Effects of inspiratory and expiratory time and high mouth pressures on calculated DLCO by the single-breath procedure. Results with different methods to measure the effective breath-holding time.

We have studied the influence of several manoeuvres modifying inspiratory and expiratory flow, with and without an external obstruction, on measured single-breath diffusing capacity (DLCO). By this method, we could evaluate the effects of increased inspiration or expiration time, independently of the influence of high (negative or positive) mouth pressures. Ten tests were performed in each of 11 trained normal subjects. The sequence of repeated manoeuvres was as follows: (1) basal; (2) inspiratory obstruction (IO); (3) expiratory obstruction (EO); (4) slow inspiration without obstruction (SI), and (5), slow expiration without obstruction (SE). A second, inverted sequence was then performed. The obstructive manoeuvres were forced by a unidirectional valve with a circular hole of 5 mm in diameter. Mouth pressures were registered. The slow flows were voluntarily controlled to be similar to the corresponding flows during the obstructive manoeuvre (approximately 15% of each vital capacity/second). Determinations of breath-holding time (tBH) were calculated by the methods of Jones-Meade, Ogilvie and the American Epidemiology Standardization Project (ESP), but using the same expiratory sample. We found that (DLCO) obtained with the three methods were statistically different (p less than 0.0001) from each other for all manoeuvres. Regarding the basal manoeuvre, there were statistical differences (p less than 0.01) with SI on the Jones-Meade, with IO on the ESP and with SI and IO on the Ogilvie timing methods. Between IO and SI, statistical differences (p less than 0.01) were observed in the three methods, but there was no statistical difference between SE and EO by any method.(ABSTRACT TRUNCATED AT 250 WORDS)

A simple method of correcting diffusing capacity for alveolar volume reduction in restrictive lung diseases.

We studied the discriminative power of the transfer factor (TLCO), KCO (TLCO/Va) and ZCO (a corrected TLCO according to alveolar volume measured (Va), introduced by our group), in order to differentiate diffuse interstitial disease from other restrictive diseases. Measurements were taken in 46 subjects, divided into two groups: Pure restriction (group 1: normal subjects with voluntary restriction and diseased subjects) and (2) diffuse interstitial restriction (group 2). There were no statistical differences in Va between groups 1 and 2. TLCO was statistically lower in groups 1 and 2 in comparison with the control group (normal values of our laboratory in test with Va greater than 90% of predicted) and showed a significant difference when group 1 was compared with group 2. Similar results (but with higher values than those of the control group) were found for KCO. A similar difference exists in ZCO only when group 2 is compared with group 1, but not when group 1 is compared with the control group. The corrected diffusion capacity ZCO yields the highest discriminative power.

Spontaneous pneumomediastinum after cocaine inhalation.

We report a case of spontaneous pneumomediastinum after cocaine inhalation. The possible mechanisms implicated in an inspiratory manoeuvre are discussed.

Pulmonary parenchymal tissue volume and pulmonary capillary blood flow in normal subjects.

We measured pulmonary parenchymal tissue volume (Vt) and pulmonary capillary blood flow (Qc) in 11 normal subjects by a rebreathing technique and end-tidal, dead-space correction (ETDS) method, using two soluble gases, acetylene (C2H2) and dimethyl ether (DME). We assessed the results using different intervals of measurement, inspired volumes and rebreathing frequencies. The mean values +/- SD of Vt were 559 +/- 58 and 511 +/- 52 ml, with C2H2 and DME, and of Qc were 3.67 +/- 0.44 and 4.18 +/- 0.54 liter/min/m2, respectively. Measurements with the interval between the 1st and the 6th end-tidal points and within the first 15 s yielded the best reproducibility. Data obtained from two satisfactory recordings from the same subject are sufficient to calculate Vt and Qc. Inspired volume shows a significant correlation with Vt values measured with both tracer gases, especially with DME. Rebreathing frequency also affects this latter gas. Despite some problems which are not easily explainable (dependence upon the inspired volume, rebreathing frequency and test gas species), we conclude that the methods allow measurements of Vt and Qc with acceptable reproducibility but that different variables may affect the results.