Respiration; international review of thoracic diseases
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Changing the depth and the frequency of breathing affects the efficiency of ventilation. This has been studied in eight normal subjects using the technique of nitrogen washout whilst breathing a mixture of 79% argon and oxygen. The signals were converted to digital data at 50 Hz and all calculations were then done with the computer. ⋯ Whilst VdA and VdS increase with increasing Vt, the proportion of VdA + VdS in each breath diminishes with such an increase, the net result is that, for each 100 ml increase in Vt, alveolar ventilation increases by 86 ml for CO2 and 78 ml for O2. The increase of absolute values and the different behaviour of N2, AMEsb and AMEmb show a progressive decrease of the parallel component of the intra-pulmonary ventilation distribution with increasing Vt. It appears that the pattern of ventilation, as well as minute ventilation, plays a role in the effectiveness of ventilation.
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The steady-state responses of upper-airway dilating muscles and diaphragm activity to elevation of lung volume induced by positive end-expiratory pressure loading were studied in 9 pentobarbital-anesthetized dogs with vagus nerves intact. The early and late effects of 5 min of expiratory threshold loads upon upper airway dilating muscle activity (the alae nasi, the genioglossus and the posterior cricoarytenoid) were compared to their effects on diaphragm activity. During resting O2 breathing, application of 5 and 10 cm H2O of positive end-expiratory pressure produced no significant change in the peak electrical activity of the upper-airway dilating muscles and diaphragm (p greater than 0.05). ⋯ In animals who developed periodic breathing by increasing levels of anesthesia, positive end-expiratory pressure loading eliminated the periodicity and made the pattern of breathing regular. Based on these results, it can be concluded that under the conditions of these experiments, increases in lung volume produced by expiratory threshold loads do not reduce the activity of upper-airway dilating muscles. The maintenance of the electrical activity of the upper-airway dilating muscles might be caused by excitatory reflex mechanisms or central habituation.