No abstract

Although the airway conductance1 increases at larger lung volumes in normal subjects (1), it is reduced in patients with asthma or emphysema who are breathing with a large functional residual capacity (FRC) (2). We have therefore tried to assess the influence of other factors which might affect the airway conductance in both normal subjects and in patients with asthma, bronchitis and emphysema. These include the interrelationship of lung volume, lung elastic pressure and airway conductance, the effect of exercise, forced breathing and normal aging, and the composition of the respired gas and bronchomotor drugs. We investigated the balance of forces regulating the diameter of the airway lumen, i.e., the tone of the airway wall, directed inward, opposed by the traction of the lung tissues, directed outward. We studied whether, in normal subjects, this balance was altered by bronchmotor drugs or by a change in lung elastic pressure following chest strapping, and whether in patients with asthma, the airway conductance/lung volume relationship was altered after forced breathing or exercise. Patterns of disturbance leading to air trapping § Established Investigator of the American Heart Association.1 Airway conductance, the reciprocal of airway resistance, is defined as the rate of airflow at the mouth for unit pressure difference between alveolus and mouth. It was measured over the range of 0 to 0.5 L per second of inspiratory airflow.were studied in patients who had emphysema or bronchitis of toxic etiology. METHODSAirway resistance and thoracic gas volume were measured during panting2 using an upright body plethysmograph (2). The methods hinge on Boyle's law for compression of gases. Volume change owing to compression of gas inside the thorax is measured by -the equal and opposite small displacement of gas around the body. After appropriate calibrations, the intrathoracic gas volume changes found when rebreathing the air of the chamber through a heated flowmeter are converted mathematically to alveolar pressure changes, thence to airway resistance and airway conductance; or, when breathing against a closed shutter and manometer, to thoracic gas volume. In practice, these values are read directly from a precalibrated scale and protractor on the face of an oscilloscope, thus reducing labor. Esophageal pressure and mouth pressures were measured alternately using a capacitance manometer and Brush recorder. Lung elastic pressure (3) at each lung volume was measured as mean esophageal pressure, while panting (4). Chest constriction was accomplished by binding the subj ect's chest or abdomen, in the expiratory position, with adhesive tape or a long strip of rubber (4). Other tests of pulmonary function were performed according to generally accepted methods. All measurements were made with the subj ect in the sitting position. Lung volumes are expressed at BTPS. RESULTS ON HEALTHY SUBJECTSSpontaneous variation of airway resistance with time. The airway resistance of six healthy subjects was studied at 20 minute intervals o...

Intimal hyperplasia (IH), which causes occlusion of arterial bypass grafts and arteriovenous (A-V) shunts, develops preferentially in low wall shear, or stagnation, regions. Arterial geometry is commonly three-dimensional, generating swirling flows, the characteristics of which include in-plane mixing and inhibition of stagnation. Clinical arterial bypass grafts are commonly two-dimensional, favouring extremes of wall shear. We have developed small amplitude helical technology (SwirlGraft) devices and shown them to generate physiological-type swirling flows. Expanded polytetrafluorethylene (ePTFE) grafts, although widely used as A-V shunts for renal dialysis access, are prone to thrombosis and IH. In a small preliminary study in pigs, we have implanted SwirlGraft ePTFE carotid artery-to-jugular vein shunts on one side and conventional ePTFE carotid artery-to-jugular vein shunts contralaterally. There was consistently less thrombosis and IH in the SwirlGraft than conventional shunts. At eight weeks (two animals), the differences were marked, with virtually no disease in the SwirlGraft devices and occlusion of the conventional grafts by thrombosis and IH. The study had limitations, but the lesser pathology in the SwirlGraft devices is likely to have resulted from their geometry and the associated swirling flow. The results could have implications for vascular biology and prolongation of the patency of arterial bypass grafts and A-V shunts.

Cardiac myxoma (CM) is by far the most common primary benign cardiac tumor, typically arising in the left atrium with an attachment point in the fossa ovalis region. Although the etiology of CM remains unclear, we know that this endocardial-based mass originates from undifferentiated mesenchymal cells. Continuous technical improvements in the field of echocardiography since the 1960s has profoundly changed the diagnostic approach by allowing a good tumor detection as well as the preoperative planning by providing crucial information concerning the attachment point location. However, echocardiography has its limitations among which lack of tissue characterization and restricted field of view can arise diagnosis difficulties in atypical presentations. With the widespread and routine use of echocardiography and chest computed tomography (CT), incidental detection of CM is not infrequent. As a consequence, it has become mandatory for cardiologists and radiologists evolving in a multimodality imaging world to be familiar with the wide range of presentations of this tumor. The authors present here a review of the common and less common aspects of CM using the main imaging modalities available: echocardiography, cardiovascular magnetic resonance imaging, CT, positron emission tomography and coronary angiography.