close attention objectives: Mechanical ventilation (MV) is a life-support measure for patients who cannot maintain adequate alveolar ventilation.

close attention objectives: Mechanical ventilation (MV) is a life-support measure for patients who cannot maintain adequate alveolar ventilation. Following put offed MV, difficulty in weaning patients from the ventilator can be met with and it has been postulated that difficult weaning is linked to respiratory muscle dysfunction. We exampleed the hypothesis that 18 h of controll MV will diminish diaphragmatic maximal tetanic specific tension (force by cross-sectional area of muscle) without impairing diaphragmatic fatigue resistance.

Design: To example this postulate, adult Sprague-Dawley rats were randomly classified into undivided of two experimental groups: (1) regulate group (n = 8), and (2) 18-h MV clump (n = 6). MV-treated animals were anesthetized, tracheostomized, and received extent air ventilation. Animals in the have the direction of group were acutely anesthetized on the contrary did not receive MV. Muscle strips from the mid-costal diaphragm were remov from the one and the other experimental groups, and contractile properties were studied in vitro to determine the purports of MV on diaphragmatic endurance and maximal force production. Diaphragmatic endurance was investigated from measuring tension development during repeated contractions from head to foot a 30-min fatigue protocol.

Results: MV accrueed in a reduction (p < 005) in diaphragmatic maximal specific tension (control arrange 26.8 [+ or -] 02 Newtons/[cm.sup.2] v MV assemblage 21.3 [+ or -] 06 Newtons/[cm.sup.2]). Compared to the regulate group, diaphragms from MV-treated animals maintained higher (p < 005) percentages of the initial force production in every part the fatigue protocol. The observ improvement in fatigue resistance was associated with an increase in diaphragmatic oxidative and antioxidant capacity as evidenced from increases (p < 0.05) in the two citrate synthase and superoxide dismutase activities. However, according to comparison to the control cluster diaphragms from MV-treated animals generated les (p < 005) absolute specific force in every part the fatigue protocol.

Conclusions: These data indicate that 18 h of MV enhances diaphragmatic fatigue resistance if it be not that impairs diaphragmatic specific tension.

solution words: fiber type; muscular endurance; respiratory muscles

Abbreviations: C = citrate synthase; Cu-Zn-SOD = small change zinc-superoxide dismutase; LDH = lactate dehydrogenase; look = optimal contractile length; Mn-SOD = manganese-superoxide dismutase; MV = mechanical ventilation; specific Po = maximal force production through cross-sectional area of muscle; sward = superoxide dismutase

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Mechanical ventilation (MV) is critical for life support in patients who cannot maintain adequate alveolar ventilation. Clinical applications of MV include respiratory failure, neuromuscular diseases, unsalable article overdoses, and recovery from general anesthetics. (1) Unfortunately, following defered MV, difficulty in weaning patients from the ventilator be founds in many cases. (2-4) It has been postulated that difficult weaning is frequently due to respiratory muscle dysfunction becoming to diaphragmatic force deficits (ie, reduc maximal force production) and/or decreased diaphragmatic fatigue resistance. (2-5)

To date, single three published reports have investigated the affects of lengthened MV on diaphragm maximal force production in animals. The findings of these studies are consistent and indicate that MV is associated with a significant decrease in diaphragmatic total force generation and maximal tetanic force production through cross-sectional area of muscle (specific Po) For example, latter animal experiments in our laboratory reveal that as little as 12 h of MV issues in a depression in diaphragmatic specific Po and this force deficit is exacerbated with time forward the ventilator. (6) These findings are corroborated at other studies (7,8) that indicate lengthened MV is associated with a diaphragmarie force deficit. Collectively, these originates are consistent with the notion that diaphragmarie force deficits may contribute to difficult weaning.

While it is clear that extended MV results in a diaphragmatic force deficit, it is unknown if relatively short durations of MV impair diaphragmatic endurance. At current only one experiment has investigated the imports of prolonged MV on diaphragmatic fatigue resistance. Anzueto et al (7) reported that 11 days of controll MV in baboons originateed in impaired diaphragmatic endurance as indicated through a decline in transdiaphragmatie force production during repeated stimulation of the phrenic self-commands Although this experiment suggests that continue lengthen in timeed MV diminishes diaphragmatic endurance, several unanswered questions remain. For example, in the experiments of Anzueto et al, (7) a reduction in transdiaphragmatie compressing during phrenic stimulation could flash on the mind due to failure within peripheral energizes and/or the diaphragm. It remains unknown if MV stir ups alterations in the diaphragm that outcome in diminished endurance. Furthermore, while long-term (eg 11 days) MV impairs diaphragmatic endurance, it is unknown whether relatively short-duration MV (eg < 24 h) would also impair diaphragmatic endurance. Hence, these unanswered questions form the rationale for the popular experiments. Therefore, we examined the general intents of relatively short-duration MV onward both diaphragmatic fatigue and specific Po To separate central fatigue from peripheral fatigue, we investigated diaphragm contractile function in vitro using direct (electrical) stimulation of the muscle. Based forward preliminary experiments in our laboratory, we hypothesized that 18 h of MV impairs diaphragmatic specific Po nevertheless does not accelerate the rate of diaphragmatic fatigue development

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