Adult respiratory-distress syndrome: changing concepts of lung injury and repair.

Assessment of passive elastic stiffness of cardiac muscle: mathematical concepts, physiologic and clinical considerations, directions of future research.

Hyperbaric oxygen therapy involves intermittent inhalation of 100% oxygen under a pressure greater than 1 atm. Despite over a century of use in medical settings, hyperbaric oxygen remains a controversial therapy. The last 20 years have seen a clarification of the mechanism of action of hyperbaric therapy and a greater understanding of its potential benefit. However, despite the substantial evidence that hyperbaric oxygen may have a therapeutic effect in certain carefully defined disease states, many practitioners remain unaware of these findings or are concerned about using hyperbaric therapy because of the controversy it has engendered. This review examines the indications currently considered appropriate for hyperbaric oxygen and briefly evaluates animal and clinical data substantiating these indications. Areas in which the mechanism of action of hyperbaric oxygen is still not well understood, as well as possible new areas of applications, are discussed. (JAMA. 1990;263:2216-2220)

https://jamanetwork.com/HttpHandlers/ArticlePdfHandler.ashx?journal=JAMA&articleId=381546&pdfFileName=jama_263_16_042.pdf

Hyperbaric oxygen therapy.

Based on a literature search, an overview is presented of the pathophysiology of venous and arterial gas embolism in the experimental and clinical environment, as well as the relevance and aims of diagnostics and treatment of gas embolism. The review starts with a few historical observations and then addresses venous air embolism by discussing pulmonary vascular filtration, entrapment, and the clinical occurrence of venous air emboli. The section on arterial gas embolism deals with the main mechanisms involved, coronary and cerebral air embolism (CAE), and the effects of bubbles on the blood-brain barrier. The diagnosis of CAE uses various techniques including ultrasound, perioperative monitoring, computed tomography, brain magnetic resonance imaging and other modalities. The section on therapy starts by addressing the primary treatment goals and the roles of adequate oxygenation and ventilation. Then the rationale for hyperbaric oxygen as a therapy for CAE based on its physiological mode of action is discussed, as well as some aspects of adjuvant drug therapy. A few animal studies are presented, which emphasize the importance of the timing of therapy, and the outcome of patients with air embolism (including clinical patients, divers and submariners) is described.

Gas embolism: pathophysiology and treatment

In patients with drug-resistant hypertension, chronic electric stimulation of the carotid baroreflex is an investigational therapy for blood pressure reduction. We hypothesized that changes in cardiac autonomic regulation can be demonstrated in response to chronic baroreceptor stimulation, and we analyzed the correlation with blood pressure changes. Twenty-one patients with drug-resistant hypertension were prospectively included in a substudy of the Device Based Therapy in Hypertension Trial. Heart rate variability and heart rate turbulence were analyzed using 24-hour ECG. Recordings were obtained 1 month after device implantation with the stimulator off and after 3 months of chronic electric stimulation (stimulator on). Chronic baroreceptor stimulation decreased office blood pressure from 185+/-31/109+/-24 mm Hg to 154+/-23/95+/-16 mm Hg (P<0.0001/P=0.002). Mean heart rate decreased from 81+/-11 to 76+/-10 beats per minute(-1) (P=0.001). Heart rate variability frequency-domain parameters assessed using fast Fourier transformation (FFT; ratio of low frequency:high frequency: 2.78 versus 2.24 for off versus on; P<0.001) were significantly changed during stimulation of the carotid baroreceptor, and heart rate turbulence onset was significantly decreased (turbulence onset: -0.002 versus -0.015 for off versus on; P=0.004). In conclusion, chronic baroreceptor stimulation causes sustained changes in heart rate variability and heart rate turbulence that are consistent with inhibition of sympathetic activity and increase of parasympathetic activity in patients with drug-resistant systemic hypertension; these changes correlate with blood pressure reduction. Whether the autonomic modulation has favorable cardiovascular effects beyond blood pressure control should be investigated in further studies.

Effects of Chronic Baroreceptor Stimulation on the Autonomic Cardiovascular Regulation in Patients With Drug-Resistant Arterial Hypertension

Specific Therapy for Arterial Air Embolism

The membrane lung

In recent years the effects of chronic pressure load upon the left ventricle have been studied from the anatomical and the hemodynamic point of view. The main question which is still not clearly answered is whether the left ventricular hyper t rophy causes an increase, a decrease or no change in contractile function. In rats with aortic constriction it was demonstrated tha t maximal cardiac output following polyvinylpyrrolidone infusion was larger than in normal animals (4). These findings suggested tha t the myocardial \"reserve toree\" was increased in the hypertrophied hearts. In the isovolumically contracting left ventricle of rabbits with myocardial hyper t rophy M E ~ s o N and PSKE~NIKOVA (20) observed a higher left ventricular peak pressure (Pmax.) and a higher left ventricular tension-time-index (TTI) than in the control animals. When Pmax. and T T I were calculated per unit left ventricular weight, however, the values were smaller in the hypertrophied hearts than in the normal ones, indicating an overall decrease in performance of the hypertrophied left ventricle. Finally, an unchanged contractile force per cross sectional wall area, in hypertrophied left ventricles of humans with aortic stcnosis, was reported by SANDLER and DODGE (3) and, in the conscious dog, the work performance per unit of gross myocardial mass of the hypertrophied right ventricle was found not to be less than normal (10). In all these observations, the assessment of the contractile state appears to be based exclusively upon parameters which, in terms of fundamental muscle mechanics (9), reflect only the force development of the hypertrophied chamber. The studies appear incomplete because the velocity aspects of vcntricular

E. Converse Peirce

Papers

Specific Therapy for Arterial Air Embolism

The membrane lung

Left ventricular dynamics in the dog under chronic pressure load from coarctation of the aorta

Techniques of Extended Perfusion Using a Membrane Lung

The membrane versus bubble oxygenator controversy.