We analyse a reduced version of the Grodins et al. control model [14] of respiration involving only CO2, andshow that it can be dramatically simplified by the use of judicious approximations. Inparticular, we show that the conceptual basis of the popular model of Mackey and Glass[20] is at odds with the important transportprocesses of the Grodins model. Despite this, a realistic approximation of the Grodinsmodel yields a Mackey-Glass type model with almost the same criterion for the onset ofCheyne-Stokes breathing.

While the reduced Grodins model does apparently provide a realistic mechanism forinstability, consideration of the buffering effect of the blood-brain barrier appears tomake it unlikely. We conclude that a realistic physiological model of Grodins type toexplain Cheyne–Stokes breathing is not yet in place, and raise the question whether thebicarbonate buffering system has a rôle to play.

Broiler ascites, first seen in the form of a high altitude disease, has increased in importance world-wide in direct proportion to the improvement in growth performance of modern broilers. At the same time, the incidence has spread gradually from high altitude (above 2000 m) down to sea level, which gave rise to proposals of alternative causes including infections, toxins and metabolic disorders. Our work centred on anatomical and physiological aspects and included hypoxia models, chemotherapy and selection for genetic resistance. The latter led to the development of ascites-resistant lines, which allowed resistant stock to become commercially available in South Africa.

The closure of the Poultry Section of the Onderstepoort Veterinary Institute brought ongoing ascites research to an abrupt end and some of the completed work was never published. This review of completed, ongoing and planned ascites work was at the time compiled as final report to the Director of the Institute in 1990. It came to light again recently and has been edited for publication. It also includes a new hypothesis on the reasons for the susceptibility of the domestic fowl and particularly broilers to hypoxic ascites.