Minimally invasive highly precise monitoring of respiratory rhythm in the mouse using an epithelial temperature probe.

BACKGROUND: Respiration is one of the essential rhythms of life. The precise measurement of respiratory behavior is of great importance in studies addressing olfactory sensory processing or the coordination of orofacial movements with respiration. An ideal method of measurement should reliably capture the distinct phases of respiration without interfering with behavior. NEW METHOD: This new method involves chronic implantation of a thermistor probe in a previously undescribed hollow space located above the anterior portion of the nasal cavity without penetrating any soft epithelial tissues. RESULTS: We demonstrate the reliability and precision of the method in head-fixed and freely moving mice by directly comparing recorded signals with simultaneous measurements of chest movements and plethysmographic measurements of respiration. COMPARISON WITH EXISTING METHODS: Current methods have drawbacks in that they are either inaccurate or require invasive placement of temperature or pressure sensors into the sensitive nasal cavity, where they interfere with airflow and cause irritation and damage to the nasal epithelium. Furthermore, surgical placement within the posterior nasal cavity adjacent to the nasal epithelium requires extensive recovery time, which is not necessary with the described method. CONCLUSIONS: Here, we describe a new method for recording the rhythm of respiration in awake mice with high precision, without damaging or irritating the nasal epithelium. This method will be effective for measurement of respiration during experiments requiring free movement, as well as those involving imaging or electrophysiology.

A model of mild hypoglycemia.

OBJECTIVE: To investigate the impact associated with mild hypoglycemia among patients with type 2 diabetes (T2DM) in the United States and to identify risk factors among different subpopulations. METHODS: We performed a literature search to gather available data allowing estimation of rates of mild hypoglycemia. Because risk factors are interdependent, risk factors included in the model were based on those reported within multivariate analyses or judged to be biologically plausible by the medical community. Based on literature search results, we built a mathematical model predicting the rates of mild hypoglycemia in individual patients as a function of the patient's antidiabetic medications, hemoglobin A1c levels, duration of diabetes, kidney function, and body mass index. RESULTS: We estimated an overall average rate of mild hypoglycemia among US patients with T2DM of 2.2 ± 0.8 events per person per year. Patients taking oral antidiabetic medications only had an average rate of 1.9 ± 0.8 events per person per year. The average rate for all patients taking insulin, including those combining it with other antidiabetic medications, was 4.9 ± 2.0 events per person per year. Mild hypoglycemia rates increased with age, with 80-year-old patients experiencing 1.5 times the risk of 40-year-old patients. Based on published values for direct and indirect medical costs for mild hypoglycemia events, we determined that the economic impact in the US of mild hypoglycemic events is approximately $900 million per year, roughly equal to that of severe hypoglycemic events. One of the key limitations to our model is that it applies to the US population under standard medical care and not to clinical trials and does not include certain known risk factors such as rigorous exercise. CONCLUSIONS: Understanding the benefit versus risk of glycemic control and hypoglycemia is fundamental to the successful management of patients with T2DM. Our validated hypoglycemia model is an important step in addressing this issue and may be helpful to researchers, clinicians, and payers to determine the patients who are at the highest risk for hypoglycemia, whether a patient is experiencing events at 'higher-than-expected' rates, and the corresponding economic burden.

Estimating health and economic benefits from using prescription omega-3 fatty acids in patients with severe hypertriglyceridemia.

Patients with increased triglyceride levels compared to those with normal levels are at higher risk for coronary heart disease. In patients with severe (≥500 mg/dl) hypertriglyceridemia (SHTG), clinical trials have demonstrated that prescription ω-3 fatty acids (P-OM3s) 4 g/day can decrease triglyceride levels by 45%. However, the precise health and economic benefits of decreasing SHTG with P-OM3 are unknown. We used the previously validated Archimedes model to simulate a 20-year trial involving subjects 45 to 75 years old with SHTG. The trial consisted of an intervention arm (P-OM3 4 g/day) and a control arm. Simulation results for the control arm indicated that subjects with SHTG are at about 2 times higher risk for myocardial infarction than those with normal triglyceride levels. Using estimates from previous epidemiologic studies and meta-analyses with OM3s, the model predicted 29% to 36% decreases in various measurements of adverse cardiac events for the intervention arm. The model also predicted a decrease in ischemic stroke of 24% (95% confidence interval 15 to 33). For the 20-year simulated trial, the cost per quality-adjusted life-year gained for the currently available P-OM3 approved by the Food and Drug Administration was $47,000. Results remained robust under different clinical assumptions. In our model P-OM3 was effective in decreasing triglyceride levels and cardiovascular disease risk in patients with SHTG. In conclusion, P-OM3 medication is cost effective in our simulated trial and comparable to other cost-effective cardiovascular interventions.

On the speed of gravity and the v/c corrections to the Shapiro time delay.

Using a relatively simple method, I compute the v/c correction to the gravitational time delay for light passing by a massive object moving with speed v. It turns out that the v/c effects are too small to have been measured in the recent experiment involving Jupiter and quasar J0842+1845 that was used to measure the speed of gravity.

Characterization of a branch of the phylogenetic tree.

We use a combination of analytic models and computer simulations to gain insight into the dynamics of evolution. Our results suggest that certain interesting phenomena should eventually emerge from the fossil record. For example, there should be a "tortoise and hare effect": those genera with the smallest species death rate are likely to survive much longer than genera with large species birth and death rates. A complete characterization of the behavior of a branch of the phylogenetic tree corresponding to a genus and accurate mathematical representations of the various stages are obtained. We apply our results to address certain controversial issues that have arisen in paleontology such as the importance of punctuated equilibrium and whether unique Cambrian phyla have survived to the present.