Changes in cerebral blood flow during hyperventilation and CO2-breathing measured transcutaneously in humans by a bidirectional, pulsed, ultrasound Doppler blood velocitymeter

The standardization of hyperventilation on EEG recording in childhood. I. The quantity of hyperventilation activation

In thirty-seven children free of neurological symptoms, we attempted the standardization of hyperventilation on EEG. We also attempted to determine the quantity of hyperventilation activation necessary to produce equivalent degrees of EEG slowing at different ages. The respiratory rate (RR), total expiratory volume/min (VE), O2 consumption volume/min (VO2), expiratory CO2 volume/min (VCO2), tcpO2 and tcpCO2 were monitored before, during and after hyperventilation. The optimal conditions for adequate activation were found to be: a respiratory rate of 30/min, a 3-fold elevation of VE and a duration of 4 minutes. With this activation, the degree of EEG slowing was found to be nearly inversely proportional to the age (in the age range of 6 years to 17 years old). Therefore, this activation may be adequate and useful for evaluating the EEG development in childhood. As to the relationship between the appearance of EEG slowing and changes in respiratory factors, the pCO2 decrease and the cerebral blood flow decrease, which may be evoked by the pCO2 decrease, are the most fundamental factors that produce EEG slowing during hyperventilation. The difference in the response on hyperventilation between children and adults may be due to age-related CNS sensitivity to CO2 and/or cerebral vascular CO2 responsiveness.

Transcranial Doppler CO2 test for the detection of hemodynamically critical carotid artery stenoses and occlusions

Cerebral CO2-reactivity was tested by transcranial Doppler sonography (Doppler CO2 test) in 232 patients. Time averaged flow velocity in the middle cerebral artery at the 40 mm Hg blood pCO2 level was taken as a reference point, and the relative increase of flow in hypercapnia of 46.5 mm Hg pCO2 was defined as "Normalized Autoregulatory Response" (NAR). A total of 82 patients with no evidence of cerebrovascular disease gave "normal" values for NAR (23.2 +/- 5.2 SD). In 150 patients with 233 stenoses and occlusions of the internal carotid artery NAR was significantly decreased in higher-grade stenoses (P = 0.01 for 80% diameter reduction, P less than 10(-6) for 90% or more). In such stenoses, patients with NAR less than 14 had suffered more frequently (P less than 0.01) from ipsilateral transient ischemic attacks and/or stroke during the previous 6 months than patients with "normal" NAR. Preoperative NAR less than 14 always improved to "normal" values following carotid surgery, while preoperative NAR greater than 19 remained unchanged (60 cases). The transcranial Doppler CO2 test is thought to be a reliable noninvasive method to detect hemodynamically critical carotid stenoses and occlusions. This may be of interest in selecting patients for superficial temporal artery-middle cerebral artery bypass and carotid surgery. For practical use 4 categories of NAR are suggested.

Evaluation of cerebral AVM's using transcranial Doppler ultrasound

Blood flow velocities in basal cerebral arteries were recorded noninvasively in 28 patients with cerebral arteriovenous malformations (AVM's) and were correlated with the angiographic findings. In normal arteries remote from the AVM, flow velocities ranged from 44 to 94 cm/sec (median 65 cm/sec) with pulsatility indexes from 0.65 to 1.10 (median 0.87). This is consistent with findings in normal individuals. Arteries feeding the AVM's were identified by the high flow velocities (ranging from 75 to 237 cm/sec, median 124 cm/sec). The pulsatility index ranged from 0.22 to 0.74 (median 0.48). The difference of these results from findings in normal remote arteries was highly significant (p less than 0.001). Hyperventilation tests illustrated the hemodynamic difference between an AVM and normal cerebrovascular beds. Flow velocity measurements permitted noninvasive diagnosis of AVM's in 26 of the 28 patients. Furthermore, the identification of individual feeding arteries permitted good definition of the anatomical localization of individual AVM's. Flow velocity measurements combined with computerized tomography scans are useful in the diagnosis of AVM's. With the feeding artery's configuration identified on angiography, flow velocity measurements permit a new insight into the "hemodynamic dimension" of an AVM and its possible effects on adjacent normal brain-tissue perfusion in the individual patient.

Transcranial measurement of blood velocities in the basal cerebral arteries using pulsed Doppler ultrasound: velocity as an index of flow

Blood velocities have been measured transcranially, at small Doppler angles, in the middle cerebral artery of normal volunteers. Cerebral blood flow was changed by varying carbon dioxide tension. In four volunteers, the relationships between arterial pCO2 and percentage change in intensity weighted mean, median, and maximum Doppler-shifted frequencies in the internal carotid and middle cerebral arteries were linear with slopes of 2.5 and 2.8% per mm Hg change in pCO2. In 38 volunteers, the relationship between end-expiratory pCO2 and time-averaged maximum Doppler frequency was linear over the range of pCO2 20-60 mm Hg with slopes of 2.5 and 2.9 percentage change per mm Hg, for internal carotid and middle cerebral, respectively. These results are very similar to those reported using direct methods of measuring cerebral blood flow. As the transcranial Doppler method is reproducible, this indicates that changes in middle cerebral blood velocity may be used to monitor changes in flow.

Efficacy and neurologic outcome of profound hypocapneic alkalosis for the treatment of persistent pulmonary hypertension in infancy

Twenty-three newborn infants with severe bilateral pulmonary disease and persistent pulmonary hypertension received mechanical ventilation to pH greater than 7.55 and PaCO2 less than 25 torr. Response, as defined by attainment of a PaO2 greater than 100 torr, occurred in 87% of patients. Analysis of sequential arterial pH determinations revealed a linear increase in the number of infants responding as arterial pH increased. However, individual patients varied greatly in the optimal pH necessary to correct hypoxemia (range pH 7.50 to 7.75). Sixteen patients who had received mechanical hyperventilation were observed for 11.1 +/- 2.3 months. Virtually all had normal growth and development on follow-up physical and neurologic examinations, often despite profound or prolonged alkalosis and hypocarbia. In 11 infants at a corrected gestational age of 1 year, Bayley Scales of Infant Development revealed normal mental developmental indices (mean 106.2 +/- 15.4) and normal, but significantly lower, psychomotor developmental indices (93.2 +/- 11.7) (P less than 0.005). Although response and short-term outcome of neonatal hyperventilation appear favorable, this technique should be reserved for critically ill infants, because its long-term effects on the central nervous system are unknown.

Dependency of blood flow velocity in the middle cerebral artery on end-tidal carbon dioxide partial pressure--a transcranial ultrasound Doppler study

The end-tidal carbon dioxide partial pressure (PCO2) response curves for the flow velocity in the middle cerebral artery were studied in 31 normal subjects with transcranial Doppler techniques. An exponential curve with an exponent of 0.034 mm Hg-1 was found to be a good fit to the recorded data. By means of this relationship, recordings of flow velocity in cerebral arteries can be normalized to a standard value of PCO2. Physiological aspects of cerebrovascular reactivity to PCO2 and the clinical implications of the PCO2 response curve are discussed. The normal material provides a reference for assessing pathological responses.

Acute effects of acetazolamide on cerebral blood flow in man

We have followed the time course of the effect of the carbonic anhydrase inhibitor acetazolamide injected i.v. in unanesthetized healthy human beings. The dose administered was 500 mg as a bolus. Cerebral blood flow (CBF) was measured continuously before, during and after the injection, using a pulsed ultrasound doppler system, which measured the instantaneous mean velocity across the lumen of the internal carotid artery, just below its entrance into the skull. Ventilation, heart-rate, end-expiratory PCO2, arterial PCO2, pH and systemic blood pressure was also measured. We found that acetazolamide caused a rise in CBF which could be detected as early as 2 min after the injection. A maximal average response of 75% increase in CBF was seen after 25 min. The half-time of the declining phase of the response was 95 min. There were no systematic differences in the CO2 reactivities, given as delta CBF/delta PACO2 in % of CBF at normocapnia, before and after acetazolamide injection, regardless of the absolute PACO2 level. The present dose of the drug caused no change in ventilation, alveolar and arterial PCO2 or in arterial blood pH indicating that the carbonic anhydrase was not fully inhibited. Our observations show that acetazolamide nevertheless caused a rapid vasodilation in the brain and over a wide range of PCO2's. We suggest that this agent has a local vasodilator effect on the cerebral arterioles, unrelated to its specific effects as a carbonic anhydrase inhibitor.

An evaluation of the plethysmographic method of measuring cranial blood flow in the new-born infant

Cranial blood flow values obtained plethysmographically in the human new-born infant have been very variable and frequently very low. We have used a doppler ultrasound velocitymeter and skull compliance measurements to investigate whether the technique itself affects the cranial arterial inflow and whether the methods of calculation used introduce bias. Blood velocities were measured in intracranial and extracranial arteries during plethysmography, i.e. before, during and after jugular vein compressions of short duration. Skull expansion after tilting was used to estimate skull compliance. In about 10% of jugular vein compressions, arterial velocities decreased immediately, due to direct pressure on the carotid artery. In the remaining compressions a fall in arterial velocities was seen four or five heartbeats after the onset of the compression. This was probably caused by a decrease in the cranial perfusion pressure consequent on rising venous pressure. Some babies demonstrated very poor skull compliance and these babies had correspondingly low estimates of cranial blood flow. We conclude that jugular venous occlusion plethysmography is not a suitable method for use in the clinical field and is only useful as a research tool in carefully selected situations.

Ultrasound study of the cranial venous system in the human new-born infant and the adult

A pulsed doppler ultrasound technique has been used to measure changes in blood velocities in the superior sagittal sinus, the jugular veins and intracranial and extracranial arteries in 13 neonates, and in the jugular veins and an extracranial artery in 13 adults, during unilateral and bilateral jugular venous compressions. The results have enabled us to determine how the subject under examination functionally uses his cranial venous drainage system in the resting state, and whether or not he can shunt obstructed venous flow through other cranial venous channels. We have found great variability between the subjects. In the resting situation the range of possibilities from total dependence on one jugular vein alone to usage of both jugular veins and the vertebral veins exists. Shunting of blood on jugular compression from either or both jugular veins to the vertebral veins may occur, and contralateral shunting between the jugular veins may be possible in both directions, in one direction or not at all.

rCBF in patients with carotid occlusion. Resting and hypercapnic flow related to collateral pattern

rCBF was measured by 133Xenon inhalation technique in 39 patients with unilateral carotid artery occlusion in a subacute-chronic stage. Resting flow values (ISI) varied between 23.7 and 52.4 ml/100 g/min. An almost constant finding was interhemispheric asymmetry, the degree of which was correlated with the severity of the initial symptoms. An ischemic focus was an insignificant finding. The CO2 response was normal in patients with angiographic signs of circle of Willis collateral flow and without significant contralateral carotid stenosis, whereas it was impaired in patients with a retrograde ophthalmic flow or collateral flow via the circle of Willis and contralateral carotid stenosis greater than or equal to 50%. It is concluded that the CO2 response in useful rCBF variable and may be applied for analysis of collateral flow capacity in patients with carotid artery occlusion considered for bypass surgery.

Skin blood flow in humans as a function of environmental temperature measured by ultrasound

We have measured the blood velocities in arteries supplying the skin in humans both in areas with arteriovenous anastomoses (AVA) and in skin areas without AVA in different temperature situations by means of a pulsed, bidirectional doppler ultrasound instrument. The instrument measures the time average of the instantaneous mean of the blood velocities present in a cross-section of a vessel. So long as the cross-sectional area of the vessel is constant, this average velocity is proportional to volume flow. We observe rapid and large fluctuations in blood velocities in arteries supplying skin areas with AVA in a comfortably warm environment. These fluctuations are substantially larger and more rapid than described by previous authors who have used plethysmograph methods. The blood velocities are more constant both at higher and lower environmental temperatures. There are no similar fluctuations in blood velocity in arteries supplying skin areas without AVA.