Study of the origin of short- and long-latency SSEP during recovery from brain ischemia in a rat model

Somatosensory evoked potentials (SSEPs) have been established as an electrophysiological tool for the prognostication of neurological outcome in patients with hypoxic–ischemic brain injury. The early and late responses in SSEPs reflect the sequential activation of neural structures along the somatosensory pathway. This study reports that the SSEP can be separated into early (short-latency, SL) and late (long-latency, LL) responses using independent component analysis (ICA), based on the assumption that these components are generated from different neural sources. Moreover, this source separation into the SL and LL components allows analysis of electrophysiological response to brain injury, even when the SSEPs are severely distorted and SL and LL components get mixed. With the help of ICA decomposition and corrected peak estimation, the latency of LL-SSEP is shown to be predictive of long-term neurological outcome. Further, it is shown that the recovery processes of SL- and LL-SSEPs follow different dynamics, with the SL-SSEP restored earlier than LL-SSEP. We predict that the SL- and LL-SSEPs reflect the timing of the progression of evoked response through the thalamocortical pathway and as such respond differently depending upon injury and recovery of the thalamic and cortical regions, respectively.     

Influence of hypoxic-preconditioning on autonomic regulation following global ischemic brain injury in rats

Experimental and clinical studies have shown that autonomic imbalance is associated with morbidity and mortality due to global ischemic brain injury following cardiac arrest (CA). Although hypoxic-preconditioning (HP) has shown promising neuro-protection in the subsequent ischemic brain injury, the underlying mechanisms and its influence on autonomic regulation have not yet well-understood. In this study, we utilized baroreflex sensitivity (BRS) to investigate the protective effect of HP on autonomic regulation. We investigated changes in heart rate, arterial blood pressure (BP), and BRS within 4 h after CA in rats. The relationship between BRS and neurodeficit score (NDS) was analyzed. Although no significant differences were found in heart rate and BP before and after CA between the control and the preconditioned groups, both BRS and NDS of preconditioned rats were clearly higher than that of the control rats during recovery after CA. Furthermore, BRS in the first 4 h after CA highly correlated with NDS 24 h after CA. These results imply that treatment with HP improves autonomic regulation and protects the brain from ischemic injury. The correlation between BRS and NDS also suggests that BRS can be a prognostic criterion for the level of brain injury after CA.     

Fronto‐Parietal Subnetworks Flexibility Compensates For Cognitive Decline Due To Mental Fatigue

Fronto‐parietal subnetworks were revealed to compensate for cognitive decline due to mental fatigue by community structure analysis. Here, we investigate changes in topology of subnetworks of resting‐state fMRI networks due to mental fatigue induced by prolonged performance of a cognitively demanding task, and their associations with cognitive decline. As it is well established that brain networks have modular organization, community structure analyses can provide valuable information about mesoscale network organization and serve as a bridge between standard fMRI approaches and brain connectomics that quantify the topology of whole brain networks. We developed inter‐ and intramodule network metrics to quantify topological characteristics of subnetworks, based on our hypothesis that mental fatigue would impact on functional relationships of subnetworks. Functional networks were constructed with wavelet correlation and a data‐driven thresholding scheme based on orthogonal minimum spanning trees, which allowed detection of communities with weak connections. A change from pre‐ to posttask runs was found for the intermodule density between the frontal and the temporal subnetworks. Seven inter‐ or intramodule network metrics, mostly at the frontal or the parietal subnetworks, showed significant predictive power of individual cognitive decline, while the network metrics for the whole network were less effective in the predictions. Our results suggest that the control‐type fronto‐parietal networks have a flexible topological architecture to compensate for declining cognitive ability due to mental fatigue. This community structure analysis provides valuable insight into connectivity dynamics under different cognitive states including mental fatigue.     

Evolution of somatosensory evoked potentials after cardiac arrest induced hypoxic-ischemic injury

Aim

We tested the hypothesis that early recovery of cortical SEP would be associated with milder hypoxic-ischemic injury and better outcome after resuscitation from CA.

Methods

Sixteen adult male Wistar rats were subjected to asphyxial cardiac arrest. Half underwent 7 min of asphyxia (Group CA7) and half underwent 9 min (Group CA9). Continuous SEPs from median nerve stimulation were recorded from these rats for 4 h immediately following CA, and at 24, 48, and 72 h. Clinical recovery was evaluated using the Neurologic Deficit Scale.

Results

All rats in group CA7 survived to 72 h, while only 50% of rats in group CA9 survived to that time. Mean NDS values in the CA7 group at 24, 48, and 72 h after CA were significantly higher than those of CA9. The N10 (first negative potential at 10 ms) amplitude was significantly lower within 1 h after CA in rats that suffered longer CA durations. SEPs were also analyzed by separating the rats into good (NDS ≥ 50) vs. bad (NDS < 50) outcomes at 72 h, again showing significant difference in N10 and peak-to-peak amplitudes between the two groups. In addition, a smaller N7 potential was consistently observed to recover earlier in all rats.

Conclusions

The diminished recovery of N10 is associated with longer CA times in rats. Higher N10 and peak-to-peak amplitudes during early recovery are associated with better neurologic outcomes. N7, which may represent thalamic activity, recovers much earlier than cortical responses (N10), suggesting failure of thalamocortical conduction during early recovery.     

Effects on growth of single short courses of fluoroquinolones

The aim of the study was to document the effects of short courses of fluoroquinolones given during an outbreak of multidrug resistant typhoid fever in southern Viet Nam on the growth of children over a period of two years. In a prospective cohort study, 326 Vietnamese children aged between 1 and 14 years were followed up for two years after receiving either ciprofloxacin (70 mg/kg given over 7 d) (n = 173) or ofloxacin (45-50 mg/kg given over 3-5 d) (n = 153) for suspected typhoid fever. Growth velocity and weight for height were compared with an age matched control group of children from the same locality (n = 223) who had not contracted typhoid or received any fluoroquinolones. In the ofloxacin and ciprofloxacin treated patients there was no evidence of acute joint toxicity, nor of any joint symptoms attributable to either of the fluoroquinolones. There was no difference in expected weight for height measurements between the three groups of children over the two year period. During the first year, height velocity in ciprofloxacin treated children was greater than in either ofloxacin treated children or untreated controls. Height velocity in the latter two groups was not significantly different. After two years height velocity was similar in the three groups. The results support the use of short course fluoroquinolone treatment in childhood typhoid, especially when caused by strains resistant to other antibiotics.     

Measurement of cardiac output: Comparison of four different methods

Background In off pump Coronary Artery Bypass Grafting (OPCAB), dislocation of the heart influences cardiac output (CO) rapidly. In this study, we compared bolus thermodilution technique (TDCO) with thermal based Continuous cardiac output (CCO), Pulse contour Cardiac Output (Pulse CO) technique and Non Invasive Cardiac Output (NICO) techniques of continuous cardiac output measurement. Methods 75 patients undergoing OPCAB were studied. In Group A (n=25), CO was measured by arterial waveform analysis. In Group B (n=25), NICO was measured by Carbon dioxide (CO₂) partial rebreathing and in Group C (n=25), it was measured continuously using CCO catheter. CO was also measured by TDCO in all patients. Data were analysed using Bland Altman and regression plot analysis. ANOVA test was applied to compare the groups. Results CO measurements were comparable in the three groups. However CCO showed closest agreement with TDCO. During distal coronary artery anastomosis and at low CO, all three techniques showed poor agreement with TDCO and showed a higher CO than TDCO. Conclusion All the methods were statistically comparable and hence interchangeable for CO measurement in OPCAB. However NICO is least expensive and easy to use.     

Laboratory diagnosis of malaria

Malaria particularly falciparum malaria is a major public health problem in India. Its correct and early diagnosis is very important for prompt treatment as a preventive and control measure. Microscopy is the traditional method for laboratory diagnosis of malaria, which is used widely. However, it is time consuming, needs expertism and the detection limit is 10-20 parasites/ml blood in thick film and 100 parasites/ml blood in thin film. Quantitative buffy coat technique (QBC) is highly sensitive method but expensive equipment is needed for this test. The serological methods involving antibody detection give information regarding exposure to malaria but do not differentiate between present and past infections. Genetic probes and PCR are highly sensitive methods but require expensive equipments. Parasite antigen detection tests are useful in field and PHC level for rapid diagnosis of P falciparum malaria.LDH based test for diagnosing malaria is sensitive but can not differentiate between species. For monitoring of drug resistance or follow-up of patients, methods which can quantify parasitaemia are needed. Simply microscopy is the best solution at present.     

Noise reduction in biological step signals: application to saccadic EOG

A weighted filter for noise reduction in nonrecurrent step signals where adaptive filtering cannot be applied is described. An optimal correction of a conventional finite impulse response (FIR) filter is achieved by using a priori knowledge of noise variance and a continuous estimation of the error signal's power. The weighted filter provides an optimal compromise between noise filtering and distortionless tracking. The prior knowledge required is that of the noise power and the lowest frequency in the noise spectrum. Application of the weighted filter to the saccadic electro-oculogram (EOG) results in better estimations of saccade duration and velocity.