Characteristics of the cardiovascular autonomic dysfunction tests
| Name of the cardiovascular test | Characteristics of the test | Autonomic nerve system |
| Heart rate response to deep breathing | The child breathes deeply in a sitting position. The maximum and minimum heart rates during each breathing cycle are measured, and the mean of the differences during three successive breathing cycles are taken to give the maximum-minimum heart rate. | Parasympathetic function |
| Heart rate response to standing up | The child lies on a couch and then stands up unassisted. An immediate increase in heart rate happens immediately, maximal amount is at about the 15th beat after starting to stand, followed by a relative bradycardia, maximal around the 30th beat. This will be calculated as the 30:15 ratio, which means the ratio of the longest R-R interval around the 30th beat to the shortest R-R interval around the 15th beat. | Parasympathetic function |
| Valsalva manoeuvre | The child blows into a mouthpiece at a pressure of 40 mm Hg for 15 s. Normally the heart rate increases, followed by a rebound bradycardia. During the manoeuvre, the ratio of the longest and shortest R-R interval will be measured. The Valsalva ratio will be calculated as the mean ratio from three consecutive Valsalva manoeuvres. | Parasympathetic function |
| Blood pressure response to standing up (orthostatic hypotension) | The blood pressure (in mm Hg) is measured in a lying and standing position using a blood pressure metre (Omron M2 Intellisense). The difference in systolic blood pressure is considered to be the extent of the change in postural blood pressure. Systolic pressure is considered to be abnormal when a fall >20 mm Hg after standing up is observed. | Sympathetic function |
| Blood pressure response to sustained handgrip | Handgrip is maintained at 30% of the maximum voluntary contraction using a handgrip dynamometer up to a maximum of 5 min, and the blood pressure is measured each minute. The difference between the diastolic blood pressure just before the release of the handgrip, and before starting, is taken as the measure of response. | Sympathetic function |