A MATHEMATICAL MODEL OF THE HUMAN RESPIRATORY CONTROL SYSTEM

The respiratory system exhibits the properties of a control system of the regulator type. Equations describing this biological control system have been derived. Transient and steady-state solutions for various CO(2) and O(2) step input disturbances were obtained utilizing a digital computer and are compared with experimental results. The effectiveness of the respiratory system as a regulator is investigated. Further extensions of the model are suggested.

AUTOMATIC CLASSIFICATION OF STAPHYLOCOCCI BY PRINCIPAL-COMPONENT ANALYSIS AND A GRADIENT METHOD

Hill, L. R. (Università Statale, Milano, Italy), L. G. Silvestri, P. Ihm, G. Farchi, and P. Lanciani. Automatic classification of staphylococci by principal-component analysis and a gradient method. J. Bacteriol. 89:1393-1401. 1965.-Forty-nine strains from the species Staphylococcus aureus, S. saprophyticus, S. lactis, S. afermentans, and S. roseus were submitted to different taxometric analyses; clustering was performed by single linkage, by the unweighted pair group method, and by principal-component analysis followed by a gradient method. Results were substantially the same with all methods. All S. aureus clustered together, sharply separated from S. roseus and S. afermentans; S. lactis and S. saprophyticus fell between, with the latter nearer to S. aureus. The main purpose of this study was to introduce a new taxometric technique, based on principal-component analysis followed by a gradient method, and to compare it with some other methods in current use. Advantages of the new method are complete automation and therefore greater objectivity, execution of the clustering in a space of reduced dimensions in which different characters have different weights, easy recognition of taxonomically important characters, and opportunity for representing clusters in three-dimensional models; the principal disadvantage is the need for large computer facilities.

THE DEPOSITION OF AEROSOLS IN THE RESPIRATORY TRACT. I. MATHEMATICAL ANALYSIS AND COMPARISON WITH EXPERIMENTAL DATA

The deposition of aerosol in the human respiratory tract was calculated as a function of the particle size and particle density of the aerosol, the manner of breathing, and various parameters which control the degree of mixing of inspired air with the dead space air and with the lung air. The computations were performed on an electronic computer, which allowed a full analysis of the effects of the various parameters. Agreement between the computed total deposition curves, and published experimental data was very satisfactory. The computed curves exhibited the minimum in total deposition previously established experimentally, in the region of 0.3 μ. The maximum in the alveolar deposition curve was about 1 μ for particles of unit density, confirming the results of Brown, Cook, Ney, and Hatch for nose breathing. Its position was a function of the density of the aerosol particles, but was relatively insensitive to the tidal volume and other breathing parameters. The opposite held in regard to the value of the maximum, which was totally uninfluenced by the particle density, but was affected by the breathing parameters.

PYRUVATE METABOLISM AND CONTROL: FACTORS AFFECTING PYRUVIC CARBOXYLASE ACTIVITY

Pyruvic carboxylase activated by acetyl coenzyme A is highly active in the mitochondria of rodent liver, and its activity is increased in fasting and alloxan diabetes. In conjunction with acyl carboxylase activated by di- and tricarboxylic acid, it forms a reciprocating control network. Analog models of similar networks tend to correct for perturbations, stabilizing the overall system.

ELECTROCONVULSIVE THERAPY AND DEPRESSION. 3. A METHOD FOR PROGNOSIS

After 25 years there is still considerable disagreement surrounding the indications for electro-convulsive therapy (E.C.T.). This is a particular problem in the treatment of depression, both because of the controversy over the division of depression into endogenous and reactive illnesses and because of the increasing use of the antidepressant drugs. These drugs will induce a remission in many patients, and will alter the clinical picture in others. As their use becomes still more widespread (Freyhan (1) has recommended that intensive imipramine treatment should be tried routinely before E.C.T. in all depressed patients) there may be further difficulties in the selection of depressed patients likely to respond well to E.C.T. Furthermore several recent reviews draw attention to a reduction in the use of E.C.T., and the lack of a consistent rationale for its use (2–4).