Measuring venous oxygenation using the photoplethysmograph waveform

Objective. We investigate the hypothesis that the photoplethysmograph (PPG) waveform can be analyzed to infer regional venous oxygen saturation. Methods. Fundamental to the successful isolation of the venous saturation is the identification of PPG characteristics that are unique to the peripheral venous system. Two such characteristics have been identified. First, the peripheral venous waveform tends to reflect atrial contraction. Second, ventilation tends to move venous blood preferentially due to the low pressure and high compliance of the venous system. Red (660 nm) and IR (940 nm) PPG waveforms were collected from 10 cardiac surgery patients using an esophageal PPG probe. These waveforms were analyzed using algorithms written in Mathematica. Four time-domain saturation algorithms (ArtSat, VenSat, ArtInstSat, VenInstSat) and four frequency-domain saturation algorithms (RespDC, RespAC, Cardiac, and Harmonic) were applied to the data set. Results. Three of the algorithms for calculating venous saturation (VenSat, VenInstSat, and RespDC) demonstrate significant difference from ArtSat (the conventional time-domain algorithm for measuring arterial saturation) using the Wilcoxon signed-rank test with Bonferroni correction (p < 0.0071). Conclusions. This work introduces new algorithms for PPG analysis. Three algorithms (VenSat, VenInstSat, and RespDC) succeed in detecting lower saturation blood. The next step is to confirm the accuracy of the measurement by comparing them to a gold standard (i.e., venous blood gas).     

A randomized, controlled trial to study the effect of exercise consultation on the promotion of physical activity in people with Type 2 diabetes: a pilot study.

AIM: To evaluate the effect of exercise consultation on promotion of physical activity in people with Type 2 diabetes. METHODS: Twenty-six sedentary people with Type 2 diabetes were randomly assigned to receive an exercise consultation and standard exercise information (experimental) or standard exercise information alone (control). Exercise consultation is a one-to-one discussion, based on the transtheoretical model, designed to educate, strengthen motivation and develop realistic strategies to promote physical activity. Changes from baseline at five weeks were assessed in (a) stage of exercise behaviour (b) physical activity levels (7-day recall questionnaire and an accelerometer) (c) quality of life (SF-36 Health Survey and 22-Item Well-Being Questionnaire). RESULTS: 82% (9/11) of participants receiving a consultation increased their stage of exercise behaviour compared to 33% (4/12) of controls (chi2 = 5.4, P = 0.02). Physical activity counts/week increased by 4% (1636 067/1696 191) in the experimental group and decreased by 9% (1560 960/1725 510) in controls. A significant difference was recorded for the change in activity counts per week from baseline to follow-up between the experimental and control group (98% CI = 60 673-710 827). The number of participants taking part in sport or leisure activity increased by 55% (6/11) in the experimental group and decreased by 6% (1/12) in controls. Positive changes were evident in the experimental group, compared to controls, in both quality of life questionnaires. CONCLUSION: Exercise consultation is more effective in stimulating exercise behaviour change in the short term than a standard exercise leaflet.     

Prescribing and Dispensing of Insulin: Margins for Error?

To investigate recent anecdotal reports of incorrect insulin dispensing, we compared retail pharmacists' and doctors' understanding of commonly used insulin brands. Eighty pharmacists, 29 general practitioners (GPs), and 31 junior hospital doctors were interviewed and completed a questionnaire concerning the duration of action and formulation of 17 insulins. Views on dispensing of alternative insulins were sought from the pharmacists. Fifteen insulin pairs in two columns, 'insulin prescribed' and 'dispense instead', were presented and pharmacists and doctors asked if substitution was appropriate. Mixtard, Penmix and Actrapid were the best understood insulins, Insulatard, Humulin Zn and Protaphane the worst. Both GPs (p = 0.014) and hospital doctors (p < 0.001) scored better than pharmacists. No pharmacist stated that they would routinely dispense alternative insulin, 27 out of 80 not even in an emergency, though 37 were prepared to do so in such a situation after checking, usually with a doctor or in the relevant literature. Sixteen pharmacists, 24 GPs, and all 31 hospital doctors completed the section on insulin pairs but accuracy at identifying appropriate substitutions was poor. These findings coupled with confusing insulin nomenclature may lead to dangerous dispensing errors.