Brown S J, Bryant M, Mundel T, Stannard S R
Institute of Food, Nutrition and Human Health, Massey University, New Zealand.
J Physiol Pharmacol. 2008 Dec;59(4):771-80.
Cardiac vagal withdrawal when moving from supine to an upright posture may be independent of respiratory sinus arrhythmia. Further, ventilatory efficiency of an upright lung may improve with clustering of heart beats during inhalation. We studied healthy human subjects (n=8, 6 male) during supine rest (SUP) and 80 degrees head-up tilt (HUT). ECG and expired breath were sampled continuously to determine heart rate, mean and end-tidal (ET) fractional content (F) of O2 and CO2, tidal volume (V(T)) and breathing frequency (Bf). HUT increased heart rate (47+/-3 vs. 59+/-9 beats min(-1), p<0.01), decreased the high frequency component of heart rate variability (8.76+/- vs. 7.07+/-1.12, p<0.05), and increased the ratio of low to high frequency components in the heart rate (0.62+/-0.6 vs. 1.79+/-2.07, p<0.05). HUT did not change VT, Bf, or minute ventilation (V'E), but decreased FCO2 (4.90+/-0.48 vs. 4.56+/-0.42 %, p<0.05) and FETCO2 (6.64+/-0.24 vs. 6.30+/-0.27 %, p<0.01). HUT increased the CO2 ventilatory equivalent (24.88+/-2.50 vs. 26.74+/-2.61, p<0.01). Mean heart rate during inhalation increased with HUT (26+/-3 vs. 34+/-6 beats min-1), with no change during exhalation. Increased clustering of heart beats during inhalation independent of a decrease in HF cardiac variability may partly offset decreases in ventilatory efficiency of an upright lung.
从仰卧位转变为直立姿势时的心脏迷走神经撤离可能与呼吸性窦性心律失常无关。此外，直立位肺部的通气效率可能会随着吸气时心跳的聚集而提高。我们对健康人类受试者（n = 8，6名男性）进行了仰卧休息（SUP）和80度头高位倾斜（HUT）期间的研究。连续采集心电图和呼出气体样本，以确定心率、氧气和二氧化碳的平均及潮气末（ET）分数含量（F）、潮气量（V(T)）和呼吸频率（Bf）。HUT使心率增加（47±3对59±9次/分钟，p<0.01），降低了心率变异性的高频成分（8.76±对7.07±1.12，p<0.05），并增加了心率中低频与高频成分的比值（0.62±0.6对1.79±2.07，p<0.05）。HUT未改变VT、Bf或分钟通气量（V'E），但降低了FCO2（4.90±0.48对4.56±0.42%，p<0.05）和FETCO2（6.64±0.24对6.30±0.27%，p<0.01）。HUT增加了二氧化碳通气当量（24.88±2.50对26.74±2.61，p<0.01）。吸气期间的平均心率随HUT增加（26±3对34±6次/分钟），呼气期间无变化。吸气时心跳聚集增加，与高频心脏变异性降低无关，这可能部分抵消直立位肺部通气效率的降低。
