Altered exercise gas exchange as related to microalbuminuria in type 2 diabetic patients.

STUDY OBJECTIVE

Microalbuminuria in diabetes mellitus is a risk factor for cardiovascular disease. We hypothesized that microalbuminuria in type 2 diabetic patients is related to impaired cardiopulmonary function during exercise, and that the severity of impairment is correlated with the degree of microalbuminuria.

DESIGN

Twenty of each of the following categories of subjects performed symptom-limited cardiopulmonary exercise testing on a cycle ergometer: (1) type 2 diabetic patients with normoalbuminuria (daily urinary albumin excretion [UAE] < 30 mg/d); (2) type 2 diabetic patients with microalbuminuria (daily UAE, 30 to 300 mg/d); and (3) normal control subjects.

MEASUREMENTS AND RESULTS

Oxygen consumption (VO(2)) of patients with microalbuminuria was lower than that of control subjects at anaerobic threshold (AT) [p < 0.001], and was lower than both control subjects (p < 0.001) and patients with normoalbuminuria (p = 0.015) at peak exercise. There was a progressive worsening in gas exchange efficiency at the lungs, as measured by minute ventilation (VE)/carbon dioxide production (VCO(2)) at AT or DeltaVE/DeltaVCO(2) slope, (p = 0.006 and p = 0.019, respectively) going from control subjects to patients with normoalbuminuria and then to patients with microalbuminuria. Left ventricular ejection fractions and BP were similar in patients with normoalbuminuria and microalbuminuria. More patients with microalbuminuria (n = 9) than with normoalbuminuria (n = 2) demonstrated diastolic dysfunction (p = 0.013). These 11 patients had lower peak VO(2) values (p = 0.001) and higher daily UAE (p = 0.028). An inverse linear relationship was found between peak VO(2) and log(10) daily UAE (r = - 0.57, r(2) = 0.29, p < 0.001).

CONCLUSIONS

Abnormalities reflecting reduced oxygen transport and impaired gas exchange efficiency were found during exercise, and were especially profound in patients with microalbuminuria. These changes could be secondary to pulmonary microangiopathy and myocardial interstitial changes. Increases in capillary permeability to proteins may take place in the myocardium as they do in the kidneys, and contribute to impaired myocardial distensibility and hence diastolic dysfunction.