CC BY-NC-ND 4.0 · Indian Journal of Cardiovascular Disease in Women - WINCARS 2020; 5(04): 364-367
DOI: 10.1055/s-0040-1722560
Student's Corner

Student’s Corner–2

Dayasagar Rao
1  Cardiology Department, KIMS, Hyderabad, Telangana, India
P. Sampath Kumar
2  Cardiology Department, Osmania, Hyderabad, Telangana, India
› Author Affiliations

Q1. Why DBP Does not Vary with AV Dissociation and Atrial Fibrillation

Answer by Prof. Dayasagar Rao

Systolic blood pressure (SBP) is mainly determined by stroke volume, while diastolic blood pressure (DBP) is determined by systemic vascular resistance (SVR), compliance of the arterial wall and duration of diastole.

When we say atrioventricular (AV) dissociation, we mean that the atria and the ventricles have independent rates and rhythms with a loss of synchrony, whereas in atrial fibrillation, the extremely high-heart rates make atrial contractions ineffective while reducing the diastolic filling time between two beats, leading to reduced ventricular filling. The variation in SBP in AV dissociation is due to variation in preload to ventricle proportional to atrial contribution to ventricle filling. No atrial contribution to ventricular filling occurs during simultaneous contraction of atria and ventricles, and maximum contribution by atria occurs when atrial contraction precedes ventricular contraction. Thus, in both these conditions, stroke volume is effectively reduced. Since DBP is not influenced by stroke volume, there are no changes seen.


Answer by Prof. Sampath

Arterial blood pressure is defined as lateral pressure exerted by contained column of blood on the walls of arteries.

Systolic blood pressure: It is the maximum pressure exerted in the arteries during systole of heart. It is calculated as a product of heart rate and stroke volume.

Diastolic blood pressure: It is the minimum pressure in the arteries during diastole of heart.

(It is multifactorial, depending on blood vessel diameter, vessel elasticity, blood viscosity, and total blood volume)

Determinants of systolic blood pressure:

Determinants of diastolic BP:

Volume of blood ejected

Volume of blood remained

Compliance of arterial wall

Compliance of arterial wall

Rate of runoff (resistance)

Peripheral resistance

In the above question, for the patient with AV dissociation and atrial fibrillation (preferably isolated), there is no change in peripheral resistance, which is the key determinant of DBP. Hence, no change in DBP.

For Students, a Few Important Formulae Relevant to the Question is Mentioned Below

Normally, diastole is longer than systole; hence, mean arterial pressure is not arithmetic mean of systolic and diastolic blood pressure.

Mean BP: DBP + 1/3rd of pulse pressure

Pulse pressure: SBP − DBP

Systolic pressure = diastolic pressure + pulse pressure

Pulse pressure = stroke volume/arterial capacitance

Mean arterial pressure = cardiac output × total peripheral resistance

Cardiac output =heart rate × stroke volume

Total peripheral resistance: blood viscosity × vascular resistance


Publication History

Publication Date:
31 December 2020 (online)

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