Stroke Volume
ஸ்ட்ரோக் வால்யூம் (அடி அளவு)
Do not confuse Stroke Volume with Cardiac Output. One is a single contraction; the other is a one-minute aggregate. NEET examiners love this distinction to filter out students who memorize without understanding.
The idea
Stroke volume is the volume of blood pumped out by each ventricle during a single cardiac cycle. In a healthy adult, this value is approximately 70 mL. It is a fundamental parameter of cardiac performance. Remember, both ventricles pump the same volume under normal physiological conditions.
Why it matters
To quantify the efficiency of a single ventricular contraction in moving blood into the circulatory system.
NEET lens
NEET asks for the exact value: 70 mL. Expect calculation-based questions where you must multiply Stroke Volume by Heart Rate to find Cardiac Output. Do not memorize the value in isolation; link it to the Cardiac Cycle duration of 0.8 seconds.
Clinical significance
If Stroke Volume drops, the heart compensates by increasing the heart rate to maintain Cardiac Output. This is a hallmark of Congestive Heart Failure. Chronic reduction leads to systemic hypoxia and organ fatigue.
Introduction
Stroke Volume (SV) is the volume of blood ejected by one ventricle in a single contraction (one heartbeat). Normal resting SV ≈ 70 mL. CO = SV × HR.
Core concept
SV = End-Diastolic Volume (EDV) − End-Systolic Volume (ESV). EDV = volume in ventricle before contraction (~120-130 mL). ESV = volume remaining after contraction (~50-60 mL). SV = 120 − 50 = 70 mL. Ejection fraction (EF) = SV/EDV × 100 = 70/120 × 100 ≈ 58%. Normal EF > 55%. Low EF (<40%) = systolic heart failure. Factors increasing SV: Increased preload (more venous return → Starling's law). Increased contractility (sympathetic stimulation, inotropic drugs). Decreased afterload (lower aortic pressure → easier ejection).
Go deeper
Preload vs afterload: Preload = degree of ventricular filling before contraction (= EDV). More preload → more stretch of myocytes → stronger contraction (Starling's law) → higher SV. Afterload = resistance against which heart pumps (essentially aortic pressure/systemic vascular resistance). High afterload (hypertension) → harder to eject → lower SV → heart works harder → eventually fails.
From Class 10
Each heartbeat pumps a specific amount of blood into the aorta. This amount per beat is the stroke volume.