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The human aorta and its terminal branches were investigated in normal subjects during elective cardiac catheterization to evaluate regional wave travel and arterial wave reflections. A specially designed catheter with six micromanometers equally spaced at 10 cm intervals was positioned with the tip sensor in the distal external iliac artery and the proximal sensor in the aortic arch. Simultaneous pressures were obtained and analyzed for foot-to-foot wave velocity, and Fourier analysis was used to derive apparent phase velocity. These quantities were assessed during control (n = 9), during Valsalva (n = 8) and Muller (n = 4) maneuvers, and during femoral artery occlusion by bilateral manual compression (n = 8). During control, regional cross-sectional areas, determined from aortography, and regional foot-to-foot pulse wave velocities were used to calculate the local reflection coefficient in the proximal descending aorta (F = 0.05), at the junction of the renal arteries (F = 0.43), and at the terminal aortic bifurcation (F = 0.13). To test the hypothesis that significant reflections originate in the aorta, at the level of the renal arteries, aortograms were used to design a latex tube model with geometric properties similar to the descending aorta. Velocities and reflection characteristics in the model and in vivo were compared. Inspection of thoracic aortic pressures under control conditions revealed a reflected wave originating from the region of the aorta at the level of the renal arterial branches while abdominal pressures exhibited reflection from a site peripheral to the terminal aortic bifurcation. In the low frequency range, apparent phase velocity was found to be higher proximal to the renal arteries as compared with at the distal sites. In addition, the minimum value occurred at a higher frequency in the lower thoracic aorta than at more distal sites. The effects of reflection on apparent wave velocity in the tube model were consistent with data obtained in vivo. The Valsalva maneuver diminished the reflection from the aortic region of the renal arteries, thus allowing the distal reflected wave to become more evident on the thoracic pressure waveforms. Bilateral femoral artery occlusion usually enhanced the distal reflection and the Muller maneuver usually resulted in small increases in reflections. In conclusion, the geometric and elastic nonuniformity of the aorta results in two major sites of arterial wave reflection that influence the aortic pressure waveforms in man. The first major reflection site is located at the aortic level of the renal arterial branches and the second reflection site is located distal to the terminal aortic bifurcation. Circulation 72, No. 6, 1257No. 6, -1269No. 6, , 1985 ALTERATIONS in the contour of the pressure wave along the aorta have been noted since the turn of the century,'-' but the mechanisms responsible for these changes have not been fully explained.

OBJECTIVE -In some studies intensive diabetes treatment in patients with type 2 diabetes may be associated with increased cardiovascular events. It is not clear whether these events are related to hypoglycemic episodes. To determine whether episodes of hypoglycemia were more likely to be associated with cardiac ischemia than normoglycemia or hyperglycemia, we carried out a study in 21 patients with coronary artery disease (CAD) and type 2 diabetes treated with insulin who had good glycemic control.RESEARCH DESIGN AND METHODS -We carried out 72-h continuous glucose monitoring along with simultaneous cardiac Holter monitoring for ischemia. Patients also recorded symptoms of cardiac ischemia (chest pain) and symptoms of hypoglycemia.RESULTS -Satisfactory continuous glucose monitoring system recordings were obtained in 19 patients. We recorded 54 episodes of hypoglycemia (blood glucose Ͻ70 mg/dl; 26 of these were symptomatic) and 59 episodes of hyperglycemia (blood glucose Ͼ200 mg/dl; none symptomatic). Of the 54 episodes of hypoglycemia, 10 were associated with symptoms of chest pain, during 4 of which electrocardiographic abnormalities were documented. In contrast, only 1 episode of chest pain occurred during 59 episodes of hyperglycemia. No chest pain or electrocardiographic abnormalities occurred when the blood glucose was within the normal range. The difference between the frequency of ischemia during hypoglycemia and the frequency during both hyperglycemia and normoglycemia was statistically significant (P Ͻ 0.01). There were 50 episodes during which the blood glucose changed by Ͼ100 mg over a 60-min period, and ischemic symptoms occurred during 9 of these episodes (P Ͻ 0.01 compared with stable normoglycemia or hyperglycemia).CONCLUSIONS -Hypoglycemia is more likely to be associated with cardiac ischemia and symptoms than normoglycemia and hyperglycemia, and it is particularly common in patients who experience considerable swings in blood glucose. These data may be important in the institution of insulin treatment and attempting near-normal glycemia in patients with known CAD. Further research is needed to determine strategies to prevent ischemia associated with hypoglycemia. Diabetes Care 26:1485-1489, 2003D iabetes is associated with an increased risk of development of coronary artery disease (CAD). Patients with CAD and diabetes have higher mortality and morbidity than patients without diabetes. Data from studies such as the U.K. Prospective Diabetes Study suggest that very good glycemic control is associated with fewer cardiovascular events (1). However, tight glycemic control may increase the risk of hypoglycemia. Increased cardiovascular events were noted in the Veterans Affairs Cooperative Study on Glycemic Control and Complications (VA CSDM), after the institution of tight glycemic control (2). It is possible that acute hypoglycemia may trigger ischemia and cardiovascular events. Hypoglycemia and rapid changes in blood glucose have been shown to increase counterregulatory hormones such as epinephrine ...

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SUMMARY Dramatic changes in the shape of pulsatile ascending aortic pressure and flow wave forms occur during the Valsalva maneuver in man. To study these changes, aortic pressure and flow signals were recorded in eight patients using a multisensor catheter. Aortic input impedance was derived during the control, strain and postrelease phases of the Valsalva maneuver. During control, well-defined minima and maxima occurred in the spectral plots of impedance moduli. This pattern was accentuated during the postrelease phase. In contrast, input impedance during strain was almost equal to the characteristic impedance for all harmonics. These results imply that during the control and postrelease phases, strong reflections return to the ascending aorta, but during the strain phase, reflections are minimal, absent or more diffuse. From wave transmission theory, it also follows that pulsatile pressure and flow wave forms should be similar in shape in the absence of reflections and dissimilar in the presence of reflections. This was observed in all eight patients. By provoking changes in the arterial tree during the Valsalva maneuver, the magnitude and timing of wave reflections were significantly altered, resulting in marked changes in the shape of pulsatile aortic pressure and flow wave forms. This study demonstrates the importance of reflections in determining the shape of the arterial pulse.THE SHAPES of ascending aortic pressure and flow wave forms are determined by cardiac function and the mechanical and geometric properties of the systemic arteries. The contribution of the arterial vascular tree to aortic pressure and flow wave shapes has been evaluated by calculation of aortic input impedance in the experimental animal' and in man.2 These studies have demonstrated that arterial wave forms are influenced by the presence of wave reflections in the arterial system.The Valsalva maneuver results in dramatic changes in the aortic pressure and flow wave shapes.3 4 The hemodynamic changes during the Valsalva maneuver have been studied by numerous investigators;5'-9 however, studies of the effects of this intervention on pulsatile pressure and flow have been extremely limited,3 and an analysis of the changes in aortic input impedance in normal man has not been reported. Mills et al.4 analyzed input impedance of the ascending and descending aorta in a patient with ischemic heart disease during the Valsalva maneuver. Although

Although the mouse is the most commonly used transgenic species, little is known regarding cardiovascular and fluid homeostasis in this animal. Therefore, the reference microsphere and dilution techniques were adapted for the measurement of cardiac output (CO), regional blood flows, and intravascular fluid volumes in the conscious mouse. Previously acclimatized C3H mice were studied 4-5 h after surgery and recovery from anesthesia. Approximately 40,000 85Sr-labeled microspheres were injected into the left ventricle while a reference sample was withdrawn at one of two rates from the femoral artery. 51Cr and 125I were used for the determination of blood volume (BV), plasma volume (PV), and Fcells ratio (whole body hematocrit/large vessel hematocrit). CO and BV in the conscious mouse were 16 +/- 1.4 ml/min and 2.3 +/- 0.1 ml, respectively. Anesthesia lowered heart rate, blood pressure, PV, and altered the distribution of CO. Two successive injections of 15,000-20,000 microspheres were tolerated in the mouse without an increase in total peripheral resistance. The results indicate that the microsphere and indicator dilution techniques can be applied to study cardiovascular and fluid homeostasis in the mouse.

SUMMARY. Input impedance of the pulmonary arterial system was determined in 10 subjects undergoing elective cardiac catheterization. No cardiovascular or pulmonary disease was found in these patients. In five of the subjects, systemic arterial input impedance was also obtained, so that both systems could be compared. Pulmonary and systemic peripheral resistances were 79 ± 9 dynes sec/cm 5 (mean ± SEM) and 1016 ± 50 dynes sec/cm 5 , respectively. Characteristic impedance of the pulmonary circulation was lower than the characteristic impedance of the systemic circulation: 20 ± 1 dynes sec/cm 5 vs. 47 ± 9 dynes sec/cm ! , respectively. Pulmonary pressure and flow spectra for both systems are also presented. The amplitudes of the harmonics of pressure and flow are smaller for the pulmonary circulation, which is consistent with the lower pressures and more rounded waveforms of the normal pulmonary circulation. In all 10 subjects, input impedance of the pulmonary system was examined during both the inspiratory and expiratory phases of respiration. There was no difference between inspiration and expiration in either pulmonary vascular resistance (77 ± 10 dynes sec/cm ! vs. 80 ± 9 dynes sec/cm 5 , respectively), characteristic impedance (20 ± 1 dynes sec/cm 5 vs. 20 ± 1 dynes sec/cm 5 ) or in the overall impedance spectrum. Quiet respiration, thus, has no effect on the pulmonary arterial load, and changes in pressure and flow must result from alterations in right ventricular performance. (CircRes 54: 666-673, 1984) UNLIKE the systemic circulation, the pulmonary vascular system in normal man is a low pressure system which is entirely exposed to changes in intrathoracic pressure during respiration. The effects of these changes on the physical characteristics of the human pulmonary circulation are unknown. It is of physiological and clinical importance to know how the pulmonary vasculature is affected by respiration, especially when evaluating the relationships between this vascular bed and right ventricular function. To study such effects, it is necessary to describe the pulmonary circulation in quantitative terms. One method is to calculate pulmonary input impedance. The input impedance of a vascular bed not only provides information about the pulsatile pressure-flow relationships, but also yields information regarding the physical characteristics of that bed (Randall and

SUMMARY The effects of supine bicycle exercise on the input impedance of the ascending aorta were studied in thirteen male subjects undergoing cardiac catheterization, but in whom no cardiovascular disease was found. Ascending aortic flow velocity and pressure were recorded simultaneously from a multisensor catheter with an electromagnetic flow velocity probe and a pressure sensor mounted at the same location. A second pressure sensor at the catheter tip provided left ventricular pressure. Fick cardiac outputs were used to scale the velocity signal to instantaneous volumetric flow. Input impedance was calculated from 10 harmonics of aortic pressure and flow. For each subject, impedance moduli and phases from a minimum of 15 beats during rest and exercise were averaged. Peripheral resistance decreased from a resting value of 1142 ± 51 (± SE) dynes sec/cm 6 to 712 ± 39 dynes sec/cm 6 during exercise. Characteristic impedance remained unchanged with a resting value of 47 ± 4 dynes sec/cm 5 and an exercise value of 45 ± 4 dynes sec/cm 5 . These results were associated with an increase in aortic pressure (96 ± 2 to 111 ± 2 mm Hg) and pulse wave velocity implying a decrease in aortic compliance. An increase in aortic cross-sectional area apparently offsets the effects of these changes in compliance and pulse wave velocity to result in an unchanged characteristic impedance. The increase in pulse wave velocity caused wave reflections to occur earlier during exercise, but the general characteristics of the pressure wave shapes remained unchanged. Circ Res 48: 334-343, 1981