of patients with diabetes, PAD, or both was determined using near-infrared spectroscopy (NIRS). ... The relative deoxygenation and oxygenation recovery times measured by ... A table elsewhere in this issue shows conventional and Syste`me International (SI) units and conversion .... fect on blood volume (data not shown).
Pathophysiology/Complications O R I G I N A L
A R T I C L E
Impaired Exercise-Induced Blood Volume in Type 2 Diabetes With or Without Peripheral Arterial Disease Measured by Continuous-Wave Near-Infrared Spectroscopy EMILE R. MOHLER, III, MD1 GWEN LECH, RN, MSNC2 GREGORY E. SUPPLE, MD1
HAO WANG, MS3 BRITTON CHANCE, PHD2
OBJECTIVE — Diabetes is a significant risk factor for peripheral arterial disease (PAD) and is associated with accelerated atherosclerosis and limb loss. However, the pathophysiology involved in PAD is unclear. This study was conducted to evaluate the hemodynamic response to exercise of patients with and without diabetes and PAD. RESEARCH DESIGN AND METHODS — The hemodynamic response in calf muscles of patients with diabetes, PAD, or both was determined using near-infrared spectroscopy (NIRS). Patients performed both a plantar-flexion and treadmill-walking exercise regimen. RESULTS — Skeletal muscle capillary blood volume expansion during exercise, as measured by NIRS, was significantly impaired in the lower extremities of diabetic patients with a normal ankle-brachial index. The relative deoxygenation and oxygenation recovery times measured by NIRS correlates significantly with the presence of PAD. CONCLUSIONS — Patients with diabetes have reduced capillary volume expansion even without PAD. This is likely due to impaired vasodilation secondary to endothelial dysfunction. Further studies are needed to determine whether pharmaceutical intervention improves the blood volume expansion in the diabetic state. Diabetes Care 29:1856 –1859, 2006
P
eripheral arterial disease (PAD) is a common manifestation of atherosclerosis and present in at least 25% of individuals over the age of 70 years (1,2). Diabetes, a well-recognized risk factor for PAD, may accelerate atherosclerosis and portends a pattern of infrapopliteal artery occlusive disease (3). Other tissue-damaging effects of hyperglycemia include those of capillary endothelial cells
in the retina, mesangial cells in the renal glomerulus, and neurons and Schwann cells in peripheral nerves. The pathophysiology of diabetic vascular disease in the extremities is complex, affecting large conduit vessels, microvessels, and skeletal muscle (4). Near-infrared spectroscopy (NIRS) provides real-time measurement of the levels of oxygenated and deoxygenated
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From the 1Cardiovascular Division, Vascular Medicine Section, Department of Medicine, University of Pennsylvania School of Medicine, Philadelphia, Pennsylvania; the 2Department of Biochemistry and Biophysics, University of Pennsylvania School of Medicine, Philadelphia, Pennsylvania; and the 3Center for Clinical Epidemiology and Biostatistics, Philadelphia, Pennsylvania. Address correspondence and reprint requests to Emile R. Mohler, III, MD, University of Pennsylvania School of Medicine, 4 Penn Tower, 3400 Spruce St., Philadelphia, PA 19104. E-mail: mohlere@ uphs.upenn.edu. Received for publication 24 January 2006 and accepted in revised form 24 April 2006. Abbreviations: ABI, ankle-brachial index; NIRS, near-infrared spectroscopy; PAD, peripheral arterial disease. A table elsewhere in this issue shows conventional and Syste`me International (SI) units and conversion factors for many substances. DOI: 10.2337/dc06-0182 © 2006 by the American Diabetes Association. The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore be hereby marked “advertisement” in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.
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hemoglobin/myoglobin in tissues (5). Prior studies have demonstrated that several NIRS measurements (such as deoxygenation and recovery times) significantly correlate with ankle-brachial index (ABI), a measure of limb pressure (6). One study indicates that NIRS correlates better with severity of exercise-induced pain than ABI in patients with PAD (7). Although several studies have evaluated NIRS in patients with PAD, there are no reports evaluating NIRS parameters in patients with diabetes and no evidence for hemodynamically significant PAD. The purpose of this study was to determine whether NIRS hemodynamic measurements are perturbed in patients with diabetes before development of hemodynamically significant PAD as measured with the ABI. RESEARCH DESIGN AND METHODS — S u b j e c t s w e r e r e cruited through the vascular laboratory at the University of Pennsylvania and from community exercise programs. The study was approved by the University of Pennsylvania Institutional Review Board. After signing informed consent, a total of 74 volunteers over the age of 50 years were recruited into four groups: 1) healthy control subjects (n ⫽ 25, 60% female), 2) diabetes only (n ⫽ 17, 18% female), 3) PAD only (n ⫽ 13, 23% female), and 4) diabetes and PAD (n ⫽ 19, 16% female). The diabetes-only group was defined as those patients diagnosed with type 2 diabetes by a physician and an ABI of ⬎0.9 and who had no claudication symptoms. The PAD-alone group was defined as those patients with an ABI of ⱕ0.9 and symptoms of claudication. The patients with PAD and diabetes were those with an ABI of ⱕ0.9 and symptoms of claudication, as well as a previous diagnosis of type 2 diabetes. DIABETES CARE, VOLUME 29, NUMBER 8, AUGUST 2006
Mohler and Associates Table 1—Demographics of study population
n Sex Male Female Age (years) Race African American Caucasian Other BMI (kg/m2) Smoking status Smokers Nonsmokers Hypertension Hypertensive Normotensive ABI
Control
Diabetes
PAD
PAD and diabetes
25
17
13
19
10 (40) 15 (60) 65.7 ⫾ 10.0
14 (82.3) 3 (17.7) 58.4 ⫾ 5.9
10 (76.9) 3 (23.1) 69.6 ⫾ 9.3
16 (84.2) 3 (15.8) 68.5 ⫾ 7.3
6 (24) 17 (68) 1 (4) 26.0 ⫾ 4.7
8 (47.1) 6 (35.3) 0 (0) 29.1 ⫾ 3.1
8 (61.5) 3 (23.1) 1 (7.7) 26.3 ⫾ 3.1
9 (47.4) 7 (36.8) 0 (0) 27.7 ⫾ 4.4
2 (8) 22 (88)
4 (23.5) 13 (76.5)
6 (46.1) 5 (38.5)
6 (31.6) 12 (63.2)
14 (56) 11 (44) 1.12 ⫾ 0.02
15 (88.2) 2 (11.8) 1.07 ⫾ 0.04
10 (76.9) 2 (15.4) 0.69 ⫾ 0.04
17 (89.5) 1 (5.3) 0.73 ⫾ 0.04
Data are n (%) or means ⫾ SD.
ABI measurement The ABI was measured after the subjects were supine on an examination table for 15 min. Subjects refrained from any significant physical activity for at least an hour before the test. Standard blood pressure cuffs were placed on both arms and both ankles, and systolic pressure was measured with a handheld continuouswave Doppler machine (Imex Elite; Nicolet Vascular, Conshohocken, PA). The ABI is calculated as a ratio of the ankle-toarm measurement of systolic pressure as previously published (8). The higher of the arm pressures is used as the denominator and the higher of the ankle pressures is used as the numerator for each respective right and left ABI. NIRS measurements The NIRS measurements were made using a continuous light source, dual-wavelength spectrophotometer (Runman) as previously published (9). The NIRS probe was placed on the belly of the medial gastrocnemious. For those with PAD, the probe was placed on the most symptomatic leg, and if bilateral claudication was present, the probe was placed on the leg with the most severely reduced ABI. After application of the probe, continuous measurements were obtained at baseline and during exercise. Subjects initially performed a 30 –plantar-flexion exercise over 1 min. After resting for 10 min, subjects walked on a treadmill according to the Gardner protocol (10). The subjects DIABETES CARE, VOLUME 29, NUMBER 8, AUGUST 2006
continued to the point of maximum claudication or up until 10 min of exercise. Of note, all hemodynamic parameters were allowed to return to normal before the next exercise phase of the study. NIRS analysis The total hemoglobin/myoglobin content (correspondent to blood volume in the vascular territory of the underlying muscle) and relative oxyhemoglobin amount (compared with resting baseline) was measured and graphed continuously during the exercise protocol. The blood volume expansion was calculated as the increase in measured volume over time (slope) during treadmill walking after the initial decrease due to muscle contraction. This calculation reflects the expansion of capillary blood volume. The blood deoxygenation was calculated as a percent change from baseline of measured oxyhemoglobin/myoglobin during exercise. The oxygen recovery time (T50) was calculated as the time it takes for oxygenation to return to half baseline after termination of exercise. Statistical analysis Linear models were used to evaluate difference among groups for each outcome of blood volume expansion, oxygen recovery time, and percent deoxygenation after plantar flexion or treadmill exercise. Since patients were not randomized to the four groups, group comparisons for NIRS measurements were adjusted with respect
to potential confounding factors, including age, race, sex, BMI, smoking status, and hypertension. P values ⬍0.05 were considered statistically significant. All analyses were carried out using SAS statistical software (version 9.1). RESULTS — The demographics of the study population are listed in Table 1. Of those enrolled in the study, there were more men than women with diabetes and PAD. The mean ABI was not significantly different between the PAD-alone and PAD with diabetes group (P ⫽ 0.44). Blood volume expansion A representative NIRS tracing is depicted in Fig. 1. The slopes of the mean values for blood volume expansion were calculated for all groups (Table 2). Group comparisons were adjusted for BMI and smoking status. Compared with healthy control subjects, the diabetes-only group did not show a significant difference in the change in blood volume during treadmill exercise. Their slope difference is ⫺0.0002 (95% CI ⫺0.0027 to 0.0023). The presence of PAD without diabetes was associated with a significant increase in the volume compared with control subjects (P ⫽ 0.039), and the difference between them in terms of the rate of blood volume expansion was 0.0032 (0.0002– 0.0062). However, diabetic patients with PAD had an attenuated blood volume response compared with PAD-only patients (P ⫽ 0.04). The rate of blood volume expansion for diabetes with PAD patients was 0.0031 units smaller than for PADonly patients (with 95% CI ⫺0.0064 to ⫺0.0001). The use of vasoactive medications (-blockers, calcium channel blockers, ACE inhibitors, and angiotensin receptor blockers) had no significant effect on blood volume (data not shown). The blood volume was not measured during plantar-flexion due to the brief period of exercise (1 min), which does not allow adequate time for responses unconfounded by blood volume changes from onset and cessation of exercise. T50 The mean values for T50 were calculated for all four groups to determine the relative oxygenation recovery time (Table 2). While diabetes had no effect (the ratio of T 50 for diabetes patients relative to healthy controls was 0.9 [95% CI 0.61– 1.4]), the presence of PAD significantly increased the T50. Compared with healthy control subjects, oxygen recovery time 1857
Impaired exercise-induced blood volume in diabetes
Figure 1—Representative example of NIRS measurement of deoxygenation and blood volume during treadmill walking in a healthy control subject compared with a subject with both diabetes and PAD. The arrow with T50 points to the line that is used to calculate the time it takes for oxygenation to return to half baseline (T50) after exercise. There was little change in blood volume during exercise in this patient as evidence from relatively flat slope. O, PAD/diabetes deoxygenation; ⽧, PAD/diabetes blood volume.
was 2.6 (1.6 – 4.1) and 2.4 (1.6 –3.6) times longer in PAD-only patients and patients with both PAD and diabetes, respectively. After adjusting for smoking status, race, and personal history of coronary artery disease, these comparisons remained significant.
Deoxygenation The mean values for deoxygenation were calculated in all four groups to determine the relative amount of desaturation of hemoglobin/myoglobin in the tissue (Table 2). The presence of claudication was associated with a significant increase in de-
oxygenation during both treadmill walking (P ⫽ 0.03) and plantar-flexion (P ⫽ 0.02) compared with healthy control subjects (P ⫽ 0.03). There was no significant increase in deoxygenation for the group with only diabetes during treadmill exercise or plantar-flexion com-
Table 2—NIRS measurements PAD
Diabetes Blood volume expansion Oxygen recovery time after plantar-flexion exercise (s) Deoxygenation during plantar-flexion exercise (%) Deoxygenation during treadmill exercise (%) No diabetes Blood volume expansion Oxygen recovery time after plantar-flexion exercise (s) Deoxygenation during plantar-flexion exercise (%) Deoxygenation during treadmill exercise (%)
Yes
No
0.00072 ⫾ 0.0069 62.11 ⫾ 46.97 18.79 ⫾ 17.61 14.25 ⫾ 16.0
0.0019 ⫾ 0.0017 22.57 ⫾ 12.55 7.61 ⫾ 7.33 6.11 ⫾ 9.04
0.0051 ⫾ 0.0076 60.58 ⫾ 37.38 17.50 ⫾ 16.61 17.75 ⫾ 16.34
0.0025 ⫾ 0.0020 26.09 ⫾ 20.29 10.42 ⫾ 11.66 6.38 ⫾ 10.96
Data are means ⫾ SD.
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Mohler and Associates pared with healthy control subjects (P ⫽ NS). CONCLUSIONS — This is the first report of impaired blood volume expansion with exercise in patients with diabetes despite a normal ABI and relatively normal parameters of deoxygenation and recovery times. The impaired blood volume expansion likely reflects a decrease in the vasodilatation capacity of capillaries in the skeletal muscle of the lower extremity during physical activity. Patients with diabetes are known to have endothelial dysfunction (11,12), and it is likely that microvascular dysfunction contributes to the impaired blood volume expansion seen in this study. Our study results also show that patients with PAD, but without diabetes, have increased blood volume during exercise compared with healthy control subjects, likely reflecting a greater local hypoxemia, causing a vasodilatation response. The hypoxemia may cause release of vasodilating factors such as lactate, CO2, and adenosine. The data indicate that patients with PAD and diabetes lose this ability to increase blood volume, indicating a severely blunted microvascular vasodilator response. Similar to a previously published study (6), the deoxygenation and recovery times were abnormal in patients with PAD. Tissue oxygenation, defined as relative saturation of oxyhemoglobin and myoglobin, depends on the balance between oxygen delivery, as reflected by the product of blood flow and oxygen content and metabolic rate or oxygen consumption. The normal response during exercise is a gradual decline in tissue oxygen saturation with increasing metabolic demand, and the initial response depends on exercise intensity. Our study results show that percent deoxygenation of hemoglobin and myoglobin occurs rapidly in both normal control subjects and those with PAD alone or with diabetes. The plateau level for percent deoxygenation is lower in the control group than in the patients with PAD, whereas the plateau for patients with diabetes and no PAD was not significantly different from healthy control subjects. The T50, a measure of oxygen recovery, is longer in patients with PAD compared with control patients, whereas the blood volume expansion is higher in PAD than control subjects and significantly lower in those with diabetes. The pathologic influences resulting from the hyperglycemic state and resultDIABETES CARE, VOLUME 29, NUMBER 8, AUGUST 2006
ing in endothelial dysfunction are multifactorial and include advanced glycation end products, increased formation of oxygen-derived free radicals, and activation of protein C (13). The presence of PAD results in reduced endothelium-derived vasodilator prostanoids and nitric oxide (4). The current study results indicate that a unique aspect of the diabetic state is impairment of blood volume during exercise that does not appear evident in patients without diabetes and hemodynamically significant lower extremity atherosclerosis. Our results are consistent with those of Kingwell et al. (14), who found that limb blood flow response to acetylcholine and exercise were significantly attenuated in patients with diabetes compared with healthy control subjects. Also, others have shown that impaired limb blood flow response to exercise may limit exercise capacity in patients with type 2 diabetes (15–17). In conclusion, our study results indicate that the impaired blood flow response occurs early in diabetic vasculopathy and may occur before hemodynamically significant PAD. These findings may partly explain the accelerated atherosclerosis observed in patients with diabetes. Further studies are needed to determine whether impaired blood volume expansion in the diabetic state portends increased risk of developing PAD. Acknowledgments — We thank Elizabeth Medenilla for her assistance with treadmill testing. References 1. Criqui MH, Fronek A, Barrett-Connor E, Klauber MR, Gabriel S, Goodman D: The prevalence of peripheral arterial disease in a defined population. Circ 71:510 –515, 1985 2. Hirsch AT, Criqui MH, Treat-Jacobson D, Regensteiner JG, Creager MA, Olin JW, Krook SH, Hunninghake DB, Comerota AJ, Walsh ME, McDermott MM, Hiatt WR: Peripheral arterial disease detection, awareness, and treatment in primary care. JAMA 286:1317–1324, 2001 3. Beckman JA, Creager MA, Libby P: Diabetes and atherosclerosis: epidemiology, pathophysiology, and management. JAMA 287:2570 –2581, 2002 4. Creager MA, Luscher TF, Cosentino F, Beckman JA: Diabetes and vascular disease: pathophysiology, clinical consequences, and medical therapy: Part I. Circ 108:1527–1532, 2003 5. Breit GA, Gross JH, Watenpaugh DE, Chance B, Hargens AR: Near-infrared
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