RESPIRATORY CONTROL ABNORMALITIES IN ALVEOLAR HYPOVENTILATION

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Abstract
Regulation of respiration was evaluated in 5 patients with past episodes of respiratory failure that could not be attributed solely to pulmonary dysfunction. At the time of the study, 3 patients were normocapnic (NC), but 2 remained hypercapnic (HC). There were no differences in vital capacity, FEV1 [1 s forced expiratory volume] and functional residual capacity in the 2 groups. Chemical respiratory control, as determined from the ventilatory and occlusion pressure responses to hypercapnia, and the ventilatory responses to progressive hypoxia were similarly abnormal in NC and HC patients. Nonchemical neural control of breathing was assessed from the ability to duplicate tidal volumes of different sizes and to quantitate tidal volume changes. Error in tidal volume duplication and in estimation of tidal volume changes in NC patients did not differ from that in normal subjects. HC patients were unable to maintain constant tidal volumes from breath to breath so that the error in duplication could not be assessed. Error in the estimation of tidal volume changes in HC patients was significantly greater than that in normal subjects. Apparently in patients with alveolar hypoventilation and chronic hypercapnia there are abnormalities of the chemical and the nonchemical respiratory control systems. Alveolar ventilation and PCO2 [CO2 partial pressure] may be maintained at normal levels, despite derangements of respiratory chemical control when nonchemical neural control mechanism is intact.