Reversal of dormancy in switchgrass with low-light photoperiod extension.

Some switchgrass (Panicum virgatum L.) cultivars originating in the northern USA show limited late-summer and fall growth when grown in more southerly locations despite adequate temperature and moisture. Our objective was to determine the effects of low-light photoperiod extension on the dry matter yield of switchgrass cultivars originating from contrasting latitudes. Seedlings of the four cultivars (Cave-in-Rock, 'Caddo', 'Kanlow', and 'Alamo') were grown for 100 d in a greenhouse in winter under ambient (11.2-12.2 h) and extended (18 h) photoperiods. Photoperiod extension was with 7 micromol m(-2) s(-1) photosynthetic photon flux density. Cultivars responded differently to photoperiod extension (P<0.05). Large increases in dry matter yield at extended photoperiods were observed in Cave-in-Rock (+98%) and Caddo (+129%). The dry matter yield of Kanlow increased by 31%, whereas dry matter yield of the southernmost cultivar Alamo was not affected by photoperiod extension. Yield increases for Cave-in-Rock and Caddo were associated with increased tiller number and weight. A reversal of dormancy for some cultivars with a photoperiodic signal verified that dormancy was not simply a result of a low radiant input.

Evaluation of tissue oximetry in perioperative monitoring of colorectal surgery.

Twenty patients undergoing elective colorectal surgery were studied during and after operation by means of tissue oximetry measuring the subcutaneous partial pressure of oxygen (PscO2) and by gastric intramural pH measurement. Mean(s.d.) PscO2 recorded 24 h after surgery was significantly lower than the peroperative value: 14(10) versus 24(14) mmHg, P less than 0.02. The postoperative PscO2 was also significantly lower than that measured in a control group of ten healthy volunteers: 14(10) versus 34(18) mmHg, P less than 0.001. The peroperative PscO2 of the patients who developed a postoperative complication was significantly lower than that of those who had an uneventful postoperative clinical outcome: 16(9) versus 32(14) mmHg, P less than 0.02. The peroperative PscO2 of the patient group with complications was also significantly lower than that of the control group: 16(9) versus 34(18) mmHg, P less than 0.02. The peroperative PscO2 of the group of patients without complications was almost identical to that of the control group. During operation only one patient developed gastric intramural acidosis. Perioperative oxygen debt and the response of subcutaneous tissue oxygen tension to oxygen breathing seemed to correlate better with clinical outcome than gastric wall pH values and the conventional parameters of tissue perfusion.

Assessment of the perfusion in peripheral tissue beds by subcutaneous oximetry and gastric intramucosal pH-metry in elective colorectal surgery.

Gastric intramucosal pH (pHi) and subcutaneous oxygen tension (PscO2) were compared with traditional perfusion parameters in patients undergoing elective colorectal surgery and were related to clinical outcome. Ten patients were studied per- and postoperatively and tissue oximetry studies were also performed in a group of 10 healthy volunteers. The response of PSCO2 to oxygen breathing proved to be the most sensitive predictor of clinical outcome. Of the 10 patients 8 failed to respond to an O2 challenge, while all 10 volunteers in the control group did so. Out of those 8 patients 6 presented with mainly infectious complications while only 3 had an inadequate perioperative urine output and none presented with signs of arterial or of gastric intramural acidosis. The present study suggests a possible relationship between clinical outcome and oxymetric signs of tissue hypoperfusion after O2 challenge in surgical patients, even in the presence of an adequate urine output and a normal gastric wall pH.