Showing papers by "James P. Butler published in 1986"

Wave‐Speed and Viscous Flow Limitation

Abstract: The sections in this article are: 1 Wave-Speed Flow-Limiting Mechanism 2 Viscous Flow Limitation 3 Relation Between Wave-Speed and Viscous Flow-Limiting Mechanisms 4 Comments on Modeling

Bio- and Immunoactive Luteinizing Hormone Responses to Low Doses of Gonadotropin-Releasing Hormone (GnRH): Dose-Response Curves in GnRH-Deficient Men*

Abstract: Previous investigations of the effects of GnRH on pituitary LH responses in normal men required pharmacological doses of GnRH to avoid the confounding effects of endogenous GnRH secretion and employed nonphysiological dose intervals. To examine the role of GnRH in determining both the qualitative and quantitative nature of physiological LH responses, we studied five GnRH-deficient men in whom pituitary and gonadal function had been normalized with GnRH replacement. Both bio- and immunoactive LH responses were evaluated in these men after a wide range of GnRH doses (7.5–250 ng/kg) administered at a physiological frequency (every 2 h), while gonadal steroid levels were within the normal adult male range. In addition, the amplitude and contour of the immunoactive LH pulses were compared to those of 15 normal men to assure that these experiments achieved physiological pituitary responses. The relationship between bio- and immunoactive LH was compared between patients, between doses as the amount of GnRH was i...

Interpulse interval sequence of LH in normal men essentially constitutes a renewal process.

Abstract: Luteinizing hormone (LH) is released from the anterior pituitary gland in an episodic pattern driven by pulses of gonadotropin-releasing hormone (GnRH) from the hypothalamus. Autocorrelation analysis of the sequence of interpulse intervals of LH secretion in normal men supports the hypothesis that the underlying mechanism driving LH secretion is a renewal process. That is, whatever "memory" the GnRH pulse generator (i.e., the hypothalamus or its antecedent neural drive) may have, it does not go back in time further than the preceding secretory pulse. Thus the hypothalamic timer starts over again each time there is a GnRH secretory episode.

Poissons' ratio of lung parenchyma and parenchymal interaction with bronchi.

Abstract: A simple theory of lung elasticity and its interaction with bronchi was developed which led to the specific results. The experimental procedure for establishing these results used lobar bronchi from excised dog lungs, following Takishima, et al. ((1975) J. Appl. Physiol., 38: 875-881). First, we found a semi-direct technique for measuring Poisson's ratio (sigma) of lung parenchyma and the effect of lung parenchyma on bronchi (interdependence). Sigma was measured at 0.424 +/- 0.045; no correlation was observed between sigma and the elastic recoil pressure of the lung (PL). The interdependence increased with a corresponding increase in PL and reduced bronchial volume. Second, we predict that a relationship exists between the specific compliances of intact and excised bronchi, and the specific compliance of the surrounding parenchyma. We suggest that the parenchyma is more important than the bronchus itself in determining the specific compliance of the intact bronchi.

Principles of Measurement: Applications to Pressure, Volume, and Flow

Abstract: The sections in this article are: 1 Preliminary Considerations 2 Loading 3 Instrument Response 4 Signal Processing 5 Interpretation of Measurements 5.1 Indirect Measurements (Inference) 5.2 Models 6 Noise 6.1 Intrinsic Noise 6.2 Extrinsic Noise 7 Calibration 7.1 Static Calibrations 7.2 Dynamic Calibrations 7.3 Additional Procedures for Specific Variables 8 Probes 9 Linear Versus Nonlinear Systems 10 Conclusion

Radial and longitudinal compartmental analysis of gas transport during high-frequency ventilation.

Abstract: A model of gas exchange by low-tidal-volume (VT), high-frequency ventilation (HFV) is presented, based on the physical principles of dispersion. These are the nonuniformity of the velocity profile and the nonreversible mixing of fluid components in a diffusive manner. A numerical method was used to incorporate these principles into a quantitative model. The airways of a symmetrically bifurcating bronchial-tree model were partitioned in the radial direction into two concentric layers representing the kinematic dispersion by nonuniformity of the velocity profile. Mixing between the layers was invoked in proportion to the diffusivity and local dimensions. The effects of frequency (f), VT, shape of the velocity profile, and bronchial-model configuration were tested in the model, with favorable comparison to available experimental data. The model predicts that for a frequency-dependent velocity profile, the rate of tracer exchange is proportional to the square root of f and to the square of VT-V0, where V0 is a constant small volume under which gas exchange was nil. Intracycle asymmetric mixing is predicted to have a stronger effect on gas exchange than asymmetric velocity profile. Gas exchange when turbulent-flow regime is assumed is predicted to be less for the higher VT values than with laminar flow and with mixing by molecular diffusivity. This model was found to be didactic, flexible, and capable of modeling combinations of factors affecting either one of the two fundamental processes of dispersion.