Diabetic autonomic neuropathy--Part II. Coefficient of variation of RR-variation and Valsalva maneuver tests

Valsalva maneuver in chagasic patients with documented past medical history of acute chagasic myocarditis

BACKGROUND

We studied the heart rate responses to the Valsalva maneuver in eight patients with documented past medical history of acute Chagas' disease.

METHODS

Four patients were studied 8-21 months after the acute episode and four, 58-68 months thereafter (age 25+/-8.65 years M+/-S.D.). Seventeen healthy subjects of similar age were included as controls (age 27+/-7.5 years, P=NS).

RESULTS

Baseline heart rate was higher in chagasic patients (88+/-15 beats/min) compared to controls (69.8+/-9.8, P=0.001). Maximum heart rate at phase II of the maneuver was also higher (114+/-16.3 vs. 101.5+/-9.9, P=0.02). Minimum heart rate at phase IV was, however, not different (57.4+/-10.4 vs. 63.3+/-7.3 P=NS). The magnitude of the absolute negative change at phase IV was larger in the chagasic patients, although, not different (-50.8+/-13.8 vs. -44+/-13.8, P=NS). The Valsalva index was 1.81+/-0.26 in the chagasic patients and 1.82+/-0.42 in the controls (P=NS). Minimum heart rate at phase IV correlated neither with the baseline heart rate (r=-0.28, P=NS) nor with the Valsalva index (r=-0.40, P=NS). The magnitude of the absolute negative change during phase IV correlated with, both, the baseline heart rate (r=-0.80, P<0.01) and the Valsalva index (r=-0.95, P<0.0001). The higher baseline high rate influenced the magnitude of the negative heart rate change, but not the minimum heart rate reached at phase IV.

CONCLUSIONS

Chagasic patients with proven past medical history of acute Chagas' disease had unimpaired heart responses to the Valsalva maneuver.

Reproducibility of the heart rate response to low-strain Valsalva manoeuvre in healthy subjects

To elucidate whether the intrastrain cardio-acceleration and cardio-deceleration responses to low-strain Valsalva manoeuvre at expiratory pressures 10 and 20 mmHg (VM10,VM20) are reproducible, a beat-to-beat heart rate study was undertaken in 46 subjects (40 male undergraduates aged 19-25 years and six laboratory workers (four females and two males aged 28-55 years). The intensity of the heart rate response (HRR) was assessed by a ratio of the mean value of the pre-strain heart rate (Valsalva means' ratio VMR). In each subject the HRR to VM10 and VM20 was measured by repeating each manoeuvre three times. Reproducibility was evaluated on a short-term (1 h), medium-term (1 and 6 months), and long-term (6 and 11 years) basis. With the individual differences the initial short-term reproducibility study revealed either an cardio-acceleration or cardio-deceleration response to VM10 and VM20, which persisted well in the repeated tests. On the ground of this result three individual modes of HRRs to VM10 and VM20 were distinguished: (i) Mode A, a deceleration response appeared both to VM10 and VM20; (ii) Mode B, a deceleration response appeared to VM10 and an acceleration response to VM20; (iii) Mode C, an acceleration response appeared both to VM10 and VM 20. All of these modes, as well as the separate acceleration and deceleration responses, were well reproducible at any cited time points. We suggest that the individual modes of HRR are induced by different states of autonomic cardiovascular reactivity: Mode A probably expresses a parasympathotonic (vagotonic), Mode C--a sympathotonic, and Mode B--an intermediate autonomic state. Thus, the individual modes of HRR to VM10 and to VM20 could be used as a method of non-invasive determination of cardiovascular autonomic reactivity.

The effect of intensive diabetes therapy on measures of autonomic nervous system function in the Diabetes Control and Complications Trial (DCCT)

In the Diabetes Control and Complications Trial (DCCT), 1441 insulin-dependent diabetic patients in the primary prevention and secondary intervention cohorts were randomly assigned to either conventional or intensive therapy and followed for up to 9 years. Baseline and biennial measurements of autonomic function (R-R variation, Valsalva ratio, and postural testing) as well as quarterly assessment of autonomic symptoms were performed throughout the trial. There were no differences at baseline between patients randomized to intensive vs conventional therapy. In general, autonomic abnormalities increased during the trial; however, R-R variation was less abnormal in the intensively treated secondary intervention (7% with abnormal results at 4-6 years) compared with the conventionally treated group (14% with abnormal results, p = 0.004) and in the combined cohorts (5% of intensive treatment subjects with abnormal results vs 9% of conventional treatment subjects, p = 0.0017). There were few abnormal Valsalva ratios or postural tests at baseline or during the trial. No significant difference in Valsalva ratio or postural tests occurred between the intensive and conventional treatment groups. Both the R-R variation and the Valsalva ratio had significantly greater slopes of decline over time in the patients randomized to conventional therapy (1.48 points per year and 0.015 per year, respectively) compared to those randomized to intensive therapy (0.912 points per year and 0.0025 per year). Of the symptoms related to autonomic function, only incomplete bladder emptying was significantly more common in the conventional group. In summary, the DCCT documented that intensive therapy can slow the progression and the development of abnormal autonomic tests.

Cardiovascular autonomic nervous system tests: determination of normative values and effect of confounding variables

OBJECTIVE

To determine normative values for heart rate variation to deep breathing (VAR) and Valsalva ratio (VAL) as well as the effect of various confounding variables on these measures using data from a large group of normal subjects collected from multiple centers.

RESEARCH DESIGN AND METHODS

VAR and VAL were measured on 611 normal subjects, age range 9-79, from 63 centers and was analyzed at a single Autonomic Nervous System Reading Center. Using simple and stepwise logistic regression the effect of age, gender, height, weight, mean arterial blood pressure (MAP) and body mass index (BMI), on VAR and VAL was evaluated.

RESULTS

The 95% normative values range (values at 2.5 to 97.5 percentile) for VAR (n = 580) was 12.8-103.5 (mean 49.7) and for VAL (n = 425) was 1.31-2.97 (mean 1.97). No gender effect was found for either VAR or VAL (p > 0.05). VAR correlated inversely with both age and MAP, while VAL correlated inversely with both age and BMI. Since age is the principal confounding variable for both VAR and VAL, normative values are also presented stratified by age.

CONCLUSION

Normative values for VAR and VAL based on a large population sample are presented. However, the values presented may not be valid in patients with morbid obesity or malignant hypertension. These data are applicable for either individual patients or for use in multicenter research trials.

Cold pressor test in diabetic autonomic neuropathy

The tests for evaluating sympathetic dysfunction seen in diabetic patients are few and insensitive. For this reason, there are some difficulties in diagnosing sympathetic dysfunction and additional tests are required. The cold pressor test causes a strong sympathetic stimulus and this study investigated whether this test could be helpful in diagnosing sympathetic dysfunction. The cold pressor test was applied to a group of diabetic patients (n = 33) and a control group (n = 15). The mean systolic cold pressor response in diabetic patients was found similar to controls (9 +/- 1.4 vs. 10.6 +/- 1.2 mmHg). However the mean diastolic cold pressor response was significantly lower in diabetic patients as compared with the control group (7.7 +/- 1.0 vs. 12.0 +/- 1.1 mmHg, P < 0.05). Cardiovascular reflex tests were also applied to diabetic patients and deep breathing and orthostatic hypotension test results were used to categorize the patients with parasympathetic and/or sympathetic dysfunction. In patients with autonomic neuropathy the diastolic cold pressor response was smaller than the controls (6.9 +/- 1.3 vs. 12.0 +/- 1.1 mmHg, P < 0.05); however, in patients without autonomic neuropathy it was not significantly different from controls (8.7 +/- 1.8 vs. 12.0 +/- 1.1). The systolic cold pressor test results showed no difference between patients with or without parasympathetic dysfunction but diastolic cold pressor results in patients with sympathetic dysfunction were significantly lower than the results of the patients without sympathetic dysfunction (3.8 +/- 1.3 vs. 9.1 +/- 1.3 mmHg, P < 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)

Reproducibility of parameters for assessment of diabetic neuropathy. The French Group for Research and Study of Diabetic Neuropathy

This study evaluated the reproducibility of nerve function assessment in a group of 132 diabetic patients with moderate peripheral polyneuropathy. Patients were investigated at the beginning and the end of the run-in period (a 1-month placebo period) of a multicentre trial of an aldose-reductase inhibitor (Ponalrestat). Reproducibility was evaluated by performing four types of tests: quantitative visual scales of symptoms, quantitative sensory assessment (vibration perception thresholds in medial malleolus and great toe, foot thermal perception threshold to hot and cold), electrophysiological investigations on the dominant side (conduction velocities and potential amplitudes of sensory and median motor nerve, sural and peroneal nerves, amplitudes of F waves of median motor and peroneal nerves) and cardiac autonomic tests (Valsalva, deep-breathing, lying-to-standing). Reproducibility was poor for symptoms, thermal sensitivity, and potential amplitudes. It was satisfactory (total coefficient of variation < 50%) for all the other parameters and even very good (total variation coefficient < 26%, intra-subject variation factors corresponding to < 56% of total variance) for velocities of sensory and median motor and peroneal nerves, the amplitudes of F waves and the three autonomic tests. For most of the parameters total variance was mainly related to inter-subject variability. However, inter-subject variability for the three cardiac autonomic tests was very low and at least one cardiac autonomic test was altered in all the patients. Inter-centre variability was low for all the parameters, except for action potential amplitudes and for F wave velocity of the median motor nerve. This study suggests those parameters that are appropriate for the assessment of diabetic neuropathy and for therapeutic trials.(ABSTRACT TRUNCATED AT 250 WORDS)

Autonomic function testing in diabetic subjects using sequential measurements

The repeatability of commonly used electrocardiographic (ECG) related autonomic function tests was investigated in 25 diabetic subjects, mean age 44 (range 18-67) years and mean duration of diabetes 10 (< 1-35) years. Tests were based on deep breathing, the Valsalva manoeuvre, relaxed normal breathing, and standing up from a lying position. All tests were repeated twice at each session, with two sessions separated by a mean of 5 (range 3-8) months. ECG and respiratory data were recorded for subsequent analysis. Maximum (max) and minimum (min) RR intervals and instantaneous heart rate (HR) were determined. The mean and repeatability data (within-subject standard deviation) for 21 different test results were calculated, and included deep breathing sitting (max-min)RR 226 +/- 39 ms and (max-min)HR 19.3 +/- 3.2 beats min-1, Valsalva manoeuvre 1.74 +/- 0.18, and lying-to-standing RR ratio 1.19 +/- 0.07. The within-subject repeatability to between-subject variability ratios consistently demonstrated that it is better to perform the deep breathing test sitting (with the smaller mean ratio of 0.37) rather than supine (0.46), with the use of three respiratory cycles rather than a single cycle (0.33 compared with 0.50 for (max-min)RR). A significant (p = 0.037) relationship was found between variability in heart rate changes and variability in air volume breathed during the deep breathing test.

Portable infrared pupillometry using Pupilscan: relation to somatic and autonomic nerve function in diabetes mellitus

The relationship between dynamic pupillary function and peripheral nerve function was studied in 85 randomly-selected diabetic patients and 67 age-matched normals using a portable infrared pupillometer (Pupilscan Version 5). Seven measurements were chosen to represent different components of the pupillary constriction-redilatation curve after a standardized light stimulus. Constriction latency was significantly prolonged in diabetic patients (p = 0.05), as was time to 63% redilatation (p = 0.001). Thermal thresholds at the feet weakly correlated with relative reflex amplitude (warm: r = -0.22, p = 0.05; cool: r = -0.23, p = 0.05), but vibration perception thresholds were more strongly associated with constriction and redilatation velocity (r = -0.42, p = 0.001; r = -0.28, p = 0.03). Among the cardiovascular autonomic function tests, only respiratory R-R variation correlated with constriction velocity (r = 0.47, p < 0.001), and Valsalva ratio with redilatation velocity (r = 0.25, p = 0.04), but postural systolic blood pressure change was also correlated with reflex amplitude and latency time (r = -0.42, p < 0.001; r = 0.41, p = 0.001). There were no significant associations with three measures of sweating function in the feet. Pupil measurements were abnormal in 4-11% of diabetic patients, while other neurological tests were abnormal in 8-35%, consistent with the length-dependence of diabetic neuropathy. Median coefficients of variation were 2.0-7.2% in diabetic patients.(ABSTRACT TRUNCATED AT 250 WORDS)

Natural history of autonomic neuropathy in chronic liver disease

To determine the natural history of autonomic neuropathy in chronic liver disease we used standard cardiovascular autonomic tests to evaluate prospectively 60 patients (33 male, 27 female) with initially well-preserved hepatic function. On initial testing, 27 patients (45%; median [range] age 56 [32-67] years) had vagal neuropathy. Autonomic dysfunction was equally common in patients with alcohol-related and nonalcoholic-related liver disease. The cumulative 4-year mortality rate in patients with vagal neuropathy was 30% compared with 6% in those with normal autonomic function. Multiple logistic regression analysis showed that presence of vagal neuropathy and severity of hepatic damage were independent predictors of mortality. Serial testing showed that whereas disease progression occurred in some patients, in others mild abnormalities in autonomic function were reversible. Vagal dysfunction is common in well-compensated chronic liver disease and its presence identifies a subgroup of patients with a substantially worse outlook.

Lower limb arterio-venous shunts, autonomic neuropathy and diabetic foot

We have quantitatively assessed the percentage of lower limb arterio-venous (a-v) shunting using a radioisotopic technique and correlated it with autonomic neuropathy evaluated by cardiovascular tests. We have studied three groups of diabetic patients: Group A, 12 non-neuropathic subjects without foot lesions; Group B, 12 neuropathic subjects without foot lesions; Group C, 12 neuropathic subjects with recurrent foot ulcers. Shunting was higher in Group C (10.4 +/- 2.7%) than in Group B (6.8 +/- 2.3%, P less than 0.01) and Group A (3.8 +/- 1.2%, P less than 0.001). Shunts in Group B were higher than in Group A (P less than 0.05). All the tests exploring autonomic function were more impaired in Groups B and C than in Group A, with no difference between Groups B and C. A direct correlation was found between a-v shunting and the following cardiovascular tests: postural hypotension (PH) (r = 0.41, P less than 0.02), sustained handgrip (SH) (r = 0.56, P less than 0.001), deep breathing (DB) (r = 0.40, P less than 0.005) and lying to standing (LS) (r = 0.44, P less than 0.01). A positive correlation was also found between a-v shunts and duration of the disease (r = 0.62, P less than 0.001). Arterio-venous shunting was found to be directly related to autonomic neuropathy even if the higher shunting found in the patients with foot ulcers was not related to a higher degree of autonomic involvement; in addition, this group of patients was characterized by having a more advanced sensory and motor neuropathy. In conclusion, autonomic neuropathy, through its influence on a-v shunts, may play a role in the pathogenesis of diabetic foot, but peripheral neuropathy probably plays a key role in conditioning the development of the overt clinical manifestations of diabetic foot.

Assessment of cardiovascular autonomic function: age-related normal ranges and reproducibility of spectral analysis, vector analysis, and standard tests of heart rate variation and blood pressure responses

To establish normal ranges for assessment of autonomic dysfunction, a battery of cardiovascular reflex tests was performed in 120 healthy subjects aged 15-67 years using a computer-based technique. Tests of heart rate variation (HRV) included 8 measures at rest: coefficient of variation (CV), root mean squared successive difference (RMSSD), spectral analysis of HRV in the low frequency, mid frequency, and high frequency bands in the supine and standing postures; 5 measures during deep breathing: CVb, RMSSDb, Expiration-Inspiration (E-I) difference, E/I ratio, and mean circular resultant of vector analysis; Valsalva ratio, and max/min 30:15 ratio. In addition, the change in systolic and diastolic blood pressure in response to standing and the diastolic blood pressure response to sustained handgrip were determined. The results of all measures, the blood pressure tests excepted, declined significantly with increasing age (r = -0.16 to -0.59; p less than 0.05). Moreover, RMSSD, RMSSDb, and E-I difference decreased considerably with increasing heart rate (r = -0.37 to -0.52; p less than 0.001). The longest and shortest R-R intervals in response to standing were distributed within beats 21-39 and 6-24, respectively. All tests were independent of sex. Log transformation was used to define the age-related lower limits of normal at the 2.3 centile for all tests of HRV, except for the E/I, Valsalva, and max/min 30:15 ratios. The results of these tests had to be analysed using a log(y-1) transformation. The intra-individual reproducibility determined on two consecutive days in 20 healthy subjects and 21 diabetic patients indicated that there were no major differences between the two groups regarding the day-to-day variation of test results, which was highest for the Valsalva ratio. We conclude that: (1) all indices of spectral and vector analyses of HRV are age-dependent and have the advantage of being independent of heart rate; (2) RMSSD, E-I difference, and the 30:15 ratio as it was used previously are not suitable for evaluation of autonomic dysfunction in diabetes; (3) log(y-1) transformation is required to determine age-dependent normal ranges and reproducibility for the three ratios.

Changes in cholinergic sweat gland activation in diabetic neuropathy identified by computerised sweatspot analysis

Peripheral small-fibre denervation has been reported to result in decreased activation of eccrine sweat glands to muscarinic cholinergic agents. Using computerised image-analysis of pilocarpine-activated sweatspot prints of a 4 cm2 area of the dorsum of the foot in 79 randomly selected diabetic patients we have identified a group of neuropathic patients (18%) with decreased sweatspot activation (less than 20/cm2), and a smaller group (6%) of younger patients with less marked neuropathy who had increased activation (greater than 132/cm2), probably resulting from denervation supersensitivity. The associations between sweatspot density and other conventional tests of peripheral nerve function were weak. The prevalence of abnormal sweatspot density, 24%, was similar to that of other tests, except thermal thresholds at the feet (35-37%), which were not correlated with sweatspot activation, suggesting that diabetic neuropathy has differing effects on afferent and efferent small fibres. The method is rapid and reproducible (median coefficient of variation 14%) and its ability to identify patients with increased, as well as decreased, peripheral nerve function may be of value in the characterisation and longitudinal follow-up of small-fibre abnormalities in diabetes.

Short- and long-term reproducibility of cardiovascular tests of autonomic function in normal subjects

Ten healthy normal subjects participated in a follow-up study in which the reproducibility of noninvasive cardiovascular autonomic function testing was studied. The tests used were the Valsalva manoeuvre, deep and quiet breathing, standing upright and isometric handgrip exercise. These tests were performed six times within a 2-year period. The reproducibility of these autonomic function tests within a day was evaluated in a separate study involving nine healthy subjects. In this study the tests were performed three times between 08.00 and 15.00. The results indicate that indices based on R-R interval ratios during testing were highly reproducible; that the indices remain reproducible over a 2-year follow up period and that reproducibility within a day was similar to that within longer time periods. The reproducibility of pressor responses to isometric exercise was poor. It is concluded that indices based on R-R ratios are suitable for use in follow up studies of autonomic function.

The relevance of persistent C-peptide secretion in type 1 (insulin-dependent) diabetes mellitus to glycaemic control and diabetic complications

The effect of residual C-peptide secretion in longer standing IDDM on glycaemic control and the prevalence and evolution of complications over 2 years was evaluated. Thirty-one subjects with IDDM of 15.4 (1.5) years duration (mean SEM)) and residual C-peptide secretion, were matched for age, duration of diabetes and body mass index with 31 subjects without detectable C-peptide secretion. At trial entry and over 2 years, levels of HbA1, fructosamine and mean blood glucose were essentially similar in both groups. Levels of glycated albumin (GSA) were significantly higher in the C-peptide negative group after 3 and 9 months (P less than 0.05). An increased prevalence of proliferative retinopathy in the C-peptide negative group and of peripheral vascular disease in the C-peptide secretor group was apparent at entry to the study (both P less than 0.05), although no significant differences were observed after 1 or 2 years. There was no difference in the prevalence of peripheral or autonomic neuropathy, hypertension, nephropathy or ischaemic heart disease. Subjects with C-peptide concentrations greater than 0.100 pmol/ml at entry to this study had lower daily insulin requirements after 1 and 2 years, but behaved like the larger group with any detectable C-peptide secretion in all other respects. Residual C-peptide secretion was lost after 1 year in 7 patients, in whom glycaemic control during the year had been particularly poor. Insulin antibody titres were no different in the 2 groups at any time point. This study suggests that residual C-peptide secretion in longer standing IDDM confers the potential for limited improvements in glycaemic control. This effect appears to be insufficient to prevent the evolution of microvascular complications over a 2-year period. Residual C-peptide secretion and relative hyperinsulinaemia may be associated with an excess of peripheral vascular disease.