Dyspnoea, peripheral airway involvement and respiratory muscle effort in patients with Type I diabetes mellitus under good metabolic control

Dyspnoea and pulmonary dysfunction have recently been associated with Type I (insulin-dependent) diabetes mellitus. The putative role of altered pulmo nary mechanics and of performance of inspiratory muscles in inducing dyspno ea has not been yet assessed in Type I diabetes. To better focus on this to pic we evaluated nine patients with Type I diabetes mellitus, aged 19 to 48 years with good and stable metabolic control, without a history of smoking and microvascular complications, alongside a group of 14 healthy control s ubjects. In each subject, pulmonary volumes, static and dynamic compliance, pleural pressure swings (PpI(sw)), maximal inspiratory pressures (PpI(sn)) , PpI(sw)(%PpI(sn)), a measure of respiratory muscle effort, and tension-ti me index [TTI = TI/TTOT X PpI(sw)(%PpI(sn))] were measured (TI = inspirator y time; TTOT = total time of the respiratory cycle). All subjects were stud ied at baseline and during hypoxic rebreathing. Patients had normal pulmona ry volumes. During hypoxic rebreathing, a normal change in respiratory musc le effort [Delta PpI(sw)(%PpI(sn))/Delta Sao(2)] and Delta TTI/Delta Sao(2) , and a lower change in tidal volume versus change in oxygen saturation [De lta VT(% vital capacity)/Delta Sao(2)], resulted in a higher ratio of respi ratory effort to tidal volume [PpIsw(%PpI(sn))/VT(% vital capacity)], a mea sure of neuroventilatory dissociation of the respiratory pump. Hypoxic dysp noea, assessed by a modified Borg scale, showed a greater rate of rise (Del ta Borg/Delta Sao(2)) and a greater increase for a given level of respirato ry effort in patients. Moreover, neuroventilatory dissociation related to t he expression of peripheral airway involvement, as assessed in terms of low dynamic compliance, and to concurrent change in dyspnoea sensation. Patien ts with Type I diabetes mellitus under good metabolic control and with norm al lung volumes may have abnormal peripheral airway function. The latter is thought to be responsible for the association between dyspnoea sensation a nd neuroventilatory dissociation.