IJCS | Volume 32, Nº1, January/ February 2019

64 Table 1 - Parameters evaluated by impedance cardiography Parameters Definition Normal values Formula HR Number of beats per minute 58-96 bpm RR interval measurement on the ECG and extrapolation to bpm MAP Mean pressure exerted by the blood on the arterial walls 84-100 mmHg Manual = ((SBP-DBP) x KP) + DBP Automatic (oscillometric method) = MAP is measured directly through SBP and DBP CO Amount of blood pumped by the left ventricle per minute 4.5-8.5 L/min CO = EjV x HR CI Standard CO for BSA 2.5-4.7 L/min/m2 CI = CO/BSA SV Amount of blood pumped by the left ventricle per heartbeat 60-130 mL/heartbeat SV = VEPT x LVET x VI (Z MARC ® Algorithm) SI Standard stroke volume for BSA 35-65 mL/heartbeat/m 2 SI = SV/BSA SVR Resistance of circulating blood to the arterial system 742-1,378 dynes sec/cm 5 SVR = 80 x ((MAP - CVP)/CO) SVRI Standard SVR for BSA 1,337-2,483 dynes.sec.m 2 /cm 5 SVRI = 80 x ((MAP - CVP)/ CI) AI Initial acceleration of blood in the aorta that occurs within the first 10-20 milliseconds after opening of the aortic valve Male: 70-150/100 sec 2 Female: 90-170/100 sec 2 AI = (d2Z/dt2Max)/ TFC VI in the aorta Peak velocity of blood flow in the aorta 33-65/1,000 sec VI = (dZ/dtMax)/ TFC TFC Electrical conductivity of the thoracic cavity (determined by intravascular, interalveolar and interstitial fluid) Male: 30-50/kohm Female: 21-37/kohm TFC = 1/ TFI LCW Indicator of the amount of work exerted by the left ventricle in each minute to pump blood into the systemic circulation 5.4-10 kg.m LCW = (MAP - PAOP) x CO LCW index Standard LCW for BSA 3.0-5.5 kg m/m 2 LCW index = (MAP - PAOP) x CI PEP The time interval from the beginning of electrical stimulation of the ventricles to the opening of the aortic valve (electrical systole) Depends on HR, contractility and resistance to diastolic filling Time interval between the beginning of the Q wave on the ECG and the B point on the dZ/dt wave (aortic valve opening) LVET Time interval from the opening to the closing of the aortic valve (mechanical systole) Depends on HR, contractility and resistance to diastolic filling Time interval between point B and point X of dZ/dt wave STR Ratio between the time of electrical and mechanical systole 0.3-0.5 STR = PEP / LVET HR: heart rate; ECG: electrocardiogram; MAP: mean arterial pressure; SBP: systolic blood pressure; DBP: diastolic blood pressure; KP: variable that depends on the pulse pressure ratio (usually varies between 0.25-0.33); CO: cardiac output; EjV: ejection volume; CI: cardiac index; BSA: body surface area; SV: stroke volume; VEPT: volume of electrically participating tissue (conductive volume for thorax size, affected by weight, height and gender); LVET: left ventricular ejection time; VI: Velocity index; SI: Stroke index; SVR: systemic vascular resistance; CVP: central venous pressure (pressure in the thoracic vena cava upon reaching the right atrium - the standard value of 7 mmHg is considered); SVRI: systemic vascular resistance index; AI: acceleration index; d2Z/ dt2Max: maximum of the second derivative of ΔZ; TFI: thoracic fluid index (baseline thoracic impedance, Z0); TFC: total fluid content; LCW: left cardiac work; PAOP: Pulmonary artery occluded pressure (the standard value is 10 mmHg); PEP: pre-ejection period; STR: systolic time ratio. Leão and Silva Impedance cardiography and hypertension Int J Cardiovasc Sci. 2019;32(1)61-69 Review Article