Within this observation remains the caveat that a substantial portion of the suspended load is mineral-bound P, and may not be immediately available to lake phytoplankton and is instead likely rapidly exported to the sediments. Moreover, variations within the data suggest some seasonality, with TN:TP relationships being generally lower in these samples during the August to October period each year. The result is that these inputs provide for variable molar TN:TP ratios (from < 25 to > 100) in both the waters at the very entrance of Lake Erie as well as farther into the western basin (Chaffin

et al., 2013). Overall the data continue to suggest a potential cryptic yet seasonal role for N input than historical theories dictate as well as GSK1120212 nmr support for seasonal variations in limiting nutrients (Chaffin et al., 2013 and Hartig and Wallen, 1984). We are indebted to Dr. Peter Richards for bringing the error to our attention and working with us in correcting it. “
“Patients in the intensive care unit (ICU) often require mechanical ventilatory support using positive pressure ventilation (Rouby et al., 2004). Estimation of lung variables benefits these patients because they help the clinician to determine the most suitable values in therapeutic measures such as positive end-expired pressure (PEEP). They could also help to avoid the common

problem of ventilator induced lung injury (VILI). Three key lung variables are: 1. alveolar

volume many at the end of an expiration, VA Current techniques for measuring these variables can require the cooperation of the patient, or selleck a modification of the patient’s ventilator system. ICU patients depend on complex life support and monitoring equipment, and thus are usually unable to cooperate with the physician. These patients are therefore some of the most difficult to assess using conventional lung function tests. Zwart et al. pioneered the non-invasive oscillating gas-forcing technique (Zwart et al., 1976 and Zwart et al., 1978), and used halothane as the forcing gas at a very low concentration (around 0.02, v/vv/v) to measure the average ventilation-perfusion ratio ( V˙/Q˙) in the lung. Hahn et al. further developed this method by using biologically inert gases such as nitrous oxide (N2O) and argon (instead of halothane) to measure V  A, V  D, and Q˙P non-invasively ( Hahn et al., 1993 and Williams et al., 1994). They later proposed that oxygen (O2) can be used to measure V  A and V  D ( Hahn, 1996 and Hamilton, 1998). When O2 was used together with N2O, their model can also be used to measure Q˙P. However, their initial technique required a respiratory mass spectrometer that presented considerable difficulty when used in the ICU due to its size, noise, complexity, high maintenance requirements, and lack of portability ( Farmery, 2008). Moreover, their prototype gas mixer is not compatible with modern ICU ventilators.