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P R Buchanan

Publications and source records attributed to P R Buchanan.

4 recordsLinked to original sources
PubMed1987

Human alveolar gas-mixing efficiency for gases of differing diffusivity in health and airflow limitation.

1. Incomplete mixing of alveolar gas may be expressed as an equivalent alveolar dead space serving a remaining alveolar space in which mixing is regarded as complete. Calculation of this dead space during multiple-breath, inert gas wash-in or wash-out leads to an estimate of 'multiple-breath alveolar mixing efficiency' (MBME). 2. We measured MBME in 25 healthy subjects and six patients with chronic airflow limitation (CAL), and in three asthmatic patients before and after bronchial provocation with histamine aerosol, from successive breaths during open-circuit, multiple-breath wash-in of a mixture containing helium (He) and sulphur hexafluoride (SF6). The simultaneous use of a light and a heavy gas helps to identify diffusive mechanisms. 3. MBME fell almost linearly with log Z, the proportion of total wash-in remaining uncompleted. For a given Z, MBME was always lower for SF6 than for He in the same subject. In health the lowest MBME (52.2%) was seen for SF6 in a man aged 21 years. The same wash-in yielded a ventilation distribution with an extreme range of specific ventilation of less than 1 decade. MBME of this order is thus consistent with estimates of ventilation distribution in health. 4. Patients with CAL showed a big increase in the volume of the conducting airways or 'series dead space' (VDS) for both gases, and VDS was always bigger for SF6 than for He. This very large VDS appears to be the main reason for wash-in delay in these patients, followed by impaired diffusive mixing in the peripheral air spaces. Ventilation maldistribution may play little part in the mixing defect.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1986

Recovery of ventilation distributions by gas wash-out of a mechanical pump.

A method for deriving virtually continuous distributions of ventilation in the lungs from multiple-breath wash-out of inert, insoluble gases has been tested using a mechanical pump in which two parallel compartments, simulating lung regions, could be differentially ventilated to any desired, and known, extent. With more than moderate non-uniformity, bimodal distributions were always recovered from wash-out data, and with high reproducibility. In a substantial proportion of wash-out experiments ventilation was recovered in regions of very low and very high turnover in addition to the expected modes. These spurious modes may be abolished by various computational devices, none entirely satisfactory. Simultaneous wash-out and wash-in of two or three gases of similar diffusivity give essentially identical solutions. When the pump is operated with the two cylinders out of phase, emptying patterns derived from gas wash-out correspond quite well with those expected from the pump setting. These results help to identify and clarify some of the errors which affect physiological wash-out studies.

Gases↗
PubMed1985

Data acquisition from a multiplex, quadrupole mass spectrometer.

Although various methods have been used to correct the output of a respiratory mass spectrometer for the delay and rise time in its response, thereby reducing the error in measured gas concentrations, there are additional considerations in the case of a multiplex mass spectrometer. The measured signal from the detector is a series of discrete samples of the concentration of several different gases rather than a continuous monitor of a single gas concentration as generated by other types of mass spectrometer. If the time constant of the mass spectrometer is of the same order as the interval between samples of a gas in the multiplex mode, correction techniques based on continuous-time analysis would not be as valid as those based on discrete-time analysis. Such correction techniques were compared to the use of a simple time shift. For multibreath gas washout analysis with simulated worst-case 'square wave breathing' it was found that, because of the complex nature of the response of the mass spectrometer, a simple time shift provided a reduction in error nearly equal to that of an additional first order response correction, and that such further corrections may be unnecessary or even invalid under some circumstances.

Humans↗