Related Experiment Video
Updated: Jun 17, 2026

Tilt Testing with Combined Lower Body Negative Pressure: a "Gold Standard" for Measuring Orthostatic Tolerance
Published on: March 21, 2013
Heart rate variability: Response to graded head up tilt in healthy men
Pramod Sharma1, B H Paudel, P N Singh
1Department of Physiology, Kathmandu Medical College, Kathmandu, Nepal. aamodsharma@yahoo.com
Background:
Heart rate variability is actually a misnomer for R to R variability in cardiac cycle. Variation in successive cycle length is called the heart rate variability (HRV). Head-up tilt is a model of studying cardiovascular haemodynamics, which reflects in heart rate variability (HRV).
Objectives:
To study the effect of 10 degrees and 70 degrees head-up tilt on HRV.
Materials And Methods:
The study was done in the Department of Physiology using graded head up tilt (passive orthostatism). HRV measurement was done at 10 degrees and 70 degrees tilt and compared with supine using standardised methods on 30 consenting healthy males (age 25.37+/-3.89 years). The HRV variables across postures were compared by ANOVA and Bonferroni test.
Results:
The heart rate increased at 70 degrees compared to 10 degrees and supine (70.48+/-8.17 Vs 70.22+/-8.67 and 88.51+/-12.84 bpm, p<0.001). The 70 degrees tilt decreased vagal HRV indicators compared to 10 degrees and supine: SDNN (31.13+/-8.12 Vs 38.07+/-11.29 and 38.13+/-10.89 ms, p<0.05), RMSSD (20.06 +/-8.47 Vs 34.23+/-14.22 and 36.16+/-12.22 ms, p<0.001), NN50 count (13.03+/-20.58 Vs 45.07+/-44.44 and 55.27+/-44.10, p<0.01), pNN50 (3.28+/-6.08 Vs 14.06+/-15.65 and 16.65+/-14.23, p<0.01), HF power (197.20+/-143.76 Vs 218.17+/-155.85 and 216.87+/-150.98 Hz, p<0.05), HFnu unit (24.28+/-14.16 Vs 45.48+/-16.34 and 47.67+/-19.89, p<0.001). The 70 degrees tilt increased LF power% (197.20+/-143.76 Vs 218.17+/-155.85 and 216.87+/-150.98, p<0.001). LFnu unit (75.72+/-14.76 Vs 54.52+/-16.34 and 52.32+/-19.89, p<0.001), LF: HF (4.96+/-4.08 Vs 1.53+/-1.138 and 1.69+/-1.67, p<0.001) compared to 10 degrees and supine.
Conclusion:
At 70 degrees tilt, HRV measures, reflecting vagal contribution to cardiac-cycle length, decreased with reciprocal increase in sympathetic activity compared to 10 degrees or supine leading to increase in sympathetic predominance. A 10 degrees tilt, which is almost equivalent to lying down with pillow, did not change HRV from supine. activity.
Related Concept Videos
Factors Influencing Heart Rate
Let us explore the significant factors affecting heart rate, including age, body temperature, posture, acute pain, chemical influences,...
Cardiac Output I:Effect of Heart Rate on Cardiac Output
Cardiac output (CO) refers to the total amount of blood ejected by one of the ventricles in liters per minute (L/min). In a resting adult, CO ranges from 5 to 6 L/min, adjusting according to the body's metabolic requirements.
Effect of Heart Rate on Cardiac Output
Cardiac output adapts to metabolic demands during stress, physical activity, or illness. The autonomic nervous system regulates heart rate via the sinoatrial node. The parasympathetic nervous system decreases heart rate...
Regulation of Heart Rates
The SNS increases heart rate through the release of norepinephrine and epinephrine, which act on beta-1 adrenergic receptors in the heart. This action increases the rate of depolarization in the sinoatrial (SA) node, the heart's...
Exercise and Cardiovascular Response
Light to moderate physical activity initiates a series of interconnected responses in the body. The heart rate modestly increases in anticipation of the workout, followed by widespread vasodilation as oxygen consumption by skeletal muscles increases. This results in decreased peripheral resistance, increased capillary blood flow, and accelerated...
Assessment of apical radial pulse
The A-R pulse assessment involves simultaneous evaluation of the apical and radial pulses. When the apical and radial pulse rates vary, this assessment helps identify a pulse deficit.
Pre-Procedural Preparation
Assessment of blood pressure in brachial artery(two-step method)

