Exploring the methods of data analysis in multifocal visual evoked potentials.

PURPOSE: The multifocal visual evoked potential (mfVEP) provides a topographical assessment of visual function, which has already shown potential for use in patients with glaucoma and multiple sclerosis. However, the variability in mfVEP measurements has limited its broader application. The purpose of this study was to compare several methods of data analysis to decrease mfVEP variability. METHODS: Twenty-three normal subjects underwent mfVEP testing. Monocular and interocular asymmetry data were analyzed. Coefficients of variability in amplitude were examined using peak-to-peak, root mean square (RMS), signal-to-noise ratio (SNR) and logSNR techniques. Coefficients of variability in latency were examined using second peak and cross-correlation methods. RESULTS: LogSNR and peak-to-peak methods had significantly lower intra-subject variability when compared with RMS and SNR methods. LogSNR had the lowest inter-subject amplitude variability when compared with peak-to-peak, RMS and SNR. Average latency asymmetry values for the cross-correlation analysis were 1.7 ms (CI 95 % 1.2-2.3 ms) and for the second peak analysis 2.5 ms (CI 95 % 1.7-3.3 ms). A significant difference was found between cross-correlation and second peak analysis for both intra-subject variability (p < 0.001) and inter-subject variability (p < 0.001). CONCLUSIONS: For a comparison of amplitude data between groups of patients, the logSNR or SNR methods are preferred because of the smaller inter-subject variability. LogSNR or peak-to-peak methods have lower intra-subject variability, so are recommended for comparing an individual mfVEP to previous published normative data. This study establishes that the choice of mfVEP data analysis method can be used to decrease variability of the mfVEP results.

Assessment of autonomic function after acute spinal cord injury using heart rate variability analyses.

OBJECTIVES: Spinal cord injury (SCI) often results in severe dysfunction of the autonomic nervous system. C1-C8 SCI affects the supraspinal control to the heart, T1-T5 SCI affects the spinal sympathetic outflow to the heart, and T6-T12 SCI leaves sympathetic control to the heart intact. Heart rate variability (HRV) analysis can serve as a surrogate measure of autonomic regulation. The aim of this study was to investigate changes in HRV patterns and alterations in patients with acute traumatic SCI. METHODS: As soon as possible after SCI patients who met the inclusion criteria had 24 h Holter monitoring of their cardiac rhythm, additional Holter monitoring were performed 1, 2, 3 and 4 weeks after SCI. RESULTS: Fifty SCI patients were included. A significant increase in standard deviation of the average normal-to-normal (SDANN) sinus intervals was seen in the first month after injury (P=0.008). The increase was only significant in C1-T5 incomplete patients and in patients who did not experience one or more episodes of cardiac arrest. Significant lower values of Low Frequency Power, Total Power and the Low Frequency over High Frequency ratio were seen in the C1-T5 SCI patients compared with T6-T12 SCI patients. CONCLUSIONS: The rise in SDANN in the incomplete C1-T5 patients could be due to spontaneous functional recovery caused by synaptic plasticity or remodelling of damaged axons. That the autonomic nervous system function differs between C1-C8, T1-T5 and T6-T12 patients suggest that the sympathovagal balance in both the C1-C8 and T1-T5 SCI patients has yet to be reached.

Evaluation of antidecubitus mattresses.

Pressure sores are a current problem in hospitals and care of the elderly, leading to protracted hospital stays and a high care burden. The trauma for the patients is severe, and the cost of pressure sore prevention and treatment, is considerable. Antidecubitus mattresses are used for prevention and in treatment, but they also contribute to the cost of treating pressure sores. The problem highlighted in the review is that the mattresses' effectiveness in preventing and treating pressure sores has not been sufficiently evaluated. When antidecubitus mattresses are evaluated, it is often only with regard to aspects of the interface pressure and the mattresses' ability to redistribute the pressure. The review points out the important observation that, to be able to evaluate the efficacy of the antidecubitus mattress, the mattress's effect on tissue viability needs to be studied. The parameters that ought to be considered when evaluating a support surface are: interface pressure, pressure and blood flow distribution, temperature and humidity in the skin-support surface interface. The authors propose that the effect on tissue viability of external loading can be assessed by simultaneous measurement of the interface pressure and tissue perfusion.

Safety of nasal budesonide in the long-term treatment of children with perennial rhinitis.

BACKGROUND: Intranasal budesonide is an efficacious treatment for perennial allergic rhinitis. Long-term effects on safety, particularly in children, need further investigation. OBJECTIVE: To investigate the long-term safety of intranasal budesonide in children. METHODS: In an open trial, 78 children (5-15 years) with perennial rhinitis were treated with intranasal budesonide pressurized metered dose inhaler 200 microg twice daily (delivered daily dose 256 microg) for 12 months; 43 children stayed in the study for 12 additional months and were switched to aqueous suspension (400 microg delivered daily dose) for 6 months. Statural growth, bone age, ophthalmologic and rhinoscopic status, cortisol and biochemical analyses in blood and urine were monitored during the first and second years, and adverse events (AEs) were continuously recorded. RESULTS: No significant effects on statural growth and bone age, compared with reference values, were observed. Morning plasma cortisol and 24-h urinary cortisol were not changed during treatment. Patients reported 195 AEs, most commonly nasal dryness (30%), blood-tinged secretions (21%) and, among non-nasal AEs, headache (13%). Rhinoscopy revealed no signs of mucosal atrophy, ulceration, or candidiasis but some nasal dryness. No treatment-related ophthalmological or biochemical aberrations were found. Reduction of blood eosinophils and nasal symptom scores, compared with pre-treatment values, indicated the efficacy of budesonide treatment. CONCLUSION: Long-term treatment for 1-2 years with intranasal budesonide 256-400 microg daily in children with perennial rhinitis revealed no negative effects on growth or endogenous cortisol production. Local side-effects were mild and patient symptoms decreased.

Time-resolved studies of light propagation in paper.

A method for time-resolved recording of light scattering in thin, highly scattering media is described. Subpicosecond pulses from a high-power Ti:sapphire laser are used, and single-shot recordings of the scattered light are made with a fast streak camera. The method is applied to the study of light scattering in paper, and a 1-ps resolution is demonstrated. The dependence of the light scattering on the basis of weight and density of the paper has been studied. A white-light continuum generated from the high-power pulses by the use of self phase modulation in water is used to study the wavelength dependence of the scattering process. A model for the propagation of light in paper has been developed and used in Monte Carlo simulations. The experimental results are used for testing this model, and absorption and scattering parameters are determined from that comparison.

Second-harmonic generation in optically trapped nonlinear particles with pulsed lasers.

Pulsed lasers are used for simultaneous single-beam three-dimensional optical trapping of and second-harmonic generation in 50-100-nm nonlinear particles. The emission power of the frequency-doubled light, the trapping stability, and the particle degradation are investigated for KTP and LiNbO(3) particles trapped by 25-kHz-repetition-rate Q-switched Nd:YAG and 76-MHz mode-locked Ti:sapphire l a s e r s . Typically 1 pW-10 nW of frequency-doubled light is detected from stably trapped particles. The particles may be used as probes for nonintrusively scanned near-field optical microscopy.

Two-color trapped-particle optical microscopy.

We demonstrate a method for nonintrusive scanned near-field optical microscopy. The microscope utilizes an optical trap to position accurately a 50-100-nm-diameter lithium niobate particle. The infrared trapping beam is frequency doubled in the particle, resulting in a visible microscopic optical probe. By separation of the trapping and detection wavelengths, objects that are transparent in the infrared (e.g., biological) may be positioned close to the particle, resulting in high resolution. The current experimental resolution is limited to approximately 500 nm by the properties of the test objects. The theoretical resolution is less than 100 nm.

Vagal and sympathetic activity during spinal analgesia.

Indices of vagal and sympathetic activity were studied in 30 elderly males, to elucidate their possible roles in causing hypotension during spinal analgesia. The technique of spinal analgesia and the regimen of intravenous fluids were standardised. An index of vagal activity was derived from the degree of heart rate variation (successive RR interval change) on ECG recordings. Sympathetic activity was evaluated by changes in the skin conductance (SCR) of 15 patients. Analgesia to pinprick reached a median dermatome level of T5-6 (range T2-T10) by 15 min. Hypotension was correlated with the level of analgesia, and was more likely when spinal analgesia was higher than T5. There was no correlation between vagal activity and the degree of hypotension. The depression of skin conductance responses was not correlated with the degree of hypotension nor with vagal activity. Vagal efferent activity, measured at the heart, does not seem to play a causative role in hypotension occurring during spinal analgesia.

A double-blind comparison between a new multidose powder inhaler (Turbuhaler) and metered dose inhaler in children with asthma.

Turbuhaler is a ready-loaded multiple dose inhaler which does not require co-ordination between release of dose and inhalation. 57 children with asthma participated in this clinical trial to compare the clinical effect and acceptance of terbutaline sulphate via Turbuhaler with that of metered dose inhaler (MDI). The trial consisted of two parts. In the first part of the study, which made use of a double-blind cross-over design, the clinical effect and number of treatment occasions with Turbuhaler were compared with those of MDI. In the second part, which was open, all patients were treated with Turbuhaler for 2 weeks. At the end of this period the patients were asked to make a subjective assessment of effect and to state their preference. There was no difference in clinical effect and number of treatment occasions between Turbuhaler and MDI. A majority of the patients thought Turbuhaler had the best effect and was easy to use.

Sympathetic blockade during extradural analgesia with mepivacaine or bupivacaine.

The extent of sympathetic blockade in 36 patients, who had been given extradural analgesia, was studied by means of the skin conductance response (SCR). The SCR was also studied in six healthy volunteers who received, in a cross-over fashion, infusions of physiological saline (placebo) and saline containing mepivacaine. Two more volunteers were given saline containing bupivacaine. Extradural analgesia caused a partial blockade of sympathetic activity. The higher the level of analgesia the greater the degree of inhibition of the SCR. Complete blockade of the SCR or only a weak response in the foot was obtained in the majority of cases when the level of analgesia reached a dermatome level of T4 or higher. There was no significant relationship between the degree of motor blockade of the lower extremities and the intensity of blockade of the SCR. Extradural injection of 2% mepivacaine had a greater effect on the SCR than did 0.5% bupivacaine. There was no indication that infusion of mepivacaine or bupivacaine in volunteers, whose blood levels were as high as or higher than those likely to be produced during extradural analgesia, affected the SCR.

Surface oxygen pressure distributions in rabbit skeletal muscle: dependence on arterial pO2.

Previous reports indicate that hyperoxemia disturbs the striated muscle tissue oxygenation in both critically ill patients and in healthy human volunteers. We believe that further studies of this problem can most conveniently be carried out in an animal model. A systematic study on the influence of higher than normal arterial pO2 levels on striated muscle surface tissue oxygen pressure distributions (OPD) was performed using an MDO oxygen electrode. Experiments were carried out during controlled ventilation in a rabbit model conceived to maintain exceptional cardiovascular stability. The PaO2 level was varied by altering FiO2 (the fraction of inspired oxygen) randomly between 0.21 (mean PaO2 10.7 kPa), 0.30 (mean PaO2 19.2 kPa), 0.5 (mean PaO2 29.1 kPa) and 0.70 (mean PaO2 44.0 kPa) with only small variations in PaCO2 (4-5 kPa). There was a clear relationship between the degree of hyperoxemia and the degree of abnormality of the muscle tissue OPD: the higher the PaO2 level, the more abnormal was the muscle tissue OPD. Slightly disturbed (scattered) muscle tissue OPD:s appeared at PaO2 levels around 19 kPa, while increasingly scattered OPD:s appeared at PaO2 29 kPa and 44 kPa, respectively. At normal baseline PaO2 levels (mean PaO2 10.7 kPa) muscle OPD:s were normal. The time needed to achieve stable muscle tissue oxygen pressure levels after PaO2 had been increased was longer than expected, i.e., on average 45 min. The OPD shapes as well as the mode of reaction to hyperoxemia were found to be the same in the rabbit as in man. Our model displayed good macro- and microvascular stability and should be useful for studies on regulatory mechanisms of skeletal muscle oxygenation.

Sympathetic activity and haemodynamic variables during spinal analgesia in man.

At present there is a lack of information concerning haemodynamic changes related to the degree of sympathetic blockade during spinal analgesia. In this investigation, involving 36 patients, changes in haemodynamic parameters were studied in 30 patients receiving spinal analgesia and in six patients having "sham spinal" analgesia. Three local anaesthetic solutions were used: bupivacaine without and with glucose and tetracaine with glucose. Skin conductance responses were used to evaluate changes in provoked sympathetic activity. It was found, as in previous studies, that a complete block of sympathetic activity in the foot was seen in only 60% of patients with an average analgesic level of T4. A partial sympathetic blockade was registered up to and above the level of analgesia. In 25/30 cases only minor alterations in cardiac output, heart rate, stroke volume, mean arterial pressure and systemic vascular resistance were seen in spinal analgesia whose level reached on average T4-5. In five cases in whom analgesia reached T4-3, mean arterial pressure fell greater than or equal to 30% with a well-preserved cardiac output, but with complete sympathetic blockade up to T5 and in two cases also in the hand. Only minor differences were observed between the different anaesthetic solutions.

A study of halothane-diethyl ether azeotrope and the Oxford miniature vaporizer.

The performances of an Oxford miniature vaporizer (OMV) and a Fluotec Mark III vaporizer filled with an azeotropic mixture of halothane and diethyl ether were studied. Gas concentrations were estimated using an EMMA gas analyser and a MIRAN spectrophotometer. Calibration tables for both vaporizers were derived. In a small clinical series with air as the carrier gas, to which a small amount of oxygen was added, the azeotrope was found to be a satisfactory anaesthetic agent, giving a short awakening time and an almost pain-free postoperative course.

Skin conductance responses during spinal analgesia.

Skin conductance responses (SCR, "sympatho-galvanic reflex") were measured before and during spinal analgesia in 17 patients scheduled for transurethral surgery. Responses were provoked by standardized electrical stimulation over the clavicle opposite to the recording side; alternatively, a short deep breath, pinching, verbal stimuli or sharp sounds were used. Measuring sites (two electrodes 6 cm apart) were the hand, levels T5, T9, T12-L1 and the foot. Spinal analgesia reached a median cephalad level of T4 (mean T4, range +/- 3 segments) 20-25 min after injection. SCR was markedly depressed in the foot in 15 of 17 patients, at T12-L1 in 12 of 17, at T9 in 10 of 17, at T5 in 9 of 16 and in the hand in 6 of 17. Total abolition of the SCR in the foot was accomplished in only seven cases and sympathetic activity reappeared long before regression of analgesia or motor blockade was observed. In four cases of five with an analgesic level T1-T2, the SCR was preserved in the hand. No consistent correlation between blood pressure change and SCR-change was seen. The conclusion from this study is that preganglionic sympathetic B-fibres are more difficult to block than A-fibres during spinal analgesia. The duration of sympathetic blockade was far shorter than analgesia and motor blockade. Thus, sympathetic blockade during spinal analgesia seems to be far less extensive than that described in the literature.

Regional blood flow in the pig cortex during increased carbon dioxide pressure with local atraumatic application of 133Xenon.

A method for measuring regional cerebral blood flow with local application of 133Xenon was used. A polyester film was placed on pig cerebral cortex under which 0.6-1.3 mCi of 133Xenon dissolved in 2-4 microliter of saline was applied atraumatically. The wash-out process was registered with an external detector. The wash-out curves were not contaminated by extra-cerebral tissue and there was no 'looking-through phenomenon' of non-perfused parts of the brain. Regional cerebral blood flow was 142 +/- 14 ml X 100 g-1 X min-1 (mean +/- S.D.) in grey matter and 34 +/- 9 ml X 100 g-1 X min-1 in white matter when PaCO2 was normal (4.92 +/- 0.43 kPa). When PaCO2 was increased to 9.3 +/- 1.39 kPa regional cerebral blood flow was increased to 313 +/- 60 ml X 100 g-1 X min-1 in grey matter and to 46 +/- 20 ml X 100g-1 X min-1 in white matter.

Can the "sympatho-galvanic reflex" (skin conductance response) be used to evaluate the extent of sympathetic block in spinal analgesia?

The skin conductance response (SCR) (the "sympatho-galvanic reflex") was studied in volunteers and in a few patients undergoing spinal analgesia. Electrical stimulation over the clavicle, breath-holding during inspiration, a short, deep breath and a sharp sound provoked a marked change in conductance not only in the hand and foot but also in dermatomes T5, T9, T12-L1. Thus, the SC response can be used to study sympathetic activity not only in the hand and foot, but also on the chest and abdomen. Electrical stimulation over the clavicle or a short, deep breath were the best means of provoking SC responses in patients receiving spinal analgesia. This restricted pilot study indicates that skin conductance response is maintained at dermatome levels far below anaesthetised levels during spinal analgesia, and a larger study is now under way to investigate these results further.

Spinal analgesia with glucose-free bupivacaine--effects of volume and concentration.

Spinal analgesia using 22.5 mg glucose-free bupivacaine, given either as 3.0 ml of 0.75% solution or 4.5 ml of 0.5% solution was studied in a double-blind fashion in 40 patients scheduled for transurethral surgery. No differences in onset, duration and regression of analgesia or motor blockade were noticed, indicating that dosage (in mg) is more important than either volume or concentration when glucose-free bupivacaine solutions are used for spinal analgesia. The cardiovascular effects were small and no side-effects attributable to the spinal anaesthetic were seen.