Concentrations On Maximal Exercise Capacity Or Ventilation
In Stable Heart Failure Essay, Research Paper
Critical Inquiry 10/31/00
The goal of the article, (Lack of Effect of Increased Inspired Oxygen Concentrations on Maximal Exercise Capacity or Ventilation in Stable Heart Failure. The American Journal of Cardiology, 84(12), Dec.15, 99. pp 1412-1416.) is to further study the effects of administration of increased inspired oxygen concentrations on maximal exercise capacity and exercise ventilation in heart failure. Recent uncontrolled studies have suggested improvement on maximal exercise capacity and a decreased exercise ventilation.
This study used 21% as normal and 60% as increased inspired oxygen concentrations. 16 patients performed staged, symptom-limited cycle ergometry using a randomized, double-blind, crossover study design. Measurements of minute ventilation, heart rate, blood pressure, leg blood flow, and arterial and venous lactate and oxygen content were obtained. The exercise times for the 2 categories did not differ (595 ? 179 seconds and 602 ? 181 seconds for 21% and 60% oxygen concentrations, respectively). Similarly there was no significant difference in any of the readings that were monitored between the 2 groups. It seems that supplemental oxygen is accepted as therapy in patients with decompensated heart failure. In this case patients have lowered hemoglobin oxygen saturation so higher concentrations could raise the hemoglobin oxygen saturation, reverse pulmonary vasoconstriction and enhance oxygen delivery to vital organs. Since this and other studies have tested patients who have normal hemoglobin oxygen concentrations even during maximal exercise, there is no way to increase oxygen uptake to the exercising limbs.
The patients in the study were men with New York Heart Association class II to III heart failure symptoms and severe left ventricular dysfunction. Mean age was 56 ? 9 years, and ejection fraction was 18 ? 6%. No patient was a current smoker. The exercise protocol was first to give a familiarization test. The patients performed pulmonary function tests including spirometry and maximum voluntary ventilation test. Then they performed an upright exercise test on an electronically braked cycle ergometer. This included a 2-minute resting period followed by increasing workloads of 25W every 3 minutes until limited by fatigue and / or shortness of breath. All tests were performed in the fasting state. Breath-by-breath ventilation, oxygen uptake, and carbon dioxide production were continuously measured through a mouthpiece connected to a metabolic cart. The EKG was continuously monitored and blood pressure was measured with sphygmomanometer. After the patients had undergone the familiarization test, they returned usually within 7 days ( 2 patients returned 27 and 34 days later), for randomized testing. A thermodilution catheter was placed into the iliac vein (via femoral vein access) under fluoroscopic guidance and was interfaced with a Gould Statham SP 1435 cardiac output computer. For continuous blood pressure monitoring a 18-gauge cannula was placed in the brachial artery. After a 20-minute rest period patients randomly breathed either 21% or 60% humidified air. Patients breathed through a 3-way nonrebreathable mouthpiece connected to a system of a 170L nondiffusable reservoir bag, a humidifier, and interchangeable tanks of 21% and 60% oxygen. Everyone involved was blinded to the oxygen concentrations. After a 10-minute equilibration period, patients performed the same protocol as in the familiarization test. During each 3-minute workload, measurements of femoral vein lactate and oxygen content, and arterial lactate and oxygen were obtained. Breath-by-breath measurements of ventilation were also acquired. Blood pressure was monitored via the arterial line. Patients rested 1-hour then repeated the protocol with the other concentration of gas.
Although the people used in this test would be harder to locate than normal healthy people I feel that 16 people is to small of a population to get maximal results. In this case the amount of participants may be invalid since performing this test on any population whose oxygen concentration is normal would be inconclusive. You cannot under the conditions of this test increase oxygen concentration of an already fully saturated patient. This study is very repeatable but useless to repeat if you look at the inability to saturate above normal levels. This test reminds me of testing athletes who breath oxygen on the sideline after a long run. Just like the test above if the athlete is already at 97% saturation, supplying oxygen has no effect on recovery or uptake.
As stated in my explanation, the study concluded that they failed to demonstrate any benefit in exercise performance with the administration of 60% oxygen to patients with chronic stable heart failure. Under conditions of normoxia (21%) and hyperoxia (60%), maximal exercise time, ventilation, and leg oxygen uptake were virtually identical.
In my conclusion, unless the question is whether or not people with chronic stable heart failure have a lower oxygen saturation percentage, then the results of this test could have been deduced from knowledge of oxygen saturation principles.