Aplicaçäo de análise multivariável ao estudo do teste de lavagem de nitrogênio com respiraçäo única / Application of multivariate analysis to the study of the single-breath nitrogen washout test

O presente trabalho trata da aplicaçäo de método numérica à análise de testes de funçäo pulmonar. Objetiva-se investigar preliminarmente a utilizaçäo de técnicas de análise de múltiplas variáveis aos dados obtidos no teste de lavagem de nitrogênio com respiraçäo única (TN2-RU). O teste foi realizado com uso de sistema experimental baseado em computador. Parâmetros do TN2-RU foram obtidos em 18 voluntários, classificados de acordo com questionário de sintomas respiratórios. Através de análise discriminante obtiveram-se equaçöes cujas variáveis independentes säo parâmetros do TN2-RU. Essas equaçöes permitiram separar, com significância estatística, grupos de sintomáticos e näo sintomáticos (p < 0,05) e tabagistas e näo tabagistas (p < 0,05). Tais resultados indicam a utilidade de métodos de análise de múltiplas variáveis na análise de dados de testes de funçäo pulmonar, possibilitando a objetivaçäo de condutas e estudos clínicos

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.

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.

The measurement of tidal volumes in spontaneously breathing children during general anaesthesia using a Haloscale infant Wright respirometer.

The accuracy of tidal volume measurements made with a Wright Haloscale infant respirometer in children breathing spontaneously during general anaesthesia was assessed by a bench test. The tidal volumes and peak flow rates of 20 spontaneously breathing, anaesthetised children were measured with a pneumotachograph before and during surgery, and similar volumes, at the same flow rates, were delivered by a calibrated syringe simultaneously to the respirometer and a pneumotachograph. The results reveal that the mean (+/- s.d.) peak gas flow rates of children aged 6 years and less, 7.5 (+/- 1.6) and 9.3 (+/- 0.1) l/min before surgery and during surgery respectively, are significantly less than the peak flow rates, 11.3 (+/- 1.0) and 11.9 (+/- 1.5) before and during surgery, respectively, of children aged more than 6 years; and that the respirometer underestimates tidal volume by 10% when the peak flow rate is 11 l/min, and the percentage error in tidal volume estimation by the respirometer increases as the peak gas flow declines below 10 l/min.

Accuracy of tidal volume, lung volume, and flow measurements by inductance vest in COPD patients.

We analyzed the accuracy of the inductance vest in measuring several ventilatory parameters in five patients with chronic obstructive pulmonary disease (COPD). We assessed tidal volume (VT) accuracy at different respiratory frequencies in different lying body positions with different thoracic and abdominal contributions to breathing and the accuracy over a 4-h time span. Mean percent error was calculated without regard to direction of error. The mean error of vest VT estimation was 7.6% for all body positions studied and 5.6% for right and left lateral positions combined. Vest VT accuracy was unchanged after 4 h and with changes in thoracic and abdominal contributions to VT. The mean errors for inspiratory and expiratory times were 3.3 and 2.0%, respectively. Volume was differentiated to flow. For respiratory rates ranging from 12 to 30 breaths/min, the mean error of the vest and our differentiation circuit in duplicating peak flows measured at the mouth was 3.5%. The ability of the vest to estimate changes in end-expiratory position or functional residual capacity was not as good as with VT; the mean error was 30.7%. For estimation of VT, ventilatory timing, and airflow in COPD patients, the inductance vest performs well. For measurement of changes in lung volume, improvements in vest design need to be made.

The respiratory inductive plethysmograph: bands versus jerkins.

The respiratory inductive plethysmograph (RIP) is used to measure ventilation from body surface movements. We have compared the accuracy of the two versions of inductance coils used with this instrument. The early version consists of rib cage and abdominal coils sewn into a one-piece jerkin, whereas the new version consists of similar coils attached to two separate bands. Following overnight studies in 12 subjects, we found that less than 50% of separate band RIP tidal volumes were accurate when compared with simultaneously measured spirometric values. The jerkin RIP, however, was accurate in 87% of the breaths measured. Therefore, we advocate the use of the jerkin RIP for prolonged studies because the separate bands appear to move more easily.

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.

A spirometer for the continuous measurement of expired tidal volume.

A spirometer is described for the continuous breath-by-breath measurement of expired tidal volume (VE). This spirometer differs from other similar equipment in using a pneumotachograph to define the duration of the inspiratory phase.

Application of the hot-wire anemometer to respiratory measurements in small animal.

A hot-wire anemometer was evaluated to determine its suitability for measurement of small tidal volumes. Used with a constant background flow of gas, the output of the hot-wire anemometer was linear and independent of respiratory frequency, temperature, and humidity. The change in output with CO2 concentration was negligible within the physiologic range. The use of a background flow eliminates the need for one-way valves, minimizes dead space, and maintains the flow velocity past the hot wire within its range of linear response.