Demonstration of non-invasive assessment of autonomic nervous functions

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BACKGROUND

Autonomic nervous functions play a major role in maintaining the normal body homeostasis. The diagnosis of the autonomic dysfunction with invasive assessments is time consuming and hence the noninvasive assessments are used.¹

The aim of the experiment is demonstration of non-invasive assessment of autonomic nervous functions

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REQUIREMENTS

Subjects:     Human

Apparatus:  Electrocardiogram

             Disposable syringe

            Sphygmomanometer

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PROCEDURE

Power spectral analysis

This involves the degeneration of the hemodynamic parameters into a sum of sinusoidal waves of different amplitudes and strengths and the results are displayed with the magnitude of variability in the power spectrum. The PSA techniques used to determine the heart rate variability (HRV) and blood pressure variability (BPV) focuses on frequencies between 0.025 and 0.50 Hz.¹

Deep breathing

The subject inhales and exhales deeply for duration of 5 seconds each and the HR is monitored with continuous electrocardiogram during this maneuver. The RR intervals during inspiration and expiration are calculated and expressed as the mean difference between maximum and minimum heart rates for the maneuver.¹

Valsalva maneuver

The subject blows into a disposable syringe with an open glottis connected to a mercury column of a sphygmomanometer and maintains a forced expiratory of 40 mmHg for 15 seconds. There are 4 distinct changes in HR and BP in valsalva maneuver. The valsalva ratio is calculated by the ratio of the longest RRI post-maneuver to the shortest RRI during the maneuver.¹

Sustained hand grip

This test provides evidence of function of efferent sympathetic nervous system. The handgrip is measured by handgrip dynamometer and maintained at 30% for duration of 5 minutes. The normal value is ≥16 mmHg increase in diastolic BP and abnormal value is ≤ 10mmHg.¹

Active orthostasis

There is a characteristic change in Heart rate when changing from supine to standing. This response is mediated via vagus nerve. The shortest RRI at 15^th beat and the longest RRI at the 30^th beat post standing are recorded. The sympathetic function is considered normal if the systolic BP decreases by <10 mmHg, borderline 11-29 mmHg and is considered abnormal if the systolic BP falls by 30 mmHg within 3-minutes post-standing.¹

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CONCLUSION

The non-invasive assessments help in diagnosing the various dysfunctions and diseases associated with the autonomic nervous system.

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REFERENCES

1. O’ Driscoll JM, Sharma R. Non-Invasive Assessment of the Autonomic Nervous System. Int J Clin Ther Diagn. 2015;3(3):85-91.