Another potential mechanism of weight loss in COPD patients is tissue hypoxemia. Oxygen consumption is often elevated in patients with COPD because of increased work of breathing. However, the ability to meet this increased demand may be limited in patients with COPD, particularly patients with emphysema. It has been known for some time that COPD patients with characteristics of emphysema are more likely to demonstrate malnutrition and a low body weight than patients with chronic bronchitis. One of the major differences between these groups of patients is the Dlco. read more
Emphysema patients demonstrate a lower cardiac index, a higher arteriovenous oxygen difference, and an inability to increase cardiac output during exercise. This inability to increase oxygen delivery in the face of increased oxygen consumption, especially by the respiratory muscles, could lead to a relative tissue oxygen debt. Patients with COPD and low oxygen levels demonstrate deficiencies in muscle levels of high-energy phosphate compounds that can be reversed with oxygen, leading to speculation that energy deficiency due to tissue oxygen debt could result in loss of tissue mass. A recent study by Pouw et al supports this speculation. That study examined concentrations of adenine nucleotides in muscle biopsies of COPD and control patients. A subset of patients was found to have high levels of inosine monophosphate, a deamination product of adenosine monophosphate, that is thought to reflect an imbalance between resynthesis and utilization of adenosine triphosphate. These patients were characterized by a significantly lower Dlco. This subset of patients also had a trend toward a lower BMI. Thus, patients with impaired oxygen transfer may have biochemical changes in the muscle that leave them prone to weight loss.