Confusion in reporting pulmonary diffusing capacity for nitric oxide and the alveolar-capillary membrane conductance for nitric oxide

Abstract

We read with interest the paper by Magini and col- leagues on the measurement of pulmonary diffusing capacity for nitric oxide in patients with heart failure (ejection fraction<40%). 1 In their study they report pulmonary diffusing capacity and the individual com- ponents of pulmonary diffusing capacity in 50 patients with heart failure (65 years of age), and 50 control sub- jects (61 years of age). We feel that there are two prob- lems with this paper that warrant discussion. First, the mean values for pulmonary diffusing capacity for nitric oxide (DLNO) for the healthy subjects are too low, and second, both their alveolar-membrane conductances (DmNO and DmCO) and pulmonary capillary blood volume (Vc) calculations, and hence conclusions, are incorrect. First, the values for DLNO for the healthy volunteers appear too low. If we assume that the women's and men's mean height in the healthy volunteers was 163 and 173 cm, respectively, then the mean DLNO values should be 96-113 and 140-154 ml/min/mm Hg, for women and men, respectively. 2,3 The combined average for DLNO should be then 118-133 ml/min/mm Hg. The author's mean values of 89 ml/min/mm Hg for the healthy volunteers are 25-33% lower than predicted. However, their values for pulmonary diffusing capacity for carbon monoxide (DLCO) were correct and the healthy volunteers was close to 100% of that pre- dicted. 2,3 Thus, if the mean DLNO in the control group is under-predicted by at least 25%, then the DLNO values in the heart failure patients could be under predicted by � 25% too. Since DLNO and DLCO are measured simultaneously, and DLCO values were appropriate (close to 100% of those predicted), there must be some mathematical error in the calcula- tion of DLNO and/or their breath-hold time was