Changes in Transcutaneous Oxygen Partial Pressure as an Index of Response to Inhaled Methacholine in Asthmatic Patients

Bronchoconstriction and hypoxemia have been reported to occur during airway challenges, but the correlation between changes in forced expiratory volume in 1 s (FEV 1 ) and transcutaneous oxygen partial pressure (tcPo 2 ) during methacholine provocation tests has not yet been established (to our knowledge). In 15 symptom-free atopic asthmatic patients and 5 normal subjects, variations in tcPo 2 and FEV 1 were simultaneously measured during inhalation of doubling methacholine concentrations; the drug concentrations causing a 20 percent decrease in control FEV 1 and tcPo 2 (PC20FEV 1 and PC20tcPo 2 , respectively) were subsequently calculated. In patients, geometric mean PC20FEV 1 and PC20tcPo 2 were 1.31 (range, 0.16 to 5.19) and 1.26 (range, 0.29 to 5.82) mg/ml, respectively. In addition, in six patients, methacholine-induced fall in tcPo 2 was accompanied by similar changes in arterial Po 2 . Methacholine inhalation caused no change in tcPo 2 or FEV 1 in normal subjects. The independent effects of deep breath tests and bronchoconstriction on PC20tcPo 2 were studied in five patients challenged on two separate occasions, with and without FEV 1 assessment; in these patients, PC20tcPo 2 were similar on both the study days. The results indicate that, in asthmatic patients, methacholine-induced bronchoconstriction causes parallel decreases in FEV 1 and tcPo 2 . The tcPo 2 monitoring may serve as a tool in the assessment of airway hyperreactivity when active patient's cooperation is scarce.