Stroke volume

The term cardiac output refers to the quantity of the blood that your heart can pump in one minute, represented in litres per minute. Cardiac output indicates how effectively your heart is supplying oxygen and nutrients throughout your body. It shows how well your heart is performing in relation to the rest of your cardiovascular system. In order to determine cardiac output, you need to determine both stroke volume and heart rate. This can only be done by a professional who will use an echocardiogram. Get a stopwatch or clock. The heart rate is simply the number of heartloads of blood that are ejected from the heart per unit of time. Typically we measure heart rate by beats per minute. Measuring your heart rate is simple, but before attempting it, make sure you have an accurate device to count the seconds. • You can attempt to keep track of the the beats and seconds in your head, but this could be inaccurate because the beats you count tend to overpower one’s inner clock.. • It is better to set a timer, so you can focus on counting the beats. Try using the timer on your cell phone. Find your pulse. Although there are many places on your body where you can find a pulse, the inner wrist is usually an easy place to find it. An alternative is on the side of your throat, on the jugular vein area. Once you have identified your pulse and have a clear beat, take the forefinger and middle finger of one hand and place them over the area where you can feel the pulse. X National Healt...

STROKE VOLUME AND CARDIAC OUTPUT Illustration from Anatomy & Physiology, Connexions Web site. http://cnx.org/content/col11496/1.6/, Jun 19, 2013. Stroke Volume Stroke Volume (SV) is the volume of blood in millilitres ejected from the each ventricle due to the contraction of the heart muscle which compresses these ventricles. SV is the difference between end diastolic volume (EDV) and end systolic volume (ESV). Multiple factors can affect SV, eg. factors that change either EDV or ESV will change SV. The three primary factors that regulate SV are Heart rate (HR) also affects SV. Changes in HR alone inversely affects SV. However, SV can increase when there is an increase in HR (during exercise for example) when other mechanisms are activated, but when these mechanisms fail, SV cannot be maintained during an elevated HR. These mechanisms include increased venous return, venous constriction, increased atrial and ventricular inotropy and enhanced rate of ventricular relaxation. The ODM+ calculates SV by multiplying the Normal values for a resting healthy individual would be approximately 60-100mL. Patients undergoing surgery or in critical illness situations may require higher than normal SV and it may be more appropriate to aim for optimal rather than normal SV. See Stoke Volume Index Stroke Volume Index (SVI) relates SV to body surface area (BSA), thus relating heart performance to the size of the individual. The unit of measurement is millilitres per square metre (ml/m 2). SV...

The LVOT Diameter is measured in the parasternal long axis view in mid systole and is usually around 2cm. ​ ​ The LVOT velocity time integral (VTI) provides information regarding blood velocity across the time period of systole and is in the units of cm. It is considered a stroke distance. Typical values are around 15 to 25cm. One needs to use pulsed wave Doppler in either the apical long axis or 5 chamber view to obtain it. The VTI can be traced out on the ultrasound machine or using digital software offline. ​ Recall that: Cardiac output is = Heart Rate x Stroke Volume ​ and ​ Stroke Volume = LVOT area x LVOT VTI so Stroke Volume= 3.14 (LVOT diameter/2)^2 x LVOT VTI. ​ In this example: LV stroke volume = 3.14 (2.0cm/2)^2 x 19cm = 60 cm^3 or 60 ml ​ If the heart rate is 100 then ​ Cardiac Output = HR x SV = 100 beats/min x 60 ml/beat = 6000 ml/min or 6.0L/min ​

Reviewed and revised 16 December 2015 OVERVIEW • Fluid responsiveness is an increase of stroke volume of 10-15% after the patient receives 500 ml of crystalloid over 10-15 minutes (as defined by Paul Marik) • Fluid responsiveness is also known as ‘volume responsiveness’ • The definitive test for fluid responsiveness is a • Fluid responsive patients have ‘preload reserve’ and will have an increase in stroke volume (and usually cardiac output) when fluid is administered • The presumption is that increased cardiac output will lead to increased oxygen delivery (DO2) and increased tissue oxygenation — but this is not always the case, and may not benefit the patient anyway! • Other haemodynamic parameters are sometimes used as surrogates for stroke volume. PREDICTING FLUID RESPONSIVENESS Static tests (less sensitive, less specific and less useful that dynamic tests) • Clinical static endpoints (e.g. heart rate, blood pressure, collapsed veins, capillary refill time, previous urine output) — not sensitive — poor inter-observer reliability • CVP/PCWP (also delta CVP post fluid challenge) — poor predictors • CXR — look for pulmonary edema — unreliable • PiCCO — EVLW and ITBV • ‘one off’ lactate or SvO2 (not useful) Dynamic tests • Passive leg raising — see — can use with pulse pressure change, PPV, VTI (echo), NICCOM, carotid Doppler flow, or ETCO2 (if ventilation and metabolic status constant) • End-expiratory occlusion test — Occluding the circuit at end-expiration prevents the c...