Isotopic composition of transpiration and rates of change in leaf water isotopologue storage in response to environmental variables.

During daylight hours, the isotope composition of leaf water generally approximates steady-state leaf water isotope enrichment model predictions. However, until very recently there was little direct confirmation that isotopic steady-state (ISS) transpiration in fact exists. Using isotope ratio infrared spectroscopy (IRIS) and leaf gas exchange systems we evaluated the isotope composition of transpiration and the rate of change in leaf water isotopologue storage (isostorage) when leaves were exposed to variable environments. In doing so, we developed a method for controlling the absolute humidity entering the gas exchange cuvette for a wide range of concentrations without changing the isotope composition of water vapour. The measurement system allowed estimation of (18)O enrichment both at the evaporation site and for bulk leaf water, in the steady state and the non-steady state. We show that non-steady-state effects dominate the transpiration isoflux even when leaves are at physiological steady state. Our results suggest that a variable environment likely prevents ISS transpiration from being achieved and that this effect may be exacerbated by lengthy leaf water turnover times due to high leaf water contents.

Outcomes associated with a cognitive-behavioral chronic pain management program implemented in three public HIV primary care clinics.

In patients with HIV/AIDS, chronic pain is common and analgesics pose serious risks. Cognitive-behavioral therapies (CBT) provide an alternative. This study evaluated feasibility and impact of a CBT-based pain management program in three public primary care clinics for HIV patients. The program included a workbook and 12-weeks of group CBT sessions. HIV-positive patients with chronic moderate to severe pain were invited to participate in the program and were assessed at enrollment, 6, 12, and 24 weeks. Despite only moderate group attendance, program enrollment was associated with significant improvements in pain intensity, pain-related functioning, anxiety and acceptance, and mental health. At 24 weeks, effect sizes for pain outcomes were -0.83 for pain intensity and -0.43 for functioning. The pattern of change in outcomes was consistent with predictions based on cognitive-behavioral theory. Effects were observed at all clinics. Adding CBT-based pain management into primary care may provide important benefits for patients with HIV/AIDS.