Measurement of umbilical blood flow in fetal lambs in utero.

We continuously measured umbilical blood flow in fetal lambs in utero by placing an electromagnetic flow transducer around the common umbilical artery. Umbilical arteries originate from a short common segment as the terminal branches of the descending aorta. This segment was isolated by a retroperitoneal surgical approach and encircled with a specially constructed electromagnetic flow transducer. Catheters were also placed in fetal vessles to monitor pressure and derive flow values by the radionuclide-labeled microsphere technique. The fetus and ewe were allowed to recover for two days before studies were performed. Average umbilical blood flow obtained in 11 animals with the transducer was 199 ml/kg per min. In seven animals flow measurements obtained with the transducer were compared with those derived from microsphere injections. Paired measurements varied by an average of only 5.3%. This technique makes possible the accurate and instantaneous measurement of umbilical blood flow in fetal lambs in utero over a prolonged period.     

Pulsatile flow in a catheterised artery

A model is presented for the physiological problem of a catheter which is inserted in a femoral artery to measure the pressure gradient. As the catheter will modify the pressure distribution in the artery, the pressure gradient which would be recorded by a perfect pressure transducer attached to it would differ from that in the uncatheterised artery. To estimate the magnitude of this error, it is assumed that the rates of flow of blood through the catheterised and the uncatheterised artery are described by the same known periodic function of time.     

The technique of detecting systolic and diastolic pressure from the transducer output of a PC-based blood pressure monitoring system

A pressure to voltage transducer is used along with a cuff, in a PC-based blood pressure and pulse rate monitoring system for human body. During the blood pressure measurement cycle, the output voltage of the pressure to voltage transducer is recorded digitally using a data acquisition system. The recorded data are then analyzed using software routines to determine the blood pressure and pulse rate of the person under test. However, it is difficult to identify the points of systole and diastole correctly from the recorded data. This paper presents the technique that may be used to determine the systolic and diastolic pressure from the collected data.     

The technique of detecting systolic and diastolic pressure from the transducer output of a PC-based blood pressure monitoring system

A pressure to voltage transducer is used along with a cuff, in a PC-based blood pressure and pulse rate monitoring system for human body. During the blood pressure measurement cycle, the output voltage of the pressure to voltage transducer is recorded digitally using a data acquisition system. The recorded data are then analyzed using software routines to determine the blood pressure and pulse rate of the person under test. However, it is difficult to identify the points of systole and diastole correctly from the recorded data. This paper presents the technique that may be used to determine the systolic and diastolic pressure from the collected data.     

Indirect systolic and mean blood pressure determination by a new tail cuff method in spontaneously hypertensive rats

A new tail cuff method for determining systolic and mean blood pressure in rats was developed based on photoelectric detection of tail arterial blood flow and pulsatile volume oscillation. Indirect systolic and mean blood pressure measured by this method correlated well with direct systolic and mean blood pressures recorded by a transducer and polygraph after carotid artery cannulation in stroke-resistant spontaneously hypertensive rats (SHR), stroke-prone SHR and normotensive Wistar Kyoto rats. Blood pressures were sharply, and transiently raised for about 1 min when rats were picked up by an investigator to be placed in a hot box or immobilized in a restrainer for measuring blood pressure. Therefore, blood pressures should be measured at least 1 min after the rats are put in a restrainer. This new tail cuff method for measuring blood pressure provides reliable mean blood pressure readings in conscious rats.     

Theory and design of disposable clinical blood viscometer

A disposable clinical whole blood viscometer which can produce viscosity measures over a wide range of shear rates in a single rapid determination has been developed and is currently under test. The design is based upon the time varying flow of blood through a capillary. The flow is driven by the pressure in a fixed volume air chamber and transmitted to the sample through a compliant membrane. The time varying pressure in the air chamber is measured by a suitable transducer. The instantaneous shear stress of the blood in the capillary is proportional to the air pressure, while the instantaneous shear rate is proportional to the pressure-time derivative. Proper design ensures that the system operates as a first order dynamic system with flow resistance entirely determined by the nonlinear sample viscosity. By constructing the air chamber in two parts coupled by a quick disconnect fitting the design can allow for the blood-containing part of the instrument to be discarded, eliminating handling and cleaning of blood contacted components. The entire determination is completed in less than a minute, so that anticoagulants are not necessary. Tests on a prototype show that the instrument gives results in excellent agreement with those obtained on a cone-plate rheogoniometer.     

Frequency response of arterial bioelastomers

This work aims at estimating the quality of arterial bioelasticity. The non invasive employed method consists to obtain phase spectrum of blood flow velocity and arterial pressure. An original transducer allows us to obtain these signals at the same point of a superficial artery then to record them on magnetic tape. A mathematical model binds the phase spectrum and rheological parameters.     

Behavioural state influences the cardiovascular response to haemorrhage in lambs

We investigated the effect of behavioural state on the cardiovascular response to an acute venous haemorrhage in 7 lambs aged 13 to 19 days. Each lamb had previously been anaesthetized and instrumented for measurements of electrocorticogram, electro-oculogram, nuchal and diaphragm electromyograms, pulmonary blood flow (electromagnetic flow transducer), aortic and right atrial blood pressures. The lambs were allowed to recover from surgery at least three days before they were studied. Measurements were made during a 1-minute control period and during a 1-minute experimental period that followed a 10 ml/kg body weight haemorrhage during quiet wakefulness, quiet sleep and active sleep; the haemorrhage took approximately 30s. Haemorrhage produced similar decreases in right atrial pressure and pulmonary blood flow during the three behavioural states. However, mean aortic pressure decreased more following haemorrhage during active sleep than during quiet sleep or quiet wakefulness. These results provide evidence that reflex control of the peripheral circulation is altered during active sleep compared to quiet sleep and quiet wakefulness in lambs.     

Effect of prostaglandins E2 and F2α on umbilical blood flow and fetal hemodynamics

The hemodynamic effects of PGF_2α, PGE₂, and norepinephrine injected into the umbilical arterial circulation were compared in nine fetal lambs in utero. Umbilical blood flow was measured with radioactive microspheres and an electromagnetic flow transducer implanted on the distal aorta of the fetus after ligation of external iliac arteries and other accessible distal aortic branches.PGF_2α and norepinephrine increased fetal arterial pressure and umbilical blood flow while umbilical vascular resistance increased slightly (PGF_2α) or not at all (norepinephrine). PGE₂ increased fetal arterial pressure, decreased umbilical blood flow, and exerted a profound active vasoconstrictor effect on the fetal placental bed. Our data taken together with the observations of others suggest that prostaglandins may play a role in the circulatory adaptations of the fetus at birth and that PGE₂ in high concentrations is likely to have deleterious hemodynamic consequences in the fetus in utero.     

Ultrasonic transit-time measurement of blood flow in the umbilical arteries and veins in the bovine fetus during stage II of labor

The vitality of the bovine fetus during parturition depends on an intact umbilical circulation to supply adequate amounts of oxygen and nutrients to the fetus. The goal of the present study was to measure the blood flow in the umbilical vessels during stage II of labor and to determine when blood flow ceases in the umbilical cord. In 20 cows, ultrasonographic transducers were placed on one umbilical vein and one umbilical artery after rupture of the allantochorionic sac, and the blood flow volume per unit time was measured. At the same time, a pressure transducer was placed into the uterus to measure uterine pressure. Parturition was spontaneous in all 20 cows. In 20 live calves born, pH, base excess and lactate concentration were measured in the blood immediately after birth. During the last 90 min before birth the mean total umbilical blood flow (artery and vein combined) was 1.186+/-0.028 L/min. Calves with a blood pH> or =7.2 (n=13) had a higher mean total blood flow than calves with a pH<7.2 (n=7; 1.243+/-0.038 versus 1.095+/-0.038 L/min). In calves with a blood pH<7.2, the mean total blood flow decreased from 1.178+/-0.134 at 20 min before birth to 0.959+/-0.126 L/min at the end of stage II of labor. During this time period, the arterial blood flow did not differ between calves with a blood pH> or =7.2 and<7.2, but venous blood flow decreased significantly in calves with a blood pH<7.2. During uterine contractions, the total umbilical blood flow decreased significantly by 0.22 L/min. The blood flow in the umbilical artery and vein ceased before the calves were completely born.     

Cardiorespiratory responses to graded reductions of uterine blood flow in the sheep fetus

Pregnant sheep were chronically instrumented with fetal and maternal catheters and an inflatable occluder and electromagnetic flow transducer were placed on the uterine artery. Uterine blood flow was reduced for approximately 15 minutes to 25 percent, 50 percent, or 75 percent of control uterine blood flow. Fetal blood gases, arterial blood pressure, heart rate and regional distribution of blood flow (by radioactive microspheres) were measured. With progressive reduction of uterine blood flow there was an increasing degree of fetal asphyxia, as measured by blood gases and acid base state. At moderate degrees of asphyxia the fetus responded by redistribution of blood flow to certain organs, namely heart, brain, and adrenal gland, thus preserving oxygenation of these organs. During the most severe degree of asphyxia induced by reduction of uterine blood flow to 25 percent of control there is a reduction of fetal blood flow due to generalized vasoconstriction of essentially all organs. We hypothesize that this is due to the inability of the vasodilator mechanisms to sufficiently oppose the vasoconstrictor mechanisms. Also, because the oxygen consumption of the "vital" organs would be decreased this can be described as the stage of decompensation.     

Measurement of human fetal blood flow.

Real-time B-mode ultrasonography was combined with a pulsed Doppler ultrasound technique for transcutaneous measurement of human fetal blood flow in the aorta and intra-abdominal part of the umbilical vein. The target vessel was located and its diameter measured in the two-dimensional real-time image. The pulsed Doppler transducer was attached to the real-time transducer at a fixed angle. By processing the Doppler shift signals the instrument estimated the mean and maximum blood velocities and the integral under the velocity curves. This permitted calculation of the blood flow. The method was applied to 26 fetuses in normal late pregnancies. Mean blood flow in the descending part of the fetal aorta based on maximum velocity was 191 ml/kg/min. Mean flow in the intra-abdominal part of the umbilical vein was 110 ml/kg/min. This method of measurement is non-invasive and opens new perspectives in studying fetal haemodynamics.     

Effect of amrinone on diaphragm blood flow

The purpose of the present study was to examine the effect of amrinone, a drug known to augment cardiac output and dilate peripheral vascular beds, on diaphragm blood flow. Studies were performed on 12 anesthetized mechanically ventilated dogs in which strips of left costal diaphragm were developed in situ. Strip blood flow was assessed with a drop counter attached to a catheter tied into the phrenic veins' draining strips. Strip tension was measured with an isometric force transducer. Amrinone was administered as an intravenous bolus of 2 mg/kg followed by a continuous infusion of 25 micrograms.kg-1.min-1. Amrinone increased cardiac output and resting diaphragm blood flow [from 1.8 +/- 0.1 to 3.2 +/- 3 (SE) l/min and from 13 +/- 2 to 29 +/- 6 (SE) ml.100 g-1.min-1, respectively, P less than 0.001 for both comparisons]. Amrinone also increased blood flow during periods of rhythmic contraction (tension time indexes of 0.1-0.4, P less than 0.05 for comparisons of flow with and without amrinone at each tension time index) and increased the magnitude of the postcontraction hyperemia (P less than 0.02 for comparisons of hyperemic flow with and without amrinone at tension time indexes of 0.3 and 0.4). Graded occlusion of the inferior vena cava produced reductions in arterial pressure, cardiac output, and diaphragm blood flow both before and after amrinone. Both cardiac output and diaphragm blood flow were greater after amrinone, however, at all levels of blood pressure examined. These findings indicate that amrinone can override diaphragm vasoregulatory systems and augment diaphragm blood flow.(ABSTRACT TRUNCATED AT 250 WORDS)     

Acidaemia reduces cardiac output and left ventricular contractility in conscious lambs

We studied the effects of HCI-induced metabolic acidaemia on cardiac output, contractile function, myocardial blood flow, and myocardial oxygen consumption in nine unanaesthetized newborn lambs. Through a left thoracotomy, catheters were placed in the aorta, left atrium and coronary sinus. A pressure transducer was placed in the left ventricle. Three to four days after surgery, we measured cardiac output, dP/dt, left ventricular end diastolic and aortic mean blood pressures, heart rate, aortic and coronary sinus blood oxygen contents, and left ventricular myocardial blood flow during a control period, during metabolic acidaemia, and after the aortic pH was restored to normal. We calculated systemic vascular resistance, myocardial oxygen consumption and left ventricular work. Acidaemia was associated with reduction in cardiac output, maximal dP/dt, and aortic mean blood pressure. Left ventricular end diastolic pressure and systemic vascular resistance increased, and heart rate did not change significantly. The reduction in myocardial blood flow and oxygen consumption was accompanied by fall in cardiac work. Cardiac output returned to control levels after the pH had been normalized but maximal dP/dt was incompletely restored. Myocardial blood flow and oxygen consumption increased beyond control levels. This study demonstrates that HCI-induced metabolic acidaemia in conscious newborn lambs is associated with a reduction in cardiac output which could have been mediated by the reduction in contractile function and/or the increase in systemic vascular resistance. The decreases in myocardial blood flow and oxygen consumption appear to reflect diminished cardiac work. The restoration of a normal cardiac output after normalization of the pH appears to have resulted from the increases in heart rate and left ventricular filling pressures in conjunction with an incomplete restoration of contractile function.     

Histamine H3 receptors modulate reactive hyperemia in rat gut.

Reactive hyperemia (RH) is an abrupt blood flow increase following release from mechanical occlusion of an artery, with restoration of intra-arterial pressure. The mechanism of this postocclusion increase in blood flow in the gut is multifactorial. Relaxation of intestinal resistance vessels, observed during RH, may involve myogenic, metabolic, hormonal and neurogenic factors. Evidence exists that histamine is an important endogenous mediator of various functions of the gut, including blood flow. The vascular effects of histamine in the intestinal circulation are due its agonistic action on histamine H1, H2 and H3 receptors. In the present study the hypothesis was tested that peripheral histamine H3 receptors are involved in the mediation of RH in the intestinal circulation. In anesthetized rats, anterior mesenteric artery blood flow (MBF) was determined with ultrasonic Doppler flowmeter, and arterial pressure (AP) was determined with a transducer. The increase in the volume of blood accumulating during RH (RH-volume), the peak increase of arterial blood flow (RH-peak response) and the duration of the hyperemia (RH-duration) were used to quantify RH after occluding the anterior mesenteric artery for 30, 60 and 120 s. Hyperemia parameters were determined before and after administration of the selective histamine H3 receptor antagonist clobenpropit. Pretreatment with clobenpropit was without any effect on control MBF and AP but significantly reduced most of RH responses. These findings support the hypothesis that histamine H3 receptors do not play any role in the control of intestinal vasculature at basal conditions but these receptors participate in the intestinal hyperemic reaction in response to complete temporal intestinal ischemia.     

Measuring Blood Pressure in Mice using Volume Pressure Recording, a Tail-cuff Method

The CODA 8-Channel High Throughput Non-Invasive Blood Pressure system measures the blood pressure in up to 8 mice or rats simultaneously. The CODA tail-cuff system uses Volume Pressure Recording (VPR) to measure the blood pressure by determining the tail blood volume. A specially designed differential pressure transducer and an occlusion tail-cuff measure the total blood volume in the tail without the need to obtain the individual pulse signal. Special attention is afforded to the length of the occlusion cuff in order to derive the most accurate blood pressure readings. VPR can easily obtain readings on dark-skinned rodents, such as C57BL6 mice and is MRI compatible. The CODA system provides you with measurements of six (6) different blood pressure parameters; systolic and diastolic blood pressure, heart rate, mean blood pressure, tail blood flow, and tail blood volume. Measurements can be made on either awake or anesthetized mice or rats. The CODA system includes a controller, laptop computer, software, cuffs, animal holders, infrared warming pads, and an infrared thermometer. There are seven different holder sizes for mice as small as 8 grams to rats as large as 900 grams.Open in a separate windowClick here to view.^{(51M, flv)}     

A simple method for obtaining blood pressure in rhesus monkeys (Macaca mulatta).

A relatively simple procedure was devised to obtain blood pressures in rhesus monkeys. This procedure utilized a polygraph, pulse transducer, pressure transducer, blood pressure mixer unit, and pediatric sphygmomanometer cuff. Previous attempts to auscultate the Korotkoff sounds by use of a sphygmomanometer cuff and stethoscope were unsuccessful. Blood pressure can be obtained by cannulation of the femoral artery, but repeated puncture may cause serious trauma to the arterial wall. This procedure was developed and used in our laboratory to obtain repeated blood pressures over a 90-da period. Results from using the cuff and polygraph have been shown to correlate favorably with cannulation of the femoral artery.     

A multichannel implantable telemetry system for flow, pressure, and ECG measurements.

The design of telemetry systems for chronic implantation within the body have progressed from simple single-channel devices to complex multichannel systems over the last 15 yr. Although chronic measurements of temperature, ECG, and pressure have been reported with good results, measurements such as dimension and blood flow have been difficult because of heavy power requirements. The design to be described is a multiplex system that will measure up to eight individual parameters simultaneously, including blood flow. Flow is measured using an electromagnetic transducer, and by special design, the normal high power requirements of the electromagnetic technique have been reduced to a few hundred milliwatts. The system is powered by two NiCad, rechargeable batteries which are periodically recharged through the intact skin by induction at 250 kHz to an implanted pickup coil. The presently constructed units have been configured to measure ECG, two pressures, temperature and ascending aortic flow.     

Laser Doppler velocimetry: The problem of fibre movement artefact

The problem of fibre movement artefact in laser Doppler velocimetry recordings of skin blood flow has been investigated. Beat frequency spectra were obtained for a stationary target, unheated skin, heated skin (43.5°C), with and without blood flow occluded for various induced amounts of fibre movement. Possible methods for either eliminating, or obtaining an indicator of, fibre movement artefact were considered. The solution proposed is to incorporate additional fibres terminating within the transducer to permit an index of fibre movement to be obtained that is independent of blood flow.     

Cardiac function and coronary flow in chronic endotoxemic pigs

We have reported that myocardial inotropism was depressed in acute and chronic endotoxemia. One possible mechanism for this observation is that endotoxemia reduces myocardial perfusion and indeed, we observed reduced myocardial perfusion in acute endotoxemia. This study tested the hypothesis that reduced inotropism of chronic endotoxemia was accompanied by reduced coronary artery blood flow. Fifteen pigs were equipped with left atrial and ventricular catheters, circumflex coronary and pulmonary artery flow meters, left ventricular pressure transducer, and ultrasonic crystals in the anterior-posterior axis to measure internal short axis diameter by sonomicrometry. The pigs recuperated for 3 days before basal data were collected over the next 3-5 days. After at least 7 postoperative days, an osmotic pump containing Salmonella enteriditis endotoxin was implanted in 12 pigs. Endotoxin was delivered at 10 micrograms/hr/kg for 2 days, at which time the animals were sacrificed. Osmotic pumps containing sterile saline were implanted in 3 pigs. Eight of the 12 endotoxemic pigs survived; 4 died before the morning of the second day. The survivors exhibited elevated heart rate, peak left ventricular systolic pressure, and cardiac output. Inotropism was evaluated by calculating the slope of the end-systolic pressure-diameter relationship (ESPDR) and % diameter-shortening. ESPDR was significantly depressed on the second endotoxemic day, while % diameter-shortening was depressed on both endotoxemic days. Coronary artery blood flow was significantly elevated on both endotoxemic days, while cross-sectional stroke work was unchanged. Therefore, the ratio of coronary blood flow to stroke work increased on both endotoxemic days. Nonsurvivors exhibited reduced heart rate, cardiac output, peak left ventricular systolic pressure, ESPDR, and % diameter-shortening. Neither coronary artery blood flow nor flow-to-work ratios increased in this group. Sham endotoxemic pigs demonstrated no cardiac or hemodynamic changes over 3 days. These results indicate that depressed inotropism during chronic endotoxemia was not caused by reduced coronary blood flow; rather, the myocardium was relatively overperfused.