Regional tidal volume assessed by gated lung imaging.

We have measured regional lung tidal volumes and functional residual capacities by accumulating and framing iso-volumic images while the patient rebreathes 127Xe. As the lung changes shape during ventilation corrections for changes in geometry were obtained by simultaneous collection of 99Tcm counts from the gated perfusion scan. Regions of interest were made to vary throughout the respiratory cycle so that a region had always the same value of 99Tcm counts. From the corrected 127Xe counts regional tidal volumes (TVr) and functional residual capacities (FRCr) were derived. In patients with established chronic bronchitis and emphysema FRCr were greater and the ratio TVr/FRCr decreased compared with patients with relatively normal static and dynamic lung volumes. Preliminary studies suggest that this ratio was a better discriminator between normal and abnormal regional function than estimates of regional xenon washout. Studies with xenon-133 have contributed to our understanding of the physiology of ventilation but have contributed somewhat less to routine clinical practice. This results in part from the unsatisfactory physical properties of xenon-133. Its relatively low gamma ray energy of 80 keV results in significant self-absorption losses and the activity which may be administered is limited by the radiation dose from the associated beta particles so that relatively poor counting statistics are obtained. With inhaled technetium-99m (99Tcm) microspheres imaging conditions are greatly improved but the distribution of these particles may not equate with the distribution of ventilation particularly if wet particles are used. Moreover, simultaneous microsphere perfusion scans with technetium-99m as a label are impossible. Krypton-81m gas has a suitable energy but the short half-life of the rubidium-81m generator (4.7 h) makes supply difficult and the ultrashort half-life of the krypton-81m gas (13 s) leads to problems in calculating the indices of ventilation. Xenon-127 (127Xe) gas has a more favourable dosimetry profile than xenon-133 because it does not have associated beta particles. Further it has an energy (203 keV) suitable for modern gamma cameras and may be used in the presence of injected 99Tcm microspheres to provide simultaneous ventilation/perfusion imaging. Conventional techniques have assumed that a static image of a dynamic process is adequate. As the lungs move during imaging, some account of this respiratory movement should be made.(ABSTRACT TRUNCATED AT 250 WORDS)

Pulmonary function testing in calves: technical data.

Measurements of airflow (V), tidal volume (Vt), and intrapleural pressure (Ppl) were tested for accuracy in 5 healthy Dutch Friesian calves with an average body weight of 153 kg. A face mask was constructed, using fiberglass and polyester, taking into account the typical facial morphology of the calf. It was tested for airtightness, dead space, laminarity of the expiratory V, and absence of saliva into the pneumotachograph. Three different systems for measuring Ppl (pleura puncturing, esophageal balloon catheter, and esophageal saline solution-filled catheter) were tested in vitro, in a Woulfe's flask, and in vivo, in the 5 calves previously described. Moreover, Ppl measured at 3 different puncture sites of the thorax and at 3 different thoracic positions of the esophagus were compared. The frequency-response was flat to 5 Hz for the intrapleural needle and the balloon catheter, but not for the saline solution-filled catheter. The pulmonary function values obtained by puncture of the pleura at the right 9th intercostal space on a line running from the tuber coxae to the shoulder joint and by the esophageal balloon catheter, the balloon being positioned between the crossing point with the aorta and the 2 largest caudal mediastinal lymph nodes, did not differ significantly. The Ppl changes during normal breathing were greatest in the ventral site of the thorax and in the caudal thoracic portion of the esophagus, less in the dorsal site of the thorax and the middle thoracic portion of the esophagus, and least in the cranial site of the thorax and the cranial thoracic portion of the esophagus.(ABSTRACT TRUNCATED AT 250 WORDS)

Comparison of barometric and pneumotachographic measurements of resting ventilation in the little penguin (Eudyptula minor).

1. We compared the use of the barometric method and pneumotachography for measurement of ventilation in the little penguin Eudyptula minor. 2. Simultaneous use of both techniques showed the barometric method to give a reliable estimate of tidal volume. 3. Comparison of birds with and without masks for pneumotachography showed wearing masks to produce a significant increase in ventilation, principally through a raised respiratory frequency.

A method for measuring tidal volume during high frequency jet ventilation.

A new method has been developed to measure tidal volume during high frequency jet ventilation. A pneumotachograph is placed in the expiratory limb of the breathing circuit. Using a model lung, the results from this method did not differ from the tidal volume calculated from pressure changes measured within the model lung. The results from the two methods correlated well (r = 0.99). The method enables the gas volumes entrained and spilled out of the airway during inspiration, true I:E ratios and mean driving pressures to be determined. The method is non-invasive and could easily be applied clinically.

Practical implementation of the barometric method for measurement of tidal volume.

The barometric method is unique in permitting measurement of tidal volume in a totally noninvasive manner. Its application and accuracy have been limited by several complex problems. These include control of inspired gas composition, base-line stability, and asymmetry of processes occurring during inspiration and expiration. A new method is described that addresses these problems and facilitates long-term measurements. New calculations, which avoid previous errors that caused the method to systematically underestimate tidal volume, are illustrated.

Step changes in end-tidal CO2: methods and implications.

A dynamic end-tidal forcing technique for producing step changes in end-tidal CO2 with end-tidal O2 held constant independent of the ventilation response or the mixed venous return is introduced for characterizing the human ventilation response to end-tidal CO2 step changes for both normoxic (PAO2 = 125 Torr) and hypoxic (PAO2 = 60 Torr) conditions. The ventilation response approaches a steady state within 5 min. In normoxia, the on-transient is faster than the off-transient, presumably reflecting the action of cerebral blood flow. The hypoxic step response is faster than the normoxic response presumably reflecting the increased contribution from the carotid body. The delay in the ventilation response after the change in end-tidal CO2 is less in hypoxia than in normoxia and reflects the action of a transport delay and that of a virtual delay. These delays are interpreted with respect to the high-frequency phase shift data for the same subject, generated using sinusoidal end-tidal forcing. The methods of others for experiments utilizing step changes in inspired CO2 are considered with respect to our methods.

[Total thoracic compliance. Determination by calculator and comparison with values obtained with the syringe method (author's transl)]. / Les compliances thoraciques totales. Détermination par calculateur et comparaison en clinique avec une méthode de référence.

The performance of a calculator was studied on 19 patients requiring therapy with mechanical ventilation. Values of total compliance displayed by this calculator device were compared with values obtained with the syringe method. The determination of compliance were made at a series of values for Tidal volume (T. V.): 3, 4, 5, 6, 8, 10, 12, 15, 18, 20, 23 and 26 ml.kg-1. Measurements were performed while patients were paralysed by pancuronium bromide. In each patient the calculator device displayed values that correlate closely with the value obtained by the syringe method. Compliance increased between 3 and 26 ml.kg-1 of T. D. Between 4 and 15 ml.kg-1 of TD the changes of compliance were nearly identical whatever the method of measurement used. The calculator can be used for reliable monitoring or recordings of total compliance.

Compression volume during mechanical ventilation: comparison of ventilators and tubing circuits.

Four ventilators (Puritan-Bennett MA-1 and MA-2, Emerson, and Bear I) and four commercially available disposable and nondisposable tubing circuits (Bennett nondisposable, Becton-Dickinson, Inspiron, and Life-line) were tested on a lung analog for differences in inspiratory-circuit compression volume. The compression ratio (Rc), equal to the gas volume compressed per cm H2O peak airway pressure, was calculated for each combination of ventilator and circuit at each of four compliance settings (0.15, 0.10, 0.05, 0.01 L/cm H2O) on the analog. Rc values ranged from 0.3 to 4.5 ml/cm H2O at the highest and lowest compliance settings, respectively, accounting for a reduction in delivered tidal volume of up to 20%. The Emerson ventilator with all tubing systems and the Bennett nondisposable circuit with each ventilator demonstrated slightly smaller compression volumes. Application of an inspiratory pause on the Bear I ventilator did not affect its compression characteristics. The clinical importance of compression volume and data from other ventilation systems are reviewed.

Limitaçäo ao fluxo aéreo e capacidade vital reduzida: distúrbio ventilatório obstrutivo ou combinado? / Vital capacity deduced and chronic airflow limitation: obstructive or combined ventilatory defect?

A diferenciaçäo entre distúrbios ventilatórios e combinados pode ser difícil porque ambos podem reduzir a CV. O valor do espirograma na separaçäo dos distúrbios ventilatórios foi avaliado em 264 indivíduos (100 com obstruçäo, 64 com restriçäo e 100 com possível defeito combinado). O diagnóstico de limitaçäo ao fluxo aéreo foi baseado em achados clínicos, radiológicos e funcionais (VEF1/CVF e/ou FEF25-75/CVF abaixo do normal). Distúrbio restritivo foi caracterizado por CV ou CPT abaixo do normal associada a VEF1/CVF e FEF25-75/CVF näo reduzidos. Um terceiro grupo com distúrbio obstrutivo e possível restritivo foi separado considerando-se VEF1/CVF e/ou FEF25-75/CVF baixos e dados clínicos e radiológicos de processo restritivo. Baseado no limite inferior para a CPT estabelecido no grupo obstrutivo (94%) do valor previsto), o terceiro grupo foi separado em obstrutivo puro (CPT * 94%; n = 54) e combinado (CPT < 94%; n = 46). CV(F) acima de 80% do valor previsto se associou em 95% com CPT acima ou igual a 94%. As diferenças entre a %CVF - %VEF1 foram derivadas nos grupos obstrutivo, restritivo e verdadeiramente combinado. Baseados na prevalência dos distúrbios ventilatórios em nosso laboratório e na presença de achados indicativos de obstruçäo ao fluxo aéreo, uma diferença entre %CVF e VEF1 abaixo ou igual a 12 se associa a distúrbio combinado em 84%, e acima ou igual a 25 a distúrbio obstrutivo isolado em 95%. Com valores entre estes limites, a CPT deve ser medida. Com valores entre estes limites, a CPT deve ser medida. Equaçöes de regresso linear para % CVF e %VEF1 foram derivadas nos diversos grupos, permitindo uma melhor estimativa para %CVF - %VEF1, de acordo como VEF1 em porcentagem do previsto. Em conclusäo, os distúrbios ventilatórios podem ser separados em grande número de casos apenas por espirometria, usando-se o algoritmo descrito