The blood transfer conductance for nitric oxide: Infinite vs. finite θ NO

Abstract

Whether the specific blood transfer conductance for nitric oxide (NO) with hemoglobin (θNO) is finite or infinite is controversial but important in the calculation of alveolar capillary membrane conductance (DmCO) and pulmonary capillary blood volume (VC) from values of lung diffusing capacity for carbon monoxide (DLCO) and nitric oxide (DLNO). In this review, we discuss the background associated with θNO, explore the resulting values of DmCO and VC when applying either assumption, and investigate the mathematical underpinnings of DmCO and VC calculations. In general, both assumptions yield reasonable rest and exercise DmCO and VC values. However, the finite θNO assumption demonstrates increasing VC, but not DmCO, with submaximal exercise. At relatively high, but physiologic, DLNO/DLCO ratios both assumptions can result in asymptotic behavior for VC values, and under the finite θNO assumption, DmCO values. In conclusion, we feel that the assumptions associated with a finite θNO require further in vivo validation against an established method before widespread research and clinical use.

Effects of intrathoracic pressure, inhalation time, and breath hold time on lung diffusing capacity

“…The DLNO/DLCO ratio was decreased at rest versus exercise across all apnea times (p = 0.011, Figure 2C). There was no significant difference in DmCO between rest and exercise at any apnea time (using the finite θ NO assumption) (Coffman et al, 2016a; Zavorsky et al, 2017).…”

“…There are two potential reasons for this discrepancy with previous studies (Rahul M. Tamhane et al, 2001; Taylor et al, 2014). First, as we have shown previously, using the finite θ NO assumption causes calculated values of DmCO to fall or rise rapidly when DLNO/DLCO is outside of a certain range (Coffman et al, 2016a). Specifically, this asymptote occurs when the DLNO/DLCO ratio approaches θ NO /θ CO , which given the most recent ERS guidelines occurs around 8.2 (depending on P A O 2 ).…”

Influence of rapidly oscillating inspired O2 and N2 concentrations on pulmonary vascular function and lung fluid balance in healthy adults

“…Pulmonary blood flow (Vc) and alveolar—capillary conductance (Dm) were calculated from the lung diffusing capacity for carbon monoxide (DLCO) and the lung diffusing capacity for nitric oxide (DLNO). Lung diffusion capacities were assessed using a rebreathe technique by taking advantage of the diffusion‐limited nature of CO and NO gas ( Coffman et al, 2017 ; Coffman et al, 2018 ). Briefly, DLCO and DLNO were determined via the rate of disappearance of CO and NO, respectively.…”

Influence of the Vibralung Acoustical Percussor on pulmonary function and sputum expectoration in individuals with cystic fibrosis

“…In contrast to DL CO , DL NO has been considered a relatively direct measure of membrane conductance (DM NO ), as the diffusion resistance of the blood is trivial, 22 – 25 but not infinite, and for our purposes of comparing change in response to a stimulus, it gives reliable results for evaluating changes in DL CO and its components in one maneuver rather than multiple maneuvers at different oxygen tensions. 26 Using this assumption, the DM NO value is used to calculate the DM for carbon monoxide (DM CO ) by adjusting for differences in diffusion constants based on molecular weight and solubility between the two gases as described previously using an alpha ratio of 2.2. 22 , 27 Pulmonary–capillary blood volume ( V C ) is then calculated from the DL CO measured by subtracting the resistance to diffusion associated with alveolar–capillary barrier (DM CO ) and correcting for differences in the rate of uptake and binding to hemoglobin (Hb; 1/θ) due to differences in Hb concentrations and the alveolar pressure of oxygen, as described previously using the Roughton and Forester 2.5 Ө CO equation.…”