Breathing Efficiency Research Articles

Respiratory mechanics during ventricular asystole in dogs with complete heart block.

Eleven mongrel dogs were studied in which complete heart block had been produced surgically. Ventricular rate was maintained by artificial stimulation until the time of study. Each experiment involved abrupt cessation of stimulation and the monitoring of pulmonary mechanical behavior during the ensuing period of ventricular asystole. These studies have shown that all aspects of the mechanical behavior of the lungs are altered during ventricular asystole in complete heart block. The changes which occur during this short interval of time are basically attributable to the systemic, stagnant hypoxia and the central vascular congestion. The pulmonary changes produced include augmentation of the rate and depth of breathing, reduction of the functional residual capacity, decreased pulmonary compliance, and increased pulmonary airway resistance. The result is that both the inspiratory and expiratory work of breathing are increased, while the efficiency of breathing is decreased. All of these alterations occur within the 20-second period of ventricular asystole and are restored to control levels soon after the re-establishment of a normal ventricular rate. The possible mechanisms involved are discussed.

Role of the diaphragm in breathing in conscious normal man: an electromyographic study.

The electrical activity of the diaphragm was detected by means of electrodes placed, via the esophagus, at the level of the diaphragmatic esophageal orifice. This activity was synchronous with the respiratory variations of transdiaphragmatic pressure. The activity of the diaphragm, which occurred during inspiration and continued into expiration for a varying length of time, affected the shape of the pressure-volume diagrams of breathing cycles and of the expiratory flow curves. The relative importance of the antagonistic activity of inspiratory muscles opposing the expiratory elastic forces decreased with increasing ventilation. The implications of the antagonistic activity of the diaphragm on the mechanical efficiency of breathing are discussed. Submitted on April 11, 1960

Mechanical efficiency of breathing.

Simultaneous measurements of mechanical work and energy cost of breathing were performed on four normal subjects with ventilation increased by adding dead space. Mechanical work was obtained from simultaneous records of endoesophageal pressure and tidal volume. The associated energy cost was estimated by measuring oxygen consumption of respiratory muscles by means of a closed-circuit spirometer. In all subjects studied and over the range of ventilations involved (ca. 30–110 l/min.), the mechanical efficiency of breathing was found to be in the order of 0.19–0.25. Submitted on July 6, 1959

Relation of Increased Airway Resistance to Breathing Work and Breath Velocity and Acceleration Patterns With Maximum and Near Maximum Breathing Effort

The oxygen cost of breathing, mechanical work done in breathing, efficiency of breathing and breath patterns have been studied at various resistance levels with maximum breathing effort. With the chest-lung complex considered as a machine for doing external work, it was observed that mechanical efficiencies increased with increasing airway resistance, to a point, after which they fell off. When the oxygen cost was corrected for work done on the chest-lung complex, efficiencies were observed to decrease with increasing airway resistance. Breath acceleration patterns were observed to provide a more sensitive appraisal of changes in the movement of the breath than either breath volume or velocity patterns. External work output increased with increasing external resistance only to a point, after which it decreased. At low resistance levels, work output was contraction speed limited and at high resistance levels it was contraction force limited. With maximum effort at all resistance levels oxygen consumption appeared to be constant. Data are also presented as peak alveolar pressure, breath velocity and change in functional residual capacity. Inspiratory breath phase percentage increased to more than half the cycle length with increasing airway resistance. Submitted on March 18, 1958

Diseases of the respiratory system; interpretations of tests of function.

The lungs are perfectly designed to fulfill their function of ensuring full oxygenation of the blood and they achieve this by possession of the follow­ ing properties: (a) The distensibility and elasticity of the lungs enables a large volume of gas to be moved in and out of the alveoli at a rapid rate and with minimal effort. (b) Gas drawn into the lungs is distributed almost evenly to all alveoli and the blood perfusing the lungs goes equally to all parts. (c) The alveolar membrane is so fine that gas diffusion through it is very rapid. (d) The very large alveolar surface (ca. 55 sq. m.) and the relatively small volume of blood contained within the alveolar capillaries (ca. 60 cc.) ensures the saturation with oxygen of blood passing through the lungs. (e) The pulmonary vascular bed can accommodate a considerable increase of blood flow withou t a corresponding increase in pulmonary arterial pressure. It might be thou ght that such detailed knowledge of the attributes of the normal lung would have led to the development of tests precise enough to measure quantitively all the various disturbances of function that occur in disease. This is not the case. One of the reasons for this state of affairs is the difficulty in assessing the normality of one function in the presence of impairment of others. Another is that the methods of investigation are often technically difficult to perform and until the introduction of rapid physical methods of gas analysis, the tests of most value were often extremely time consuming. Pulmonary function tests are concerned with the first three of the attri­ butes of normal lung function detailed above, and may be conveniently considered under the following headings:(a) the mechanical efficiency of breathing and the subdivisions of lung volume, (b) measurements of the uni­ formity of gas distribution within the lungs, (c) measurements of the effi­ ciency of haemo-respiratory exchange. In this review, an attempt is made to assess the clinical value of some of these tests, although in our opinion their main valu e is in research. In general,

Mechanics of breathing in man.

Mechanics of breathing in man.