Spiking patterns and synchronization dynamics of thalamic neurons along the sleep-wake cycle are studied in a minimal model of four coupled conductance-based neurons. The model simulates two thalamic neurons coupled via a gap junction and driven by a synaptic input from a two-neuron model of sleep regulation by the hypothalamus. In accord with experimental data, the model shows that during sleep, when hypothalamic wake-active neurons are silent, the thalamic neurons discharge bursts of spikes. During wake, the excitatory synaptic input from the hypothalamus drives the coupled thalamic neurons to a state of tonic firing (single spikes). In the deterministic case, the thalamic neurons synchronize in-phase in the bursting regime but demonstrate multi-stability of out-of-phase, in-phase, and asynchronous states in the tonic firing. However, along the sleep-wake cycle, once the neurons synchronize in-phase during sleep (bursting), they stay synchronized in wake (tonic firing). It is thus found that noise is needed to reproduce the experimentally observed transitions between synchronized bursting during sleep and asynchronous tonic firing during wake. Overall, synchronization of bursting is found to be more robust to noise than synchronization of tonic firing, where a small disturbance is sufficient to desynchronize the thalamic neurons. The model predicts that the transitions between sleep and wake happen via chaos because a single thalamic neuron exhibits chaos between regular bursting and tonic activity. The results of this study suggest that the sleep- and wake-related dynamics in the thalamus may be generated at a level of gap junction-coupled clusters of thalamic neurons driven from the hypothalamus which would then propagate throughout the thalamus and cortex via axonal long-range connections.
Spinal anesthesia is widely used for emergency and elective C/S delivery. However its main drawback is hypotension which may cause nausea, vomiting and cardiovascular collapse and loss of consciousness in mother as well as fetal hypoxia and acidosis due to placental hypo perfusion. AIMS AND OBJECTIVE: To compare the incidence of hypotension in intraoperative period and to compare the fetal outcome in two groups (Preloading and co loading group). STUDY DESIGN: Prospective randomized double blind study. MATERIALS AND METHOD: This study was conducted in the obstetric emergency OT of Malda Medical College. 100 primi gravid mothers aged between 18-29 years with ASA-1 physical status posted for emergency C/S for fetal distress was randomly allocated for either preloading (Group P) or co loading (Group C). RESULT AND ANALYSIS: Fluid requirement is significantly less in group C. There was no significant difference in the incidence of hypotension and ephedrine use. Fetal outcome in 1 min Apgar score in group C is significantly better as the baby could be delivered quickly in group C. CONCLUSION: Our study revealed that preloading can be safely avoided for spinal anesthesia in C/S for fetal distress. By using co loading method we can save valuable time required to deliver the baby and avoid circulatory overload without increasing the incidence of hypotension.
Travel across time zones disrupts circadian rhythms causing increased daytime sleepiness, impaired alertness and sleep disturbance. However, the effect of repeated consecutive transmeridian travel on sleep-wake cycles and circadian dynamics is unknown. The aim of this study was to investigate changes in alertness, sleep-wake schedule and sleepiness and predict circadian and sleep dynamics of an individual undergoing demanding transmeridian travel. A 47-year-old healthy male flew 16 international flights over 12 consecutive days. He maintained a sleep-wake schedule based on Sydney, Australia time (GMT + 10 h). The participant completed a sleep diary and wore an Actiwatch before, during and after the flights. Subjective alertness, fatigue and sleepiness were rated 4 hourly (08:00-00:00), if awake during the flights. A validated physiologically based mathematical model of arousal dynamics was used to further explore the dynamics and compare sleep time predictions with observational data and to estimate circadian phase changes. The participant completed 191 h and 159 736 km of flying and traversed a total of 144 time-zones. Total sleep time during the flights decreased (357.5 min actigraphy; 292.4 min diary) compared to baseline (430.8 min actigraphy; 472.1 min diary), predominately due to restricted sleep opportunities. The daily range of alertness, sleepiness and fatigue increased compared to baseline, with heightened fatigue towards the end of the flight schedule. The arousal dynamics model predicted sleep/wake states during and post travel with 88% and 95% agreement with sleep diary data. The circadian phase predicted a delay of only 34 min over the 16 transmeridian flights. Despite repeated changes in transmeridian travel direction and flight duration, the participant was able to maintain a stable sleep schedule aligned with the Sydney night. Modelling revealed only minor circadian misalignment during the flying period. This was likely due to the transitory time spent in the overseas airports that did not allow for resynchronisation to the new time zone. The robustness of the arousal model in the real-world was demonstrated for the first time using unique transmeridian travel.
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