Quality of spirometry in primary care for case finding of airway obstruction in smokers.

BACKGROUND: Diagnosis of chronic obstructive pulmonary disease (COPD) and its severity determination is based on spirometry. The quality of spirometry is crucial. OBJECTIVES: Our aim was to assess the quality of spirometry performed using a spirometer with automated feedback and quality control in a general practice setting in Switzerland and to determine the prevalence of airflow limitation in smokers aged > or =40 years. METHOD: Current smokers > or =40 years of age were consecutively recruited for spirometry testing by general practitioners. General practitioners received spirometry training and were provided with an EasyOne spirometer. Spirometry tests were assigned a quality grade from A to D and F, based on the criteria of the National Lung Health Education Program. Only spirometry tests graded A-C (reproducible measurements) were included in the analysis of airflow limitation. RESULTS: A total of 29,817 spirometries were analyzed. Quality grades A-D and F were assigned to 33.9, 7.1, 19.4, 27.8 and 11.8% of spirometries, respectively. 95% required < or =5 trials to achieve spirometries assigned grade A. The prevalence of mild, moderate, severe and very severe airway obstruction in individuals with spirometries graded A-C was 6, 15, 5 and 1%, respectively. CONCLUSION: Spirometries in general practice are of acceptable quality with reproducible spirometry in 60% of measurements. Airway obstruction was found in 27% of current smokers aged > or =40 years. Office spirometry provides a simple and quick means of detecting airflow limitation, allowing earlier diagnosis and intervention in many patients with early COPD.

A pulsed diagonal-beam ultrasonic airflow meter.

The construction and specific function of a new ultrasonic flowmeter are described. The mean velocity of the respiratory airflow is calculated by measuring the transit times of short ultrasonic pulse trains, simultaneously transmitted upstream and downstream at a 500-Hz rate. The flowmeter system consists of a control unit and a separate flow head. The former includes the power supplies, a controlling microprocessor, most of the signal-processing circuitry, and three analog outputs for flow, volume, and temperature. The flow head contains the respiratory tube with a constant circular cross section (length 90 mm, diam 20 mm, dead space 35 ml), a fast temperature sensor, two electronic circuits for processing of flow and temperature data, and a sound transmission channel with two capacitive ultrasonic wide-band transducers. This respiratory airflow meter, suitable for spirometric maneuvers (vital capacity, forced vital capacity) as well as for long-term breath-by-breath respiratory analysis, is extremely fast (response time 1-2 ms) and accurate (volume accuracy with room air +/- 0.7%), with low noise (below 9 ml/s), a wide flow range (bidirectional from 0 to 9 l/s), and a flat frequency response up to 70 Hz.

Pulmonary gas exchange in panting dogs.

Pulmonary gas exchange during panting was studied in seven conscious dogs (32 kg mean body wt) provided with a chronic tracheostomy and an exteriorized carotid artery loop. The animals were acutely exposed to moderately elevated ambient temperature (27.5 degrees C, 65% relative humidity) for 2 h. O2 and CO2 in the tracheostomy tube were continuously monitored by mass spectrometry using a special sample-hold phase-locked sampling technique. PO2 and PCO2 were determined in blood samples obtained from the carotid artery. During the exposure to heat, central body temperature remained unchanged (38.6 +/- 0.6 degrees C) while all animals rapidly switched to steady shallow panting at frequencies close to the resonant frequency of the respiratory system. During panting, the following values were measured (means +/- SD): breathing frequency, 313 +/- 19 breaths/min; tidal volume, 167 +/- 21 ml; total ventilation, 52 +/- 9 l/min; effective alveolar ventilation, 5.5 +/- 1.3 l/min; PaO2, 106.2 +/- 5.9 Torr; PaCO2, 27.2 +/- 3.9 Torr; end-tidal-arterial PO2 difference [(PE' - Pa)O2], 26.0 +/- 5.3 Torr; and arterial-end-tidal PCO2 difference, [(Pa - PE')CO2], 14.9 +/- 2.5 Torr. On the basis of the classical ideal alveolar air approach, parallel dead-space ventilation accounted for 54% of alveolar ventilation and 66% of the (PE' - Pa)O2 difference. But the steepness of the CO2 and O2 expirogram plotted against expired volume suggested a contribution of series in homogeneity due to incomplete gas mixing.

Mechanical respiratory system input impedance during high-frequency oscillatory ventilation in rabbits.

OBJECTIVES: To study the mechanical properties of the rabbit respiratory system during high-frequency oscillatory ventilation by means of mechanical respiratory impedance measurement and to characterize the changes in oscillation mechanics of the respiratory system occurring after bilateral vagotomy. DESIGN: Acute experimental trial. SETTING: Physiology laboratory. SUBJECTS: Ten adult rabbits (mean body weight 3.1 kg). MEASUREMENTS AND MAIN RESULTS: Anesthetized rabbits were exposed to short runs of high-frequency oscillatory ventilation, with stroke volumes of 5.0, 6.6, and 10.0 mL, applied at oscillation frequencies of 10, 15, 20, and 25 Hz before and after vagotomy. Mechanical respiratory input impedance was determined from the pressure and flow signals simultaneously measured at the airway opening and analyzed in terms of its real and imaginary parts. (The real part of respiratory impedance characterizes the resistive property of the lungs and chest wall; the imaginary part of respiratory impedance characterizes the elastic and inertial properties of the lungs and chest wall.) At all stroke volumes and oscillation frequencies studied, vagotomy resulted in a decrease in the real part of respiratory impedance. After vagotomy, the real part of respiratory impedance was stroke volume-independent, and exhibited negative frequency dependency. Vagotomy also led to a decrease in the imaginary part of respiratory impedance, mainly at lower oscillation frequencies, and thus, to a higher resonant frequency of the respiratory system. CONCLUSIONS: Mechanical respiratory impedance measurement proved to be a useful method to study the mechanical properties of the respiratory system during high-frequency oscillatory ventilation. The results suggest that vagally mediated reflex changes in respiratory system mechanics are associated with high-frequency oscillatory ventilation, depending on the ventilatory variables that are used.

Multiple breath washout of He and SF6 in panting dogs.

Pulmonary gas transport mechanisms in panting were studied by multiple breath washout of two poorly soluble inert gases of similar solubility but different diffusivity (He and SF6). The experiments were performed in 6 chronically tracheotomized conscious dogs (mean body weight 31.0 kg) which, upon exposure to elevated room temperature, were enforced to thermal panting (mean breathing frequency 288/min). After equilibration of lung gas with 1% He and 1% SF6 followed by changeover to test gas-free air, end-tidal gas concentrations during multiple breath washout were recorded by mass spectrometry. The washout time course was analyzed into 3 exponential components. The initial fast component was considered to be in part determined by the transient response of the measuring system, whereas the intermediate and the slow component could be attributed to lung washout. The mean He/SF6 ratio of medium and slow rate constants was 1.06 and 1.13, respectively (both values differing from 1.0 at P less than 0.001). It is concluded that gas transport in dog lungs during panting was mainly determined by convection, diffusion-dependent processes being discernible but playing a minor role.