Examination of the Carbon Monoxide Diffusing Capacity (Dl_CO) in Relation to Its Kcoand VaComponents

Abstract

The single-breath carbon monoxide diffusing capacity (DL(CO)) is the product of two measurements during breath holding at full inflation: (1) the rate constant for carbon monoxide uptake from alveolar gas (kco [minute(-1)]) and (2) the "accessible" alveolar volume (Va). kco expressed per mm Hg alveolar dry gas pressure (Pb*) as kco/Pb*, and then multiplied by Va, equals Dl(CO); thus, Dl(CO) divided by Va (DL(CO)/Va, also called Kco) is only kco/Pb* in different units, remaining, essentially, a rate constant. The notion that DL(CO)/Va "corrects" DL(CO) for reduced Va is physiologically incorrect, because DL(CO)/Va is not constant as Va changes; thus, the term Kco reflects the physiology more appropriately. Crucially, the same DL(CO) may occur with various combinations of Kco and Va, each suggesting different pathologies. Decreased Kco occurs in alveolar-capillary damage, microvascular pathology, or anemia. Increased Kco occurs with (1) failure to expand normal lungs to predicted full inflation (extrapulmonary restriction); or (2) increased capillary volume and flow, either globally (left-to-right intracardiac shunting) or from flow and volume diversion from lost or damaged units to surviving normal units (e.g., pneumonectomy). Decreased Va occurs in (1) reduced alveolar expansion, (2) alveolar damage or loss, or (3) maldistribution of inspired gases with airflow obstruction. Kco will be greater than 120% predicted in case 1, 100-120% in case 2, and 40-120% in case 3, depending on pathology. Kco and Va values should be available to clinicians, as fundamental to understanding the clinical implications of DL(CO). The diffusing capacity for nitric oxide (DL(NO)), and the DL(NO)/DL(CO) ratio, provide additional insights.

The reproducibility and responsiveness of the lung clearance index in bronchiectasis

“…In CF, a treatment effect has been demonstrated with dornase alpha [12], hypertonic saline [13] and post treatment for a pulmonary exacerbation [14][15][16], although the clinically meaningful change in LCI has not yet been determined. In contrast, short-term physiotherapy was not found to have a consistent effect on the LCI results in a cohort of stable CF patients [17].…”

Increased Cardiac Output and Preserved Gas Exchange Despite Decreased Alveolar Surface Area in Rats Exposed to Neonatal Hyperoxia and Adult Hypoxia

“…Because CO is highly diffusible and binds to hemoglobin in the pulmonary capillary vessels, [CO] 9s represents its uptake across the alveolar-capillary membrane during the 9-second breath hold (19). Conversely, Ne does not diffuse across the alveolar-capillary membrane; therefore, [Ne] 9s represents the degree of Ne dilution by the alveolar gas and estimates alveolar volume.…”

“…DF CO , thus, correlates to the clinically used diffusing capacity of the lung for carbon monoxide per unit of alveolar volume (DL CO /VA) (19). Increases in alveolar membrane surface area, capillary density, hematocrit, and cardiac output increase DF CO , whereas alveolar-capillary simplification, anemia, pulmonary hypertension, and diminished cardiac output decrease DF CO (19)(20)(21). After determination of DF CO , lungs were immediately inflation fixed.…”

Carbon monoxide diffusing capacity and the complexity of diagnosis in pulmonary arterial hypertension

“…In this sense, coexistence of multiple clinical conditions such as mild emphysema or pulmonary fibrosis, or even mild heart failure with preserved ejection fraction, which is commonly seen in the elderly, might complicate the appropriate diagnosis. Thus, we need better diagnostic markers to define and distinguish the various phenotypes of pulmonary vascular disease.Diffusing capacity of the lung for carbon monoxide (DLCO) is one of these potential markers thanks to its characteristic of reflecting alveolar and microvascular integrity [15]. For many years, a low DLCO has been associated with the development of PAH in patients with systemic sclerosis [16].…”

“…Diffusing capacity of the lung for carbon monoxide (DLCO) is one of these potential markers thanks to its characteristic of reflecting alveolar and microvascular integrity [15]. For many years, a low DLCO has been associated with the development of PAH in patients with systemic sclerosis [16].…”