A novel technique to measure position-dependent resistance changes in the vertebral arteries postmortem: new insights into the aetiology of SIDS?

AIM

A central respiratory regulation disturbance--triggered by impaired oxygen supply to the brainstem--is being discussed as an aetiological factor in sudden infant death syndrome. In this experimental study, further insight was sought into how far cervical spine movements may induce critical narrowing of the vertebral arteries.

METHODS

In 10 infant bodies, the vertebral arteries were cannulated close to their origin and perfused with a fluid bolus of 5 ml in 2 s. The intravascular peak pressure created was memorized. Individual resistance indices were computed for every vertebral artery by relating the average pressure maximum from 10 measurements each with maximal rotation of the neck to either side alone and then with additional hyperextension of the cervical spine to the average peak pressure in neutral head position.

RESULTS

Alterations of position-induced pressure changes occurred in the vertebral arteries of all children. Considering exclusively the combined movements of rotation plus extension, resistance increased ipsi- and contralaterally--no matter which side the head was turned--in three infants. A further three reacted with resistance surges only contralateral to the direction of rotation, and one only ipsilateral. Double contralateral associated with only one-directional ipsilateral rise was observed twice, and vice versa once.

CONCLUSION

The presented method enables crude quantification of postmortem dynamic resistance alterations in the vertebral arteries. How far such measurements reflect authentic circulatory conditions during life remains to be assessed.

Effects of oral creatine supplementation in a patient with MELAS phenotype and associated nephropathy

An 18-year-old male patient with MELAS phenotype and 2 previous episodes of cerebral stroke, recurrent seizures and nephropathy, was treated with creatine monohydrate after the acute onset of psychomental regression and changing states of somnolence and aggressive and agitated behaviour. These symptoms disappeared completely after 4 weeks of treatment with creatine after which the patient regained all his previous mental abilites. Brain (white matter) proton magnetic resonance spectroscopy (chemical shift imaging) performed at 6 and 12 months of treatment showed lactic acid (Lac) accumulation and high creatine (Cr) levels in relation to choline-containing compounds (Cho). Urinary creatinine excretion as an indicator of the muscle and brain creatine pool increased upon short-term (12 days) high-dosage creatine supplementation (20 g per day) while plasma creatinine concentrations as possible indicators both of increasing creatine pool and of renal insufficiency increased during the course (28 months) of low-dosage creatine supplementation (5 g per day). Deterioration of renal function was finally indicated by urea retention and by impairment of renal creatinine clearance. These observations suggest that creatine supplementation may have a neuroprotective effect in patients with MELAS and episodes of acute mental deterioration. Adverse effects of creatine supplementation on renal function must be considered especially in patients with preexisting nephropathy.

Position dependent changes of cerebral blood flow velocities in premature infants

The supine or prone positioning of infants has been a cause of much controversy. Recently it has been postulated that the position dependent hypoperfusion of the brainstem represents a possible cause of sudden infant death. To demonstrate position dependency and maturational changes of cerebral perfusion in premature newborn infants we investigated cerebral blood flow velocities (CBFV) in the main supratentorial and brainstem cerebral arteries. Measurements of CBFV were done with transfontanellar colour-coded Doppler sonography in the internal carotid artery (ICA), basilar artery (BA), and vertebral artery (VA) in the prone (head centered-baseline) and supine positions (maximal rotation to both sides) in 23 premature infants aged between 3-5 days of life. We performed follow-up measurements in 17 infants 7-10 days later and in 16 infants at the corrected age of 1 month. There was no difference in mean CBFVs between the prone and supine position at the first investigation. At the third investigation, CBFVs were significantly higher in the supine compared to the prone position. The CBFVs of the ICA were higher than in the BA and VA. This difference was not influenced by the body position but increased with post-natal age more in the VA (159%) than in the BA (129%) and ICA (128%). Position dependency was not seen in the ICA perfusion. In the prone position, five infants showed an incomplete steal effect in the contralateral VA. There was no significant side difference in the CBFVs of the ICA and VA, but in the resistance indices in the VA (left > right).

CONCLUSION

in premature newborns, position dependent changes of cerebral blood flow velocity develop with maturation and are most pronounced in the vertebrobasilar system. These changes are possibly due to compression of the vertebral artery by neck movement and suggest an individual risk of brainstem perfusion deficits that may be aggravated with age and head rotation in a prone position.

Can hypocapnia reduce cerebral embolization during cardiopulmonary bypass?

BACKGROUND

Cerebral embolization is a major cause of central nervous dysfunction after cardiopulmonary bypass. Experimental studies demonstrate that reductions in arterial carbon dioxide tension (PaCO2) can reduce cerebral embolization during cardiopulmonary bypass. This study examined the effects of brief PaCO2 manipulations on cerebral embolization in patients undergoing cardiac valve procedures.

METHODS

Patients were prospectively randomized to either hypocapnia (PaCO2 = 30 to 32 mm Hg, n = 30) or normocapnia (PaCO2 = 40 to 42 mm Hg, n = 31) before aortic cross-clamp removal. With removal of the aortic cross-clamp embolic signals were recorded by transcranial Doppler ultrasonography for the next 15 minutes.

RESULTS

Despite significant differences in PaCO2, groups did not differ statistically in total cerebral emboli counts. The mean number of embolic events was 107 +/- 100 (median, 80) in the hypocapnic group and 135 +/- 115 (median, 96) in the normocapnic group, respectively (p = 0.315).

CONCLUSIONS

Due to the high between-patient variability in embolization, reductions in PaCO2 did not result in a statistically significant decrease in cerebral emboli. In contrast to experimental studies, the beneficial effect of hypocapnia on cerebral embolization could not be demonstrated in humans.

[Diagnostic imaging in neonatal stroke]

A cerebral artery infarction is an important differential diagnosis in the newborn with neurological abnormalities. Based on clinical data, its incidence is estimated to be 1 in 4000 newborns. Since the course is often subclinical, the true incidence is probably higher.

DIAGNOSIS

Cerebral ultrasound and Doppler sonography as readily available screening tools play a central role in the initial diagnosis of neonatal cerebral infarction. Definitive diagnosis is made by computed tomography or magnetic resonance imaging. Beside symptomatic anticonvulsive therapy, treatment aims at the prevention of secondary ischemic injury.

DISCUSSION

Three term infants with different clinical courses of neonatal stroke are presented to sensitize the clinician and the radiologist for this probably underdiagnosed entity. The role of imaging modalities in the diagnosis and follow-up of neonatal cerebral infarction is discussed.

Systemic blood pressure and cerebral blood flow velocity during carotid surgery

BACKGROUND

To evaluate the effect of mean arterial blood pressure (MAP) on cerebral perfusion during carotid surgery, we investigated blood flow velocity in the middle cerebral (Vs,mca) using transcranial Doppler ultrasonography (TCD).

METHODS

During carotid crossclamping, treatment included either phenylephrine-induced hypertension without shunting (Group XC; n = 11) or insertion of a shunt (Group S; n = 12).

RESULTS

Increasing MAP in Group XC before crossclamping (81 + /-13 mmHg to 107 +/- 12 mmHg) caused an increase of Vs,mca (59 +/- 17 cm/s to 75 +/- 20 cm/s; p < 0.001). During crossclamping without a shunt, Vs,mca was not dependent on MAP, and was reduced (mean 47 +/- 24 cm/s) in relation to preclamp values. In Group S, Vs,mca was always dependent on MAP and the preclamp velocity was maintained (before shunt: 75 +/- 26 cm/sec; during shunt: 79 +/- 30 cm/sec).

CONCLUSIONS

Although we found an impaired cerebral autoregulation, Vs,mca was independent of MAP during carotid crossclamping. Thus, TCD measurements have to be interpreted with caution during crossclamping, and the effect of induced hypertension has to be confirmed with more invasive measures of cerebral blood flow.