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Biomedical subjects

I M Williams

Publications and source records attributed to I M Williams.

At least 37 records · Page 2Linked to original sources
PubMed1995

Effects of stimulus velocity and acceleration on smooth pursuit in motor neuron disease.

Sinusoidal smooth pursuit eye movements were evaluated in 11 normals, five moderately and four severely affected motor neuron disease (MND) patients, using two target amplitudes and a range of frequencies. This enabled us to examine separately the effects of peak target velocity and acceleration on pursuit gain. Moderately affected patients showed an acceleration, but not a velocity saturation; severely impaired patients' performance declined with increased velocity. Smooth pursuit eye movements are thus impaired in MND, but the nature of this pursuit deficit is complex and changes with the progression of the disease.

Aged↗
PubMed1995

The influence of contralateral carotid stenosis and occlusion on cerebral oxygen saturation during carotid artery surgery.

OBJECTIVES: To study the effect of contralateral carotid stenosis on oxygen saturation (CsO2) of both cerebral hemispheres monitored by reflective near-infrared spectroscopy (NIRS) during carotid surgery. METHODS: NIRS was compared to ipsilateral transcranial Doppler ultrasonography (TCD) of the middle cerebral artery and jugular bulb venous oxygen saturation (JvSO2) in 54 patients undergoing carotid endarterectomy. RESULTS: Median operated side and contralateral CsO2 were 68(54-88)% and 69(55-85)% before carotid clamping falling to 63(44-80)% and 69(55-84)% respectively on clamping the carotid (p < 0.0001 and p = NS). JvSO2 fell from 78(38-98)% to 72(30-97)% on carotid clamping with a percentage fall in peak TCD of -28(0 to -100)% (p < 0.0001). Patients with a contralateral carotid artery occlusion experienced falls in ipsi and contralateral CsO2 of -8(-4 to -10)% and -3(2 to -7)% compared to -4(0 to -14)% and 0(-5 to 4)% in those with a lesser stenosis (p < 0.05). On declamping, median ipsilateral and contralateral CsO2 rose from 65(46-82)% and 67(52-87)% to 68(53-84)% respectively (p < 0.0001 and p = NS). JvSO2 increased from 75(33-95)% to 79(42-95)% (p < 0.0001) with an increase in median peak TCD of 35(-34 to 506)%. CONCLUSIONS: The greatest changes in CsO2 occurred in the operated side cerebral hemispheres in those with a contralateral carotid artery occlusion. However, a contralateral carotid artery occlusion does not reliably predict the need for a shunt and cerebral monitoring remains essential; although is only required on the operated side.

Brain↗
PubMed1994

Cerebral oxygen saturation, transcranial Doppler ultrasonography and stump pressure in carotid surgery.

Transcranial Doppler ultrasonography (TCD) of the middle cerebral artery (MCA), light-reflective cerebral oximetry and measurement of internal carotid artery stump pressure were compared as methods of monitoring cerebral perfusion during carotid surgery in 33 patients. Median cerebral oxygen saturation was 70 (range 62-85) per cent and TCD-measured mean blood velocity 42 (range 19-91) cm/s before carotid cross-clamping, falling to 68 (53-83) per cent and 16 (0-50) cm/s respectively on application of the clamps (P < 0.001). Stump pressure correlated closely with MCA blood velocity 30 s after the start of cross-clamping (rs = 0.58, P < 0.001), but not with cerebral oxygen saturation. A fall of 5 per cent or more in cerebral oxygen saturation following cross-clamp application was predicted by a decrease in mean MCA blood velocity of at least 60 per cent. Changes in cerebral oxygen saturation correlated significantly with systolic blood pressure throughout the perioperative period (rs = 0.41, P < 0.001). Significant falls in cerebral oxygenation were not predicted by low stump pressure but were associated with large reductions in the mean MCA blood velocity measured by TCD.

Blood Flow Velocity↗
PubMed1994

Light-reflective cerebral oximetry and jugular bulb venous oxygen saturation during carotid endarterectomy.

A novel instrument using reflected near-infra-red light spectroscopy to measure cerebral oxygen saturation non-invasively was evaluated during carotid endarterectomy; cerebral perfusion was compared with jugular bulb venous oxygen saturation and transcranial Doppler ultrasonographic measurements. Initially, oximetry sensors with light source-detector separation distances of 10 and 27 mm were positioned over the frontal area, while a cannula positioned in the jugular bulb permitted sampling for jugular bulb venous oxygen saturation. To increase cerebral oxygen saturation sensitivity, modified sensors with light source-detector separation distances of 30 and 40 mm were relocated over the middle cerebral artery territory. The changes in cerebral and jugular bulb venous oxygen saturation, and in peak blood flow velocity before and 30 s after carotid clamping and declamping were recorded. The modified cerebral perfusion system achieved improved correlations between cerebral and jugular bulb venous oxygen saturation changes during carotid clamping and declamping (r = 0.92, P < 0.001). The correlation between change in cerebral oxygen saturation and the percentage change in peak flow velocity on both cross-clamping and declamping was equally strong (r = 0.90, P < 0.001). Near-infra-red cerebral spectroscopy reliably detects changes in cerebral oxygen saturation during carotid endarterectomy and may have wide applications in monitoring brain perfusion during neurosurgery and cardiopulmonary bypass surgery, and in closed head injury.

Blood Flow Velocity↗
PubMed1994

Cerebral hypoxia detected by near infrared spectroscopy.

Near infrared spectroscopy is a relatively new technique for monitoring intracerebral oxygen saturation. Using the technique, three episodes of cerebral hypoxia were detected during elective carotid endarterectomy which were not reliably recorded by more standard monitoring of cerebral perfusion. In one case, cerebral hypoxia was related to slippage of the tracheal tube into the right main bronchus and in the other two to episodes of hypotension. Near infrared spectroscopy is a reliable indicator of peripheral cortical perfusion and provides continuous and noninvasive monitoring of intracerebral oxygen saturation.

Aged↗
PubMed1994

Laparoscopic cholecystectomy: laser or electrocautery?

Laparoscopic cholecystectomy is now an accepted part of general surgery. With the recent upsurge of interest in laparoscopic techniques, an optimum method of ensuring secure haemostasis is important particularly during dissection of the gall bladder from its mesenteric attachments. The use of laser to ensure haemostasis has been well practised in the treatment of peptic ulceration. Electrocautery is a time-honoured method of controlling local bleeding points by coagulation of tissue. The aim of this study was to assess whether one procedure showed any advantage over the other in terms of the length of operation time, postoperative drainage volume, time to dissect the gall bladder and length of the hospital stay.

Adult↗
PubMed1991

Intermittent oscillopsia in a case of congenital nystagmus. Dependence upon waveform.

Spontaneous reports of oscillopsia are rare in cases of congenital nystagmus (CN). We examined the relationship between nystagmus waveform characteristics and oscillopsia in one such case. To reduce the patient's nystagmus, she was fitted with contact lenses. We examined the effects of tactile feedback by applying local anesthetic while she wore the lenses. When she was without lenses, we provided tactile feedback by applying gentle finger pressure to one eyelid. She was also asked to look at a peripheral afterimage. Nystagmus was analyzed for frequency, amplitude, foveation duration, and drift velocity, if foveation was not perfectly stable. Perceived target stability was recorded. The patient noted oscillopsia during the initial baseline recording and with lid pressure. The image was stable with contact lenses with and without anesthesia and during the second session baseline; at these times, drift velocity was less than 4 degrees/sec and foveation duration was greater than 100 msec. No oscillopsia of the afterimage in dark was noted; she perceived it moving with her gaze as she attempted to look at it. It appears that in some CN patients, the suppression of oscillopsia operates only within fixed limits of foveation stability and duration. When, because of internal or external factors, their nystagmus exceeds these, oscillopsia results.

Adolescent↗