Oxygen consumption

Oxygen consumption to support resting metabolic needs is (Dawson, 1991) 

This relationship was obtained by assuming 4.8kcal (20,000 N -m) of heat to be equivalent to IL of oxygen. Adolph (1949) gives the scaling relation for basal oxygen consumption of mammals as 

V02 is the oxygen consumption of unit mass of tissue, mVs hr is the heart rate, beats/s m is the body mass, kg 

The liver is one of the most metabolicaUy active organs of the body (Table A.9), and, consequently, one of the greatest consumers of oxygen. Adolph (1949) gave the oxygen consumption of the liver of mammals to be 

FIGURE 7.4.9 Maximum oxygen consumption of exercising mammals. (From Taylor, C.R. et al., Respir. Physiol., 44, 25, 1981. With permission.) 

---

Natural occurring oxygen 18 is stable and available commercially, as is water (H20 with 15% 180). Commercial oxygen consumption in the U.S. is estimated at 20 million short tons per year and the demand is expected to increase substantially. 

In situations where conserved internal markers caimot be used, such as in spills of essentially pure compounds, the evidence for enhanced biodegradation may have to be more indirect. Oxygen consumption, increases in microbial activity or population, and carbon dioxide evolution have all been used with success. 

Thermal Oxidative Stability. ABS undergoes autoxidation and the kinetic features of the oxygen consumption reaction are consistent with an autocatalytic free-radical chain mechanism. Comparisons of the rate of oxidation of ABS with that of polybutadiene and styrene—acrylonitrile copolymer indicate that the polybutadiene component is significantly more sensitive to oxidation than the thermoplastic component (31—33). Oxidation of polybutadiene under these conditions results in embrittlement of the mbber because of cross-linking such embrittlement of the elastomer in ABS results in the loss of impact resistance. Studies have also indicated that oxidation causes detachment of the grafted styrene—acrylonitrile copolymer from the elastomer which contributes to impact deterioration (34). 

Insects poisoned with rotenone exhibit a steady decline ia oxygen consumption and the iasecticide has been shown to have a specific action ia interfering with the electron transport iavolved ia the oxidation of reduced nicotinamide adenine dinucleotide (NADH) to nicotinamide adenine dinucleotide (NAD) by cytochrome b. Poisoning, therefore, inhibits the mitochondrial oxidation of Krebs-cycle iatermediates which is catalysed by NAD. 

Metabolic Functions. The functions of the thyroid hormones and thus of iodine are control of energy transductions (121). These hormones increase oxygen consumption and basal metaboHc rate by accelerating reactions in nearly all cells of the body. A part of this effect is attributed to increase in activity of many enzymes. Additionally, protein synthesis is affected by the thyroid hormones (121,122). 

The mouse anoxia or oxygen-consumption test is based on the stimulation of the basal metaboHc rate by thyromimetic compounds. Mice or other small animals are placed in airtight containers of known volume and their survival time is determined (34). 

A large number of thyroid hormone analogues have been tested for this effect (6). Among others, i-T (3) and 3,3 -T2 (5) and their propionic acid side-chain analogues decrease oxygen consumption at molar ratios of 50—200 1 of T. Nevertheless, no potent or clinically usehil peripheral antagonists have been found. 

In all cases, water and carbonic acid, the latter of which is the source of protons, are the main reactants. The net result of the reaction is the release of cations (Ca " ), Mg ", K", Na" ) and the production of alkalinity via HCO. When ferrous iron is present in the lattice, as in biotite, oxygen consumption may become an important factor affecting the weathering mechanism and the rate of dissolution. 

As discussed above, deposits can cause accelerated localized corrosion by creating differential aeration cells. This same phenomenon occurs with a biofilm. The nonuniform nature of biofilm formation creates an inherent differential, which is enhanced by the oxygen consumption of organisms in the biofilm. 

Amiodarone dilates arteriolar vascular smooth muscle, especiady coronary arteries, and thus exhibits antianginal effects. Its effects on the peripheral vasculature to decrease resistance leads to a decrease in left ventricular stroke work and a decrease in myocardial oxygen consumption. The dmg rarely produces hypotension that requires discontinuation of the dmg (1,2). 

Verapamil. Verapamil hydrochloride is a pbenyl alkyl amine and is considered the prototype of the Class I calcium channel blockers. Verapamil is also a potent inhibitor of coronary artery spasm and is useful in Prinzmetal s angina and in unstable angina at rest. Verapamil produces negative chronotropic and inotropic effects. These two actions reduce myocardial oxygen consumption and probably account for the effectiveness of verapamil in chronic stable effort angina (98,99). Moreover, verapamil is an effective antihypertensive agent. 

Temperature, pH, and feed rate are often measured and controlled. Dissolved oxygen (DO) can be controlled using aeration, agitation, pressure, and/or feed rate. Oxygen consumption and carbon dioxide formation can be measured in the outgoing air to provide insight into the metaboHc status of the microorganism. No rehable on-line measurement exists for biomass, substrate, or products. Most optimization is based on empirical methods simulation of quantitative models may provide more efficient optimization of fermentation. 

Another technique for organics measurement that overcomes the long period required for the BOD test is the use of continuous respirometry. Here the waste (full-strength rather than diluted as in the standard BOD test) is contacted with biomass in an apparatus that continuously measures the dissolved oxygen consumption. This test determines the ultimate BOD in a few hours if a high level of biomass is used. The test can also yield information on toxicity, the need to... 

The second method is by use of the heart rate. The total heart rate is regarded as a sum of several components and, in general, is linearly related to the metabolic heat production for heart rates above 120 beats per minute. Heat stress will, however, also increase the heat rate. The third method is to calculate the metabolic heat production from measures of oxygen consumption, and carbon dioxide production during activity and recovery. 

Basal metabolic rate The rate of oxygen consumption by a person at rest. 

Metabolic rate, basal (BM) Metabolic energy transformation calculated from measurements of heat production or oxygen consumption in an organism in a rested, awake, fasting, and thermoneutral state, in W nr. ... 

Oxygen consumption The rate at which the lungs take up oxygen. 

Vehicle Pigment Rate of oxygen consumption (g cm y ) Reference... 

In practice, carbon limited chemostat cultures are used to estimate the P/O quotient These conditions are used because they favour the most efficient conversion of the carbon substrate into cellular material, ie the highest efficiency of energy conservation. The steady state respiration rate (qo,) is measured as a function of dilution rate (specific growth rate) and Yq can be obtained from the reciprocal of the slope of the plot. qo, is also known as the metabolic quotient for oxygen or the specific rate of oxygen consumption. 

Contamination of the production vessel leads to serious financial penalties and each step in the inoculum train is monitored for contamination. To reduce the risk of contamination during sampling it is usual to take a sample from the residue left in each vessel after its contents have been transferred to the next reactor. Since these contamination checks are retrospective, a heavy reliance is placed on the growth characteristics of the production organism. Kinetic variables such as growth rate and oxygen consumption rate are also used to assess the quality of the inoculum. 

Mallefet, J., and Baguet, F. (1993). Metabolic control of luminescence in isolated photophores of Porichthys effects of glucose on oxygen consumption and luminescence./. Exp. Biol. 181 279-293. 

---