📚 Short-term Effects on the Cardiovascular System | 短期对心血管系统的影响
The cardiovascular system exhibits immediate and reversible adjustments when the body encounters a stressor such as exercise. These short-term responses are orchestrated by neural and hormonal mechanisms to increase oxygen delivery to active tissues and remove metabolic waste products.
当身体遇到如运动等压力源时，心血管系统会立即做出可逆的调整。这些短期反应由神经和激素机制协调，以增加向活性组织输送氧气并清除代谢废物。
1. Overview of Short-term Cardiovascular Responses | 短期心血管反应概述
Short-term cardiovascular changes occur within seconds of the onset of exercise. They involve increases in heart rate, stroke volume, and cardiac output, along with a redistribution of blood flow to active skeletal muscles. These responses are essential for matching oxygen supply with the heightened metabolic demand.
短期心血管变化在运动开始后的几秒内发生，包括心率、搏出量和心输出量的增加，以及血流向活跃骨骼肌的重新分配。这些反应对于使氧气供应与增加的代谢需求相匹配至关重要。
2. Neural Regulation: Sympathetic Activation | 神经调节：交感神经激活
The sympathetic nervous system is rapidly stimulated via the cardiovascular centre in the medulla oblongata. Sympathetic nerves release noradrenaline at the sinoatrial (SA) node, atrioventricular (AV) node, and ventricular muscle fibres. This increases the rate of spontaneous depolarisation at the SA node and enhances myocardial contractility.
通过延髓心血管中枢，交感神经系统迅速被激活。交感神经在窦房结、房室结和心室肌纤维处释放去甲肾上腺素，这加快了窦房结自发去极化的速率，并增强了心肌收缩力。
Concurrently, parasympathetic (vagal) tone to the heart is reduced. Withdrawal of vagal inhibition further elevates heart rate.
同时，支配心脏的副交感（迷走）张力降低。撤回迷走抑制进一步提升了心率。
3. Hormonal Influence: Adrenaline Release | 激素影响：肾上腺素释放
The sympathetic stimulation of the adrenal medulla triggers the secretion of adrenaline and noradrenaline into the bloodstream. Circulating adrenaline binds to beta-1 adrenergic receptors on the heart, mimicking and reinforcing sympathetic nerve effects. It increases heart rate (chronotropic effect) and force of contraction (inotropic effect).
交感神经刺激肾上腺髓质，促使肾上腺素和去甲肾上腺素分泌进入血液。循环中的肾上腺素与心脏上的β-1肾上腺素能受体结合，模拟并增强交感神经的作用，提升心率（变时效应）和收缩力（变力效应）。
4. Increase in Heart Rate | 心率增加
Heart rate (HR) rises almost immediately, from a resting value of around 70 beats per minute (bpm) to 100 bpm or more within the first few seconds, and can reach up to 200 bpm in a trained athlete during maximal effort. The increase results from SA node acceleration and vagal withdrawal.
心率几乎立即增加，从静息时的约每分钟70次，在最初几秒内升至100次/分或更高，经过训练的运动员在最大努力时可达200次/分。这一增加源于窦房结加速和迷走神经撤回。
Resting HR ≈ 70 bpm → Exercising HR up to 200 bpm
5. Enhanced Stroke Volume: Starling’s Law | 搏出量增强：施塔林定律
Stroke volume (SV) increases due to stronger ventricular contraction and greater ventricular filling. According to the Frank-Starling mechanism, an increase in end-diastolic volume stretches cardiac muscle fibres, leading to a more forceful contraction. Additionally, sympathetic stimulation raises intracellular Ca²⁺ levels in cardiomyocytes, boosting contractility.
搏出量因更强的心室收缩和更大的心室充盈而增加。根据弗兰克-施塔林机制，舒张末期容积的增加拉伸心肌纤维，导致更有力的收缩。此外，交感刺激升高心肌细胞内的Ca²⁺水平，增强收缩力。
Venous return is enhanced by the skeletal muscle pump and respiratory pump, which increases preload and thus stroke volume.
骨骼肌泵和呼吸泵增强了静脉回流，从而增加前负荷和搏出量。
6. Cardiac Output Rise | 心输出量上升
Cardiac output (Q) is the product of heart rate and stroke volume: Q = HR × SV. During intense exercise, cardiac output can rise from approximately 5 L/min at rest to over 20–25 L/min in elite athletes. This dramatic increase delivers more oxygenated blood per unit time.
心输出量是心率与搏出量的乘积：Q = HR × SV。剧烈运动时，心输出量可从静息时约5升/分钟升至精英运动员的20–25升/分钟以上。这一显著增长每单位时间输送了更多含氧血液。
Q = HR × SV
The table below contrasts typical cardiovascular parameters at rest and during strenuous exercise.
下表对比了休息和剧烈运动时的典型心血管参数。
| Parameter | At Rest | During Strenuous Exercise |
|---|---|---|
| Heart Rate (bpm) | 70 | 180-200 |
| Stroke Volume (mL/beat) | 70 | 110-130 |
| Cardiac Output (L/min) | ~5 | 20-25 |
These changes illustrate the enormous capacity of the cardiovascular system to adapt acutely.
这些变化显示了心血管系统急性适应的巨大能力。
7. Blood Pressure Regulation | 血压调节
Mean arterial blood pressure (BP) is determined by cardiac output and total peripheral resistance (TPR): BP = CO × TPR. During dynamic exercise, systolic pressure rises significantly (e.g., from 120 mmHg to 180 mmHg or more) while diastolic pressure changes only slightly or may even decrease due to vasodilation in active muscles. The baroreceptor reflex is reset to tolerate higher pressures, preventing excessive bradycardia.
平均动脉血压由心输出量和总外周阻力决定：BP = CO × TPR。在动态运动中，收缩压显著升高（例如从120 mmHg升至180 mmHg或更高），而舒张压变化很小甚至可能因活动肌肉血管舒张而下降。压力感受器反射被重置以耐受较高压力，防止过度心动过缓。
BP = CO × TPR
8. Vasomotor Adjustments: Vasodilation & Vasoconstriction | 血管舒缩调节：血管舒张与收缩
Arterioles in active skeletal muscles undergo pronounced vasodilation triggered by local metabolites such as CO₂, H⁺, K⁺, adenosine, and increased temperature. This reduces resistance and allows increased blood flow. In contrast, arterioles in non-essential regions—such as the gut, kidneys, and skin (initially)—constrict via sympathetic α-adrenergic stimulation, diverting blood away.
活跃骨骼肌中的小动脉在局部代谢产物（如CO₂、H⁺、K⁺、腺苷和温度升高）的作用下发生显著的血管舒张，降低阻力，增加血流量。相反，非必需区域（如肠道、肾脏和皮肤（最初））的小动脉通过交感α-肾上腺素能刺激而收缩，以分流血液。
The net effect is a controlled reduction in TPR despite widespread vasoconstriction, because vasodilation in a large mass of active muscle dominates.
净效果是在广泛的血管收缩中受控降低TPR，因为大块活跃肌肉中的血管舒张占主导地位。
9. Redistribution of Blood Flow | 血流重新分配
At rest, approximately 15–20% of cardiac output goes to skeletal muscle; during maximal exercise, this can exceed 85%. Blood flow to the brain is maintained at a nearly constant level, while coronary flow increases to meet the heart’s own elevated oxygen demand. Flow to kidneys and splanchnic organs is substantially reduced.Published by TutorHao | A-Level Biology Revision Series | aleveler.com
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