Sharma Pramod, Paudel B H, Singh P N, Limbu P
Department of Physiology, Kathmandu Medical College, Kathmandu, Nepal.
Kathmandu Univ Med J (KUMJ). 2009 Jul-Sep;7(27):252-7. doi: 10.3126/kumj.v7i3.2733.
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).
To study the effect of 10 degrees and 70 degrees head-up tilt on HRV.
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.
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.
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.
心率变异性实际上是心动周期中R-R间期变异性的误称。连续心动周期长度的变化称为心率变异性（HRV）。头高位倾斜是研究心血管血液动力学的一种模型，可在心率变异性（HRV）中得到体现。
研究10度和70度头高位倾斜对HRV的影响。
本研究在生理学系采用分级头高位倾斜（被动直立位）进行。在10度和70度倾斜时进行HRV测量，并使用标准化方法与30名自愿参与的健康男性（年龄25.37±3.89岁）的仰卧位测量结果进行比较。通过方差分析和Bonferroni检验比较不同体位下的HRV变量。
与10度和仰卧位相比，70度时心率增加（70.48±8.17次/分钟 vs 70.22±8.67次/分钟和88.51±12.84次/分钟，p<0.001）。与10度和仰卧位相比，70度倾斜时迷走神经HRV指标降低：SDNN（31.13±8.12毫秒 vs 38.07±11.29毫秒和38.13±10.89毫秒，p<0.05），RMSSD（20.06±8.47毫秒 vs 34.23±14.22毫秒和36.16±12.22毫秒，p<0.001），NN50计数（13.03±20.58 vs 45.07±44.44和55.27±44.10，p<0.01），pNN50（3.28±6.08 vs 14.06±15.65和16.65±14.23，p<0.01），HF功率（197.20±143.76赫兹 vs 218.17±155.85赫兹和216.87±150.98赫兹，p<0.05），HFnu单位（24.28±14.16 vs 45.48±16.34和47.67±19.89，p<0.001）。与10度和仰卧位相比，70度倾斜时LF功率百分比增加（197.20±143.76 vs 与10度和仰卧位相比，70度倾斜时LF功率百分比增加（197.20±143.76 vs 218.17±155.85和216.87±150.98，p<0.001）。LFnu单位（75.72±14.76 vs 54.52±16.34和52.32±19.89，p<0.001），LF:HF（4.96±4.08 vs 1.53±1.138和1.69±1.67，p<0.001）。
与10度或仰卧位相比，70度倾斜时，反映迷走神经对心动周期长度贡献的HRV指标降低，同时交感神经活动相应增加，导致交感神经优势增强。10度倾斜几乎相当于垫着枕头躺下，与仰卧位相比，HRV没有变化。
