THE SQUATTING TEST - A USEFUL TOOL TO ASSESS BOTH PARASYMPATHETIC AND SYMPATHETIC INVOLVEMENT OF THE CARDIOVASCULAR AUTONOMIC NEUROPATHY IN DIABETES

The heart rate responses observed after both squatting and standing are thought to be of reflex nature and may be useful to assess the functional integrity of parasympathetic and sympathetic nerves in diabetes. In the standard maneuver, each subject stood still for 3 min, then squatted down for 1 min, and at last stood up during an inspiratory phase. In 10 healthy subjects (25-31 years of age), lengthening of the R-R interval during squatting was abolished by atropine, whereas propranolol markedly attenuated shortening of the R-R interval at standing from squatting. Squatting test (SqT) ratios (SqT vagal [SqTv] = ratio between the R-R interval mean before squatting and the longest R-R interval after squatting; SqT sympathetic [SqTs] = ratio between the basal R-R interval and the shortest R-R interval at standing) were calculated in 558 healthy subjects and 346 diabetic patients (insulin-dependent diabetes mellitus/non-insulin-dependent diabetes mellitus: 103/243). Normal ranges (95 and 99% confidence intervals [CIs]) for subjects 20-74 years of age showed a statistically significant negative correlation with age. SqTv was outside the 99% CI in 145 (42%) diabetic patients and in 7 (1.3%) of the control subjects. The corresponding figures for SqTs were 40 and 0.8%, respectively. Age and duration of diabetes had a negative influence on SqT ratios. SqT ratios were compared with other reflex tests currently used for diagnosis of autonomic neuropathy: deep breathing (DB), lying-to-standing (LS), Valsalva manuever, and blood pressure change after standing (orthostatic hypotension [OH]). Autonomic involvement was arbitrarily defined as mild (one test pathological), definite (two tests pathological), or severe (three or more tests pathological). In patients with definite or severe involvement, SqT ratios and DB and LS tests showed the least overlap between healthy subjects and diabetic patients; however, for patients with mild or no autonomic involvement, SqT ratios were significantly better than DB, LS, or OH tests. In conclusion, 1) SqT ratios can discriminate between healthy subjects and diabetic patients to an equal or greater extent than the other tests; 2) SqT ratios give information on both parasympathetic and sympathetic activity; and 3) SqT ratios are better than other single tests in identifying mild autonomic involvement. These results may be important for early intervention trials.