from january 1999 to december 2000 , aft was performed on patients aged 2575 years who had type 2 diabetes at the university - affiliated diabetes center of st .
patients with normal aft results were recruited ( n = 1,021 ) and received follow - up aft from january 2006 to february 2008 .
patients were excluded if they were > 75 years old , if they were mentally ill or unable to undertake the test , if they had arrhythmia including atrial fibrillation , or if they had any severe illness , such as malignancy , severe infection , severe hypoglycemia , liver cirrhosis , heart failure , or alcoholism .
our institutional ethics committee approved the study . at the beginning of the study , patient height , body weight , and systolic and diastolic blood pressure
hypertension was defined as systolic blood pressure 140 mmhg or diastolic blood pressure 90 mmhg or as any use of antihypertensive medications .
fasting and postprandial plasma glucose levels were measured using an automated enzymatic method and a1c levels were determined by high - performance liquid chromatography with a reference range of 4.46.4% .
a1c levels were measured every 6 months to evaluate the status of glycemic control during the follow - up period .
blood lipid concentrations for total cholesterol , triglycerides , and hdl cholesterol were measured enzymatically using an automatic analyzer ( model 736 - 40 ; hitachi , tokyo , japan ) .
biochemical laboratory tests were performed at baseline and at the follow - up time points .
cardiovascular aft was performed by one examiner using the ewing method , which includes tests for heart rate variability , such as the expiration - to - inspiration ( e / i ) ratio and responses to the valsalva maneuver and to a postural change from lying to standing ( 2,6,14 ) .
patients were asked to fast for 12 h before aft and to avoid taking antidepressants , neuroleptics , caffeine , nicotine , or antihistamines .
the e / i ratio was calculated as the mean of the longest r - r interval during expiration divided by the mean of the shortest r - r interval during inspiration .
the ratio of postural change was the ratio of the longest r - r interval during beats 2040 after standing to the shortest r - r interval during beats 525 after standing .
for the heart rate response to the valsalva maneuver , the ratio of the longest r - r interval to the shortest r - r interval was checked during forced exhalation into the mouthpiece of a manometer to 40 mmhg for 15 s ( 2,14 ) .
an e / i ratio below the age - related reference value , a valsalva ratio < 1.2 , and a posture ratio < 1.03 were considered abnormal ( 14 ) .
each of the three items was scored as 0 for normal or 1 for abnormal , to a maximum score of 3 .
normal aft was defined as a score of 0 , and can was defined on the basis of at least one abnormal standard test .
progression of can was defined as an increase in a follow - up aft score from the baseline value ( a score of 0 ) to a score of 13 ; such patients were designated the  progressor  group .
 nonprogressors  were defined as type 2 diabetic patients whose can scores did not show any increase at the follow - up time point .
the urinary albumin excretion ( uae ) rate was measured by enzyme immunoassay from a single 24-h urine collection ( 15 ) using immunoturbidimetry ( eiken , tokyo , japan ) .
patients were classified into three groups : those with no diabetic nephropathy ( uae < 20 g / min ) , those with microalbuminuria ( mau ) defined as a uae of 20200 g / min , and those with overt proteinuria with uae > 200 g / min .
diabetic retinopathy was assessed from retinal photographs at baseline , and the findings were reviewed by one ophthalmologist .
all of the results are expressed as means  sd or median ( range ) .
statistical analyses were performed using spss statistical software ( spss , chicago , il ) .
because of their skewed distribution , triglyceride and hdl cholesterol concentrations and microalbuminuria levels were compared after logarithmic transformation .
 tests were used to test the univariate relationships of categorical variables , and independent student 's t tests were used for continuous variables .
we used multiple logistic regression analysis to test associations between the outcome ( progression of aft at follow - up ) and potential explanatory variables .
the relationships were analyzed after adjustment for the following risk factors : age , duration of diabetes , presence of hypertension , smoking , diabetic foot ulceration , and diabetic retinopathy and nephropathy .
all of the results are expressed as means  sd or median ( range ) .
statistical analyses were performed using spss statistical software ( spss , chicago , il ) .
because of their skewed distribution , triglyceride and hdl cholesterol concentrations and microalbuminuria levels were compared after logarithmic transformation .
 tests were used to test the univariate relationships of categorical variables , and independent student 's t tests were used for continuous variables .
we used multiple logistic regression analysis to test associations between the outcome ( progression of aft at follow - up ) and potential explanatory variables .
the relationships were analyzed after adjustment for the following risk factors : age , duration of diabetes , presence of hypertension , smoking , diabetic foot ulceration , and diabetic retinopathy and nephropathy .
of the 1,021 patients who had normal cardiovascular aft results , 783 ( 76.7% ) completed a follow - up aft evaluation ( fig .
the total study population consisted of 392 men and 629 women with mean  sd age of 50.2  10.7 years .
duration of diabetes was 7.1  6.5 years , and a1c level was 8.6  2.2% .
the 783 participants who were evaluated did not differ from the 248 patients who were not assessed , with respect to age ( 50.7  10.4 vs. 51.7  11.6 years , p = 0.190 ) , sex ratio ( p = 0.649 ) , presence of hypertension ( p = 0.279 ) , duration of diabetes ( 7.7  6.7 vs. 7.4  7.7 years , p = 0.390 ) , or a1c level ( 8.7  2.0% vs. 8.5  2.4% , p = 0.915 ) . during follow - up , seven patients died : four women and three men .
the causes of death were sepsis in two patients , myocardial infarction in two patients , cerebral hemorrhage in one patient , and malignancy in two patients .
307 ( 39.2% ) patients had hypertension and all of them were taking antihypertensive medication .
thirty - two ( 10.4% ) patients were treated for hypertension with calcium channel blockers , 6 ( 2.0% ) with -blockers , 140 ( 45.6% ) with ace inhibitors or angiotensin receptor blockers , 4 ( 1.3% ) with thiazides , and 125 ( 40.7% ) with any combination of antihypertensive agents .
baseline sex ratios and bmis were similar , and there was no difference in the treatment of diabetes ( p = 0.773 ) or hypertension ( p = 0.326 ) in the progressor and nonprogressor groups .
however , the patients with progression were older ( p < 0.001 ) with a longer duration of diabetes ( p < 0.001 ) , more were smokers ( p = 0.045 ) , and more had hypertension ( p < 0.001 ) .
moreover , the progressor group had higher levels of fasting glucose ( p = 0.004 ) , postprandial glucose ( p = 0.010 ) , and microalbuminuria ( p = 0.002 ) than patients without progression ( table 1 ) . however , there were no differences in total cholesterol , triglyceride , or hdl cholesterol levels between the two groups .
the patients with progression also showed higher frequencies of diabetic nephropathy ( p = 0.004 ) and diabetic retinopathy ( p < 0.001 ) during the observation period than the patients in the nonprogressor group ( table 1 ) . at follow - up , 270 patients ( 34.5% ) showed abnormal cardiovascular aft scores ( total score 1 , the progressor group ) .
the results of the deep breathing , valsalva maneuver , and lying - to - standing tests were abnormal in 59 ( 21.9% ) , 210 ( 77.8% ) , and 159 ( 58.9% ) patients , respectively . in terms of total score , 138 ( 51.1% )
patients had a score of 1 , 106 ( 39.3% ) had a score of 2 , and 26 ( 9.6% ) had a score of 3 .
the distribution of abnormal e / i ratio , valsalva maneuver , and posture ratios in patients with a total score of 1 ( n = 138 ) at follow - up was 12 ( 8.7% ) , 83 ( 60.1% ) , and 43 ( 31.2% ) patients , respectively . even among the 133 patients with newly diagnosed diabetes at baseline , 43 ( 32.3% ) showed abnormal aft results at follow - up , with total scores of 1 . these included an abnormal e / i score in 4 ( 9% ) , an abnormal valsalva ratio score in 34 ( 79% ) , and an abnormal posture score in 21 ( 49% ) ( table 2 ) .
logistic regression analysis revealed that the mean value of biannually measured a1c was correlated significantly with the future development of can . compared with the patients whose mean a1c value was 7.0% , having a level of > 11.0%
the conventional risk factors , such as age ( p < 0.001 ) , diabetic retinopathy ( p = 0.036 ) , and diabetic nephropathy ( p = 0.035 ) at baseline predicted the progression of can after adjustments were made for baseline age , hypertension , smoking habit , and the duration of diabetes .
duration of diabetes or having a smoking habit was not associated with the progression of aft . in this study ,
this was a longitudinal observational study designed to investigate factors that might influence the progression of can in patients with type 2 diabetes .
we demonstrate that can progressed according to glycemic control status and that it was associated with preexisting chronic diabetes complications .
diabetes is an important risk factor for development of cardiovascular and cerebrovascular diseases ( 16,17 ) .
dan is a serious and common complication of diabetes associated with an increased risk of cardiovascular mortality .
many studies have shown consistently that there is an increased risk of cardiovascular mortality among patients with an abnormal can assessment , compared with those with normal assessment ( 18,19 ) . therefore
, early detection of high - risk diabetic patients and aggressive intervention should be promising therapeutic strategies . in 2005 , a consensus statement from the american diabetes association ( ada ) recommended the battery of tests for the assessment of can including heart rate variability ( hrv ) , e / i ratio , response to the valsalva maneuver , and standing up ( 2,14 ) .
hrv methods are age dependent but independent of the intrinsic heart rate ( 2,14,20 ) . until now
, measuring hrv has been a standard screening method in the diagnosis of autonomic dysfunction .
aft is easy to perform and is a reproducible test using a simple device at the patient 's bedside ( 21,22 ) .
there have been limited observations with regard to the progression of can in patients with type 2 diabetes .
poor glycemic control plays a central role in its development and progression ( 12,13 ) .
moreover , strict glycemic control can slow the progression and delay the appearance of abnormal afts ( 10,23 ) . in the european diabetes ( eurodiab )
prospective complication study , the incidence of neuropathy was 23.5% , and the change in a1c value during a follow - up period of 7 years was independently associated with the incidence of neuropathy ( 11 ) . the diabetes control and
complications trial ( dcct ) research group also documented that intensive therapy can slow the progression and the development of an abnormal autonomic test .
however , these well - performed prospective studies were only conducted on patients with type 1 diabetes .
similar to the eurodiab study , we found that 35% of our patients showed progression of can . even in the patients with newly diagnosed type 2 diabetes , 30% showed abnormal aft results after 7.5 years .
we used the mean a1c value , measured every 6 months for 7.5 years , as a representative index of glycemic control status .
blood glucose control , as determined by a1c levels , seemed to be improved more during follow - up in the progressor group than in the nonprogressor group .
however , the mean a1c values during the observation period were significantly higher in the progressor group .
we suggest that , as for type 1 diabetes , glycemic control could influence the development and progression of can in patients with type 2 diabetes . in addition , previous reports about can were designed to test only the e / i ratio or orthostatic hypotension .
however , in our results , each of the three aft tests showed a different rate of progression ; a partial measurement of aft offers only limited information about can . with use of the ada criteria for the diagnosis of can in this study , the frequency of abnormal aft results were , in order , the valsalva maneuver , posture , and the e / i ratio among patients whose initial aft results were normal .
we suggest that the valsalva ratio is the most sensitive parameter of the three values .
interestingly , the duration of diabetes was not significantly associated with the development of can .
although diabetes duration has been reported to play an important role in patients with type 1 diabetes ( 12 ) , the influence of diabetes duration seems to play a less important role in type 2 diabetes .
consistent with previous studies , we found an association between can and microvascular complications ( 24,25 ) . can progression is correlated with diabetic retinopathy , diabetic nephropathy , and an increased urinary microalbumin excretion rate .
this finding suggests that clinicians should pay more attention to patients with diabetic retinopathy or nephropathy , over and above the strict glycemic control required for the prevention of can
first , there have been no normal values established for the e / i ratio , valsalva maneuver , and posture tests specific to normal korean subjects or to korean patients with diabetes .
it remains to be clarified whether the normal values for western populations can be applied to korean subjects ; however , we performed aft with the same method by one examiner throughout .
second , tests of blood pressure response to standing , blood pressure response to a sustained handgrip , and the presence of orthostatic hypotension were not checked because these tests were not available in our diabetes center from 1999 to 2000 .
however , each of the three tests of cardiovascular autonomic function used had a sensitivity and specificity of > 90% ( 2 ) .
moreover , the ada suggests that the three tests used here adequately fulfill their requirements because of their reliability , reproducibility , general mutual correlation , and correlation with the tests of peripheral somatic nerve function and well - established normal values .
however , our ongoing follow - up studies should provide some insight into this issue . in summary
, prolonged exposure to uncontrolled hyperglycemic conditions could predict future can , independent of the duration of diabetes among patients at baseline .
cardiovascular aft should be monitored to pay attention to major potential cardiovascular complications even in asymptomatic patients , but especially among those for whom glycemic control is not maintained adequately .
 objective  we investigated whether cardiovascular autonomic dysfunction was associated with glycemic control status over time in patients with type 2 diabetes.research design and methods  from 1999 to 2000 , cardiovascular autonomic nerve function testing ( aft ) was performed on patients with type 2 diabetes ( n = 1,021 ) and was followed - up in 2006 and february 2008 . 
 tests for cardiovascular autonomic functions measured heart rate variability parameters ( expiration - to - inspiration [ e / i ] ratio , responses to the valsalva maneuver , and standing ) . 
 aft scores were determined from the results of the each test as follows : 0 for normal and 1 for abnormal . 
 we began with those who had a score of 0 and assessed the changes in total score along with biannual a1c levels.resultsat follow - up , the development of cardiovascular autonomic dysfunction was 34.5% ( e / i ratio 21.9% , valsalva maneuver 77.8% , and posture 58.9% ; n = 783 ) . 
 the development of cardiovascular autonomic dysfunction was higher in older patients ( p < 0.001 ) ; in those with longer duration of diabetes ( p < 0.001 ) ; of hypertension ( p = 0.005 ) , and of diabetic retinopathy ( p < 0.001 ) ; and in those who had higher levels of microalbuminuria ( p = 0.002 ) . 
 logistic regression analysis revealed that the development of cardiovascular autonomic dysfunction was strongly associated with the mean a1c level during the follow - up period ( mean a1c > 9.0% vs. 7.0% , odds ratio 2.984 , 95% ci 1.1777.561 ; p = 0.021).conclusions  the development of cardiovascular autonomic dysfunction was independently associated with microvascular complications and glycemic control status during this 7.5-year follow - up in patients with type 2 diabetes . 
RESEARCH DESIGN AND METHODS
Statistical analyses
RESULTS
CONCLUSIONS