August 2002 / Volume 47 / Number 8 / Page 887
Maintaining Oxygenation via Demand Oxygen Delivery During Rest and Exercise
The primary goals of medical care for patients with chronic lung disease are to manage the disease, improve physical and psychological function, and enhance quality of life. Oxygen therapy for patients with chronic obstructive pulmonary disease and hypoxemia is directed toward maintaining oxygen saturation at rest and preventing desaturation during exercise and sleep. Several portable oxygen systems have been designed to provide adequate oxygenation while minimizing the size and weight of the oxygen system. Further benefit is achieved through the use of portable systems that promote ambulation away from the home.
See The Related Editorial on Page 879
Portable oxygen supports chronic lung disease patients' ability to maintain an active lifestyle and participate in many of life's pleasures, thus improving quality of life. Oxygen conservation technology is among the most important developments in portable oxygen therapy in recent years. As the efficiency of oxygen delivery devices improve, these devices become smaller and more portable, thereby reducing the burden on the patient, from both an economic and physical perspective. A variety of oxygen-conserving devices, including reservoir cannulas, transtracheal catheters, and demand oxygen delivery systems (DODS), have provided the hypoxemic patient with choices and tradeoffs. The most efficient of these systems is the DODS, which delivers oxygen early in the inhalation phase, ensuring that a bolus of oxygen reaches the alveoli and avoiding the waste of oxygen that occurs with systems that deliver oxygen throughout inhalation and exhalation. DODS oxygen-use efficiency ranges from 2-fold to 7-fold better than continuous-flow oxygen delivery. That is, DODS can achieve the same oxygen saturation levels as continuous flow while using only one half to one seventh the oxygen.
Previous studies found DODS effective during rest, sleep, and exercise. Recently, however, it became apparent that some DODS users desaturate during exercise at DODS settings that correspond to continuous flow. In other words, DODS settings equivalent to continuous flow were insufficient to achieve equivalent oxygen saturation. That difference in equivalency between rest and exercise appears to result from several physiologic and mechanical factors. In an attempt to improve on several of those factors and fully meet the oxygenation needs of patients who do not adequately saturate with existing DODS during exercise, one of the DODS models, the Oxymatic 401 (CHAD Therapeutics, Chatsworth, California), was redesigned. Specifically, the pulse volume and sensitivity to inspiratory flow were increased, the delivery waveform was modified, and higher flow settings were added, all while retaining the DODS oxygen-use efficiency advantage.
The present study was designed to investigate if those design modifications achieve adequate oxygenation in DODS patients who desaturate during exercise.