Marc J. Jaeger

Determination of the longitudinal dispersion coefficient in flows subjected to high‐frequency oscillations

Experimental measurements of the longitudinal dispersion coefficient in oscillatory pipe flow of binary gas mixtures at high oscillation frequencies are presented. The magnitude of the dispersion coefficient is shown to be directly proportional to the product of the square of the oscillation amplitude and the first power of frequency.

Enhanced dispersion in oscillatory flows

Measurements of the dispersion coefficient in oscillating pipe flows for a wide range of Womersley numbers, tidal displacements, and tube radii are presented. The results are shown to be in good agreement with those of a recent laminar dispersion theory for oscillatory flows.

Transport of gases in high-frequency ventilation

We found that the transport of gases in oscillating gas columns was proportional to oscillation frequency and the square of oscillation amplitude. When these results were applied to high-frequency oscillation and high-frequency jet ventilation in dogs, alveolar ventilation was proportional to frequency and to the square of tidal volume, and inversely proportional to anatomic dead space.

Diffusional separation of gases by sinusoidal oscillations

It is shown that gas mixtures can be separated at relatively high differential flow rates by an enhanced diffusion technique involving the oscillation of gases within a capillary bundle in the presence of axial concentration gradients. Experimental data for the diffusional separation of both He–CO2 and CO2–SF6 mixtures into an O2 carrier are presented.

Nitric oxide inhalation increases alveolar gas exchange by decreasing deadspace volume.

Objective To test the hypothesis that nitric oxide inhalation facilitates CO2 elimination by decreasing alveolar deadspace in an ovine model of acute lung injury. Design Prospective, placebo-controlled, randomized, crossover model. Setting University research laboratory. Subjects Eleven mixed-breed adult sheep. Interventions To induce acute lung injury, hydrochloric acid was instilled into the tracheas of paralyzed sheep receiving controlled mechanical ventilation. Each sheep breathed 0 ppm, 5 ppm, and 20 ppm nitric oxide in random order. Measurements and Main Results Estimates of alveolar deadspace volumes and arterial-to-end tidal CO2 partial pressure differences were used as indicators of CO2 elimination efficiency. At a constant minute ventilation, nitric oxide inhalation caused dose-independent decreases in Paco2 (p < .05), alveolar deadspace (p < .01), and arterial-to-end tidal CO2 partial pressure differences (p < .01). We found that estimates of arterial-to-end tidal CO2 partial pressure differences may be used to predict alveolar deadspace volume (r2 = .86, p < .05). Conclusions Estimates of arterial-to-end tidal CO2 partial pressure differences are reliable indicators of alveolar deadspace. Both values decreased during nitric oxide inhalation in our model of acutely injured lungs. This finding supports the idea that nitric oxide inhalation facilitates CO2 elimination in acutely injured lungs. Future studies are needed to determine whether nitric oxide therapy can be used to reduce the work of breathing in selected patients with cardiopulmonary disorders.

Pulmonary Diffusing Capacity and Physical Working Capacity in Swimmers and Non-Swimmers during Growth

We measured physical working capacity at a heart rate of 170 bpm (PWC170) and diffusing capacity for carbon monoxide (DLCO) in two groups of children ranging in age from 9 to 17 years. One group was formed of highly trained competitive swimmers and the other of age, sex and size matched untrained counterparts. Bicycle ergometry was used to establish PWC170. The DLCO was measured at rest (DLCO rest) and while pedalling at 170 bpm (DLCO ex). The PWC 170, DLCO rest and DLCO ex were significantly higher in swimmers than in non-swimmers. Repeated measurements in the same subjects show that individual increases in DLCO rest and DLCO ex were result of both growth and training.

A lung model of carbon dioxide concentrations with mechanical or spontaneous ventilation

Modifications of a commercially available mechanical lung model (Vent-Aid Training Test Lung, Michigan Instruments, Inc., Grand Rapids, MI) enabled the study of CO2 concentration, distribution, and washout curves. An additional modification allowed either simultaneous or separate study of spontaneous ventilation and work of breathing.

Tuning effect in enhanced gas dispersion under oscillatory conditions

It is shown that the effective axial dispersion coefficient for partially mixed gases confined to cylindrical tubes and subjected to sinusoidal oscillations reaches a maximum, at a constant oscillation frequency, when the Womersley number is equal to α=3.3. Such a tuned condition in oxygen–nitrogen mixtures corresponds, for example, to tubes of 2.0 mm in diameter when the oscillation frequency is 27.7 Hz and occurs when the time for gas diffusion from the tube axis to the walls is comparable with the oscillation period.

Effect of Positive End-Expiratory Pressure on Dynamic Respiratory Compliance in Neonates

A simplified method of determining dynamic respiratory compliance (C dyn) in the newborn is described. Studies were performed during mechanical ventilation on 24 infants with respiratory distress syndrome (RDS) and 6 infants without RDS. Cdyn was evaluated at pressure settinghs of 20/0, 25/5 and 30/10 cm H2O. Significant decreases (p < 0.05) in Cdyn were noted with each increase in end-expiratory pressure setting. The values for Cdyn in RDS patients obtained by this method closely approximated previously published data for lung compliance in babies with RDS. This simple and reproducible method may be useful in following the course of illness in infants with RDS.

Non-invasive lung function tests in rats with progressive papain-induced emphysema

Non-invasive plethysmographic methods for measurement of thoracic gas volume (TGV), airway resistance (Raw) and phase difference (PD) between flow rate at the nose and mean alveolar pressure were adapted for use in anesthetized rats. Thirty-six male Sprague-Dawley rats (200-250 g), were treated in groups of six by a single transoral, intratracheal instillation of 2 mg . kg-1 or 4 mg . kg-1 of papain in saline, or left untreated as controls. Measurements of TGV, Raw, and PD were made before treatment and at 4-day intervals after treatment for 8 or 16 days. TGV increased 65 percent by the fourth day and showed no change beyond the eighth day. Raw (0.4 +/- 0.04 cm H20 . ml-1 . sec) was not different from that of the controls. PD did not change significantly from the pretreatment value (4.7 +/0 0.41 degrees). The TGV, Raw, and PD responses were similar in the 2 mg . kg-1 and 4 mg . kg-1 papain treated rats. The TGV results suggest that the destructive effects of papain on the lungs are complete by the eighth day. The Raw results indicate that the airways are unaffected. The PD data are consistent with theoretical modeling studies for uneven distribution of compliances but neglible inequality of peripheral resistances.