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Relationship between heart rate and oxygen kinetics during constant workload exercise

G N Kay¹, M S Ashar, R S Bubien

¹Division of Cardiovascular Disease, University of Alabama at Birmingham 35294, USA.

Pacing and Clinical Electrophysiology : PACE

|October 1, 1995

Summary

Abruptly increasing pacemaker heart rate at exercise onset improves oxygen deficit and reduces perceived exertion in patients with normal sinus node function. An overly aggressive response, however, did not enhance these benefits.

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Area of Science:

Exercise Physiology
Cardiovascular Physiology
Pacemaker Technology

Background:

Oxygen uptake during exercise exhibits an exponential increase to a steady state, with the difference termed the oxygen deficit.
The heart rate also increases, creating a heart rate deficit compared to the steady state.
This study investigates if eliminating the heart rate deficit impacts the oxygen deficit and perceived exertion.

Purpose of the Study:

To test if an instantaneous increase in heart rate to steady-state levels at exercise onset reduces the oxygen deficit.
To determine if this intervention improves perceived exertion compared to normal sinus node response.
To evaluate the effects of different pacemaker chronotropic responses on exercise physiology.

Main Methods:

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Ten subjects with normal sinus node function and DDD pacemakers underwent maximal exercise testing.

Constant workload exercise tests were performed with pacemakers programmed to three chronotropic responses: DDD, Fast, and Overpaced.

Oxygen deficit, VO2 kinetics, and perceived exertion (Borg scale) were measured.

Main Results:

The oxygen deficit was significantly lower with the fast chronotropic response compared to DDD and overpaced responses.
The rate constant for oxygen uptake (VO2 kinetics) was highest with the fast chronotropic pattern.
Perceived exertion ratings were lowest with the fast chronotropic response.

Conclusions:

An abrupt increase in pacing rate to match metabolic demand improves oxygen kinetics and reduces exertional symptoms in patients with normal sinus node function.
The DDD pacing mode resulted in a larger oxygen deficit and higher perceived exertion.
An overly aggressive chronotropic response did not provide additional benefits for oxygen kinetics or exertional symptoms.