Nitric oxide (NO) has a much stronger affinity for hemoglobin than carbon monoxide (CO); therefore, the DL(NO) (diffusing capacity for NO) is less influenced by changes in capillary blood volume than the DL(CO) (diffusing capacity for CO), and represents the true membrane diffusing capacity. We measured the combined single breath DL(NO)/DL(CO) in 124 healthy subjects, and generated reference equations for the DL(NO) and K(NO). In a subset of 21 subjects the measurements were performed on different inspiratory levels. The reference equation for DL(NO) in females is 53.47*H(height)0.077*A(age)-48.28(RSD5.22) and for males 59.84*H-0.25*A-44.20(RSD6.39). Reference equations for K(NO) in females is -2.03*H-0.025*A+11.52(RSD0.48) and for males -0.15*H-0.045*A+9.47(RSD0.65). The K(CO) (DL(CO)/V(A)) increases when V(A) (alveolar volume) decreases, probably due to an increase of blood volume per unit lung volume. The DL(NO) was much stronger related to the V(A), the K(NO) was almost independent of V(A). Because of the relative independence of the K(NO) on V(A), the K(NO) appears to be a much better index for the diffusion capacity per unit lung volume (transfer coefficient) than the K(CO).

<b><i>Background:</i></b> Non-invasive home mechanical ventilation (HMV) is a complex treatment in myotonic dystrophy type 1 (DM1) patients, due to a presumed poor adherence, variable symptom improvement, and uncertainty regarding survival benefits. <b><i>Objectives:</i></b> We aimed to investigate indications, adherence to HMV and its effects on mortality in a large cohort of DM1 patients. <b><i>Methods:</i></b> In this retrospective cohort study, we evaluated 224 DM1 patients. Different groups based on hypercapnia and HMV treatment were compared. Cox regression analyses were performed to compare mortality between different defined groups. <b><i>Results:</i></b> 224 patients were analysed of whom 111 started non-invasive HMV. Indications were daytime hypercapnia (<i>n</i> = 75), only nocturnal hypercapnia (<i>n</i> = 33), or other reasons (<i>n</i> = 3). Adequate adherence (≥4 h/night) was found in 84.9% of patients. Adequate ventilation was reached in 86.5% of patients. In 33 patients (29.7%), HMV was stopped prematurely due to not reaching patients’ expectations on symptom relief or treatment burden (<i>n</i> = 22), or intolerance (<i>n</i> = 8), or other reasons (<i>n</i> = 3). HMV did not improve survival in daytime hypercapnic patients (<i>p</i> = 0.61) nor in nocturnal hypercapnia patients compared to daytime hypercapnia (<i>p</i> = 0.21). Significant survival benefits after starting HMV were found for patients with HMV adherence ≥5 h/24 h compared to patients who used HMV less. <b><i>Conclusion:</i></b> In this large cohort, daytime hypercapnia is the main reason for starting HMV, which is well tolerated and used. Mortality is not associated with the reason why HMV was started, but once started, patients with ≥5 h/24 h adherence have significantly better survival compared to patients who use it less.

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