Peripheral resistance

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The (total) peripheral resistance ( English total peripheral resistance , TPR ) is a parameter from the physiology of the cardiovascular system with medical significance. It quantifies the resistance that the blood vessels and the viscosity of the blood oppose the volume flow generated by the heart . In this context, periphery means “outside the heart” based in the vessels; an increased non-peripheral resistance would e.g. B. assume a narrowed aortic valve .

The peripheral resistance can vary within the framework of circulatory regulation . It decreases due to a widening (dilation) and increases due to a narrowing (constriction) of the arterioles , which locally determine the blood flow . Vascular constriction is mediated by the sympathetic nervous system and, as part of the baroreflex, counteracts short-term drops in blood pressure . Most antihypertensive drugs have vasodilating properties ( vasodilation ) that lower the total peripheral resistance.

Synonyms are: circuit resistance , vascular resistance, discharge resistance , afterload (afterload), hemodynamic resistance , afterload, total circulation resistance , peripheral vascular resistance and peripheral vascular resistance overall. The elasticity and stiffness of the blood vessels influence the peripheral resistance. The fact that the peripheral resistance is approximately the quotient of blood pressure and cardiac output is called the pressure-flow relationship . The fact that the cardiac output is approximately the quotient of blood pressure and peripheral resistance or the square root of the quotient of cardiac output and peripheral resistance applies independently of one another to the small and large blood circulation .

definition

The difference between mean arterial blood pressure and central venous pressure is what drives the blood flow through the body . The peripheral resistance is defined (analogous to the ohmic resistance ) as the quotient of the pressure difference and cardiac output (CO): This applies to both the (small) pulmonary circulation and the (large) body circulation ; in the small circuit the pressure difference corresponds to the pulmonary artery pressure .

The SI - unit in the peripheral resistance is Pa · s / m 3 =  N · s / m 5 . To older units have the relation 1  mmHg · min / l = 7,999,320 N · s / m 5 ≈ 80  dynes · sec / cm 5 . The dimension of the peripheral resistance is the quotient of the dimensions of pressure and volume flow. The pressure has the dimension ML −1 T −2 . The volume flow has the dimension L 3 T −1 . So the peripheral resistance has the dimension ML −4 T −1 .

The peripheral resistance results from the individual vessel resistances with analogous application of the rules for adding electrical resistances in series and parallel connection .

Measurement

The measurement of the peripheral resistance consists in the measurement of the pressure difference and the cardiac output. The pressures can be precisely determined during a cardiac catheter examination . Using a table value for the central venous pressure and a rule of thumb for calculating the mean arterial pressure, systolic and diastolic blood pressure from the usual blood pressure measurement can also be evaluated (with low accuracy) .

The cardiac output can be determined, for example, by echocardiography or impedance cardiography .

The peripheral resistance can be roughly estimated at the skin temperature (cool skin: high peripheral resistance; warm skin: low peripheral resistance). The shock index (heart rate divided by the arterial blood pressure) can be viewed as a measure of the peripheral resistance, whereby a normal stroke volume must be assumed so that the heart rate can be used to infer the cardiac output. A low peripheral resistance is then expressed in a high shock index.

Normal values

  • Great circulation: systemic or peripheral vascular resistance (SVR): 900–1400 dyn × sec × cm −5 = 11.3–17.5 mmHg × min / l =  90−140 N × s / m 5
  • Small circulation: pulmonary vascular resistance (PVR): 45–120 dyn × sec × cm −5 = 0.56–0.94 mmHg × min / l =  4.5–7.5 N × s / m 5

Influencing factors

Conditions with increased peripheral resistance
Conditions with decreased peripheral resistance
  • dynamic muscle work, recovery after muscle work
  • increased blood flow to the skin to give off heat
  • pregnancy
  • Shunts
  • anaphylactic shock
  • Hypoxia in the vessels of the great circulation

The hyperthyroidism (overactive thyroid) is a condition are simultaneously effective in the resistance-lowering effects and resistance. In total, the peripheral resistance is reduced.

Web links

Individual evidence

  1. ↑ F. Gross, R. Gotzen (Ed.): Diuresis and vasodilation in high pressure therapy. MMW Medizin Verlag, Munich 1982, ISBN 3-8208-1013-7 , p. 36.
  2. ↑ Georg Sabin: Der cardiogenic shock , Verlag W. Kohlhammer , Stuttgart, Berlin, Cologne, Mainz 1984, ISBN 3-17-008618-9 , pages 26 and 30.
  3. ^ Wolfgang Trautwein , Otto Heinrich Gauer , Hans-Peter Koepchen : Heart and Circulation , Urban & Schwarzenberg , Munich, Berlin, Vienna 1972, ISBN 3-541-05411-5 , p. 127.
  4. ^ Myron G. Sulyma: Dictionary of Cardiology , Medikon-Verlag, Volume I (A − D), Munich 1983, ISBN 3-923066-02-X , p. 9 f.
  5. ^ Walter Bleifeld, Christian W. Hamm: Heart and circulation , Springer-Verlag, Berlin / Heidelberg / New York 1987, ISBN 3-540-17931-3 .
  6. ^ Already Franz Volhard wrote that "one can regard the diastolic pressure as a measure of the [peripheral] resistance". Source: Hans Erhard Bock , KH Hildebrand, Hans Joachim Sarre (eds.): Franz Volhard Memories , Schattauer Verlag , Stuttgart, New York 1982, ISBN 3-7845-0898-X , p. 65.
  7. ↑ Another view, H. Schieffer: Arterial hypertension. Verlag Karl Thiemig, Munich 1983, OCLC 634917262 , p. 11. Quote: "According to Ohm's law p = CO x R, the blood pressure p is guaranteed by the product of the cardiac output (CO) and the peripheral resistance (R)." is the actual blood pressure and not a pressure difference.
  8. ↑ Another view: Wolfgang Trautwein , Otto Heinrich Gauer , Hans-Peter Koepchen: Heart and circulation. Urban & Schwarzenberg, Munich / Berlin / Vienna 1972, ISBN 3-541-05411-5 , p. 177: "Current-time volume or current strength I, pressure p and resistance W are linked to one another by Ohm's law when the flow is stationary : I = p / W. "
  9. ↑ Another view: Myron G. Sulyma: Dictionary of Cardiology. Volume III: L-Q. Medikon Verlag, Munich 1984, ISBN 3-923866-07-0 , p. 551: “ peripheral flow resistance : Peripherer flow resistance . Quotient of pressure gradient and blood flow. "
  10. ↑ Otto M. Hess, Rüdiger WR Simon (Ed.): Herzkatheter. Springer-Verlag, Berlin / Heidelberg 2000, ISBN 3-642-62957-1 , p. 21: "Resistance R as quotient of mean pressure gradient Δp and mean flow Q as static or direct current resistance".
  11. ↑ Another view: D. Kleinknecht et alii: Transplantation, Nephrectomy and Hypertension , in: Karl Klütsch, Ernst Wollheim, Hans-Jürgen Holtmeier (Ed.): Die Niere im Kreis , Georg Thieme Verlag, Stuttgart 1971, ISBN 3-13- 468201-X , p. 219. Here the total peripheral resistance (TPR) is defined as the quotient of the mean arterial pressure (MBP) and the cardiac output CO.
  12. ↑ Christian Mewis, Reimer Riessen, Ioakim Spyridopoulos (eds.): Kardiologie compact - Everything for ward and specialist examination . 2nd Edition. Thieme, Stuttgart / New York 2006, ISBN 3-13-130742-0 , pp. 110 ( books.google.de ).