Effect of salicylate on respiratory mechanics and postinspiratory muscle pressure.

In 5 spontaneously breathing anesthetized dogs, sodium salicylate (250 mg/kg) was administered. Air flow, volume, and tracheal pressure were measured. The passive mechanical properties of the respiratory system, control of breathing parameters, and the postinspiratory pressure generated by the inspiratory muscles (PmusI) were computed both before and during progressive salicylate-induced hyperventilation. Resistance fell, whereas elastance and time constant were not altered with increased ventilation (VE). The relationship between PmusI and expiratory duration (TE) presented a sigmoidal decay rate, which did not vary with hyperventilation. PmusI at TE = 0 (PmusI, 0); the times for PmusI to decay to 50 (T50), 25 (T25), and 0 percent (TZ) of PmusI, 0; inspiratory (TI), expiratory (TE) and total cycle duration (TT) decreased with increasing VE. As expiration shortened more than inspiration and TI fell more than VT rose, TI/TT and VT/TI increased during hyperventilation. In conclusion, in the face of salicylic intoxication: Rrs diminished, TI and TE decreased markedly, yielding higher values of TI/TT and VT/TI, and although T50, T25, and TZ fell, the relative time profile of PmusI remained unaltered.

Aortic input impedance during hypovolemic shock and after hyperosmotic solution infusion.

Aortic input impedance (Zin) was determined in 7 chloralose-urethane-anesthetized dogs. Flow and pressure were recorded in the ascending aorta during random cardiac pacing. These signals were processed on a spectrum analyzer utilizing the Fast Fourier Transform. Measurements were made 1) under control conditions; 2) every 5 min throughout 1 hr of hypovolemic shock; 3) every 5 min for 30 min after ending infusion of hyperosmotic solution (7.5% NaCl, 4.5 ml/kg body weight). We conclude that the determination of characteristic impedance (Zc) (average value of Zin from 4 to 10 Hz) can be useful for determining the initial phase of vascular decompensation in hypovolemic shock. After hyperosmotic solution infusion we observed a reduction in peripheral resistance, Zin, Zc, frequency of minimal Zin and frequency of phase crossover. These data strongly suggest a decrease in arterial vascular tonus.

Magnetic localisation of a current dipole implanted in dogs.

In order to evaluate the difficulty in localising a current dipole due to volume conductor current contributions to the magnetocardiogram, accuracy of depth localisation of a commercial coaxial pacemaker cable, used as a current dipole, was studied in two experimental situations: immersed in a prismatic container with NaCl solution and introduced into the lower oesophagus of dogs. Isofield contour maps were obtained by interpolation of the magnetic field measured over a plane and perpendicular to it with a third-order gradiometer coupled to a SQUID. The dipole can be accurately localised in the prismatic container. The observation of an isofield map that is symmetric about the maximum-minimum axis when the dogs are in the dorsal decubitus position with the dipole in the cephalocaudal direction implies that internal inhomogeneities in the dog's volume conductor produce no appreciable effect on the magnetic field. Nevertheless, a large distortion of the magnetic field lines is observed and can be explained by calculations using models that take into account the external boundary of the volume conductor.

Respiratory and acid-base parameters during salicylic intoxication in dogs.

This paper examines the mechanism responsible for hyperventilation and accompanying respiratory alkalosis during acute salicylism. Sodium salicylate (250 mg/kg) was administered to 8 spontaneously breathing anesthetized dogs (alpha-chloralose, 50 mg/kg, and urethane, 500 mg/kg, iv). The trachea was sectioned and connected to a pneumotachograph. A catheter was placed in the cisterna magna for sampling cerebrospinal fluid (CSF) and a femoral artery was cannulated for blood sampling and pressure determinations. Once the cardiorespiratory steady-state was obtained, air flow, tidal volume, arterial pressure, ECG and rectal temperature were measured for baseline control. The measurements were repeated 8 times during 100 min after salicylate infusion. Simultaneous determinations of CSF and plasma salicylate showed that plasmatic levels were maximal just after infusion, diminishing with time. CSF concentration increased gradually as the salicylate diffused through the blood-brain barrier. Minute ventilation increased to more than 600% of control values and was maximal between 60-100 min after salicylate infusion. Respiratory alkalosis and hyperthermia (up to 40.3 degrees C) followed the time-course of hyperventilation. Only a small part of hyperventilation can be attributed to the temperature increase. A high correlation coefficient (r = 0.974) was obtained by regression analysis of the values for ventilation and CSF salicylate. We conclude that the central action of salicylate is much more important for increasing ventilation than effects related to oxidative phosphorylation uncoupling.

Use of SI-units in cardiorespiratory physiology and biophysics.

The Système International d'Unités (SI) is progressively being adopted in all branches of science. Physiology and biophysics are no exceptions. Resistance to the use of SI-units derives from the ingrained habit of utilizing traditional units, which may appear simpler but have many limitations. The SI not only simplifies units but also involves the standardization of spelling, symbols and presentation. This article describes the relationship between the SI and the units commonly used in cardiovascular and pulmonary physiology and biophysics. It provides conversion factors for SI units in the hope that it will stimulate a wider use of these new international units.

Detection and quantification of small right-to-left shunts by the phase-plane method.

In six anesthetized dogs 70 indicator-dilution curves and phase-plane plots were recorded. Indocyanine green was injected into the superior vena cava and sampled through a dichromatic cuvette densitometer from the femoral artery. Dye-dilution curves were recorded from dogs with normal cardiovascular systems and repeated after right-to-left shunts of different magnitude were surgically produced. The percent of blood shunting was calculated according to standard indicator-dilution equations and also by means of oximetric determination of blood samples. They were compared with shunt estimates based on phase-plane loop measurements. Good correlation was found with standard indicator-dilution procedures (r = 0.890) but not with oximetry (r = 0.466). The phase plane shows its utility in the detection and evaluation of small right-to-left shunts. These shunts affect the initial portion of the phase plane and the alterations appear to be more evident than in the corresponding concentration-vs.-time curves.

Relationship between mouth and esophageal pressures in different body postures.

Static voluntary efforts, both inspiratory and expiratory (executed with the glottis open against a closed airway) are commonly utilized for the evaluation of correct esophageal balloon positioning for indirect pleural pressure measurement. Agreement between delta Pm (change in mouth pressure) and delta Pes (change in esophageal pressure) indicates the valid indirect determination of pleural pressure. Measurements of delta Pes are more commonly made with the thorax in the upright position, and some investigators have reservations about determinations carried out in the supine position. In the present investigation, the airway shutter occlusion test as well as Müller's maneuver were applied to patients sitting in a plethysmographic box to determine the validity of delta Pes in several body positions. Measurements were made on 8 patients sitting with the thorax in the vertical (90 degrees) position and at angles of 45 degrees, 0 degree and -10 degrees. Thoracic gas volume was also determined at each angle studied. The esophageal balloon was shown to need frequent repositioning when body position was changed. With proper care, valid delta Pes measurements could be made in all positions studied. A plot of the delta Pes/delta POm ratio showed values closer to one for the "occlusion test" than for Müller's maneuver. Phase differences between delta Pes and delta Pm were very small in different body positions. Cardiac artifacts in esophageal measurements were more pronounced in the horizontal and -10 degrees positions. The "occlusion test" is particularly useful for clinical application because it does not require patient cooperation and is a very simple technique for evaluating correct esophageal catheter placement.

Detection and quantification of small left-to-right shunts by the phase-plane method.

Sixty-five pairs of indicator-dilution curves were obtained in five anesthetized dogs. After the injection of indocyanine dye into the left atrium, blood was simultaneously sampled through dichromatic cuvette densitometers from the femoral artery and the distal pulmonary artery. Dye-dilution curves were recorded from dogs with normal cardiovascular systems and after the surgical production of left-to-right shunts of different magnitudes. The percent of blood shunting was calculated according to the double sampling method and compared with a new method based on the deviation observed in the terminal portion of the indicator-dilution phase-plane loop. A high level of correlation was observed between both methods (r = 0.961). The phase plane shows its utility in the quantification of small left-to-right shunts. The use of only one sampling site at a peripheral systemic artery is an important advantage because there is complete mixture between shunted and unshunted blood.

Hemodynamic action of verapamil in dogs with controlled aortic pressure--influence of sympathetic activation.

Verapamil was given to 18 anesthetized dogs (alpha-chloralose 100 mg/kg) as a bolus injection (200 micrograms/kg) followed by constant rate infusion (10 micrograms/kg per min). Hemodynamic parameters were evaluated before and during verapamil administration. After a suitable period of time for complete reversal of hemodynamic effects, verapamil administration as well as hemodynamic measurements were repeated during graded aortic occlusion. This technique stabilized central aortic pressure so that the level of reflex baroreceptor stimulation could be kept constant. Atrio-ventricular conduction disturbances observed in 5 dogs during balloon occlusion are attributed to lack of sympathetic stimulation. Without balloon occlusion, verapamil produced significant decreases in peripheral systemic vascular resistance and pressure and marked increases in cardiac output. Heart rate, pulmonary arterial and pulmonary wedge pressures did not change significantly. During graded aortic occlusion, systemic resistance and cardiac output were less markedly affected but there was an increase in both pulmonary arterial and wedge pressures.

Fourier analysis of airflow and transpulmonary pressure signals filtered on-line.

Airflow and transpulmonary pressure curves obtained from a normal man and a dog, during hyperventilation or when breathing spontaneously, were analysed on a digital computer by means of the fast Fourier transform. The same curves were also analysed after passing through an on-line RC filtering algorithm having cutoff frequencies extending from 10 down to 0.1562 Hz. Results show that respiratory parameters can contain a large amount of biological background noise mainly related to cardiovascular motion. The only instance in which the magnitude of fundamental harmonic was not the largest was for the airflow of the dog measured during spontaneous breathing. It was concluded that the cutoff frequency should be adjusted to a value 3-4 times that of the fundamental frequency. More pronounced filtering would cause important distortions of the physiologic signals.

Cardiac output and mean transit time using the phase plane of dye-dilution curves.

Thirty-five indicator-dilution curves were recorded in dogs following the injection of indocyanine dye into the femoral vein, right atrium, pulmonary artery, or left ventricle. Sampling was from the femoral artery through a dichromatic cuvette densitometer. The exponential decay constant of each dye-dilution curve was calculated by a new method utilizing the phase plane and compared with the value obtained by the Stewart-Hamilton procedure. A high level of correlation was found between the two methods. Mean difference between areas was only 1.04 mg.1(-1).s (r = 0.999) and between mean transit times 0.02 s (r = 0.999). The phase plane method has the additional advantage of demonstrating the portion of exponential decay, enabling the elimination of indicator-dilution curves and abnormal downslopes.