Journal of applied physiology
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Transdiaphragmatic pressures generated by phrenic nerve twitches have been proposed as a means to assess diaphragmatic function and central drive, but their validity and reliability have not been determined. We evaluated diaphragmatic twitch and twitch occlusion measurements in a rabbit model of diaphragmatic contractile dysfunction and diaphragmatic fatigue to determine whether 1) diaphragmatic twitch pressures accurately assess changes in low- and high-frequency diaphragm trains during the development of, and recovery from, contractile fatigue; 2) twitch occlusion measurements accurately quantify the intensity of central drive to the diaphragm; and 3) twitch measurements are affected by thoracoabdominal binding or twitch potentiation. Single-twitch and 20-Hz double- and triple-twitch pressures accurately reflected changes in low-frequency diaphragm train pressures, whereas only 80-Hz triple-twitch pressures accurately reflected changes in high-frequency trains. ⋯ Thoracoabdominal binding increased twitch and train pressures, and repetitive electrical stimulations further potentiated twitch pressure. However, twitch potentiation and a lack of thoracoabdominal binding had no effect on twitch measurements of diaphragmatic function during the induction and recovery from fatigue or on twitch occlusion measurements of intensity of central drive. Thus, twitch measurements can be used to accurately assess diaphragmatic low- and high-frequency fatigue and to quantify the intensity of central drive to the diaphragm.
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Editorial Comment Review
Invited editorial on "Effect of enhanced supramaximal flows on cough clearance".
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Our aim was to assess whether endotoxemia impairs the ability of the diaphragm to extract O2 and whether this defect leads to a greater dependence of O2 uptake on O2 delivery. In two groups of anesthetized mechanically ventilated dogs, the left hemidiaphragm was vascularly isolated. Diaphragmatic blood flow and cardiac output (CO) were measured simultaneously in all animals. ⋯ Similarly, critical diaphragmatic O2 delivery in the E group increased to 14.8 ml.kg-1.min-1 (P < 0.05), whereas critical and maximum O2 ER declined to 51.8 and 72.8%, respectively (P < 0.05). Thus, endotoxemia impairs diaphragmatic O2 extraction. This, in turn, leads to a greater dependence of diaphragmatic O2 uptake on O2 delivery.
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Clinical Trial
Pressure transmission across the respiratory system at raised lung volumes in infants.
Forced expiratory flow-volume (FEFV) curves can be generated from end-tidal inspiration in infants with use of an inflatable jacket. We have developed a technique to raise lung volume in the infant before generation of FEFV curves. Measurements of pressure transmission to the airway opening by use of static maneuvers have shown no change with increasing lung volume above end-tidal inspiration. ⋯ Isovolume static pressure transmission (Ptx,st) was measured in three of the five infants by inflation of the jacket in a stepwise manner with the airway closed. Measurements were made at end-tidal inspiration and lung volumes at 10, 15, and 20 cmH2O preset pressure. Resulting changes in Pj, esophageal pressure, and airway opening pressure were compared using linear regressions to determine Ptx,st.(ABSTRACT TRUNCATED AT 250 WORDS)
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When tissue O2 delivery falls below a critical threshold, tissue O2 uptake (VO2) becomes limited. We compared critical O2 delivery and critical and maximum O2 extraction ratios of the resting and contracting left hemidiaphragm with those of nondiaphragmatic tissues in seven dogs. The left hemidiaphragm was perfused through the left inferior phrenic artery with blood from the left femoral artery. ⋯ By comparison, supply limitation of VO2 occurred at a higher systemic O2 delivery in the contracting diaphragm than in the rest of the body despite the increase in critical diaphragmatic extraction ratio. Thus, oxygenation of the isolated diaphragm does not appear to be preferentially preserved during generalized reductions in O2 delivery. These results suggest that, in diseases associated with increased work of breathing and decreased O2 delivery, the diaphragm may become metabolically impaired before limitation of VO2 is observed systemically.