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Biomedical subjects

M J Jaeger

Publications and source records attributed to M J Jaeger.

At least 19 recordsLinked to original sources
PubMed2001

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.

Administration, Inhalation↗
PubMed1994

Evaluation of the interrupter technique for the use of assessing airway obstruction in children.

The purpose of this study was to determine if the interrupter technique, a noninvasive method for measuring airflow resistance, could be used to assess airway obstruction in children. In 107 children (74 with asthma, 12 with cystic fibrosis, and 21 without lung disease) conductance (mostly of airways) measured with the interrupter technique (Gint) was correlated with both forced expiratory volume in 1 second (FEV1) and the forced expired flow rate between 25% and 75% of vital capacity (FEF25-75). In addition, 17 children with significant airway obstruction due to asthma also had airway resistance measured by body plethysmography (R(aw)) before and after treatment. Resistance and conductance measurements made with the interrupter technique were subdivided into inspiratory (Rint-insp, Gint-insp) and expiratory (Rint-exp, Gint-exp) values. In the 107 children, a high degree of linear correlation was found between Gint and FEV1; for Gint-exp, r = 0.77 (P < 0.001), and for Gint-insp, r = 0.76 (P < 0.001). There was also good linear correlation between Gint and FEF25-75; for Gint-exp, r = 0.70 (P < 0.001), and for Gint-insp, r = 0.67 (P < 0.001). In the 17 asthmatic children who were tested before and after treatment of their airway obstruction, Rint correlated highly with R(aw); for Rint-exp, r = 0.91 (P < 0.001), and for Rint-insp, r = 0.83 (P < 0.001). The pre- to post-treatment changes in Rint and R(aw) were similar.(ABSTRACT TRUNCATED AT 250 WORDS)

Airway Obstruction↗
PubMed1994

Components of the work of breathing and implications for monitoring ventilator-dependent patients.

OBJECTIVES: a) To discuss the components of the work of breathing using an established physiologic model (Campbell diagram); b) to describe the requirements of a monitor to measure work; and c) to discuss the implications and relevance for assessing the work of breathing of ventilator-dependent patients. DATA SOURCES: Relevant articles from the medical and physiologic literature are referenced, as well as the authors' experience. STUDY SELECTION: Identified (by authors) laboratory and clinical research establishing the need and physiologic importance for correctly measuring the work of breathing. DATA EXTRACTION: A physiologic model of the various components of the work of breathing is used in conjunction with data from published literature. SYNTHESIS: Diagrams of increasing complexity based on the Campbell diagram depict the physiologic elastic and resistive work of breathing for the lungs and chest wall under normal and abnormal conditions. Decreases in compliance and increases in airways resistance are associated with increases in elastic and resistive work, respectively. A modification of the Campbell diagram to include an additional area depicting the imposed work of the breathing apparatus is suggested; i.e., the additional resistive load imposed on the respiratory muscles by the endotracheal tube, breathing circuit, and the ventilator's demand-flow system during spontaneous breathing. Increases in physiologic and/or imposed work result in respiratory muscle loading, predisposing to increases in oxygen consumption and the development of fatigue and hypercapnia. Measuring work of breathing by integrating the area of the esophageal pressure-volume loop alone underestimates the work of breathing relative to the Campbell diagram and, therefore, should not be used. Because the site of pressure measurement and mode of ventilation influence measurements of the work of breathing as well as compliance, clinicians should be aware of these factors when interpreting measurements. Monitors that are used in clinical practice to assess the work of breathing should be able to measure pressure at the airway opening (between the Y-piece of the breathing circuit and the endotracheal tube), at the carinal end of the endotracheal tube, and in the esophagus (inference of intrapleural pressure); as well as measure flow rate and volume at the airway opening; and calculate the various components of the work of breathing based on the Campbell diagram. CONCLUSIONS: Accurate measurement of physiologic and imposed work performed by the patient are essential to assess the afterload on the respiratory muscles, diagnose specific work of breathing abnormalities, and monitor the effects of interventions to mitigate respiratory muscle loading. Work of breathing data are useful in formulating objective guidelines for setting the ventilator appropriately to optimize respiratory muscle loads, e.g., selecting an appropriate amount of pressure support ventilation to decrease the work of breathing to a specific level.

Airway Resistance↗
PubMed1994

CO2 binding by Baralyme in three different carrier gases.

The absorptive properties of Baralyme and Sodasorb for CO2 in a container were studied by measuring the lifetime T0.5 of the unit, i.e., the time until the exit concentration of CO2 reaches 0.5%. The container size, the inlet gas flow rate, and the inlet CO2 concentration were varied. The experiments were repeated with either He, N2, or SF6 as the inert gas to evaluate the effect of increased gas density due to hyperbaric conditions on scrubber performance. It was found that T0.5 is best described by an exponential function of the type b (ttr)a, where ttr is the transit time of the gas through the container. The exponent a equals about 1.5 and varies relatively little. The constant b, however, is strongly dependent on inert gas density and on CO2 concentration in the inlet gas; it is independent of container size and gas flow rate. In addition, the amount of absorber reaching up to time T0.5 was measured in all conditions. It is strongly dependent on CO2 concentration; however, surprisingly it is nearly independent of inert gas properties. These results are compared with a mathematical model of scrubber behavior that is based on the chemical reaction rate of an imaginary absorber. The model neglects possible effects of CO2 diffusion in the gas phase, of ash formation, and of heat produced by the reaction. Differences between our experimental data and the model are analyzed as a function of these effects. The results give some simple predictive equations for the lifetime and the amount of absorber reacting.

Barium Compounds↗
PubMed1994

Application of a valveless anesthesia circuit for deep diving.

The Mapleson E breathing circuit used in anesthesia has no valves or CO2-absorbent canisters and thus entails low resistance to breathing and has low requirements for fresh gas flow (FGF). The authors investigated whether these advantages would make a circuit, modified for hyperbaric use, able to support ventilation during heavy work on the surface and at deep depths with reduced FGF rates. The current recommended FGF for free-flowing diving circuits is 170 liters/min. Six Navy divers participated in 10-min graded exercise sequences, peak workload 220 W. Measurements were made of inspired and end-tidal concentrations of CO2, tidal volume, respiratory rate, and CO2 production at both sea level and 2.7 MPa dry environment. At sea level, all six divers were able to finish their exercises using the modified circuit with all tested rates of FGF. At 2.7 MPa the exercise sequence could be finished by all subjects when FGF was 170 liter/min and by five subjects when FGF was 127.5 liter/min, but high end-tidal CO2 measurements and hypercapnia symptoms were common at 127.5 liter/min. None of the subjects was able or allowed to finish the exercise sequence when FGF was 85 liter/min. Lower work-loads of 75 and 150 W for up to 4 min were completed easily by all subjects at all three rates of FGF. We conclude that this circuit concept warrants further study because it requires lower FGF than is currently used with open-circuit helmets and is valveless; how much of a reduction in FGF could be tolerated with heavy work at depths such as 2.7 MPa requires further study.

Adult↗
PubMed1991

High-frequency ventilation in dogs with three gases of different densities.

Dogs were ventilated with a high-frequency oscillation device varying the frequency (5-15 Hz), the tidal volume (25-100 ml), and the resident gas (He, N2, SF6). Tidal volume was measured with a body plethysmograph. Blood gases were measured after a quasi-steady state was established. The kinematic viscosity of the breathing gas mixture, which changed by 1,700%, was found to have little effect on arterial PO2 and PCO2. The results are consistent with findings in a branched model that consisted of tubes with a diameter of 1 cm and with the theory of Taylor-type diffusion in turbulent flow. In addition, experiments were performed reducing and increasing the equipment dead space. This resulted in changes of PO2 and PCO2 that were appreciably less than those resulting from variations of tidal volume of the same magnitude.

Animals↗
PubMed1987

Effect of posture on ventilation and breathing pattern during room air breathing at rest.

We measured minute ventilation (VE), tidal volume (VT), mean inspiratory flow (VT/TI), and occlusion pressure (P.1) in 10 resting subjects breathing room air, in sitting, supine, right and left lateral positions, and compared them with corresponding data on static lung compliance [Cst(l)], dynamic lung compliance [Cdyn(l)], and pulmonary flow resistance [R(l)]. Highest values for VT, VE, VT/TI, P.1, and effective inspiratory impedance [P.1/(VT/Ti)] were observed in the supine posture. Values for P.1 and P.1/(VT/TI in lateral decubitus were intermediate to those obtained when seated and supine. While the increases in P.1 and P.1/(VT/TI) in recumbent postures were qualitatively similar to the decrease in Cdyn(l) and increase in R(l), there was no significant correlation between them, probably reflecting the complex relationship between P.1/(VT/TI) and lung compliance and resistance, as the former, in addition to lung mechanics, also depends on the shape of the inspiratory driving pressure wave, the active inspiratory impedance, the mechanics of the chest wall, and the duration of inspiration.

Adult↗
PubMed1987

The effect of the Bain circuit on gas exchange.

This is an experimental and theoretical analysis of the Mapleson D (Bain) circuit. A bench model was used to determine the effects of breathing rate, tidal volume, and fresh gas flow on the simulated alveolar gas composition when a commercial Bain breathing circuit is used. In addition, an effort was made to derive mathematical equations that describe the CO2-profile in the expiratory limb of the Bain circuit, the amount of CO2 rebreathed, and the effect of this rebreathing on the alveolar gas composition. Data obtained with the bench model and with the equations were compared to data from the literature. The effect of the Bain circuit on gas exchange was compared to that of an equivalent dead space.

Anesthesiology↗
PubMed1987

Effects of extracapsular cataract extraction on the lens zonules.

The zonules of 27 postmortem eyes were studied grossly using a histologic staining technique that allowed easy visualization of the zonules. Large disinsertions of the zonules were present in 5 of the 20 eyes that had undergone extracapsular cataract extraction (ECCE).

Cataract Extraction↗
PubMed1987

Epikeratoplasty for keratoconus. A clinicopathologic case report.

A 20-year-old man with bilateral keratoconus underwent an epikeratoplasty in the left eye. The postoperative course was uneventful. Five years postepikeratoplasty he developed progressive myopia in the operated eye. A contact lens would not remain centered and the spectacle correction in a trial frame was not tolerated. A successful penetrating keratoplasty was performed six years after the epikeratoplasty procedure. Light and electron microscopic studies of the corneal button showed hypocellularity and irregular distribution of the keratocytes in the lenticule and the accumulation of a periodic acid-Schiff-positive, electron-dense fibrillogranular material at the interface between the lenticule and the recipient Bowman's layer.

Adult↗
PubMed1987

Reversible and irreversible components of central-airway flow resistance.

The flow energy loss (head loss) through a cast of canine central airways is found to be nearly independent of flow direction. By contrast, head loss in geometrically-simpler branching sections at comparable flow conditions is highly irreversible, with inspiratory loss being greater by nearly two units of dynamic pressure (2 X 1/2 rho V2). In these branching sections head loss appears to be independent of important geometric parameters such as the branch length/diameter ratio and the exit/inlet flow-area ratio. An analysis of these observations suggests that kinetic energy factors, not shear stresses, account for most of the energy dissipated in central airways and in simple bifurcating sections. Inspiratory loss in bifurcations is greatly increased by the onset of flow separation: irreversibility is minimal in central airways, where separation either is absent or else is much less pronounced.

Airway Resistance↗
PubMed1986

Continuous positive airway pressure and expiratory positive airway pressure increase functional residual capacity equivalently.

The effect of continuous positive airway pressure (CPAP) and expiratory positive airway pressure (EPAP) on functional residual capacity (FRC) of ten healthy, spontaneously breathing, lightly anesthetized intubated mongrel dogs was studied. The CPAP and EPAP at 5, 10, 15, and 20 cm H2O were alternately applied to all animals. Total (lung and chest wall) compliance, esophageal pressure, airway pressure, transpulmonary pressure, control FRC, and the change in FRC (delta FRC) were measured before and after each application of CPAP and EPAP. Neither expiratory transpulmonary pressure nor delta FRC with CPAP differed significantly from that with EPAP at all levels (p greater than 0.05). These data suggest that CPAP and EPAP, when applied at the same expiratory pressure, result in an equivalent increase in FRC due to passive mechanical distention of the lungs.

Animals↗
PubMed1984

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.

Animals↗
PubMed1983

Lobar flow patterns in a hollow cast of canine central airways.

To demonstrate that the regional partitioning of flow in central airways is direction dependent, we compared inspiratory and expiratory lobar flows in a hollow rigid cast of canine lungs. Lobar flows were measured by a hot-wire anemometer, simultaneous tracheal flows by a pneumotachograph, and data displayed as (lobar) flow-(tracheal) flow curves. For tracheal airflows between 50 and 370 ml/s, we found that inspiratory apical flows were smaller, and basal flows larger, than corresponding expiratory distributions. This effect was largely extinguished by substituting a gas mixture of 85% He-15% N2; resulting regional flows were comparable to expiratory distributions obtained on room air. Thus canine central airways structure induces a kinematically irreversible flow pattern, consistent with a model of "cascade flow" in which branching structure modifies the distribution only of inspiratory flow. These results support Fowler's concept that lung regions fill and empty sequentially and may be pertinent to analyses of regional washout.

Animals↗
PubMed1983

Lung mechanics in sitting and horizontal body positions.

We measured lung compliance, pulmonary flow-resistance, and expiratory reserve volume (ERV) in ten healthy young adults in sitting, supine, and lateral positions. Average lung compliance was 0.21 in sitting, 0.19 in lateral and 0.16 L.cm H2O-1 in supine positions. The change was significant (p less than 0.01) between sitting and supine position. Flow-resistance increased from 1.78 in sitting to 2.5 cm H2O.L-1.s (p less than 0.001) in lateral positions, and did not increase further in the supine posture in spite of a 35 percent decrease in ERV (p less than 0.001). Since it is known that lower airways resistance increases with decreasing lung volume, the lack of change in flow-resistance when shifting from lateral to supine posture suggests that upper airways flow-resistance (larynx and oropharynx) is greater in the lateral decubitus than in the supine positions. The decrease of lung compliance in horizontal postures probably reflects increased pulmonary blood volume and small airways closure.

Adult↗
PubMed1982

Effect of the cheeks and the compliance of alveolar gas on the measurement of respiratory variables.

The distensibility of the upper airways was found to range in 8 subjects between 0.01 and 0.001 L/cm H2O. This distensibility may cause a number of errors in standard respiratory measurements in normal subjects and in patients with airway obstruction due to delays in pressure and flow equilibration between alveoli and mouth. The error include overestimation of thoracic gas volume with the body plethysmograph; of airway inertance and of dynamic lung compliance; underestimation of respiratory resistance with the forced oscillation technique and with interruption pressure; underestimation of total pressure exerted by respiratory muscles with the P o.1 technique during occlusions of the airway opening. The errors are often quite appreciable and may exceed 100%. Ways to reduce them or to compensate for them are discussed.

Airway Resistance↗