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Maximal heart rate does not limit cardiovascular capacity in healthy humans: insight from right atrial pacing during maximal exercise
Author(s) -
Munch G. D. W.,
Svendsen J. H.,
Damsgaard R.,
Secher N. H.,
GonzálezAlonso J.,
Mortensen S. P.
Publication year - 2014
Publication title -
the journal of physiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.802
H-Index - 240
eISSN - 1469-7793
pISSN - 0022-3751
DOI - 10.1113/jphysiol.2013.262246
Subject(s) - cardiology , medicine , heart rate , cardiac output , preload , stroke volume , tachycardia , cardiac function curve , aerobic exercise , hemodynamics , blood pressure , heart failure
Key points During high intensity whole‐body exercise, systemic and contracting skeletal muscle O 2 delivery and uptake ( V ̇ O 2 ) are compromised, but the underlying mechanisms remain unclear. We evaluated the effect of a ∼20 beats min −1 increase in heart rate (HR) by right atrial pacing during incremental cycling and knee‐extensor exercise on cardiac output ( Q ̇ ) and stroke volume (SV). An increase in HR during both exercise modalities did not alter Q ̇ due to a proportional decrease in SV. The lower SV during atrial pacing in the cycling trial was associated with a diminished cardiac filling pressure, but similar arterial pressure. The results demonstrate that the human heart can achieve a higher HR than observed during maximal exercise, suggesting that HR max and myocardial work capacity do not limit cardiac performance in trained human subjects. Instead, restrictions in ventricular filling appear to compromise cardiac preload, SV and Q ̇ at exercise intensities close toV ̇O 2 max.Abstract In humans, maximal aerobic power ( V ̇O 2 max) is associated with a plateau in cardiac output ( Q ̇ ), but the mechanisms regulating the interplay between maximal heart rate (HR max ) and stroke volume (SV) are unclear. To evaluate the effect of tachycardia and elevations in HR max on cardiovascular function and capacity during maximal exercise in healthy humans, 12 young male cyclists performed incremental cycling and one‐legged knee‐extensor exercise (KEE) to exhaustion with and without right atrial pacing to increase HR. During control cycling, Q ̇ and leg blood flow increased up to 85% of maximal workload (WL max ) and remained unchanged until exhaustion. SV initially increased, plateaued and then decreased before exhaustion ( P < 0.05) despite an increase in right atrial pressure (RAP) and a tendency ( P = 0.056) for a reduction in left ventricular transmural filling pressure (LVFP). Atrial pacing increased HR max from 184 ± 2 to 206 ± 3 beats min −1 ( P < 0.05), but Q ̇ remained similar to the control condition at all intensities because of a lower SV and LVFP ( P < 0.05). No differences in arterial pressure, peripheral haemodynamics, catecholamines orV ̇ O 2were observed, but pacing increased the rate pressure product and RAP ( P < 0.05). Atrial pacing had a similar effect on haemodynamics during KEE, except that pacing decreased RAP. In conclusion, the human heart can be paced to a higher HR than observed during maximal exercise, suggesting that HR max and myocardial work capacity do not limitV ̇O 2 maxin healthy individuals. A limited left ventricular filling and possibly altered contractility reduce SV during atrial pacing, whereas a plateau in LVFP appears to restrict Q ̇ close toV ̇O 2 max.