Nontraumatic aortic blood flow sensing by use of an ultrasonic esophageal probe.

The measurement of blood velocity fields, volume flow, and arterial wall motion in the descending thoracic aorta provides essential hemodynamic information for both research and clinical diagnosis. The close proximity of the esophagus to the aorta in the dog makes it possible to obtain such data nonsurgically using an ultrasonic esophageal probe; however, the accuracy of such a probe is limited if the angle between the sound beam and the flow axis, known as the Doppler angle, is not precisely known. By use of a pulsed Doppler velocity meter (PUDVM) and a triangulation procedure, accurate empirical measurement of the Doppler angle has been obtained, allowing quantification of blood velocity scans across the aorta. Volume flow is obtained by integration of blood velocity profiles and arterial wall motion is measured with an ultrasonic echo tracking device. Accuracy of the probe was substantiated by comparison with ultrasonic and electromagnetic implanted flow cuff measurements. Use of the probe in measurement of blood velocity, volume flow and arterial wall motion at various locations along the 8- and 10-cm length of the descending thoracic aorta in adult beagle dogs is detailed. The simplicity, accuracy, and nontraumatic aspect of the technique should allow increasing use of such a probe in numerous research and clinical applications.     

New method of cardiac output measurement using ultrasound velocity dilution in rats.

The aim of this study was to validate a new technique for the measurement of cardiac output (CO) based on ultrasound and dilution (COUD) in anesthetized rats. A transit time ultrasound (TTU) probe was placed around the rat carotid artery, and ultrasound velocity dilution curves were generated on intravenous injections of saline. CO by COUD were calculated from the dilution curves for normal and portal hypertensive rats in which CO was known to be increased. COUD was compared with the radiolabeled microsphere method and with direct aortic TTU flowmetry for baseline CO and drug-induced CO variations. CO in direct aortic TTU flowmetry was the ascending aorta blood flow measured directly by TTU probe (normal use of TTU flowmetry). The reproducibility of COUD within the same animal was also determined under baseline conditions. COUD detected the known CO increase in portal hypertensive rats compared with normal rats. CO values by COUD were correlated with those provided by microsphere technique or direct aortic TTU flowmetry (adjusted r = 0.76, P < 10(-4) and r = 0.79, P < 0.05, respectively). Baseline CO values and terlipressin-induced CO variations were detected by COUD and the other techniques. Intra- and interobserver agreements for COUD were excellent (intraclass r = 0.99 and 0.98, respectively). COUD was reproducible at least 10 times in 20 min. COUD is an accurate and reproducible method providing low-cost, repetitive CO measurements without open-chest surgery. It can be used in rats as an alternative to the microsphere method and to direct aortic flowmetry.     

Continuous measurement of gas uptake and elimination in anesthetized patients using an extractable marker gas.

Measurement of pulmonary gas uptake and elimination is often performed, using nitrogen as marker gas to measure gas flow, by applying the Haldane transformation. Because of the inability to measure nitrogen with conventional equipment, measurement is difficult during inhalational anesthesia. A new method is described, which is compatible with any inspired gas mixture, in which fresh gas and exhaust gas flows are measured using carbon dioxide as an extractable marker gas. A system was tested in eight patients undergoing colonic surgery for automated measurement of uptake of oxygen, nitrous oxide, isoflurane, and elimination of carbon dioxide with this method. Its accuracy and precision were compared with simultaneous measurements made with the Haldane transformation and corrected for predicted nitrogen excretion by the lungs. Good agreement was obtained for measurement of uptake or elimination of all gases studied. Mean bias was -0.003 l/min for both oxygen and nitrous oxide uptake, -0.0002 l/min for isoflurane uptake, and 0.003 l/min for carbon dioxide elimination. Limits of agreement lay within 30% of the mean uptake rate for nitrous oxide, within 15% for oxygen, within 10% for isoflurane, and within 5% for carbon dioxide. The extractable marker gas method allows accurate and continuous measurement of gas uptake and elimination in an anesthetic breathing system with any inspired gas mixture.     

Continuous capillary blood collection by means of cooling of the wound]

By cooling of a capillary wound to 5 degrees C it is possible to obtain blood continuously without anticoagulants. Thus it is possible to measure blood constituents (like bilirubin, glucose, gases, cellular elements etc.) over longer periods of time in patients for whom indwelling venous catheters are not feasible.     

Continuous measurement of oxygen concentration in citrus soil by means of a waterproof zirconia oxygen sensor

A limiting-current type of zirconia oxygen sensor has been developed and its efficiency was tested for the determination of oxygen in soil air. This oxygen sensor is waterproof and has a very short response time. By the use of the sensor, changes in soil oxygen concentration, due to undecomposed organic material and waterlogging, were observed. The sensor was found to be highly stable in the soil and suitable for continuous oxygen monitoring in the field.     

Sensing the dissociation of a polymeric enzyme by means of an engineered intrinsic probe

One of the most remarkable characteristics of Brucella lumazine synthase (BLS) is its versatility to undergo reversible dissociation and reassociation as a polymeric scaffold. We have proposed a mechanism of dissociation and unfolding of BLS. Using static light scattering (SLS) analysis, we were able to demonstrate that the decameric assembly dissociates into two different conditions [pH 5 or 2M guanidinium chloride (GdnHCl) pH 7] forming stable folded pentamers. The transition from folded pentamers to unfolded monomers by GdnHCl denaturation is highly cooperative and can be measured by different spectroscopic techniques. In this work, we show the successful insertion of an intrinsic probe to study in more detail the equilibria described in previous publications. For that purpose, we performed single-point mutations of Phe residues 121 and 127, located at the pentamer-pentamer and monomer-monomer interface, respectively, to Trp residues. These mutations produced only a marginal perturbation of the BLS structure. We analyzed the unfolding and stability of the mutants through different techniques: far-and near-UV CD, SLS, dynamic light scattering, and fluorescence spectroscopy. The introduced intrinsic probe could be used to gain insights into the detailed folding and assembly mechanism of this protein.     

Measuring stroke volume of the ascending aorta with an extravascular Doppler ultrasound probe in comparison with aortic thermodilution]

Currently, no reliable minimally invasive method of measuring cardiac output continuously in neonates and children undergoing cardiac surgery is available. An extravascular Doppler probe was used to measure cardiac output in 15 New Zealand White rabbits (average weight 3.5 kg, range 2.5-4.5 kg). The results obtained were compared with cardiac outputs determined using the aortic thermodilution principle. The mean cardiac outputs measured with the extravascular Doppler probe was 0.37 +/- 0.01 l/min as compared with 0.39 +/- 0.01 l/min with aortic thermodilution. Regression analysis revealed a close correlation (r = 0.973) between the two techniques. The extravascular Doppler techniques is an option for continuous and reliable cardiac output measurement in small animals used in surgical experiments (open chest models) and in neonates or children during surgical repair of complicated congenital heart conditions.     

Simultaneous measurement of blood coagulation and erythrocyte sedimentation by means of a rheological technique

With a damped-oscillation rheometer, changes in the rheological properties, i.e., logarithmic damping factor (LDF) and period, as obtained from a damped-oscillation curve, were monitored during the coagulation of blood. In our earlier studies, the time of onset of coagulation (Ti) of the blood sample was only determined from the change in LDF. When coagulation of the blood and sedimentation of erythrocytes occurred together, the Ti value could not be determined from the change in LDF. In this paper, a method for determining the Ti value from the change in the period of the damped-oscillation curve was investigated. It was found that the period increased and leveled off as blood coagulation progressed, and the Ti value was determined from the middle point between the minimum and maximum values of the period. In addition, it was suggested that the level of erythrocyte sedimentation could be estimated from the initial decrease in LDF. In blood obtained from diabetic patients, a good correlation between the initial decrease in the LDF and the concentration of fibrinogen was observed. Our study demonstrates that when erythrocyte sedimentation and blood coagulation occur simultaneously, this rheological technique makes it possible to measure the Ti value and erythrocyte sedimentation.     

Continuous monitoring of human erythrocyte breakdown in the circulating blood by means of multiple light scattering

The method of hemolysis control in human circulating blood is described. The method was used for studying erythrocyte destruction resulting from osmotic swelling and shear stress in the blood flow and may be applied in the artificial blood circulation system.     

Evaluation of diffusion coefficients by means of an approximate steady-state condition in sedimentation velocity distributions

This investigation examined the feasibility of manipulating the rotor speed in sedimentation velocity experiments to spontaneously generate an approximate steady-state condition where the extent of diffusional spreading is matched exactly by the boundary sharpening arising from negative s–c dependence. Simulated sedimentation velocity distributions based on the sedimentation characteristics for a purified mucin preparation were used to illustrate a simple procedure for determining the diffusion coefficient from such steady-state distributions in situations where the concentration dependence of the sedimentation coefficient, s = s⁰/(1 + Kc), was quantified in terms of the limiting sedimentation coefficient as c → 0 (s⁰) and the concentration coefficient (K). Those simulations established that spontaneous generation of the approximate steady state could well be a feature of sedimentation velocity distributions for many unstructured polymer systems because the requirement that Kc_oω²s⁰/D be between 46 and 183 cm⁻² is not unduly restrictive. Although spontaneous generation of the approximate steady state is also a theoretical prediction for structured macromolecular solutes exhibiting linear concentration dependence of the sedimentation coefficient, s = s⁰(1 − kc), the required value of k is far too large for any practical advantage to be taken of this approach with globular proteins.     

Monoamine oxidase, an intracellular probe of oxygen pressure in isolated cardiac myocytes

The activity of monamine oxidase, an enzyme located almost exclusively at the outer mitochondrial membrane, toward the substrate phenylethylamine is used to report the oxygen pressure at the outer mitochondrial membrane of intact cardiac myocytes isolated from hearts of adult rats. The rate of substrate oxidation, under the conditions used, follows the Michaelis-Menten relation, and accordingly can be used as a measure of the local chemical activity of dissolved oxygen. The oxygen pressure at the outer mitochondrial membrane of myocytes, at rest and after 2- to 3-fold stimulation of respiratory oxygen consumption, differs from the extracellular oxygen pressure by at most 2 torr. This implies that most of the large, about 20 torr, difference in oxygen pressure between capillary lumen and mitochondria of the working heart must be extracellular. At physiologically relevant concentrations of the substrates phenylethylamine and norepinephrine, monoamine oxidase activity is relatively insensitive to extracellular oxygen pressure in the range 155 to 8 torr, suggesting a limited role for regulation of biogenic amine oxidation by oxygen availability.     

Pressure wave cardiography; cardiac diagnosis by means of noninvasive continuous blood pressure record.

The pulse pressure (PP) is proportional to the preceding interval (T) because of the restitution of contractility and the Starling mechanism, and is inversely proportional to the pre-preceding interval (T-1) because of potentiation of contractility. The aim of the present paper was to find if this relationship can be used for diagnostic purposes. Blood pressure was noninvasively and continuously recorded for 3 minutes (Penáz method), in 26 healthy subjects, in 13 patients with congestive heart failure (NYHA I,II) and sinusoidal rhythms and in 21 patients with atrial fibrillations. By means of multidimensional regression analysis the coefficient D[T] and D[T-1] were calculated in each subject. D[T] expresses the relative role of the preceding, D[T-1] of the pre-preceding interval. The correlation between PP and T was small in subjects with sinusoidal rhythms. Subjects with particular correlation coefficients between PP and T-1 higher than 0.5 were used for further analysis (18 controls, 7 patients). The difference between D[T-1] in controls (0.30 +/- 0.20) and in patients (0.48 +/- 0.19) was significant (Wilcoxon P less than 0.05). In subjects with atrial fibrillations both D[T] and D[T-1] were higher in decompensated patients (Wilcoxon P less than 0.05). The ratio D[T]/D[T-1] was higher in patients with mitral stenosis than in patients with ischaemic heart disease (t-test, P less than 0.05). The test can be usefully employed as a screening test in medical practice.