Time course evolution of ventilatory responses to inspiratory unloading in patients

Inspiratory muscle unloading decreases ventilatory drive. In this study, we examined the time course of this effect in patients with chronic obstructive pulmonary disease receiving two modes of ventilatory support: pressure support ventilation (PSV), during which each cycle was assisted, and biphasic positive airway pressure (BIPAP), set up in such a manner that one spontaneous breath took place between two consecutive pressure-assisted breaths. The first breath following the switch from spontaneous breathing to PSV was associated with an increase in tidal volume (VT) and a drop in mean transdiaphragmatic pressure (mean Pdi) and inspiratory work (WI) performed per liter but with unchanged values of esophageal occlusion pressure at 100 ms (Pes 0.1), diaphragmatic electrical activity (EMGdi), and WI performed by breath. The same phenomena were observed for the assisted breath of BIPAP as compared with the preceding spontaneous breath. During the subsequent breaths of PSV, Pes 0.1, EMGdi, and WI performed per breath decreased progressively up to the sixth to eighth breaths, and VT returned to pre-PSV values. We conclude that in patients with chronic obstructive pulmonary disease the decrease in ventilatory drive associated with PSV takes place from the first breath onwards but requires six to eight breaths to be fully achieved. During BIPAP, as a consequence of the kinetics of the PSV-induced downregulation of ventilatory drive, assisted breaths following spontaneous breaths are characterized by an enhanced inspiratory efficiency.     

The role of phytosterols in host plant utilization by cactophilicDrosophila

The Cactus-Drosophila Model System of the Sonoran Desert consists of four endemic species ofDrosophila (D. mojavensis, D. nigrospiracula, D. mettleri andD. pachea) and five species of columnar cacti (agria, organpipe, saguaro, cardón and senita). Extensive collection records indicate that each cactus species has only one species ofDrosophila as the primary resident. The elimination of six of the twenty possible random combinations ofDrosophila species and cactus species can be attributed directly to phytosterols.Drosophila pachea has a strict requirement for Δ⁷-sterols such as 7-cholestenol and 7-campestenol. Since Δ⁷-sterols are found only in senita cactus,D. pachea cannot use agria, organpipe, saguaro or cardón as host plants. The lipid fractions of agria and organpipe are chemically similar and contain high concentrations of several 3β,6α-dihydroxysterols. Larval viability tests using chemical constitutents of organpipe cactus demonstrate that the sterol diols are toxic toD. nigrospiracula but not to the resident, species,D. mojavensis. Agria and organpipe are therefore unsuitable as host plants forD. nigrospiracula. These results suggest that phytosterols play a major role in determining host plant utilization by cactophilicDrosophila in the Sonoran Desert. Deceased.