📚 6B1 The Circulatory System: Experimental Design | 6B1 循环系统：实验设计
Designing experiments to explore the circulatory system allows students to connect theoretical knowledge with practical skills. From measuring pulse rate to dissecting a heart, each investigation reinforces understanding of how blood is pumped, transported, and regulated. This article presents a series of experimental designs, highlighting key variables, methods, safety considerations, and data analysis techniques for GCSE and A-Level biology.
设计探索循环系统的实验可以帮助学生将理论知识与实践技能联系起来。从测量脉搏到解剖心脏，每项探究都强化了对血液如何被泵出、运输和调节的理解。本文介绍一系列实验设计，重点突出了 GCSE 和 A-Level 生物学中的关键变量、方法、安全考量和数据分析技巧。
1. Measuring Resting and Post-Exercise Heart Rate | 测量静息和运动后心率
The aim of this experiment is to determine how short bursts of exercise affect heart rate. The independent variable is the exercise condition (resting vs. immediately after 2 minutes of step-ups), and the dependent variable is heart rate measured in beats per minute (bpm). Controlled variables include the duration of exercise, the type of exercise step, the age and fitness level of the subject, and the time interval before taking the pulse.
本实验的目的是确定短时间运动如何影响心率。自变量是运动条件（静息状态与进行2分钟台阶测试后即刻），因变量是以每分钟心跳次数（bpm）表示的心率。控制变量包括运动持续时间、台阶运动的类型、受试者的年龄和体能水平以及测量脉搏前的时间间隔。
| Variable Type | Description (English) | 描述 (中文) |
|---|---|---|
| Independent | Exercise condition (rest vs. after exercise) | 运动条件（静息 vs. 运动后） |
| Dependent | Heart rate (bpm) | 心率（次/分钟） |
| Controlled | Exercise time (2 min), step height, subject's age, time after exercise | 运动时长（2分钟）、台阶高度、受试者年龄、运动后时间 |
The subject sits quietly for 5 minutes. The radial pulse is located on the wrist using the index and middle fingers. Count the beats for 15 seconds and multiply by 4 to obtain beats per minute. Record three readings and calculate the mean resting heart rate. Then the subject performs step-ups on a low bench (20 cm) at a steady pace for exactly 2 minutes. Immediately after stopping, the pulse is counted again for 15 seconds and converted to bpm. Repeat the entire procedure on three different volunteers to increase reliability.
受试者静坐5分钟。用食指和中指在手腕处找到桡动脉脉搏。计数15秒的搏动次数，乘以4得到每分钟心率。记录三个读数并计算平均静息心率。然后受试者在低凳（20厘米）上以稳定速度进行台阶运动，正好2分钟。停止后立即再次测量脉搏15秒并转换为次/分钟。对三位不同志愿者重复整个流程以提高可靠性。
Risk assessment: ensure the test subject is in good health and not suffering from any cardiovascular condition. Stop the exercise if the subject feels dizzy or unwell. Use a sturdy bench and a non-slip floor.
风险评估：确保受试者身体健康，无心血管疾病。若受试者感到头晕或不适，立即停止运动。使用稳固的凳子，地面防滑。
Analysis: plot heart rate (bpm) against condition (rest, post-exercise) as a bar chart. Evaluate whether the increase in heart rate is significant. Discuss the role of the sympathetic nervous system and adrenaline in elevating heart rate to supply more oxygen to muscles.
分析：绘制心率（次/分钟）对运动状态（静止、运动后）的条形图。评估心率增加是否显著。讨论交感神经系统和肾上腺素在加快心率以向肌肉供给更多氧气方面的作用。
2. Investigating the Effect of Caffeine on Daphnia Heart Rate | 研究咖啡因对水蚤心率的影响
Many exam boards use Daphnia (water fleas) to investigate the effect of chemicals on heart rate. The transparent body of Daphnia allows direct observation of the heart under a light microscope. The independent variable is the concentration of caffeine solution (e.g., 0%, 0.1%, 0.5%, 1.0%). The dependent variable is the heart rate of Daphnia, measured in beats per minute. Controlled variables include temperature, volume of solution added, species and size of Daphnia, and time allowed for equilibration.
许多考试局使用水蚤来研究化学物质对心率的影响。水蚤透明的身体使得在光学显微镜下可以直接观察心脏。自变量是咖啡因溶液的浓度（如0%、0.1%、0.5%、1.0%）。因变量是水蚤的心率，以每分钟搏动次数测量。控制变量包括温度、加入溶液的体积、水蚤的种类和大小以及平衡时间。
Place a single Daphnia ion (×40) and locate the beating heart. Count the number of beats in 15 seconds using a hand tally counter, then calculate bpm. This is the baseline reading. Replace the water carefully with a pad of filter paper and add a drop of 0.1% er 1 minute, record heart rate again. Repeat for each caffeine concentration using a fresh Daphnia each time to avoid cumulative effects.
将一只水蚤置于凹玻片上，滴一滴池水。放入少量棉花纤维以限制其活动而不损伤生物体。在低倍镜（×40）下聚焦，找到跳动的心脏。使用手持计数器记录15秒内的搏动次数，然后计算次/分钟。此为基线读数。用滤纸小心吸走水分，加入一滴0.1%咖啡因溶液。1分钟后再次记录心率。每种浓度使用一只新的水蚤重复上述步骤，以避免累积效应。
Ethical considerations: Daphnia are living organisms and should be handled with care. Minimise exposure time to chemicals, and return them to fresh pond water promptly after the experiment. Ensure not to overheat the microscope light to avoid thermal stress.
伦理考量：水蚤是活体，应小心处理。尽量减少暴露在化学品中的时间，实验后迅速将其放回新鲜池水中。确保不要使显微镜光源过热，以避免热应激。
Plot a line graph of heart rate against caffeine concentration. The expected result is an increase in heart rate due to caffeine acting as a stimulant that blocks adenosine receptors. Identify sources of error, such as difficulty in counting rapid beats or variation between individual Daphnia.
绘制心率对咖啡因浓度的线形图。预期结果是心率加快，因为咖啡因作为兴奋剂阻断腺苷受体。确认误差来源，例如快速搏动难以计数或个体水蚤之间的差异。
3. Observing Capillary Refill Time and Blood Flow in Skin | 观察毛细血管再充盈时间和皮肤血流
Capillary refill time (CRT) is a simple clinical test to assess peripheral circulation and hydration. Pressing on a fingernail or skin bed blanches the area; measuring the time for colour to return gives an indication of blood flow rate. The independent variable could be the digit pressed (e.g., thumb vs. little finger) or the ambient temperature. The dependent variable is the refill time in seconds. Controlled variables include the pressure applied and the duration of blanching.
毛细血管再充盈时间是评估外周循环和水分状况的简单临床测试。按压指甲或皮肤床使区域变白；测量颜色恢复所需的时间可以指示血流速度。自变量可以是被按压的指头（如拇指与小指）或环境温度。因变量是以秒为单位的再充盈时间。控制变量包括施加的压力和按压持续时间。
Ask the subject to hold their hand at heart level. Firmly press the fingernail of the index finger for 5 seconds until the nail bed turns white. Release and start a stopwatch. Stop timing when the colour fully returns to the nail bed. Repeat three times and compute the average. Perform the same procedure on a different finger or at a cooler room temperature. Compare CRT values: normal CRT is less than 2 seconds; prolonged CRT may indicate vasoconstriction or dehydration.
让受试者将手保持在心脏水平。用力按压食指指甲5秒，直到甲床变白。松开并启动秒表。当颜色完全恢复至甲床时停止计时。重复三次并计算平均值。对另一根手指或在较冷的室温下重复相同步骤。比较CRT数值：正常CRT小于2秒；延长可能表明血管收缩或脱水。
This experiment illustrates how arterioles regulate local blood flow. A risk assessment should note that pressing too hard might cause discomfort, but no serious hazard exists. Wash hands before and after.
本实验说明了小动脉如何调节局部血流。风险评估需注意按压过重可能导致不适，但无严重危险。前后洗手。
4. Auscultation of Heart Sounds Using a Stethoscope | 使用听诊器听心音
Auscultation enables the detection of the characteristic 'lub-dub' sounds produced by the closing of heart valves. The first sound ('lub') is caused by the closure of the atrioventricular (tricuspid and mitral) valves at the start of ventricular systole; the second sound ('dub') is due to the closure of the semilunar valves. This non-invasive experiment helps students link valve action to the cardiac cycle.
听诊可以检测到心脏瓣膜关闭时产生的特征性“lub-dub”声。第一心音（“lub”）由心室收缩初期房室瓣（三尖瓣和二尖瓣）的关闭引起；第二心音（“dub”）则因半月瓣关闭产生。这项非侵入性实验有助于学生将瓣膜活动与心动周期联系起来。
Using an alcohol swab, clean the earpieces and the chest piece of the stethoscope. Place the chest piece firmly on the subject's chest at the fourth intercostal space left of the sternum. Identify the two distinct sounds. Calculate the heart rate from the sounds over 15 seconds. Then, ask the subject to perform light jogging for 1 minute and listen again immediately. Note the increased rate and the shorter interval between 'lub' and 'dub', which reflects reduced filling time during high cardiac output.
用酒精棉片清洁听诊器耳塞和胸件。将胸件紧贴于受试者胸骨左缘第四肋间。识别两种不同的声音。从15秒内的心音计算心率。然后，让受试者轻度慢跑1分钟，立即再次听诊。注意心率的增加和“lub”与“dub”之间间隔的缩短，这反映高心输出量时充盈时间缩短。
Do not apply excessive pressure; maintain hygiene. Discuss possible sources of error, such as extraneous room noise. Compare the recorded heart rate with the pulse rate measured at the wrist to illustrate the pulse deficit sometimes observed in arrhythmias.
不要施加过大压力；保持卫生。讨论可能的误差来源，如室外来音。将记录的心率与手腕处测得的脉搏率进行比较，阐释心律失常时有时观察到的脉搏短绌。
5. Measuring Blood Pressure with a Sphygmomanometer | 使用血压计测量血压
Blood pressure measurement demonstrates the force exerted by circulating blood on artery walls. The independent variable can be posture (lying, sitting, standing), and the dependent variable is systolic and diastolic pressure in mmHg. Controlled variables include the cuff size, the arm position at heart level, and the subject's resting period.
血压测量展示了循环血液对动脉壁施加的力量。自变量可以是姿势（躺、坐、站），因变量是以 mmHg 为单位的收缩压和舒张压。控制变量包括袖带尺寸、手臂置于心脏水平的位置以及受试者的静息时间。
| Variable Type | Value | 中文 |
|---|---|---|
| Independent | Body posture (lying, sitting, standing) | 身体姿势（躺、坐、站） |
| Dependent | Blood pressure (mmHg) | 血压（毫米汞柱） |
Have the subject rest for 5 minutes in a seated position. Wrap the cuff snugly around the upper arm, aligning the artery mark with the brachial artery. Close the valve, inflate the cuff to about 180 mmHg, then slowly release the valve at 2–3 mmHg per second. Using a stethoscope placed over the brachial artery, note the pressure at which the first Korotkoff sound is heard (systolic) and the pressure at which the sound disappears (diastolic). Repeat in lying and standing positions after a rest interval. Explain how gravity and venous return influence blood pressure readings.
让受试者静坐休息5分钟。将袖带紧贴上臂缠绕，使动脉标记对准肱动脉。关闭阀门，将袖带充气至约180 mmHg，然后以每秒2-3 mmHg的速度缓慢放气。将听诊器置于肱动脉上方，记录听到第一声柯氏音时的压力（收缩压）和声音消失时的压力（舒张压）。休息后重复躺姿和站姿的测量。解释重力和静脉回流如何影响血压读数。
6. Modelling the Circulatory System with a Pump and Plastic Tubing | 用泵和塑料管模拟循环系统
Building a physical model helps visualise the relationship between flow, pressure, and vessel diameter. The model uses a water pump (representing the heart), two tubes of different diameters (representing artery and vein), and a sponge-filled chamber (representing capillary bed). By adding a clamp to partly occlude a tube, students can simulate the effect of atherosclerosis.
构建物理模型有助于直观了解血流、压力和血管直径之间的关系。该模型使用水泵（代表心脏）、两根不同直径的管子（代表动脉和静脉）以及填充海绵的腔室（代表毛细血管床）。通过添加夹子部分阻塞管腔，学生可以模拟动脉粥样硬化的影响。
ure flow rate (mL/s) using a measuring cylinder and stopwatch. Record the pressure difference using a manometer or simply by observing the height of water column in vertical side tubes. Then partially clamp the ‘ antitative analysis: use the relationship Flow = Pressure / Resistance, though simplified.
设置一个水箱，用蠕动泵连接一根宽管，通向装填海绵的狭窄段，然后进入回流管。使用量筒和秒表测量流速（毫升/秒）。用压力计或通过观察侧管中水柱高度记录压力差。然后部分夹闭“动脉”，观察下游流量的减少。这展示了斑块积聚如何增加阻力并降低灌注。定量分析：使用简化的流量 = 压力 / 阻力关系。
This model is an approximate representation; note that blood is a non-Newtonian fluid and vessels are elastic. Yet it allows manipulation of 'vessel' diameter and 'heart' rate to see the effect on capillary flow, reinforcing the concept of double circulation.
此模型为近似表示；注意血液是非牛顿流体，血管有弹性。然而它可以操控“血管”直径和“心率”来观察对毛细血管流量的影响，强化双循环概念。
7. Dissection of a Mammalian Heart | 哺乳动物心脏解剖
Heart dissection allows tactile and visual exploration of the four chambers, valves, and major blood vessels. A sheep or pig heart is commonly used. The experiment helps identify the thicker left ventricular wall, the chordae tendineae, and the difference between the aorta and the pulmonary artery. Ethical sourcing from a butcher or biological supplier is required.
心脏解剖可以从触觉和视觉上探索四个心腔、瓣膜和主要血管。通常使用羊心或猪心。实验有助于识别较厚的左心室壁、腱索以及主动脉和肺动脉之间的区别。需要从肉店或生物供应商合乎伦理地获取材料。
Wear gloves and eye protection. Place the heart on a dissecting board. Identify the anterior side by locating the coronary artery running along the surface. Make a shallow incision along the right ventricle from the pulmonary artery to the apex, exposing the tricuspid valve. Similarly, open the left ventricle to compare wall thickness and observe the bicuspid valve. Probe the aorta to see the opening of the coronary arteries. Draw labelled diagrams of both external and internal structures. Calculate the ventricular mass ratio (left/right) by carefully trimming away the atria and weighing the ventricles.
戴手套和护目镜。将心脏置于解剖板上。通过表面走向的冠状动脉确定前面。从肺动脉沿右心室浅切至心尖，暴露三尖瓣。同样打开左心室以比较壁厚并观察二尖瓣。探入主动脉查看冠状动脉开口。绘制标注清晰的内外部结构图。通过切除心房并称重心室，计算心室质量比（左/右）。
Risk assessment: blades are sharp, so cut away from the body. Disinfect workspace afterwards. Relate the greater muscle mass of the left ventricle to its role in pumping blood through the high-resistance systemic circuit.
风险评估：刀片锋利，切割时远离身体。事后对工作区进行消毒。将左心室较大的肌肉质量与其通过高阻力体循环泵血的作用联系起来。
8. Designing an Investigation to Test How Temperature Affects Heart Rate | 设计实验测试温度对心率的影响
In the context of the circulatory system, temperature can be investigated using a Daphnia model or using human subjects by varying environmental temperature within safe limits. For ethical and practical reasons, the Daphnia experiment is preferred. The independent variable is water temperature (e.g., 10, 15, 20, 25, 30 °C). The dependent variable is Daphnia heart rate. Controlled variables include caffeine absence, light intensity, Daphnia species, and acclimation time.
在循环系统专题中，可以使用水蚤模型或通过将环境温度控制在安全范围内的人体受试者来研究温度的影响。出于伦理和实际原因，水蚤实验更为可取。自变量是水温（如10、15、20、25、30 °C）。因变量是水蚤心率。控制变量包括无咖啡因、光照强度、水蚤种类和适应时间。
Place a Daphnia on a cavity slide and cover with a cover slip supported by cotton fibres. Place the slide on a temperature-controlled stage (or use a Petri dish with water of known temperature). Using a thermometer, allow the specimen to acclimatise for 2 minutes. Record heart rate over 15 seconds and convert to bpm. Repeat at each temperature with a fresh Daphnia. Plot heart rate against temperature. Expect an increase in heart rate with temperature due to higher metabolic rate, following the Q10 coefficient (approximately 2 for biological reactions). Discuss how excessive heat can denature enzymes and become lethal.
将水蚤置于凹玻片上，盖上盖玻片并用棉花纤维支撑。将玻片放在温控台上（或使用已知水温的培养皿）。用温度计让标本适应2分钟。记录15秒内的心率并转换为次/分钟。每种温度使用一只新的水蚤重复。绘制心率对温度的图。预期心率随温度升高而加快，因为代谢率提高，遵循 Q10 系数（生物反应约为2）。讨论过热如何使酶变性并致死。
Evaluate the difficulty in controlling exact temperature and the rapid heat loss from the slide. A water bath with a transparent bottom and a microscope would be an ideal but more complex design.
评估控制精确温度的困难以及玻片上热量的快速散失。带有透明底水浴槽和显微镜将是理想但更复杂的设计。
9. Analysing an ECG Trace to Determine Heart Rate and Rhythm | 分析心电描记图确定心率和节律
Electrocardiography (ECG) records the electrical activity of the heart. This exercise involves interpreting a normal and an abnormal ECG trace as an experimental design in a data-based task. The independent variable could be the type of trace (normal, tachycardia, bradycardia) or the lead placement. The dependent variable is the calculated heart rate and intervals like the PR and QT segments.
心电图记录心脏的电活动。本练习将解释正常和异常心电图迹线作为基于数据的实验设计任务。自变量可以是迹线类型（正常、心动过速、心动过缓）或导联放置位置。因变量是计算出的心率和PR间期、QT间期等。
s. Heart rate (bpm) = 60 / R-R interval. For a normal trace at rest, R-R is about 0.8 s, giving a rate of 75 bpm. Determine whether the rhythm is regular. Compare with a trace showing atrial fibrillation (irregular R-R intervals). Discuss the physiological significance of a prolonged PR interval (first-degree heart block) and an elevated ST segment (possible myocardial infarction).
检查提供的心电图纸条。识别P波、QRS波群和T波。测量连续两个R波之间的时间（R-R间期），单位为秒。心率（次/分钟）= 60 / R-R间期。对于静息正常迹线，R-R约0.8秒，心率为75次/分钟。判断节律是否规则。与显示房颤（不规则R-R间期）的迹线进行比较。讨论PR间期延长（一度房室传导阻滞）和ST段抬高（可能的心肌梗死）的生理意义。
This analytical experiment requires no wet lab and can be assessed on data-handling skills. Students could design an investigation on how electrolyte imbalances (e.g., hyperkalemia) alter the ECG. Summarise by linking electrical events to mechanical contraction: P wave precedes atrial systole, and the QRS triggers ventricular systole.
这项分析性实验不需要湿实验室操作，可评估数据处理技能。学生可以设计实验探究电解质失衡（如高钾血症）如何改变心电图。总结时将电活动与机械收缩联系起来：P波在心房收缩之前，QRS波群触发心室收缩。
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