Contributions of alpha 1- and alpha 2-adrenoceptors to contractile response in canine blood vessels.

Strips of canine saphenous vein, inferior vena cava, and femoral artery were studied isometrically in vitro to compare quantitatively the alpha 1- and postsynaptic alpha 2-adrenoceptor contributions to the contractile force generated by l-norepinephrine (NE). Effects mediated by each receptor type were measured independently by quantitative blockade of virtually all alpha 1-receptors with prazosin, or alpha 2-receptors with rauwolscine. Appropriate concentrations of the antagonists were calculated from dissociation constants previously determined by binding or competition with [3H]prazosin or [3H]rauwolscine in tissue homogenates. The contribution of alpha 1-adrenoceptors was larger than that of alpha 2-receptors in all vessels. The alpha 2-type was responsible for 38% of the maximum unblocked response to NE in saphenous vein, 32% in vena cava, and 28% in femoral artery. The occupation-response relationship for alpha 1-receptors was almost linear, without the marked upward convexity reported in some other vessels. alpha 2-Occupation-response curves were convex towards the occupation axis, with a relatively small response at low levels of occupation.

Changes in circulating blood volume influence aortic characteristic impedance in awake dogs.

Experiments on five chronically instrumented dogs were performed to study the effects of changes in circulating blood volume on the aortic smooth muscle activity in awake animals. The external diameter of the proximal descending aorta was measured with a sonomicrometer. Aortic pressure was measured in the same cross-sectional area with a catheter-tip transducer. Acute hemorrhage of 15% of the estimated blood volume was performed 17 times by quickly withdrawing blood through a jugular cannula. At any given arterial pressure within the range of overlap the aortic diameter (D) was always decreased after hemorrhage compared with control, and the pressure-strain elastic modulus (Ep) and the characteristic impedance (Zc) were always increased. For example at 140 kdyn X cm-2 (104.5 mmHg) delta D = -0.61 +/- 0.12 mm or delta D = -3.44 +/- 0.68% of control, delta Ep = 31.0 +/- 8.6%, and delta Zc = 22.6 +/- 4.5%. Each of these changes was significant with P less than 0.01. Volume expansion of 30% was performed eight times by infusing warm saline. At any given arterial pressure D was always increased and Ep and Zc were always decreased. At 140 kdyn X cm-2 delta D = 0.55 +/- 0.15 mm or delta D = 3.12 +/- 0.95% of control, delta Ep = -12.4 +/- 3.2%, and delta Zc = -12.0 +/- 2.1%. Each of these changes was significant with P less than 0.01. Since in these awake animals the changes in circulatory blood volume modified the arterial pressure only slightly, the contribution of viscoelasticity and myogenicity to the observed responses was minimal.

Changes in smooth muscle tone influence characteristic impedance of the aorta.

Experiments were performed on anesthetized dogs to quantitate the effects of changes in aortic smooth muscle tone on the passive pressure dependence of the aortic characteristic impedance (Zc). Zc was calculated from the diastolic pressure-diameter relationship in a wide pressure range induced by forced slow oscillations in pressure. Changes in aortic smooth muscle activity were induced by hemorrhage (-15% of the estimated blood volume), by volume expansion (+15 and +30%), and by alpha-adrenergic blockade. Curves relating Zc to pressure showed a minimum in the physiological pressure range and were well described by parabolas under all conditions. Under control conditions, the minimum Zc pressure was located close to the mean arterial pressure. Both levels of volume expansion as well as alpha-blockade reduced Zc at all pressure levels. Hemorrhage increased Zc at each pressure level and caused the minimum in the Zc vs. pressure curves to shift to higher values. The observed changes in Zc may play an important role in the hemodynamic adjustments to hemorrhage and to volume expansion.

Effects of blood volume changes on characteristic impedance of the pulmonary artery.

Experiments were performed on eight anesthetized dogs to study the response of the characteristic impedance (Zc) of the main pulmonary artery to changes in circulating blood volume. Pressure and flow were measured in the proximal main pulmonary artery under control conditions, after hemorrhage (-15% of the estimated blood volume), again under control conditions, and finally after volume expansion (+30% of the estimated blood volume). Two different methods were used to determine Zc from these recordings. With the frequency-domain method values for Zc were obtained by averaging the input impedance moduli between 2 and 15 Hz. With the time-domain method Zc was derived as the slope of the early ejection pressure-flow relationship. The values for Zc obtained with the two methods were not statistically different. In the time-domain method the average increase in Zc with hemorrhage was 30.7 +/- 7.4 (SE) %, and the average decrease with volume expansion was -21.1 +/- 5.0 (SE) %. Because the time-domain method allowed the values of Zc during control conditions and after hemorrhage to be obtained in the same pressure range, it was concluded that the observed changes were caused by a change in the activity of the smooth muscle in the pulmonary arterial wall. Similarly, it was concluded that the decrease in Zc after volume expansion was active in nature.

The effects of phenoxybenzamine on the aortic pressure-diameter relationship in dogs.

The normalized diameter (D/D13.3 where D13.3 equals D at 13.3 kPa under control conditions) was measured at selected pressure levels under different hemodynamic conditions. Hemorrhage caused the normalized diameter to decrease (-3.3%) when compared to control values at a given pressure. Volume expansion and alpha-blockade with phenoxybenzamine caused D/D13.3 to increase (+3.3% and +8.5% respectively).

Efficient use of a digital oscilloscope-computer combination in the physiology laboratory.

This communication outlines a system that has been implemented to interface a digital oscilloscope with a general purpose digital computer. The computer chosen was the Digital Equipment Corporation PDP 11/34, the oscilloscope chosen was the Nicolet Explorer III. To illustrate the capabilities of this combination, two examples of data analysis from our cardiovascular research laboratory were included. The combination of the two devices yields a more powerful research tool, which allows data manipulation beyond the capabilities of the oscilloscope.

Parotid CT sialography.

Computed tomographic (CT) scanning of the parotid gland during the injection of water-soluble contrast medium allows precise mapping of the gland's parenchyma and of any filling defects or extrinsic masses. Thirty-six patients were examined in this way. The most valuable information that was gained was the differentiation of extrinsic and intrinsic tumors and an accurate appraisal of the location of the facial nerve with respect to intrinsic parotid lesions. In the majority of patients the diagnosis of benign or malignant tumor is suggested by the patterns of tumor growth. Inflammatory disease shows diminution in the amount of parotid parenchyma in relationship to interstitial tissues, but the appearance is not sufficiently characteristic for definitive diagnosis.

Anomalous left pulmonary artery: two new adult cases.

Two adult cases of anomalous left pulmonary artery (pulmonary artery sling) are described. Findings on plain radiography, conventional pluridirectional tomography, and barium esophagography led to diagnosis. Computed tomography (CT), not previously described in this anomaly, was done in each case, confirming the diagnosis and excluding other mediastinal abnormalities. Pulmonary arteriography was incidentally performed in one patient and was diagnostic. Tracheobronchial anomalies were seen in both cases. The authors suggest the diagnosis of anomalous left pulmonary artery may be made by noninvasive conventional methods and CT without the need for pulmonary arteriography.

Response of systemic arterial input impedance to volume expansion and hemorrhage.

Experiments on 12 anesthetized dogs were performed to study the effects of changes in blood volume on the pulsatile hemodynamics of the arterial system as seen from its input. Pressure and flow were measured in the ascending aorta under control conditions, after volume expansion with dextran 70 (+30% of estimated blood volume), and after hemorrhage (-15% of estimated blood volume). The input inpedance of the arterial system was calculated for each condition. It was found that after volume expansion the characteristic impedance of the proximal aorta, Zc, was decreased by 26.6 +/- 5.1% (SE) (P less than 0.01). After hemorrhage Zc was increased by 30.4 +/- 3.4% (P less than 0.01). Since it is well known that Zc is a very weak function of the mean arterial pressure, it is concluded that the changes in Zc seen with volume expansion or hemorrhage are caused mainly by changes in aortic smooth muscle activity. This conclusion is also supported by direct measurements of aortic pressure diameter relationships in earlier work from our lab.

Jejunal intussusception in children.

Jejunal intussusception in children is an uncommon form of intussusception often presenting with chronic intermittent abdominal pain and weight loss. Two cases of jejunal intussusception caused by enteric duplication are presented. It is concluded that in the absence of generalized small bowel disease, enteric duplication is the most likely cause of jejunal intussusception in children.