Journal of applied physiology
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In eight tracheotomized adult rabbits placed in the supine position, we employed a catheter-tip piezoresistive pressure transducer to measure esophageal pressure (Pes) and assessed the validity of taking the changes in Pes to be the changes in pleural pressure (Ppl). We applied an occlusion test in which the tracheal cannula was occluded during either spontaneous inspiratory efforts or body surface oscillations ranging from 3 to 50 Hz. ⋯ In all instances, the changes in Pes and Pao were virtually identical in both amplitude and phase. We conclude that, as evaluated by the occlusion test, a catheter-tip pressure transducer placed in the esophagus of rabbits can give adequate estimation of local pleural changes up to at least 50 Hz.
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In our previous study, we investigated the relationship between mucus rheology, depth of mucus layer, and clearance by simulated cough. The purpose of the present study was to examine the effect of airway wall flexibility on the clearance of mucuslike gels. Transient airflows similar to cough were generated by both positive and negative pressure, the latter to mimic the dynamic compression that occurs during real cough. ⋯ We also examined the effect of negative-pressure cough in excised canine tracheae, comparing the case where the tracheal membrane was free to deform vs. the case where it was secured. For the rigid-walled model, clearance by positive or negative pressure, with matched flow pattern, was the same. With the mucus simulant lining the flexible bottom surface, clearance increased with increasing membrane flexibility for negative-pressure cough and decreased for positive-pressure cough.(ABSTRACT TRUNCATED AT 250 WORDS)
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High-frequency chest percussion (HFP) with constant fresh gas flow (VBF) at the tracheal carina is a variant of high-frequency ventilation (HFV) previously shown to be effective with extremely low tracheal oscillatory volumes (approximately 0.1 ml/kg). We studied the effects of VBF on gas exchange during HFP. In eight anesthetized and paralyzed dogs we measured arterial and alveolar partial pressures of CO2 (PaCO2) and O2 (PaO2) during total body vibration at a frequency of 30 Hz, amplitude of 0.17 +/- 0.019 cm, and tidal volume of 1.56 +/- 0.58 ml. ⋯ VBF was also hyperbolic but at substantially higher levels of PaCO2. It is concluded that, in the range of VBF used, intraairway gas exchange was limited by the 30-Hz vibration. The fresh gas flow was important only to maintain near atmospheric conditions at the tracheal carina.
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Although the influence of altitude acclimatization on respiration has been carefully studied, the associated changes in hypoxic and hypercapnic ventilatory responses are the subject of controversy with neither response being previously evaluated during sleep at altitude. Therefore, six healthy males were studied at sea level and on nights 1, 4, and 7 after arrival at altitude (14,110 ft). ⋯ During both non-rapid-eye-movement and rapid-eye-movement sleep, ventilation, ventilatory pattern, and the hypercapnic ventilatory response (measured at ambient arterial O2 saturation) were determined. There were four primary observations from this study: 1) the hypoxic ventilatory response, although similar to sea level values on arrival at altitude, increased steadily with acclimatization up to 7 days; 2) the slope of the hypercapnic ventilatory response increased on initial exposure to a hypoxic environment (altitude) but did not increase further with acclimatization, although the position of this response shifted steadily to the left (lower PCO2 values); 3) the sleep-induced decrements in both ventilation and hypercapnic responsiveness at altitude were equivalent to those observed at sea level with similar acclimatization occurring during wakefulness and sleep; and 4) the quantity of periodic breathing during sleep at altitude was highly variable and tended to occur more frequently in individuals with higher ventilatory responses to both hypoxia and hypercapnia.
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The occurrence of upper airway obstruction during sleep and with anesthesia suggests the possibility that upper airway size might be compromised by the gravitational effects of the supine position. We used an acoustic reflection technique to image airway geometry and made 180 estimates of effective cross-sectional area as a function of distance along the airway in 10 healthy volunteers while they were supine and also while they were seated upright. We calculated z-scores along the airway and found that pharyngeal cross-sectional area was smaller in the supine than in the upright position in 9 of the 10 subjects. ⋯ Because changing from the upright to the supine position causes a decrease in functional residual capacity (FRC), six of these subjects were placed in an Emerson cuirass, which was evacuated producing a positive transrespiratory pressure so as to restore end-expiratory lung volume to that seen before the position change. In the supine posture an increase in end-expiratory lung volume did not change the cross-sectional area at any point along the airway. We conclude that pharyngeal cross-sectional area decreases as a result of a change from the upright to the supine position and that the mechanism of this change is independent of the change in FRC.