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In order to lift the mass the force must be at least equal to the weight of the object cardiovascular system uk generic propranolol 20mg mastercard. This potential energy represents a capacity to do work cardiovascular medicine davenport propranolol 40 mg with visa, or may be converted to another form of energy such as kinetic energy, if the object were allowed to fall. As the object falls it loses potential energy but gains kinetic energy (energy by virtue of its velocity). To calculate the power output of a machine or process, divide the total energy expended by the time taken. For example: calculate the power output of intermediate metabolism over 24 hours, given a basal metabolic rate of 2400 kcal per day. Consider the work done by a force F raising an object of mass m through a Use of potential energy in the Manley ventilator An example of the application of potential energy lies in the action of the bellows weight in a Manley ventilator. This potential energy is then used by allowing the weight to fall and compress the bellows of a ventilator. The work done in compressing the ventilator bellows is converted into the potential energy gained by the gas as it becomes pressurised. This is analogous to the storage of potential energy in a spring when it is compressed. Work = V1 p dV V2 In order to estimate the inspiratory work in delivering a breath of 500 ml, a simple example can be taken. This stores potential energy as elastic energy in the gases and tissues of the respiratory system, which then performs work in restoring the lungs to their original volume (expiratory curve). In an ideal system with 100% efficiency the inspiratory and expiratory curves would coincide since no energy is wasted in frictional losses. The amount of energy put into the system during inspiration is thus returned in full during expiration. Inspiration Work of breathing 1 Under resting conditions the work done in inspiration can be approximated by considering a simple model as described above. Under stressful or pathological conditions work of breathing may increase tenfold or more and represent a significant energy requirement. The work of breathing during spontaneous respiration is considered in further detail in Section 2, Chapter 8 (page 370). Heat Heat is a form of energy which can be transferred from hot objects to cooler objects. Temperature is a measure of how hot or cold an object is, in other words a measure of its thermal state. Therefore heat energy will tend to pass across a temperature gradient from high to low temperatures. When heat is transferred to an object its temperature will increase, and the loss of heat energy from an object will be accompanied by a fall in temperature. Units of heat energy Heat energy is measured in joules (J), but traditionally has also been measured in calories (cal) or kilocalories (kcal or Cal). The unit used in the Kelvin scale is the kelvin (K), which has precisely the same magnitude as a one-degree increment (C) on the Celsius scale. At sea level water boils at 100 C, but at 5500 m, where atmospheric pressure is approximately halved, the boiling point of water decreases to 80 C. Critical temperature Both pressure and temperature can change the state of a substance. However, there is a temperature above which any gas cannot be liquefied by increasing pressure. The critical temperature for oxygen is -119 C, and therefore oxygen in a cylinder at room temperature is always gaseous. This means that at normal room temperature a cylinder of nitrous oxide contains a mixture of liquid and gas, unless the ambient temperature exceeds 36. Specific heat capacity and heat capacity In an object the relationship between temperature change and amount of heat energy added or removed depends on the size of the object and the material it is composed of. Specific heat capacity, c (kJ kg-1 K-1) is the amount of heat required to raise the temperature of 1 kg of a substance by 1 C.

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The performance of a measurement system can be characterised by its static and dynamic characteristics cardiovascular disease heart foundation generic propranolol 80mg on-line. These determine the relationship between the quantity being measured (input) and the reading (output) coronary artery 3 buy generic propranolol canada. Static characteristics Static characteristics define the performance of a measurement system when it is dealing with an input which is not changing (or changing only slowly). Under these circumstances there is enough time for the system to reach a steady state before the measured quantity changes, so that the output follows changes in the input accurately. For example, if a pressure has a true value of 10 cmH2 O, an accurate system may read 10. The sensitivity of a pressure measurement system may be described as the change in output signal voltage for a given change in pressure. Thus, in a linear pressure measurement system, if the pressure doubles the output voltage will double. When the output voltage is plotted against the input pressure, a straight line is obtained. Some instruments may be intrinsically non-linear, reflecting their underlying mechanism. Hysteresis in a mechanical device is caused by elastic energy stored in the system, or frictional losses between moving parts. It is usually caused by the effect of internal or external temperature changes on the measurement system, and unstable components in the system. This response time may affect the accuracy of the measurement, since if the input is changing rapidly the measuring system may not have adequate time to reach steady state, and thus will not give an accurate reading. The dynamic characteristics of a system reflect its ability to respond to rapidly changing inputs. In a perfect measuring instrument, the output or step response produced by a step input should also be a step function occurring instantaneously to give a reading of the measured quantity. In practice, the step response differs from the ideal due to the properties of the system, and the output only reaches a true steady-state value after a finite time. In curve (b) the response does not reach the true value in the time plotted; in curve (c) the output reaches a steady reading of the true value within the shortest time compatible with no overshoot. The property that determines these effects in the step response is called the damping of the system. In an electromechanical device such as a galvanometer there are mechanical moving parts such as the meter needle and bearings. This may arise unintentionally or may be applied as part of the instrument design to control oscillation of the needle when it records a measurement. In a fluid- (gas or liquid) operated device, damping occurs due to viscous forces that oppose the motion of the fluid. In an electrical system, damping is provided electronically by electrical resistance that opposes the passage of electrical currents. In a measurement system it can lead to inaccuracy of the readings or display: r Under-damping can result in oscillation and overestimation of the measurement. Frequency response of a measurement system Any measurement system in practice will only respond to a restricted range of frequencies, either by design or due to the limitations of its components. Within this frequency range the system may respond more sensitively to some frequencies than to others. Bandwidth the highest frequency that a system responds to is the high cutoff frequency, above which input signals will produce no output. An example of such a cutoff is in the frequency response of the human auditory system, which at best may have a high cutoff frequency of 20 kHz. Similarly, a system may possess a low cutoff frequency, the lowest frequency audible by the human ear being 15 Hz. The frequency range between low and high cutoff frequencies is referred to as the bandwidth.

This device system is a primary cell which maintains itself by the consumption of externally supplied gas cardiovascular disease journal safe propranolol 20mg. Since the electrolyte solution is continually replenished by the redox reaction at the cathode capillaries growth discount propranolol 40 mg online, it has a longer working life than a simple galvanic cell in which the electrolyte solution is consumed by the redox reactions. Theoretically its working life is only determined chemically by consumption of the lead anode. This is thought to reflect the delay caused by oxygen diffusion in blood, and the localised depletion of oxygen that occurs at the cathode. To prevent this, a combination of regular electrode cleaning and quality control is necessary. If a patient has a temperature that differs by more than 2 C mathematical correction is necessary. In vivo oxygen measurement Intravascular oxygen electrodes this is a bipolar variant of the Clark electrode in which both the anode and the cathode are mounted within a fine tube covered by an oxygen-permeable membrane. Access of oxygen to the cathode is flow-dependent, which can introduce error at low-blood-flow states (largely overcome by using a pulsed polarising current). Rapid response times are only achieved at the expense of poor accuracy at low flow rates. Transcutaneous oxygen electrodes these provide a measure of the oxygen that has diffused from capillaries in the dermis of the skin. The electrode housing contains a heating element and a thermistor to allow temperature compensation. This provides the basis for the technique, which uses an intravascular probe, composed of an optical fibre with a dye-coated tip, covered by an oxygenpermeable membrane. The intensity of fluorescence is dependent on the concentration of oxygen present at the tip, and it is measured using a photomultiplier. In addition, prolonged use may result in the deterioration of the dye, making measurements invalid. These elements are covered by a membrane composed of either silicon oxide or polyethylene, and mounted on an ophthalmic former. This is placed under the eyelid in the conjuctival fornix (local anaesthesia is necessary for the awake patient), and held in place by the orbicularis occuli. Mass spectrometer In addition to its in vitro application, the mass spectrometer can also be used as an in vivo analyser. In vivo the mass spectrometer is in direct continuity with the patient either via an intravascular perforated metal catheter covered with a gas-permeable membrane or by means of a transcutaneous oxygen electrode. These can be applied in vitro, where the measurements are made on blood or gas samples remote from the subject, or in vivo, where the oxygen measurement system is in direct continuity with the patient. Optodes this method is different from the others described, in that measurement does not depend on the consumption of oxygen. It uses two electrodes, a glass pH electrode, and a silver/silver chloride reference electrode, both maintained at 37 C. The electrode is part of a housing, which also contains a heating element and thermistor (for temperature compensation). The glass electrode is covered by a layer of cellophane or nylon mesh with a thin layer of sodium bicarbonate between the electrode and the covering. The intravascular probe is composed of an optical fibre with a dye-coated tip covered by a thin layer of buffer. Accuracy depends on membrane integrity, since it is vital to ensure that the only change in pH at the electrode results from the shift in the carbonic acid equilibrium. This can be monitored by measurement of electrical resistance across the membrane. The sensor window must remain clean to prevent inaccuracy and calibration problems.

Multiple word descriptor lists can be used to produce multidimensional pain assessment heart disease red wine propranolol 80mg lowest price. It consists of a body map and word descriptor sections for evaluating the intensity and other characteristics of pain cardiovascular disease websites propranolol 80 mg online. It is a relatively involved questionnaire taking around 20 minutes or more to complete, depending on patient skills. This limits its application since it is not suitable for children, highly anxious patients or patients in the immediate postoperative period. Alternatively pain charts can be designed for observers or carers to record objective assessment data on a diary/timetable basis, to optimise postoperative analgesia. Assessment of pain in children Pain assessment in children is dependent on the age and skills of the child, and is affected significantly by their interaction with their parents. Equipment can then be connected to these outlets by non-interchangeable flexible hosing. The pipeline terminal outlets consist of Schrader sockets that are clearly labelled and colour-coded for the service or gas. They are matched for a specific connecting flexible pipeline by a collar indexing system. The terminal end consists of an indexed Schrader probe that fits into its specific terminal socket. These design features of the hoses and terminal sockets ensure that the gases or services cannot be cross-connected to equipment. Nitrous oxide supply Nitrous oxide is supplied from a central bank of gas cylinders, which contain a mixture of liquid and gas (critical temperature of nitrous oxide is 36. These are connected to the distribution pipeline network by a control panel, which regulates the gas pressure. The control may also provide local heating in order to avoid condensation and freezing due to the cooling caused by the evaporation of the liquid nitrous oxide. In a hospital two types of supply are required, a low-pressure supply (420 kPa) for anaesthetic machines and ventilators, and a higher-pressure supply (700 kPa) to provide power for surgical equipment. The pipeline network may be supplied either by a bank of air cylinders or by a local compressor system. If a local compressor is used care must be taken to ensure the purity of the compressed air produced. The high flow rates used to remove waste anaesthetic gases could reduce suction levels during surgery. Suction vacuum systems incorporate bacterial filtration and drainage to dispose of aspirated body fluids. Random cylinders from a batch may be destructively tested by the manufacturers using water under pressure. Cylinders may be inspected endoscopically for cracks and defects on their inner surfaces, and they can also be tested ultrasonically. Cylinder valve outlet Pin index holes Bodok seal Index pins Estimation of cylinder contents the contents of a cylinder, for both gases and vapours, are estimated by weighing the cylinder and subtracting the weight of the empty cylinder or tare weight. Cylinder contents can thus be estimated by weighing a cylinder and subtracting the tare weight of the cylinder. Since gases are not liquefied in the cylinder (temperature < critical temperature), the cylinder contents can also be estimated by the cylinder pressure. This system prevents the wrong cylinder from being connected to an anaesthetic machine. The cylinder valve block face matches up to the inlet port of the anaesthetic machine. This face contains the gas outlet from the cylinder, which is made gas-tight by a metal and rubber ring seal, the Bodok seal. If the positions of these pins do not match the index holes on the valve block outlet, the cylinder cannot be fitted to that particular inlet on the anaesthetic machine. In the case of vapours (such as nitrous oxide or carbon dioxide) the contents of the cylinders are a mixture of gas and liquid. The filling ratio is defined as the weight of the substance contained divided by the weight of a volume of water equal to the internal volume of the cylinder. The cylinder pressure cannot be used to estimate cylinder contents in the case of a vapour, because it does not vary as the cylinder empties.