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Giaja’s gas exchange apparatus

The study of bioenergetics in living beings was mainly based on the measurement of their gas exchange with an apparatus that Djaja designed himself while in confinement in Vienna during WWI.

The animal is contained in a glass respiratory chamber, and its oxygen consumption is measured based on the rate of air pressure decrease (B. barometer; M, manometer; H, chronometer connected to a kymograph). The exhaled carbon dioxide is eliminated by binding to potassium hydroxide. The consumed oxygen is replenished with a precisely measured volume pumped out from the oxygen reservoir by an equal volume of water (Giaja, 1953).

Giaja’s diagram of thermoregulation

The second period of Giaja’s work actually started with his return to Belgrade after WWI and lasted over 20 years. In this period, his research interest became more focused on bioenergetics and the relationship between metabolism, temperature and asphyxia, and definitely led him to intense studies on hypothermia and its practical use. The work from this period was compiled in Giaja’s seminal two-volume monograph “Homeothermia and thermoregulation” (Giaja, 1938a,b), in which he published his classical curve of thermoregulation (“Djaja’s diagram”).

Metabolic quotient

Giaja published a paper on the minimal energy consumption for life support with B. Maleš in 1921, showing that, as in poikilotherms, the energy consumption in homeotherms also depends on external temperature*. This paper is considered his first venture into studying hypothermia. In line with this study, in another paper in 1922 with B. Maleš, Giaja defines the oxygen consumption at normal and lethally high (40°C) external temperatures. He then introduced a parameter termed “peak metabolism” and defined its relationship to the classical basal metabolism and the dependence of both on various environmental factors. Thus, he defined peak metabolism as a counterpoint to basal metabolism – the limiting point of thermoregulation during fasting or in the cold. Giaja also introduced the “metabolic quotient”, or the ratio of peak to basal metabolism that defines caloric consumption. In 1925, he reported on the relationship between the loss of heat and basal metabolism as well as the role of some endocrine factors (insulin and adrenergics) in heat production.

Thermogenic potential and thermogenic fatigue

In 1930, Giaja published a paper entitled “Muscle fatigue and thermogenic potential”, in which he found that the maximal thermogenic potential decreases with intense muscle fatigue. This was his first foray into the research of adaptation, which he considered to be essential; in fact, he wrote that physiology could be defined as the science of functional adaptation of living beings. In the same paper, he showed that laboratory rats living at a variable room temperature could survive in temperatures close to 0°C without weight loss or hypothermia, while animals kept at the temperature of their thermal neutrality (32°C) die or experience hypothermia at the same low external temperature. Thus, Giaja concluded that the prolonged maintenance of animals at thermal neutrality significantly decreased their thermogenic potential by lowering the peak metabolism by 30%. In other work, he demonstrated that the growth of animals kept at thermal neutrality is slowed in comparison to that of animals exposed to lower temperatures. In the series of papers that followed, Giaja conducted a comparative study on different homeothermic organisms and demonstrated that the limit of resistance to cold depends on the previous thermal adaptation of the subject. Giaja termed this decrease in resistance to cold during combating low temperatures “thermogenic fatigue”.

Biochemistry & marine biology

Giaja’s first papers were in the field of physiological chemistry with an emphasis on enzymology and comparative physiology. He focused on mammals and birds, as well as lower animals, particularly marine organisms. His interest in marine animals stemmed from a study visit to the marine laboratory of professor Yves Delage at the Marine Station in Roscoff. He wrote in 1914 of his interest in the chemical phenomena of life and energy of living beings. With this work, Giaja built a foundation of experimental physiology and physiological chemistry (now biochemistry). In his view, the physiology of man and animal were not separate. Thus, he also introduced the principle of physiological studies of phenomena that are common to all living beings, as well as the studies of particular mechanisms that are unique to certain organisms. These studies actually led to the foundation of General Physiology that is taught even today in Giaja’s Institute at the University of Belgrade School of Biology. Some of the major problems that interested him in this period were pancreatic coenzymes, fermentation and digestion processes and the chemistry of carbohydrate metabolism. He also suggested a new rationale for a nomenclature of enzymes.

Respiratory hypothermia

What is respiratory hypothermia?

Respiratory hypothermia — by slowly lowering the body temperature by asphyxia in a tightly sealed vessel (hypercapnic hypoxia) at a low ambient temperature, a physiological state resembling lethargy can be induced 1.

Previous attempts to rewarm deeply cooled rats were regularly unsuccessful, and it was concluded by the German physiologists that below 15°C, non-hibernating animals could not be successfully reanimated. Giaja’s Ph.D. student, Radoslav Andjus (1926-2003), was the first to reanimate a rat that was in deep hypothermia, with a colonic temperature of 0 to 2°C (Andjus, 1953). The closed vessel method of cooling animals, in which hypoxia and hypercapnia are combined, initiated an anecdote about this method introduced by Giaja 2.