Solid-state Pressure Transducer Research Articles

The effect of locomotion speed on the anterior tibial intramuscular pressure of normal humans

We examined the hypothesis that anterior tibial intramuscular pressure increases with the speed of locomotion. A solidstate pressure transducer was placed near the tip of an intramuscular fluid-filled catheter and each of ten normal subjects walked, jogged and ran barefoot, at 1.5, 2.5 and 3.5 m s −1 respectively, on a treadmill to which they had been previously familiarized. The pressure signals during ten gait cycles from each subject were sampled at 600 Hz and were averaged at each speed. The peak pressures increased in magnitude as a function of increasing locomotion speed, while the mean pressure remained constant.

A simple, sensitive and versatile solid-state pressure transducer.

ABSTRACT Sensitive and accurate pressure transducers are useful in many areas of biology. Two common applications are the measurement of pressure changes within the respiratory system of an animal, and quantification of the small pressure fluctuations that accompany the humidification and warming of inspired air in whole-body closed-system or open-system flow-through plethysmography (see Malan, 1973; Bucher, 1981). The design of such transducers is often complicated by the requirement to measure very small pressure fluctuations in the presence of a substantial pressure offset. Moreover, such pressure offsets often vary slowly with time. Frequent adjustments are then required to keep the output of the pressure transducer from saturating in either direction.

A low-cost modular oxygen-consumption device for small animals.

This paper describes a simple apparatus enabling the O2 consumption of small animals to be monitored. The system consists of a sensitive solid-state pressure transducer linked via a relay to a small peristaltic pump. While the animal breathes air in its closed chamber the CO2 expired is removed by an absorber; hence the pressure falls. The signal is sensed by the transducer triggering the pump to deliver a set volume of O2 to the chamber. The number of pump operations per unit time necessary to keep the system equilibrated is a measure of the O2 consumption rate. Each device is built as a module, up to four being mounted in one assembly controlled by a microcomputer. A balance control, priming switch, pump-volume setting, and electromagnetic counter are built into each front panel. Calibration is achieved be removing a known volume of air from the system with no animal present and counting the number of operations to return the chamber to equilibrium.

Modulation of cardiovascular response to dynamic exercise by fastigial nucleus.

Mongrel dogs (n = 34) were used to record the cardiovascular responses during submaximal exercise-tolerance tests (ETT) before and after the placement of lesions in rostral portions of the cerebellar fastigial nucleus (FN). Sterile surgical procedures were used to implant solid-state pressure transducers into the left ventricle or descending aorta (anesthesia 1% halothane in O2) and multipolar stainless steel electrodes into FN (anesthesia alpha-chloralose 115 mg/kg iv). Heart rate (HR), maximal left ventricular systolic pressure ( LVPmax ) and its first derivative ( dLVP /dt), and mean arterial blood pressure (MAP) were recorded during a motorized treadmill ETT. Electrolytic direct-current or radio-frequency lesions were made through the indwelling FN electrodes, and the ETT was repeated following 10-14 days recovery. Two-way analysis of variance (ANOVA), with repeated measures on one, and one-way ANOVA for simple effects indicated a significant reduction in HR and MAP (P less than 0.01) but not LVPmax and dLVP /dt occurred during exercise as a result of rostral FN lesions. Although the trend for reduced LVPmax and dLVP /dt was also evident, a relatively greater decrease in blood pressure occurred in the peripheral vasculature during exercise. It was concluded that FN acts as a modulator of HR and MAP during dynamic exercise because of the observed deficits, and because FN is known to both send efferent projections to medullary vasomotor areas and receive projections from motor cortex and muscle and joint afferents.

Left ventricular oxygen consumption and function in hypoxemia in conscious lambs.

The effects of hypoxemia on left ventricular myocardial blood flow, myocardial oxygen consumption, and contractile function were studied in 12 conscious newborn lambs 4-24 days after birth. Through a left thoracotomy, we placed fluid-filled catheters in the ascending aorta, coronary sinus, and left atrium. An electromagnetic flow transducer was placed around the ascending aorta, and a solid-state pressure transducer was introduced into the left ventricle. Three to four days later we measured aortic and coronary sinus blood oxygen contents, left ventricular myocardial blood flow, heart rate, aortic and left ventricular blood pressures, ascending aortic blood flow velocity, and the first derivative of left ventricular pressure (dP/dt) and ascending aortic blood flow velocity (dV/dt) during a control period and during 50 and 75% reductions in ascending aortic oxygen content. Myocardial oxygen consumption was calculated. There was no significant change in aortic or coronary sinus blood pH or CO2 tension during the study. Coronary sinus blood oxygen content and the arteriovenous difference of oxygen across the left ventricle decreased as a linear function of the aortic blood oxygen content. Myocardial blood flow increased in proportion to the reduction in aortic blood oxygen content. Myocardial oxygen consumption increased during hypoxemia but not as a function of aortic blood oxygen content. There was no significant change in left ventricular end-diastolic pressure or aortic mean blood pressure. dP/dt and dV/dt doubled during hypoxemia, but the increases did not occur as a function of the aortic blood oxygen content. In conscious, unanesthetized newborn lambs, 50 and 75% reductions of aortic blood oxygen content were associated with significant increases of left ventricular myocardial blood flow, oxygen consumption, and contractile function.

Cardiac dose response relationship for intravenously infused glucagon in normal intact dogs and men

The mechanism of glucagon's cardiac effects is not well understood. As the cardiac dose response to glucagon in intact animals has not been elucidated, this was determined in normal men and dogs. In man, heart rate, blood pressure, systolic time intervals and echocardiographic indices of ventricular wall motion were determined. Plasma glucagon levels (PGL) were measured by radioimmunoassay. Men received 3 glucagon infusions of 10 −10 to 10 −8 moles/minute followed by a bolus of 0.5 mg. or 1.0 mg. Small but significant changes were observed in ejection fraction and left ventricular posterior wall displacement at the 10 −9 moles/minute infusion rate (mean PGL 1.9 ng./ml.), a PGL close to that of some pathophysiologic states such as burns, ketoacidosis, and acute myocardial infarction, while cardiac output, heart rate, and other indices of cardiac performance were significantly changed only at the 10 −8 moles/minute and bolus injections. Some indices, notably stroke volume, were unchanged. In dogs, left ventricular (LV) pressure, LV pressure derivative (LV dP dt ), and aortic flow were measured with implanted LV solid state pressure transducers and electromagnetic flow probes. Dogs received six infusions from 2.7 × 10 −11 to 2.7 × 10 −8 moles/minute followed by a bolus of 2 mg. In dogs, significant changes occurred in LV dP dt at 2.7 × 10 −9 moles/minute (mean PGL 31.5 ng./ml.) and in heart rate at 2.7 × 10 −8 moles/minute only. It appears that substantial hemodynamic effects do not appear in man or dogs until PGL 10 to 100 times those seen in pathophysiologic states are achieved. Thus, it seems unlikely that glucagon contributes substantially to the hyperdynamic circulatory conditions observed in these states. Significant hemodynamic response to glucagon was noted in normal men, however, at a PGL less than that achieved by usual pharmacologic doses of glucagon and this lower PGL was not associated with the gastrointestinal symptoms commonly observed clinically.

A Method for Direct Determination of Sub-glottal Pressure and Its Applications

A newly developed method for direct measurement of sub-glottal pressure is described. The technique involves employment of a miniaturized solid-state pressure transducer which is inserted into the sub-glottal space via the glottis. The minute size and wide frequency response of this series of transducers provides a new approach to the study of the rapid air-pressure variations inside the vocal mechanism.Advantages of this procedure are discussed in comparison with other methods of measuring the sub-glottal pressure, such as those that employ an esophageal baloon, a thin catheter through the glottis, or a tracheal puncture. Some qualitative data, including the sub-glottal plessure wave recorded simultaneously with the supra-glottal pressure wave, or with the high speed motion picture of the larynx, are presented and debated. Limitations of the technique are considered together with the technical modification of the equipment needed for speech research.

An Experiment to Determine Nose Tip Transition with Fluctuating Pressure Measurements

Theme A accurate assessment of the altitude at which nose tip boundary-layer transition onset occurs is required to design and evaluate the heat protection system of high performance re-entry vehicles. Theoretical approaches to the transition phenomena are lacking, consequently the re-entry vehicle designer has relied almost exclusively on experimental data. Although transition onset has been determined on the frustum of R/V's in both ground and flight test experiments, and nose tip transition has been obtained and detected in ground tests with thermal instrumentation, there is a noticeable lack of transition detection techniques based on pressure measurements for the nose tip region. The purpose of this paper is to present the results of an exploratory ground test program to assess possible flight pressure instrumentation concepts to detect nose tip transition for full scale R/V flight test applications. l Specific ground test objectives were: a) to determine the feasibility of detecting nose tip transition by fluctuating pressure measurements using a miniaturized solid-state pressure transducer, and b) to demonstrate that the solid-state pressure sensor can make both steady-state and fluctuating pressure measurements simultaneously in a wind tunnel test for possible flight test application. Simultaneous fluctuating and steady-state pressure measurements were made and transition could be detected on the nose tip frustum 3.3 nose radii aft of the stagnation point. Transition onset was not detected at more forward stations possibly due to a porous nose.

Effect of varying differentiator frequency response on recorded peak dP/dt.

The effects of varying the differentiator cutoff frequency on the recorded peak first derivative of left ventricular pressure were assessed. High fidelity, solid state pressure transducers and recording equipment were used. In the canine heart with a basic periodicity of 1-3 Hz, the differentiator frequency response required to record an accurate peak dP/dt is influenced by the value of peak dP/dt. In the range of peak dP/dt between 1 500 and 9 000 mm Hg/s (200 and 1 200 kPa/s), a differentiator cutoff frequency of at least 90 Hz was required to record accurately peak dP/dt.

A miniature solid state pressure transducer for R/V flight test applications

A miniature solid state pressure transducer for R/V flight test applications

Solid-state pressure transducer for pressuremetric titrations

Solid-state pressure transducer for pressuremetric titrations

Solid-state digital pressure transducer

The solid-state digital transducer represents a new standard in precision pressure transduction for the next generation of airborne sensors. The pressure transducer produces pulse train outputs as a measure of pressure by developing strains in a silicon diaphragm which incorporates piezoresistive sensing elements. These elements are distributed resistance-capacitance (RC) networks which are diffused into a diaphragm surface as the control elements of phase shift oscillators. By this approach, a digital (frequency) signal generated at the source can be transmitted without noise and distance limitations and the need for precision analog to digital conversion is eliminated. The device exhibits advantages in the areas of reliability, accuracy, size and cost over present day analog devices. The solid-state digital pressure transducer is being developed to meet the requirements of supersonic and subsonic air data applications when coupled with a high-performance air data computer. This application requires low hysteresis with repeatability and stability which are the main features of the solid-state pressure transducer. Other possible applications are FM data acquisition systems and industrial robots.