John Brackenbury

Airflow dynamics in the avian lung as determined by direct and indirect methods

Abstract Intrapulmonic airflow was investigated directly using a flowmeter in the posterior dorsal secondary bronchi, and indirectly by measuring CO2 content of airstreams passed into the trachea and out of the various air sacs. Secondary bronchial flow was found to be unidirectional in voluntary breathing but bidirectional when air was passed experimentally into and out of the trachea and air sacs. CO2 analysis indicates that air, in the conditions of the experiment and probably also in eupnea, enters the anterior sacs, partially at least, by the tertiary bronchi and enters the posterior sacs via the direct non-exchanging connections. The role of the anterior air sacs in determining inspiratory airflow through the lung is discussed and an attempt is made at integrating the ideas of aerodynamics and lung-air-sac topology in the context of airflow in the avian lung.

Fast locomotion in caterpillars

The maximum forward crawling speeds of caterpillars are limited by the hydraulic design of the body and the peristaltic mode of operation of the segmental muscles. High speed locomotory manoeuvers can be achieved by reversing the direction of the normal peristaltic wave (from posterior-anterior to anterior-posterior) although the penalty is a dramatically reduced duty factor of the legs and potential instability. This study describes the suite of reverse gaits available to caterpillars, from reverse walking (the kinematic inverse of normal forward walking), through to reverse galloping (in which all the legs save the claspers are wrenched free of the ground with each step) to recoil-and-roll, a unique form of locomotion in which the insect free-wheels backwards at high-speed. These reverse forms of locomotion are produced primarily in response to threat, involve bilateral activation of the intersegmental muscles and are relatively simple in terms of neural control. The ecological roles of high-speed locomotion are considered in the light of potential predators and the normal habitat and terrain.

Energy consumption and ventilatory mechanisms in the exercising fowl.

Abstract 1. 1. Gas exchange and respiratory movements were monitored in domestic cocks running on a treadmill for continuous periods of 10–12 min. 2. 2. At normal temperatures a linear relationship was observed between . V O 2 and running speed. The maximum . V O 2 was 112.5ml O 2 kg −1 min −1 at a speed of 9km hr −1 . 3. 3. The incremental cost of locomotion at normal temperatures was 0.66 ml O 2 kg −1 m −1 . 4. 4. At temperatures of 27–33°C the energy requirement for running increased at speeds above 2–3 km hr −1 and this increase accounted for 12% of the total metabolic energy at speeds of 6.5–8 km hr −1 . 5. 5. The pattern of ventilation in the vigorously exercising, hyperthermic bird consisted of almost unbroken sequences of deep panting which sometimes synchronised with the striding movements of the legs. 6. 6. It is suggested that the energy required for this form of panting may account for a significant fraction of the increased energy requirement for running at high temperatures.

Physiological Responses Of Birds To Flight And Running

1. The energy required for sustained physical activity in flying and running birds is obtained from fatty acids mobilized from adipose stores under the influence of hormones. There is some evidence that glucagon, insulin and growth hormone may be involved in this process.

Physical determinants of air flow pattern within the avian lung

Abstract The pressure/flow relationship was determined across the air sac/lung system, and between different points within the system, in birds ventilated normally and artificially. Resistances were also calculated for pathways to individual sacs. In all cases resistance rose with increasing flow rates. Pathways supplying anterior sacs had lower resistances than those to the posterior sacs. During both voluntary and artificial bidirectional ventilation flow across the lung was caudo-craniad in each phase. Airstreams were introduced into various air sacs and resultant intrapulmonic flows monitored. Observations supported the idea that the anterior sacs during inspiration and the posterior sacs during expiration are primarily responsible for flow through the lung. Patterns measured in different circumstances, combined with a physical analysis of the pressure/flow relationship, enabled the formulation of a scheme for the anatomical and aerodynamical determinants of normal intrapulmonic flows.

RESPIRATION AND PRODUCTION OF SOUNDS BY BIRDS

CONTENTS

Changes in plasma glucose and lipid concentrations during treadmill exercise in domestic fowl

Abstract 1. 1. Plasma glucose, non-esterified fatty acid, triglyceride, cholesterol and lactate concentrations were measured during 90 min treadmill exercise at a work intensity of 55–60% maximum. 2. 2. After 90 min exercise plasma glucose fell by 35% whilst the non-esterified fatty acid concentration rose to as much as 3–4 times resting. 3. 3. Exercise had no significant effect on plasma cholesterol, triglyceride or lactate concentrations. 4. 4. The findings indicate a progressive increase in fat utilization during prolonged exercise. Possible hormonal mechanisms underlying exercise-induced changes in lipid and carbohydrate metabolism are discussed.

Corrections to the Hazelhoff model of airflow in the avian lung.

The ventilatory activity of the anterior and posterior groups of air sacs was simulated in unidirectionally-ventilated geese and the resultant flow of air in the mediodorsal secondary bronchi was used as an indicator of the route which air followed through the lung. The results were used to isolate the roles of the respective groups of air sacs in the shaping of the unidirectional pattern of airflow known to exist during normal respiration. Findings indicated that, in contrast to Hazelhoffs model, the anterior and not the posterior sacs are responsible for producing the caudo-cranial flow of air through the parabronchi during inspiration. The posterior sacs, as predicted by Hazelhoffs model, and primarily responsible for driving the caudo-cranial current through the parabronchi during expiration.

Respiratory mechanics in the bird.

Abstract 1. 1. Air sac and coelomic pressures were measured in chickens and geese. 2. 2. The coelomic pressure wave is composed of the air sac wave together with a wave originating from the stretching or bulging of internal septa during respiration. 3. 3. A model is presented which features the overall mechanical characteristics of the respiratory system, and which generates pressures that are related to each other in the manner of those in the normal bird.

Plasma glucagon and energy substrate responses of domestic fowl to treadmill exercise

Exercise-induced alterations in the concentrations of plasma glucagon-like immunoreactivity (GLI), plasma free fatty acids (FFA) and blood glucose and lactate were measured in separate groups of male and female domestic fowl. There were only small changes in blood glucose and lactate concentrations but plasma FFA and GLI rose by up to 450 and 200% respectively. There was evidence that the GLI response was stronger at higher exercise intensities. It is suggested that the mobilization of FFA for use as energy substrates by the working muscles may be stimulated by the enhanced secretion of glucagon.