The pressure-time product (PTP) and work of breathing (W) were measured in 19 intubated patients during weaning from mechanical ventilation after aortocoronary bypass surgery. The patients were supported by two different ventilatory modes: biphasic continuous positive airway pressure (Biphasic CPAP; a ventilatory mode that permits spontaneous breathing at two different levels of airway pressure during inspiration and during expiration) and pressure-support ventilation (denominated as assisted spontaneous breathing, ASB). Our aim was to compare the energy cost of breathing imposed by both modes. The PTP was obtained by integrating the area enclosed by the esophageal and chest-wall static recoil pressure curves. The W performed by the patient (Wp) was calculated using Campbell's diagram method, based on the esophageal pressure curve and normalized per liter of ventilation. Two comparable support levels, corresponding to a high and a low degree of mechanical support, were studied for each ventilator mode. The levels of support were generally higher than that necessary to overcome inspiratory resistance. We found significantly higher PTP values during biphasic CPAP than during ASB (p < 0.01), whereas the Wp was the same with biphasic CPAP and ASB at both support levels. We conclude that because of the higher PTP values measured during biphasic CPAP, this mode of ventilation appears to have been more exhausting for our patients. The discrepancy between PTP and Wp is probably due to the different mechanisms of support given by the two ventilatory modes and the greater patient effort is related to those respiratory cycles that are not helped by the ventilator and which represent nearly half of the breaths during biphasic.

The typical wound respiration drift (O2 und CO2) of 1 mm disks, which amounts to 6 times the values measured immediately after derepression, develops only if cicatrization takes place, but never in proliferating or non-proliferating tissues without suberin biosynthesis. The respiration rate of the latter is merely approximately doubled during the first 8 hours and maintains a steady state level continuously for 6 days. The respiratory drift is not affected by methods of tissue preparation and CO2-concentration per se but only depends on the induction or inhibition of suberin synthesis.Cyanide inhibition experiments evidently indicate an electron transfer mechanism by suberizing cells during the first 48 hours which is linked to cytochrome oxidase activity to a considerable extent, whereas proliferating tissue respiration nearly quantitatively follows a different pathway of cyanide-resistant terminal oxidation.Malonate inhibition experiments show the total respiration of proliferating tissue to be resistant, which therefore is bound to the activity of a pathway different from the tricarboxylic acid cycle. Predominantly the action of the pentose-phosphate-shunt must be responsible for energy producing processes and metabolism which finally regulate cell proliferation as well as cell division. Malonate sensitive respiration, that is TCA-cycle activity, is developed only in periderm-forming tissue. Its volume is shown to be in congruence with the amount of "induced respiration" evolved after 8 hours and is responsible for the typical maximum curve. In contrast the resistant basal level is in congruence with the total respiration volume of proliferating disks.The results indicate a direct relationship between increased TCA-cycle activity and suberin synthesis rather than a relationship between TCA-cycle and cellular processes such as protein synthesis, cell division or elongation, as emphasized by other authors.

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Differential derepression of the genome of potato tuber cells by slicing of the tuber tissue leads to cell divisions. This mitotic activity is totally suppressed by Tris-(hydroxymethyl)-aminomethane (Tris)-buffer widely used in biochemical research. The blockage is reversible if tissue slices are transferred to water in order to wash out the Tris-ions.The actual reason for the inhibition of mitotic activity by Tris is as yet unknown. As a possible mechanism of action an uncoupling of electron transfer from phosphorylation in the mitochondrial respiratory chain is discussed. However, experiments show no difference in O2-absorption between Tris-treated tissue and control in water. Moreover the application of several inhibitors of respiration causes exactly the same effects in both tissues. Amytal (blockage of flavoproteids) has no influence on the respiratory rate at any time. Antimycin A (blockage of electron flow from cytochrome b to cytochrome c) as well as HCN (inhibition of cytochrome-oxidase) inhibit respiration of both tissues during the first 24 hours after derepression. Later on the respiration becomes resistant to both inhibitors. So the quality of respiration is assumed to be the same in mitotic active potato slices as in the Tris-treated tissue.Recent results of biochemical analyses of events in carbohydrate breakdown of the tissues in question point to a differential effect of Tris on several enzymes as possible reason for its inhibitory action.

Experiments with potato tuber fragments under normal atmospheric conditions (0.03% CO2) suggest that a wound periderm, prominently marked by suberin synthesis, develops regularly, independently of preparation technics. It has been demonstrated that potato parenchym is able to perform differentiated reactions depending on the changing influences on the reacting cells caused by the wound stimulus and partial isolation. Suberin synthesis and the cicatrization effect can be suppressed totally if changes remain insignificant as compared with the cellular state in the intact organ. This requires: 1. separating the tissue without bruising it to avoid deformations of the protoplasmatic structure; 2. removing adjacent fragments of destroyed cells by rinsing the slices; 3. maintaining cell turgidity by keeping the moisture in the reaction atmosphere at 100%. Moreover 10% CO2-concentration is necessary, corresponding to the intercellular air in situ.Whithin 24 hours after depression these conditions induce spontaneous proliferation uniformly in all superficial cell layers of tissue slices, accompanied by multiple mitosis in place of the typical suberized wound periderm. Inhibition of suberin biosynthesis is reversible by subsequent modification of reaction conditions. In contrast a method has been found to induce suberin formation only and to suppress any cell division activity (Kahl et al., 1969 a). This provides the opportunity to analyse causal corresponding physiological reactions in genetically identical cells. The advantage of this method-compared with long term experiments involving hormone-activated growth in sterile tissue culture - is the possibility of controlling quantitative and qualitative changes in biochemical pathways immediately after derepression.