Background
Resistance training for leg muscles is recommended for patients with postural tachycardia syndrome (POTS). However, no study has characterized the relationships between orthostatic symptoms, heart rate (HR) increase, and the mass of the lower leg muscle in patients with POTS. We sought to determine the relationships between the mass of the lower leg muscle, HR increase during the head-up tilt (HUT) test, and orthostatic symptoms in patients with POTS.
Methods
We prospectively enrolled 42 patients with POTS who were older than 16 years. The muscle mass was estimated using bioelectrical impedance analysis. We used the International Physical Activity Questionnaire-Short Form to measure self-reported physical activity. All patients were asked to complete the Korean version of the Orthostatic Grading Scale (KOGS).
Results
The HR increased during the HUT test by 38.7±7.88 beats/minutes. Both the HR increase during the HUT test and the total KOGS score were negatively correlated with the total metabolic equivalent of the task. The leg circumference and muscle mass were not correlated with the HR increase during the HUT test or the KOGS score.
Conclusions
The leg circumference and muscle mass were not related to orthostatic symptoms in patients with POTS. Cardiac remodeling or blood volume increase may be responsible for improvement in POTS after physical activity.

Orthostatic dizziness is feeling dizzy or lightheaded when standing up. Hemodynamic orthostatic dizziness can be caused by autonomic dysfunction such as orthostatic hypotension or postural tachycardia syndrome. The interpretation of the autonomic function test results in patients with orthostatic dizziness is crucial for diagnosing and managing the underlying condition. The head-up tilt and Valsalva tests are especially important for evaluating adrenergic function in patients with hemodynamic orthostatic dizziness. However, it is important to note that autonomic function tests do not cover the entire diagnostic process, since their findings need to be considered along with the detailed history and physical examination results of the patient because various differential diagnoses exist for orthostatic dizziness. Ensuring appropriate treatment by interpreting the autonomic function test results can help to determine the improvement of and prevents falls from orthostatic dizziness.

This paper introduces new diagnostic criteria and differential diagnosis of orthostatic dizziness to help clinicians to diagnose hemodynamic orthostatic dizziness. Clinicians need to be able to discriminate hemodynamic orthostatic dizziness from other types of dizziness that are induced or aggravated when standing or walking. Measurements of the orthostatic blood pressure and heart rate are important when screening hemodynamic orthostatic dizziness. Detailed history-taking, a physical examination, and laboratory tests are essential for finding the cause of hemodynamic orthostatic dizziness. The differential diagnosis of hemodynamic orthostatic dizziness is crucial because it can be caused by various autonomic neuropathies.

Citations

• Mareo y vértigo ortostático, funcional y cinetosis
  Liliana F. Invencio-Da-Costa, Carmen Sánchez-Blanco, Raquel Yáñez-González, Hortensia Sánchez-Gómez, Paula Peña-Navarro, Sofía Pacheco-López, Susana Marcos-Alonso, Cristina Nicole Almeida-Ayerve, Luis Cabrera-Pérez, Victoria Díaz-Sánchez
  Revista ORL.2023; 15(3): e31540.     CrossRef

Background
The standardized autonomic function test has become widely available. However, there are no reference data for this test for the Korean population. This study explored reference data for sudomotor and cardiovagal function tests for the Korean population.
Methods
The sweat volume by quantitative sudomotor axon reflex test, heart-rate response to deep breathing (HRdb), expiration:inspiration (E:I) ratio, and Valsalva ratio (VR) were measured in 297 healthy Korean volunteers aged from 20 to 69 years. Multivariate regression analysis was performed to evaluate the effects of age, sex, and body mass index on these variables. The 2.5th, 5th, 10th, 90th, 95th, and 97.5th percentile values were obtained for each investigation.
Results
The sweat volume was higher in males than in females. The HRdb and E:I ratio were negatively correlated with age, and were higher in males than in females. The VR was negatively correlated with age, but it was not correlated with sex.
Conclusions
This study has provided data on the reference ranges for sudomotor and cardiovagal function tests in healthy Korean adults.

Citations

• Abnormal quantitative sudomotor axon reflex test results in patients with tinnitus as a possible indicator of small fiber neuropathy
  Hye Lim Lee, Hyun Ji Lyou, Jae-Jun Song, Chi Kyung Kim
  Frontiers in Neurology.2024;[Epub]     CrossRef
• Generalized anhidrosis with preganglionic sudomotor dysfunction in Fabry disease: a case report
  Eun Bin Cho, Seung Joo Kim, Tae-Won Yang, Heejeong Jeong, Changhyo Yoon, Seunguk Jung, Ki-Jong Park
  Clinical Autonomic Research.2021; 31(4): 585.     CrossRef
• Interpretation of Autonomic Function Test
  Kee Hong Park, Eun Hee Sohn
  Journal of the Korean Neurological Association.2021; 39(2): 61.     CrossRef