The CO single breath transfer factor of the lung. Generally acceptable normal values

Theta values for C16O18O and C18O2 related to respective pulmonary diffusing capacities

The single-breath diffusing capacities for singly and doubly 18O-labeled CO2, DLC16O18O and DLC18O2, as well as for NO, were determined in seven anesthetized rabbits to investigate whether the theoretically predicted ratio of specific blood uptake rates of both isotopic CO2 species, theta C18O2/theta C16O18O = 2.0, can be derived from the measured values of DLC16O18O and DLC18O2. Data of DL were obtained by inflating the lungs with gas mixtures containing 0.35% C16O18O or 0.8% C18O2 or 0.05% NO in nitrogen, with breath-holding periods of 0.05-0.5 s and 2-12 s for the CO2 and NO tests, respectively. theta C18O2/theta C16O18O was calculated by applying the double-reciprocal Roughton-Forster equation to DL values obtained in each animal and by assuming that NO diffusing capacity represents the gas conductance of the alveolar-capillary membrane. The measured ratio was theta C18O2/theta C16O18O = 1.9 +/- 0.2 (mean +/- SD), thus comparing reasonably with the predicted one. Therefore, our findings provide evidence that the greater value of DLC18O2 is mainly due to the twofold higher probability (or theta value) for C18O2 than for C16O18O to disappear within red blood cells via isotopic exchange reactions.

Components of carbon monoxide transfer at different alveolar volumes during mechanical ventilation in pigs

We studied the effect of increasing alveolar volume on pulmonary carbon monoxide transfer (DLCO) and its components, i.e. membrane diffusing capacity (DM) and capillary blood volume (Qc), during mechanical ventilation in eight anaesthetized and paralysed healthy pigs (mean weight 11.2 kg). We used an inspiratory pause procedure for simulation of the single-breath technique, and inflated 15, 20, 25 and 30 ml kg-1 in random order. DM and Qc were derived using the Roughton-Forster equation. Per litre BTPS increase in effective VA, DLCO (inspiratory oxygen fraction 0.30) decreased on average by 11.8 mumol s-1 kPa-1, DM slightly increased by 2.7 mumol s-1 kPa-1 and Qc decreased by 241 ml. The increase in DM was much smaller than might be expected from the increase in VA, which we ascribe to a loss of the alveolar capillary membrane for gas transfer because of the concomitant decrease in Qc. The decrease in Qc may be explained by a squeezing effect of the intrapulmonary pressure rise on the alveolar wall and by stretching of lung tissue.

Carbon monoxide diffusing capacity in asthmatic patients with mild airflow limitation

The aim of this study was to test the hypothesis that carbon monoxide diffusing capacity (DCO) is elevated in asthmatic patients with minimal airflow limitation and/or hyperinflation; the latter factors should reduce the possibility of technical errors in the measurement of DCO. In ten asthmatic and ten healthy subjects, DCO and its components, membrane diffusing capacity (Dm) and pulmonary capillary blood volume (Qc) were measured by the single-breath method. Values were normalized for alveolar volume (VA). The mean DCO/VA was higher in the asthma groups as was the Qc/VA. The Dm/Qc was also higher in the asthma group. In the asthmatic but not the healthy subjects, both DCO/VA and Qc/VA were negatively correlated with the forced expiratory flow at 50 percent of vital capacity and peak inspiratory flow rate. Thus, DCO/VA may be increased in asthmatic patients with only mild airflow limitation; this may be due to an elevated capillary blood volume.

Pulmonary function in young insulin-dependent diabetic subjects

To clarify the issue of pulmonary dysfunction in diabetes mellitus, lung mechanics and CO transfer were investigated in 22 young (mean age 19.5 +/- 5 years) non-smoking, insulin-dependent diabetic patients and an equal number of matched healthy subjects. Mean closing capacity/total lung capacity (CC/TLC) was significantly greater in the diabetic than in the control group (31.4 +/- 6.8 vs 27.2 +/- 2.9 percent, p less than 0.01), as was the mean value of the volume independent index of lung elasticity (exponent constant, Kst(L)) (0.148 +/- 0.045 vs 0.118 +/- 0.030, p less than 0.05). The transfer factor expressed per unit alveolar volume (TL/VA) was also significantly lower in the diabetic than in the control group (5.25 +/- 0.68 vs 5.61 +/- 0.57 ml/min/mm Hg/L, p less than 0.05) and this could be ascribed to a lower pulmonary capillary blood volume. There was evidence of mildly abnormal lung mechanics and/or a decreased pulmonary capillary blood volume in 16 (73 percent) of the diabetic group. Since pulmonary dysfunction was either an isolated non-endocrine finding or was associated with only early systemic complications in these young patients, our findings suggest that pulmonary dysfunction is an early measurable complication in insulin-dependent diabetes mellitus.

Kinetics of pulmonary CO2 transfer studied by using labeled carbon dioxide C16O18O

The kinetics of alveolar-capillary CO2 transfer was investigated, using 18O-labeled carbon dioxide (C16O18O), in 21 experiments on 2 resting human subjects. Single-breath experiments were performed. After the subjects expired to residual volume, they inspired a gas mixture containing 20% O2 and 2.8% CO2 - a quarter of CO2 was labeled with 18O. The breath-hold time ranged between 0.5 and 20 sec. After expiration the gas mixture was analysed by mass spectrometry. The C16O18O concentration of the end-expiratory gas decreased with the increasing breath-hold time. The relationship of both showed a biexponential characteristic with the two time constants 0.4 and 16 sec. The lower time constant characterizes the CO2 transfer from the alveolar space to the capillary blood, as well as the isotopic equilibration of the 18O within the blood. The higher time constant could result from small admixtures of the label from the dead spaces or the lung tissues. The diffusing capacity of C16O18O was calculated by using the first part of the indicator clearance curve. The derived mean value of 862 ml X mm Hg-1 X min-1 is considered to be a lower limit of the 'membrane diffusing capacity' for CO2 (DMCO2).

The effects of minor and moderately severe accidental chest injuries on pulmonary function in man

Pulmonary function has been measured at intervals after direct chest injuries of mild and moderate severity in 46 patients. Ventilatory capacity (e.g. FEV1) and vital capacity were reduced and the residual volume was increased. Total lung capacity and alveolar volume were also reduced and as a result total pulmonary diffusing capacity (transfer factor) was decreased, however, the remaining lung had a normal diffusion coefficient. Intercostal nerve block at the fracture site did not improve ventilatory capacity although marked pain relief was achieved. Recovery was slower in those patients not admitted to hospital than in the more seriously injured patients who were admitted. It is suggested that more attention should be paid to the outpatient follow-up of such patients, perhaps paying particular attention to physiotherapy.