Respiratory muscle function and hypoxic ventilatory control in patients with type I diabetes

Study objectives: The interaction among pulmonary mechanics, respiratory mu scle performance, and ventilatory control in subjects with insulin-dependen t diabetes mellitus has so far received little attention, We therefore deci ded to assess the role of central factors and peripheral factors on the ven tilatory response to a hypoxic stimulus in type I diabetic patients, Subjects: Eight patients in stable condition aged 19 to 48 years old, with insulin-dependent diabetes mellitus (duration of the disease, 36 to 240 mon ths) and no history of smoking, cardiopulmonary involvement, or autonomic n europathy; and an age- and gender-matched control group. Measurements: In each patient, we measured the following: pulmonary volumes ; diffusing capacity of the lung for carbon monoxide (DLCO); time and volum e components of ventilation (tidal volume [VT] and respiratory frequency); static compliance (Clstat) and dynamic compliance (Cldyn); swings in pleura l pressure (Pes) and gastric pressure (Pg); and transdiaphragmatic pressure (Pdi), obtained by subtracting Pes from Pg, Maximal inspiratory Pes and Pd i during a maximal sniff maneuver were also measured. Swings in Pes and Pdi during VT as a percentage of Pes and Pdi during the maximal sniff maneuver [Pessw(%Pessn) and Pdisw(%Pdisn), respectively] were both considered as a measure of central respiratory output, and the Pessw(%Pessn)/VT ratio was c onsidered as an index of neuroventilatory dissociation (NVD) of the inspira tory pump, Subjects were studied at baseline and during hypoxic rebreathing , Results: Pulmonary volumes and DLCO were normal or slightly reduced. A lowe r Cldyn, higher central respiratory output, and NVD were found. During hypo xic rebreathing, patients had lower VT, similar central respiratory output, and greater NVD per unit change in arterial oxygen saturation compared wit h values in control subjects. An increase in dynamic elastance, computed as 1/Cldyn, during hypoxia was found in patients, but not in normal subjects, and was directly related to concurrent changes in NVD. Conclusions: We have shown that the assessment of a normal Clstat and norma l routine parameters of airway obstruction does not permit the definite exc lusion of the role of peripheral airway involvement in insulin-dependent di abetes mellitus, Peripheral airway involvement is likely tb influence indic es of hypoxic ventilatory drive by modulating a normal central motor output into a rapid and shallow pattern of ventilatory response.