Myocardial Perfusion Imaging
Michael Ljungberg in Handbook of Nuclear Medicine and Molecular Imaging for Physicists, 2022
Myocardial ischemia occurs when the supply of oxygen to the myocytes is lower than the demand (Figure 15.1). The inotropic and chronotrophic states determine the myocardial demand. For example, during physical exercise, the increasing heart rate and blood pressure lead to an increased demand for oxygen. In normal conditions, the arterioles can dilate during exercise, and perfusion can increase from a resting value of 1 mL/min/g tissue to more than 3 mL/min/g. IHD is often caused by atherosclerotic stenosis in the coronary arteries, which increase the resistance in the vessels and limits the blood flow. The heart will compensate for this at rest by dilation of the arterioles, thereby preventing a flow decrease. This, however, means that part of the flow vasodilator reserve is already being used at rest, and the arterioles cannot dilate further during stress. Thus, there is a lower supply of oxygen to the myocytes at stress, but not at rest, which is why patients who have stress-induced ischemia often have normal perfusion at rest.
Dysfunctions of COVID-19
Wenguang Xia, Xiaolin Huang in Rehabilitation from COVID-19, 2021
Oxygen uptake reflects the body’s ability to absorb and consume oxygen, which is determined by the level of oxygen demand in cells and the maximum amount of oxygen transport. Oxygen uptake can be calculated by oxygen uptake into the bloodstream and tissues. Maximal oxygen uptake (VO2max) is the most important index to reflect aerobic capacity and exercise potential. Factors affecting oxygen uptake include oxygen-carrying capacity of blood, cardiac function, peripheral blood flow redistribution, tissue uptake, etc. The relationship between heart rate and oxygen uptake is usually nonlinear in low power motion but becomes nearly linear when the power gradually increases to the maximum. When an age-predicted heart rate is reached during exercise, it usually reflects that the patient has made the most effort and is close to reaching VO2max. The difference between the heart rate predicted by age and the maximum heart rate during exercise is the heart rate reserve. For COVID-19 patients, after correction of hypoxemia, anemia, and hypoproteinemia, tachycardia in calm state and low metabolic equivalent during exercise exceed the predicted value, both of which reflect the patient’s reduced exercise ability.
Nutrition
Peter Kam, Ian Power, Michael J. Cousins, Philip J. Siddal in Principles of Physiology for the Anaesthetist, 2020
Three main methods are used in indirect calorimetry: The Benedict–Roth spirometer is a simple closed-circuit breathing system that is filled with 6 L of oxygen and held in a drum, floating on a water seal. The subject breathes in from this drum through an inspiratory valve, and expired air is passed back to the drum through an expiratory valve and a soda-lime canister, which removes the CO2 produced. As oxygen is consumed, the volume of the drum decreases, and this is recorded. The rate of oxygen consumption is determined and the metabolic rate calculated.In the Douglas bag technique, all expired air is collected using a mouthpiece with inspiratory and expiratory valves. The expired air collected in the Douglas bag is analysed for the content of oxygen and carbon dioxide so that oxygen utilization and carbon dioxide production can be calculated.The Max Planck respirometer is based on the Douglas bag method, and the volume of expired gas is measured directly in a dry gas meter. A device within the spirometer diverts an adjustable volume of the expired gas into a breathing bag, from which the expired gas may be sampled and analysed. This type of respirometer is used for measuring very high rates of oxygen consumption, and for prolonged periods.
Effect of mycobacterial proteins that target mitochondria on the alveolar macrophages activation during Mycobacterium tuberculosis infection
Published in Experimental Lung Research, 2022
Iris Selene Paredes-González, Omar Emiliano Aparicio-Trejo, Octavio Ramos-Espinosa, Manuel Othoniel López-Torres, Milena Maya-Hoyos, Monserrat Mendoza-Trujillo, Alejandra Barrera-Rosales, Dulce Mata-Espinosa, Juan Carlos León-Contreras, José Pedraza-Chaverri, Clara Espitia, Rogelio Hernández-Pando
The oxygen consumption rate of intact cells was measured at 37 °C using a Clark-type electrode and polytetrafluoroethylene-co-hexafluoropropylene (FEP) membranes (SI021, Strathkelvin Instruments, Chapelhall, NL, Scotland). 3 × 106 cells were pre-incubated with P27 or PE_PGRS33 Mtb recombinant proteins (2 µg/mL) or without protein for 4 h in 6 mL of RPMI medium supplemented with 10% FBS. Cells were loaded into the chamber containing 200 µL of supplemented RPMI medium. The following respiratory parameters were measured as previously described.26 Routine respiration: Oxygen consumption in the presence of cells alone. Leak respiration: Correspond to the cellular oxygen consumption without ATP synthesis in the presence of 2.5 µM oligomycin (75351, Sigma-Aldrich, St Louis, MO, USA). P: Oxygen consumption directly attributable to OXPHOS (ATP synthesis) was calculated by the following formula: P = Routine-Leak. RCI (Respiratory control index): Mitochondrial coupling between respiration and OXPHOS (a marker of mitochondrial dysfunction) was calculated using the: RCI = Routine/Leak formula. All parameters were corrected by subtracting the non-mitochondrial respiration, obtained by adding 0.5 µM rotenone (R8875, Sigma-Aldrich) plus 2.5 µM antimycin A (75351, Sigma-Aldrich), and normalized by the initial number of cells. Data were analyzed with 782 System software version 4.4 (Strathkelvin Instruments).
Association between physical and mental health variables among software professionals working at home: a secondary analysis
Published in International Journal of Occupational Safety and Ergonomics, 2022
Prabhu Muniswamy, Irene Grace Peter, Varadayini Gorhe, Baskaran Chandrasekaran
The baseline characteristics including the demographicvariables and physical and mental health variables are presented in Table 1. Fifty-two (65%) respondents were male. Males had an average maximal oxygen consumption of 46.05 ± 4.17 ml/kg/min while females had 39.82 ± 4.20 ml/kg/min. Females were found to have a lower maximal oxygen consumption (−6.23 [−8.17 to −4.28] ml/kg/min) than males. We found that majority of the participants (n = 76, 95%) did not meet the global guidelines of 30 min of PA per day. Average daily sitting time was found to be 9.58 ± 2.5 h regardless of work or non-work day. We did not observe statistical difference in the average daily sitting time, PA levels or sleep duration between males and females. We found a significant difference (t = −10.17; p < 0.001) in total daily sitting time between work days (417.82 ± 87.08 min) and non-work days (593.51 ± 151.67 min) whereas we did not find a significant difference in PA levels between work days (16.02 ± 4.18 min) and non-work days (15.76 ± 2.63 min). Total daily sitting time during non-work days was –175.69 ± 154.50 min higher than total daily sitting time during work days. We found a higher prevalence of stress (n = 43, 53.75%), anxiety (n = 60, 75%) and depression (n = 49, 61.25%) in the study participants. Females were found to have higher levels of stress (10%), anxiety (11%) and depression (6%) when compared to males. The baseline physical and mental health variables are presented in Table 1.
The relationship between heart rate and VO2 in moderate-to-severe asthmatics
Published in Journal of Asthma, 2020
Felipe A. Rodrigues Mendes, Renata Nakata Teixeira, Milton A. Martins, Alberto Cukier, Rafael Stelmach, Wladimir Musetti Medeiros, Celso R. F. Carvalho
In our study, the resting oxygen consumption was assumed to be 3.5 mL min−1 kg−1, that has been internationally accepted (9, 33), instead of the basal value obtained in our patients (3.8 ± 0.3 mL min−1 kg−1). We believe that the resting VO2 observed in our patients was a bit greater because our patients had a shorter resting period compared with those in the study of Compher (36) (respectively, 5 vs. 15 min) that established 3.5 mL min−1 kg−1 as the resting oxygen consumption. We recalculated the regressions using 3.8 mL min−1 kg−1 as resting VO2 and the resultant slope and intercept maintained not distinguishable from the line of identity (respectively, 1.03 ± 0.03, P = 0.34; and −2.12 ± 2.20, P = 0.35). However, we choose to maintain the 3.5 mL min−1 kg−1 because it is a value internationally accepted as a resting VO2 (33) and because the resting value in every clinical practice could be different.
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