Applied Respiratory Physiology
Peter Kam, Ian Power, Michael J. Cousins, Philip J. Siddal in Principles of Physiology for the Anaesthetist, 2020
The physiological effects of intermittent positive pressure ventilation are related to increased mean airway and intrathoracic pressures throughout the respiratory cycle, which are influenced by the mode, as well as the settings, of ventilation. The physiological consequences may be classified as respiratory effects, cardiovascular effects and endocrine effects. When the breath is held after breathing air, alveolar gas reaches equilibrium with mixed venous blood within a few minutes, and the partial pressure of carbon dioxide will increase at a rate of 3–6 mmHg/min The ‘break point’ for breath holding is the point at which the stimulus to breathe overwhelms any voluntary effort to hold the breath. Hypoxia refers to a decrease in oxygen delivery to tissues at which aerobic metabolism ceases and anaerobic metabolism takes over. It is classified in terms of the underlying causes: hypoxic (hypoxaemic) hypoxia, anaemic hypoxia, stagnant hypoxia, and histotoxic (cytotoxic) hypoxia.
Compensatory Mechanisms in Acid–Base Disorders
Peter Kam, Ian Power, Michael J. Cousins, Philip J. Siddal in Principles of Physiology for the Anaesthetist, 2020
In metabolic alkalosis, there is an increase in plasma concentration and the respiratory drive is decreased, resulting in a rise in partial pressure of carbon dioxide. The capacity of the respiratory system to buffer acid–base disturbances is approximately twice the buffering capacity of the chemical buffers in extracellular fluid. The other important feature of the respiratory control of acid–base balance is that it responds rapidly and, hence, prevents large acute changes in plasma. Renal regulation of hydrogen balance is brought about by secretion of hydrogen ions associated with reabsorption of bicarbonate ion by renal tubules, excretion of titratable acidity, and excretion of ammonia. Acid–base disturbances have widespread physiological and biochemical effects, either by direct action on various organs or indirectly through changes in the autonomic nervous or endocrine systems. Severe acidosis can lead to impaired consciousness. However, the overall effects of acid–base changes on the central nervous system are due to changes in cerebral blood flow and intracranial pressure.
Clinical Aspects of Acid–Base Control
Peter Kam, Ian Power, Michael J. Cousins, Philip J. Siddal in Principles of Physiology for the Anaesthetist, 2020
The Astrup method is an in vitro equilibration method used to determine the partial pressure of carbon dioxide (PaCO2). The base excess system is based on the principle that when the pH of blood is normal, the ratios and total concentrations of non-carbonic buffers are normal. Buffer base is the sum of the concentrations of all the buffer anions in the blood, including haemoglobin, bicarbonate, protein and phosphate. Whole-blood buffer base refers to the concentrations of these buffers in fully oxygenated blood. An acid–base disturbance is described by three parameters: pH, which measures acidity or alkalinity; PaCO2, which measures the respiratory component; and bicarbonate, which measures the metabolic component pH and PaCO2. Various graphical acid–base diagrams have been used; the most useful one has pH on one axis and PaCO2 on the other, and it demonstrates the in vivo relationship between hydrogen and PaCO2 in primary acid–base disorders.
Effect of Nitrogen Partial Pressure on the Electrochemical Evaluation of (Ti-A1)N Coatings Deposited by Reactive Magnetron Sputtering
Published in Transactions of the IMF, 2001
Kulwant Singh, A.K. Grover, M.K Totlani, A.K. Suri
SUMMARY Titanium aluminium nitride films were deposited on stainless steel substrates by reactive magnetron sputtering under various nitrogen partial pressures, using a composite target consisting of alternate arc segments of titanium and aluminium. Electrochemical evaluation of these coatings, carried out by the potentiodynamic measurement technique in deaerated 1N H2S04 solution at room temperature, has shown that initially there is a rapid increase in corrosion resistance of the coatings with increase in partial pressure of nitrogen; a further increase in nitrogen partial pressure leads to a much lower increase in the corrosion rate. The corrosion potential (Ecorr) increased from -339.8 to -268.0 mV with the increase in nitrogen partial pressure from 0.18 to 0.63 mtorr. With further increase in partial pressure of nitrogen to 1.08 mtorr, Ecorr decreased to -303.6 mV. The corrosion current density (Icorr) was found to be least 4.6 μA cm−2 at nitrogen partial pressure of 1.08 mtorr. Coatings were characterized by X-ray diffraction phase analysis, which showed the presence of microcrystalline cubic TiN structure for nitrogen partial pressures of up to 0.88 mtorr. A cubic TiN plus hexagonal AIN structure was present at 0.98 mtorr, while only hexagonal AIN structure was observed at 1.08 mtorr nitrogen partial pressure. Surface hardness measured by microhardness tester using a Knoop indenter showed an increase in surface hardness values with increase in partial pressure of nitrogen. The maximum hardness of 2790 HK25 was observed at a nitrogen partial pressure of 0.98 mtorr. At nitrogen partial pressure of 1.08 mtorr the hardness value decreased drastically to 1746 HK25
Effects of piperazine concentration and operating conditions on the solubility of CO
Published in Separation Science and Technology, 2019
Alireza Jahangiri, Mojtaba Nabipoor Hassankiadeh
ABSTRACT In this study, new equilibrium solubility data for carbon dioxide in aqueous solutions of 2-amino-2-methyl-1-propanol and piperazine (PZ) are provided. The two famous Deshmukh–Mather and Kent Eisenberg thermodynamic models are utilized to predict the CO2 absorption. The experimental data show that the solubility of CO2 decreases as the temperature increases. Our data suggest that the addition of PZ has different effects on CO2 absorption under different partial pressure of the CO2 in the gas stream. For high partial pressure, the addition of PZ promotes the absorption performance. However, at low CO2 partial pressure, PZ addition results in less saturated CO2 loading. The Deshmukh–Mather model can provide an accurate prediction of the experimental data at high partial pressure of CO2 (i.e. AAD = 3.4%) whereas the modified Kent–Eisenberg model can capture the inverse effects of the PZ at low partial pressure and provides a relatively good approximation of experimental data at low partial pressure (i.e. AAD = 10%).
The effects of nitrogen partial pressure on the microstructure of amorphous carbon nitride films
Published in Integrated Ferroelectrics, 2017
Wu Jinxin, Xu Feng, Ye Peng, Tang Xiaolong, Zuo Dunwen
ABSTRACT The amorphous carbon nitride (a-CNx) films with varying nitrogen content were deposited on Si (100) wafers substrates using radio frequency magnetron sputtering (RFMS) from graphite target at different nitrogen partial pressure. The influence of nitrogen partial pressure on the microstructure and phase composition of a-CNx films were researched systematically. The films were characterized by atom force spectroscopy (AFM), Raman spectroscopy, X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM). AFM results showed cluster structure in a range of tens to hundreds namometers existed on the surface of the films and the surface roughness increased with the increase of nitrogen partial pressure. Ratio of ID/IG increased with the nitrogen partial pressure, while the sp3 phase content from fitting results of XPS displayed reverse trend. The nanohardness of a-CNx films characterized by nanoindentation test decreased with the increase of nitrogen partial pressure, which consisted with the results of Raman and XPS. Thus high nitrogen partial pressure caused the mechanical properties of a-CNx films decrease.
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