Characterisation of linear predictability and non-stationarity of subcutaneous glucose profiles.

Continuous glucose monitoring is increasingly used in the management of diabetes. Subcutaneous glucose profiles are characterised by a strong non-stationarity, which limits the application of correlation-spectral analysis. We derived an index of linear predictability by calculating the autocorrelation function of time series increments and applied detrended fluctuation analysis to assess the non-stationarity of the profiles. Time series from volunteers with both type 1 and type 2 diabetes and from control subjects were analysed. The results suggest that in control subjects, blood glucose variation is relatively uncorrelated, and this variation could be modelled as a random walk with no retention of 'memory' of previous values. In diabetes, variation is both greater and smoother, with retention of inter-dependence between neighbouring values. Essential components for adequate longer term prediction were identified via a decomposition of time series into a slow trend and responses to external stimuli. Implications for diabetes management are discussed.

A chaotic model for tight diabetes control.

The principles of non-linear dynamics ('chaos') theory may improve our understanding of the difficulties of blood glucose control in diabetes, may lead to alternative control strategies in selected individuals, and might even enlighten the issues involved in automated glucose control for the future. Possible experimental and mathematical methods of identifying chaotic behaviour in glucose profiles are briefly discussed. Advice based on this model is suggested for those aiming at tight blood glucose control.

Acute hemodynamic responses to weightlessness in humans.

As NASA designs space flights requiring prolonged periods of weightlessness for a broader segment of the population, it will be important to know the acute and sustained effects of weightlessness on the cardiovascular system since this information will contribute to understanding of the clinical pharmacology of drugs administered in space. Due to operational constraints on space flights, earliest effects of weightlessness have not been documented. We examined hemodynamic responses of humans to transitions from acceleration to weightlessness during parabolic flight on NASA's KC-135 aircraft. Impedance cardiography data were collected over four sets of 8-10 parabolas, with a brief rest period between sets. Each parabola included a period of 1.8 Gz, then approximately 20 seconds of weightlessness, and finally a period of 1.6 Gz; the cycle repeated almost immediately for the remainder of the set. Subjects were semi-supine (Shuttle launch posture) for the first set, then randomly supine, sitting and standing for each subsequent set. Transition to weightlessness while standing produced decreased heart rate, increased thoracic fluid content, and increased stroke index. Surprisingly, the onset of weightlessness in the semi-supine posture produced little evidence of a headward fluid shift. Heart rate, stroke index, and cardiac index are virtually unchanged after 20 seconds of weightlessness, and thoracic fluid content is slightly decreased. Semi-supine responses run counter to Shuttle crewmember reports of noticeable fluid shift after minutes to hours in orbit. Apparently, the headward fluid shift commences in the semi-supine posture before launch. is augmented by launch acceleration, but briefly interrupted immediately in orbit, then resumes and is completed over the next hours.

The bacteriology of a rural general practice: a retrospective six-year study.

The organisms cultured and their antibiotic sensitivities, together with clinical details, were obtained from all the available bacteriology requestlresult forms from a rural practice over a six-year period. The 3022 bacteriology specimens analysed yielded 997 potential pathogens. The main infections studied were those of the urinary tract, the upper respiratory tract and the skin and soft tissue. In spite of the fact that trimethoprim alone had never been used in the practice, 29% of urinary tract pathogens were resistant to this drug. Ninety-six per cent of isolates of Haemophilus influenzae were sensitive to ampicillin. The overall results suggest that most infectious disease in rural general practice can be managed with a limited and inexpensive antibiotic regimen. Such a regimen is described.