Journal of applied physiology
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Comparative Study
Effect of enhanced supramaximal flows on cough clearance.
Efficiency of cough for clearing mucus from the lungs is believed to be a function of peak airflow velocities in the airways. Initial transient supramaximal flows are characteristic of cough, and these peak flow rates can be enhanced by placing a triggered shutter at the mouth, serving the role of the epiglottis. Using radiolabeled monodispersed aerosols (99mTc-iron oxide) and gamma camera analysis, we measured over a 2-h period the efficacy of 60 voluntary vs. shutter coughs for clearing mucus from the airways of patients (n = 15) with chronic airway obstruction (mean ratio of forced expired volume in 1 s to forced vital capacity = 0.55). ⋯ Retention at 60 min (as a fraction of initial deposition) was significantly different for the 3 study days (control, 0.83 +/- 0.17; voluntary cough, 0.69 +/- 0.18; shutter cough, 0.75 +/- 0.19; P = 0.01), but only control vs. voluntary cough values were significantly different from each other (P = 0.01). In contrast, retention at 120 min was significantly different for the 3 days, but both voluntary and shutter coughs were significantly different from control (P = 0.01 and P = 0.02, respectively) (control, 0.73 +/- 0.16; voluntary cough, 0.61 +/- 0.20; shutter cough, 0.65 +/- 0.20). Patients studied with buffs showed a clearance rate faster than control and similar to that associated with voluntary cough.(ABSTRACT TRUNCATED AT 250 WORDS)
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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".