groups C and D showed higher coefficients (p less than 0.05). The elevation of the Fourier coefficients occurred in an alternating pattern in group C and a decremental pattern in group D. This distinction was attributed to possible differences in the underlying pathophysiological processes. The degree of vascular distensibility of the cerebral arterioles, inferred from the shape of the Fourier analysis curves, was compared in all four groups. Vascular distensibility was characterized as abnormal in arteriovenous malformations, vasospasm, and arterial hypertension. Fourier coefficients may be better indicators of cerebrovascular abnormalities than mean blood flow velocity in hypertension and pulsatility index in arteriovenous malformations, vasospasm, and hypertension.
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PMID:Fourier analysis of the cerebrovascular system. 205 69

The authors describe a method for Doppler ultrasound recording of flow velocity in the basilar artery of normal rabbits and rabbits with experimental subarachnoid hemorrhage (SAH). With this transcranial Doppler (TCD) model, clinical assumptions regarding flow velocity/cerebral blood flow (CBF) relationships, autoregulatory responses, and Doppler spectral waveform analysis can be tested under controlled conditions and compared with established methods of CBF measurement (hydrogen clearance). The time course of changes in flow velocity following SAH (cerebral vasospasm) is successfully demonstrated using the experimental TCD method. There are significant differences in the flow velocity and CBF responses to hypercapnia, hypocapnia, and trimethaphan-induced hypotension which indicate that TCD cannot be considered a simple alternative to CBF measurement for the study of cerebrovascular reactivity and cerebral autoregulation.
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PMID:Transcranial Doppler ultrasound studies of cerebral autoregulation and subarachnoid hemorrhage in the rabbit. 211 49

CO2 reactivity of the brain vessels was investigated in 33 patients (Grade I-III after Hunt and Hess) with cerebral vasospasm after an aneurysmal subarachnoid haemorrhage (SAH) and after early operation within 72 hours. In all cases, transcranial Doppler sonography was used to measure flow velocities in the middle cerebral artery (MCA) and internal carotid artery (ICA) and vasomotor reactivity to CO2 changes. Vasospastic conditions lead to higher flow velocities through the narrow segment, lower peripheral stream resistance due to the post-stenotic pressure drop and lower vasodilating capacities of arterioles under hypercapnia. In severe vasospastic conditions, the peripheral stream bed is already maximally dilated and the hypercapnic response is weak. On the other hand, the peripheral vascular bed reacts normally to hypocapnia in all vasospastic situations. Our results point out two dangerous conditions of vasospastic disease: 1) exhaustion of peripheral vasodilating capacities, and 2) hyperventilatory therapy. Both of these situations can result in a reduction of CBF to brain tissue, mainly for two reasons: 1) In the former, a further increase in vasospasm cannot be compensated for anymore when the peripheral arterioles are maximally dilated, and 2) in the latter, hypocapnia produces a strong peripheral vasoconstrictor response with further reduction of CBF.
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PMID:CO2 reactivity of cerebral vasospasm after aneurysmal subarachnoid haemorrhage. 250 Aug 37

The two major neurological complications of subarachnoid haemorrhage (SAH) due to an intracranial aneurysm are rebleeding and delayed cerebral ischaemia related to cerebral vasospasm. The best way to prevent rebleeding is early surgery. Even when surgery is performed within the first 72 hours posthaemorrhage, the risk of cerebral ischaemia due to vasospasm is high. Conventional medical treatment of cerebral vasospasm includes haemodilution, hypervolaemia and increase of arterial blood pressure. Haemodilution is of limited value as the patients suffering from SAH have usually a low haematocrit. The effectiveness of hypervolaemia is controversial and it may worsen cerebral and pulmonary oedema. Systemic hypertension is an effective therapy of vasospasm, but which can only be used once the aneurysm is controlled. Nimodipine and nicardipine, two calcium antagonists, have a beneficial effect on neurologic outcome following SAH. Today, it is still debated whether the beneficial effect of nimodipine results from the vascular effect of the drug or from a direct cerebral cytoprotective mechanism. Early surgery implies that surgeons operate on brains in acute inflammatory state. Thus, it is mandatory to use peroperative techniques improving cerebral exposure. These techniques include infusion of mannitol, lumbar cerebrospinal fluid (CSF) drainage, administration of anaesthetic agents known to decrease cerebral blood flow (CBF) and hypocapnia. Usually, the effect of CSF drainage is very effective and sufficient by itself. The second objective in the peroperative period is to avoid ischaemia. In areas with decreased flow distal to vasospasm, autoregulation is impaired and CBF is directly dependent on cerebral perfusion pressure. Furthermore, the safe practice of transient clipping of vessels supplying the aneurysm has dramatically reduced the indications of controlled hypotension. During temporary clipping, some authors recommend a pharmacological brain protection using barbiturates, etomidate or propofol, but this practice has not been validated by randomized studies. However, it is generally agreed that the arterial pressure should be increased during temporary clipping to improve collateral blood flow and to maintain it after the aneurysm has been secured. To conclude, together with lumbar CSF drainage and transient clipping, the anaesthetic management of the patients should include: maintenance of the arterial blood pressure close to its preoperative level, maintenance of PaCO2 between 30 and 35 mmHg and of normovolaemia through replacement of fluid and blood losses. After completion of surgery, recovery from anaesthesia should be rapid to allow fast diagnosis of neurological complications. The monitoring of the status of consciousness is the key of the diagnosis of early postoperative complications.
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PMID:[Anesthesia in surgery for intracranial aneurysms]. 781 6

Transcranial Doppler (TCD) enables indirect assessment of cerebral circulation by measurement of cerebral blood flow velocity. Stenosis and occlusion of cerebral vessels or cerebral vasospasm can be detected with this non-invasive method. Moreover, changes in cerebral blood flow velocity in response to hypercapnia or hypocapnia, exercise, temperature, orthostatic stress, visual and intellectual stimulation can be recorded and vasoreactivity or autoregulation mechanisms assessed. Migraine is considered to be a vasomotor disorder; its pathogenesis, however, is complex and requires further studies. TCD may help to detect mechanisms leading to migraine attack as well as during the attack and help to understand its pathophysiology. In this paper, the results of TCD examination in migraine patients in headache-free periods and during the attacks, in basal condition and during different stimulations, are presented. The influence of triptans on cerebral circulation is also described. Additionally, the role of TCD in diagnosis of patent foramen ovale in migraineurs is discussed.
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PMID:Transcranial Doppler evaluation in migraineurs. 1948 94