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A new method for measuring total respiratory input impedance (Zrs), which ensures minimal motion of extrathoracic airway walls, was tested over frequencies of 4-30 Hz in 14 normal subjects and 10 patients with airway obstruction. It consists of applying pressure variations around the head, rather than at the mouth, so that transmural pressure across upper airway walls is equal to the small pressure drop across the pneumotachograph. Compared with reference Zrs values obtained by directly measuring airway wall motion with a head plethysmograph and correcting the data for it, the investigated method provided similar values for respiratory resistance at all frequencies (30 Hz, 3.67 +/- 2.24 cmH2O X 1(-1) X s compared with 3.55 +/- 2.00) but slightly overestimated respiratory reactance at the largest frequencies (30 Hz, 2.82 +/- 1.28 cmH2O X 1(-1) X s compared with 2.52 +/- 1.22, P less than 0.01). In contrast, when the data were not corrected for airway wall motion, resistance was largely underestimated, especially in patients (-48% at 30 Hz, P less than 0.001), and the reactance-frequency curve was shifted to the right. The investigated method is almost as accurate as the reference method, provides equally reproducible data, and is much simpler.

The validity of a new method for measuring thoracic gas volume (TGV) was studied in 69 children, 4-16 yrs old, including twelve normal children and 57 children with an obstructive (n = 38) or restrictive (n = 19) respiratory disease. The method consisted of applying very slow (0.05 Hz) sinusoidal variations of ambient pressure around the body (delta Pam = 40 cmH2O peak to peak) and studying the relationship between delta Pam and the resulting gas displacement at the mouth (Vaw): TGVapc = PB.delta Vaw/delta Pam.cos phi, where PB is barometric minus alveolar water vapour pressure and phi the phase angle between Pam and Vaw. Functional residual capacities derived from TGVapc (FRCapc) were compared to the values obtained by plethysmography (FRCplet) and by helium dilution (FRCdil). FRCapc did not differ significantly from FRCplet in either the entire group (1.75 +/- 0.62 l vs 1.79 +/- 0.45 l) or in the patient subgroups. However, with the new method a trend to slightly lower FRCs was seen in patients with the most obstruction (p less than 0.05). FRCdil was significantly lower than both FRCapc and FRCplet (p less than 0.001), particularly in children with obstruction. Significant correlations were found between the three methods (p less than 0.001). On the other hand, the method investigated requires that the subject breathe very regularly for a period of several minutes. This was rarely achieved, so that the reproducibility of the measurements was unacceptably low. At present, the method cannot be recommended for routine use in 4-16 yr old children.

Thoracic gas volume (TGV) and specific airway resistance (sRaw) are commonly measured using pressure type and flow type body plethysmographs. Within-subject variability of the data, defined as the coefficient of variation of eight to ten measurements during the same session, was assessed with the two kinds of instruments and compared in fifteen normal subjects. The reproducibility of data obtained several days apart was also compared. All measurements were made in a 480-l body chamber, which could be used in both the pressure and the flow mode. The signals were processed digitally using three different algorithms: 1) simple linear regression (LR); 2) linear regression with drift correction achieved by adding to, or subtracting from the plethysmographic signal a term proportional to time (LRC); 3) Fourier analysis (FFT). Within-subject variability of TGV was much larger with flow than with pressure plethysmography when the signals were processed by LR (14.5 +/- 7.5 vs 6.3 +/- 3.0%; p less than 0.001), but almost the same using LRC (6.7 +/- 3.2 vs 5.4 +/- 2.7%) and FFT (6.1 +/- 2.4 vs 5.0 +/- 2.4%). For sRaw, variabilities were larger and less influenced by methodological factors. Adequate digital processing may therefore largely remedy the inherently greater variability of TGV measurements with flow plethysmographs.

Total respiratory impedance was obtained from 4 to 30 Hz in 39 healthy males and in 140 iron miners by studying the relationship between transrespiratory pressure and mouth flow when forced oscillations were applied to the respiratory system in two different ways: by varying pressure at the mouth (input impedance, Zin); by varying pressure around the chest (transfer impedance, Ztr). Zin was characterized by the slope (S) and intercept (R0) of the resistance-frequency curve, by the resonant frequency (fn), and by total respiratory inertance (I) and compliance (C) obtained from the reactance. Transfer resistance and reactance curves were respectively analysed with a two-parameter (m1, m3) and a three-parameter (m0, m2, m4) equation. Significant correlations were found between impedance indices, particularly between m1 and both R0 (r = 0.931; p less than 0.001) and m2 (r = 0.739; p less than 0.001), and also between impedance indices and maximal expiratory flows. Nonsmoking miners (n = 40), compared to control nonsmokers (n = 16), had slightly lower maximal flows at high lung volumes (p less than 0.05) and higher values of m1 (p less than 0.001), R0, S, m3 (p less than 0.01) and m2 (p less than 0.05). In contrast, miners who smoked (n = 46) mainly differed from miners who did not smoke by lower flows at middle and low lung volumes (p less than 0.01) and larger m0 (p less than 0.01), m2 and m4 (p less than 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)

A new method of studying the linearity of gas flowmeters was tested on different models of Fleisch pneumotachographs. The method applies a steady flow to the test flowmeter, which is increased in a stepwise manner by adding a constant flow-increment. This is achieved using two flow sources in parallel. The method does not require any reference flow channel and may be implemented with standard laboratory equipment. Using this method, the gain of Fleisch pneumotachographs, whatever their size, decreased by about 2-3% from low flows to about 40% of their nominal full scale (FS), and then increased almost linearly with increasing flow. The error was 8-13% at 200% FS. The following equation was devised to correct the data at high flow: Vc = Vt (1-K (Vt-S] where Vc and Vt are the corrected and measured flow respectively, K a gain correction factor and S a flow threshold below which no correction is needed. Applying this correction with suitable coefficients, the maximal error was below 3% from 0-200% FS.

Reference values for respiratory impedances in children are scarce and limited to the situation where pressure is varied at the mouth. Total respiratory impedance was therefore measured from 4 to 30 Hz in 69 healthy children (9-13 yr) with both a pressure input at the mouth (input impedance, Zin) and a pressure input at the chest (transfer impedance, Ztr). Zin was characterized by the average resistance (R), the low-frequency limit of resistance (R0), the slope of the resistance-frequency curve (S), respiratory elastance (E) and respiratory inertance (I). Similar coefficients (R0', S', E', I'), some of which however have slightly different physiological meanings, were derived from Ztr. R, R0 and R0' were found to be significantly correlated to body height (p less than 0.001) and, independently, to age (p less than 0.05): R (kPa X l-1 X s) = 1.76-5.29 10(-3) height (cm) -4.13 10(-2) age (yr). Elastances were better correlated to height than to age: E (kPa X l-1) = 20.95-0.101 height (cm) and inertances better correlated to age than to height: I (Pa X l-1 X s2) = 4.39-0.128 age (yr). S and S' were not correlated to biometric variables. No difference was found between children living in polluted (n = 36) and nonpolluted (n = 33) areas, except for S which was significantly lower in the first group (p less than 0.01).

Total respiratory input (Zrs,in) and transfer (Zrs,tr) impedances were obtained from 4 to 30 Hz in 10 healthy males by simultaneously measuring mouth and chest flow while applying pseudo-random pressure variations at the mouth. Compared with Zrs,in, the real part of Zrs,tr was larger up to 10 Hz but exhibited a much stronger negative frequency dependence. The imaginary part was larger at all frequencies, with a resonant frequency (fn) at 6.0 +/- 0.8 Hz compared with 8.2 +/- 2.9 Hz for Zrs,in. The two impedances were analyzed with a model featuring airway resistance and inertance, alveolar gas compressibility, and tissue resistance, inertance, and compliance. A good fit was generally obtained but, in most cases, with a different partitioning of resistance between airway and tissue for Zrs,in and Zrs,tr. The data were also used to compute separately airway and tissue (Zt) impedances. In most subjects Zt could not be properly fitted with a simple resistance-inertance-compliance unit and was consistent with a slow (fn = 7.4 +/- 2.3 Hz) overdamped compartment in parallel with a fast (fn = 37.1 +/- 5.6 Hz) underdamped one.

Total respiratory impedance was assessed from 4 to 30 Hz in ten normal subjects breathing air and a helium-oxygen gas mixture using two methods of applying pressure oscillations at the airway opening: 1) the conventional method where pressure is varied at the mouth: 2) the method recently developed by Peslin et al. (J Appl Physiol, 1985, 59, 1790-1795) in which pressure is varied both at the mouth and around the head to minimize transmural pressure across upper airway walls, and the corresponding artefact. When breathing air slightly lower resistances (p less than 0.05) and considerably higher inertances (p less than 0.001) were found using the head generator. Breathing helium-oxygen reduced respiratory resistance and its frequency dependence, as well as respiratory inertance very significantly (p less than 0.001), with minor differences between the changes seen with the two methods. In contrast, the changes in respiratory compliance were small, and not in the same direction, when pressure was varied at the mouth and around the head. It is concluded that the accuracy of the conventional method may be sufficient for diagnostic purposes in subjects without gross mechanical abnormalities, i.e. for early detection of mechanical abnormalities.

The influence of inspiratory and expiratory flow magnitude, lung volume, and lung volume history on respiratory system properties was studied by measuring transfer impedances (4-30 Hz) in seven normal subjects during various constant flow maneuvers. The measured impedances were analyzed with a six-coefficient model including airway resistance (Raw) and inertance (Iaw), tissue resistance (Rti), inertance (Iti), and compliance (Cti), and alveolar gas compressibility. Increasing respiratory flow from 0.1 to 0.4 1/s was found to increase inspiratory and expiratory Raw by 63% and 32%, respectively, and to decrease Iaw, but did not change tissue properties. Raw, Iti, and Cti were larger and Rti was lower during expiration than during inspiration. Decreasing lung volume from 70 to 30% of vital capacity increased Raw by 80%. Cti was larger at functional residual capacity than at the volume extremes. Preceding the measurement by a full expiration rather than by a full inspiration increased Iaw by 15%. The data suggest that the determinants of Raw and Iaw are not identical, that airway hysteresis is larger than lung hysteresis, and that respiratory muscle activity influences tissue properties.

The mechanics of the ventilatory system were studied in 29 sleeping infants and young children by the analysis of a passive expiration following an end-inspiratory airway occlusion ('single breath' method). The ventilatory system time constant (tau rs) to compliance ratio yielded the value of ventilatory system resistance (Rrs). The calculated ventilatory system compliance correlated well with the slope of the quasi static pressure-volume curve (r = 0.97). The allometric relationship between Rrs and height (Rrs = 81.9.10(3).Ht (cm)-1.76, r = -0.82) is in agreement with forced oscillation measurements during the first year of life (Wohl et al., 1969). tau rs was found to increase significantly over the first months of life (P less than 0.01).

Horse liver phosphopantothenoylcysteine decarboxylase (EC 4.1.1.36) is rapidly inactivated by N-acetoacetylation with diketene following a pseudo-first-order kinetics: the presence of substrate quantitatively protects against this inactivation. Histidine photo-oxidation with methylene blue or rose bengal brings about the total loss of activity. These results indicate the presence of functional lysyl and histidyl groups at the active site of the enzyme. The substrate sulphydryl group is essential for enzyme activity. Enzymatic decarboxylation is proposed to result from a combined action of the keto group of the enzyme-bound pyruvate protonated by an essential histidine and a protonated amino group of a lysine.

Two methods of measuring respiratory transfer impedance (Ztr) were compared in 14 normal subjects, from 4 to 30 Hz, 1) studying the relationship between transrespiratory pressure (Prs) and flow at the chest when varying pressure at the mouth (Ztrm) and 2) studying the relationship between Prs and flow at the mouth when varying pressure around the chest wall (Ztrw). The similarity of the two relationships was expected on the basis of a T-network model. Almost identical phase responses were obtained from the two methods. Pressure-flow ratios were slightly larger for Ztrw than for Ztrm, but differences did not exceed 2% on average in 11 of 14 subjects. When the data were analyzed with the six-coefficient model proposed by DuBois et al. (J. Appl. Physiol. 8: 587-594, 1956), similar values were found for tissue compliance and tissue inertance but slightly different values for gaseous inertance in the airways (1.97 +/- 0.35 X 10(-2) cmH2O X l-1 X s2 for Ztrw vs. 1.73 +/- 0.26 for Ztrm; P less than 0.01). Similar results were also found for total respiratory resistance but with a slightly larger contribution of airway resistance for Ztrw (64 +/- 14 vs. 57 +/- 10%; P less than 0.05). As a practical conclusion it is recommended to measure Ztrw, which is technically much easier.

The validity of a new method for measuring thoracic gas volume (Vtg) was studied in 18 bronchitic patients with mild to severe airway obstruction. The method entailed submitting the subject to very slow sinusoidal variations of ambient pressure (delta Pam) and studying the relationship between delta Pam and the resulting gas displacement at the mouth (delta Vaw): Vtgapc = PB.delta Vaw/delta Pam.cos phi, where PB is barometric minus alveolar water vapor pressure, and phi is the phase angle between Pam and Vaw. delta Pam of 40 cm H2O at 0.05 Hz were achieved by placing the subject in a 410-I body chamber connected to a large stroke volume reciprocating pump. Pam and Vaw were processed digitally by Fourier transform to obtain their amplitude ratio and phase angle at the frequency of interest. Vtg was also measured by body plethysmography (Vtgplet) during slow panting maneuvers (0.79 +/- 0.19 Hz) and also in order to detect any artifactual frequency dependence at a higher panting frequency (1.71 +/- 0.27 Hz); the agreement between the 2 estimates in all subjects (r = 0.975) suggested that Vtgplet could be taken as a valid reference. Functional residual capacities derived from Vtgapc and Vtgplet were not significantly different (5.113 +/- 1.198 versus 5.260 +/- 1.328 L) and were highly correlated (r = 0.915). Intermethod differences averaged 1.7 +/- 10.5% and were not significantly correlated to functional indices. We conclude that the new method provides accurate Vtg values in patients with chronic airway obstruction.

Two methods of measuring ventilatory mechanical impedance (Z) by forced oscillations between 6 and 20 Hz were compared in 24 infants aged 2 to 49 months: 1) the application of pressure oscillations at the airway opening (Z1); and 2) the application of pressure oscillations around the head (Z2). The latter has been recently proposed to minimize the influence of compliant upper airway walls (Peslin et al., J Appl Physiol. 1985, 59:1790-1795). Ventilatory resistance and compliance (Rsb, Csb) were also obtained with the single breath method. The real part of Z1 (R1) was markedly lower than that of the corresponding Z2 (R2), at any frequency. R1 exhibited a systematic negative frequency dependence, in contrast with R2. At any frequency, the slope of the regression equation on Rsb was closer to unity for R2 than for R1. The imaginary part of Z1 (X1) was negative over the whole frequency interval, and negative values of inertance were derived from X1. X2 was negative at low and positive at high frequencies. Resonant frequency (mean +/- SD = 10.5 +/- 3.5 Hz) was always reached with Z2 and correlated negatively with body weight (r = -0.61). Inertance estimated from X2 was positive and correlated negatively with body height (r = -0.66). The compliance derived from Z1 (C1 = 3.35 +/- 2.32 10(-3) L.cm H2O-1) was not significantly different from that derived from Z2 (C2 = 2.99 +/- 2.02 10(-3) L.cm H2O-1). The marked difference observed between Z1 and Z2 is related to the importance of the upper airway shunt and may be explained by inaccuracies of both methods.(ABSTRACT TRUNCATED AT 250 WORDS)

When the whole body is exposed to sinusoidal variations of ambient pressure (delta Pam) at very low frequencies (f), the resulting compression and expansion of alveolar gas is almost entirely achieved by gas flow through the airways (Vaw). As a consequence thoracic gas volume (TGV) may be computed from the imaginary part (Im) of the delta Pam/Vaw relationship: TGV = PB/[2 pi f X Im(delta Pam/Vaw)], where PB is barometric minus alveolar water vapor pressure. The method was tested in 35 normal subjects and compared with body plethysmography. The subjects sat in a chamber connected to a large-stroke-volume reciprocating pump that brought about pressure swings of 40 cmH2O at 0.05 Hz. delta Pam and Vaw were digitally processed by fast Fourier transform to extract the low-frequency component from the much larger respiratory flow. Total lung capacities (TLC) obtained by ambient pressure changes and by plethylsmography were highly correlated (r = 0.959, p less than 0.001) and not significantly different (6.96 +/- 1.38 l vs. 6.99 +/- 1.38). TLC obtained by ambient pressure changes were not influenced by lowering the frequency to 0.03 Hz, adding an external resistance at the mouth, or increasing abdominal gas volume. We conclude that the method is practical and in agreement with body plethysmography in normal subjects.

The real--Re(Z)--and imaginary--Im(Z)--parts of the ventilatory system impedance were measured between 6 and 30 Hz in 18 normal infants and in 19 with airway obstruction. The intercept (R0) and slope (S) of the Re(Z)-frequency function, as well as inertance (I) and compliance (C) estimated from Im(Z), were compared with ventilatory system resistance (Rrs) and compliance (Crs) (single-breath method). R0 correlated significantly with Rrs (r = 0.86), although the slope of the regression equation was significantly lower than 1 (P less than 0.01). Negative frequency dependence of Re(Z) was observed in all subjects and a significant correlation was found between S and Rrs (r = -0.80). "Inertance" was negative in 20 subjects and correlated negatively with Rrs (r = -0.61). C correlated with Crs (r = 0.64) and with 1/Rrs (r = 0.85). The ratio of C to Crs (mean +/- SD = 0.168 +/- 0.082) also correlated with 1/Rrs (r = 0.51). The main characteristics of the total impedance/frequency function could be simulated with a model featuring the upper airway wall (Zuaw) in parallel with the ventilatory system (Zrs). It is suggested that the differential change in Zuaw and Zrs with growth accounts for the marked frequency dependence of Re(Z) as well as the inaccurate estimation of both I and C in this population.