Affiliation:
1. Department of Medicine, University of Udine, Udine, ITALY
2. Physical Exercise Prescription Center, Gemona del Friuli Hospital, Gemona del Friuli, ITALY
3. Department of Cardiology, San Daniele del Friuli Hospital, San Daniele del Friuli, ITALY
Abstract
ABSTRACT
Purpose
Exercise prescription based on fixed heart rate (HR) values is not associated with a specific work rate (WR) during prolonged exercise. This phenomenon has never been evaluated in cardiac patients and might be associated with a slow component of HR kinetics and β-adrenergic activity. The aims were to quantify, in cardiac patients, the WR decrease at a fixed HR and to test if it would be attenuated by β-blockers.
Methods
Seventeen patients with coronary artery disease in stable conditions (69 ± 9 yr) were divided into two groups according to the presence (BB) or absence (no-BB) of a therapy with β-blockers, and performed on a cycle ergometer: an incremental exercise (INCR) and a 15-min “HRCLAMPED” exercise, in which WR was continuously adjusted to maintain a constant HR, corresponding to the gas exchange threshold +15%. HR was determined by the ECG signal, and pulmonary gas exchange was assessed breath-by-breath.
Results
During INCR, HRpeak was lower in BB versus no-BB (P < 0.05), whereas no differences were observed for other variables. During HRCLAMPED, the decrease in WR needed to maintain HR constant was less pronounced in BB versus no-BB (−16% ± 10% vs −27 ± 10, P = 0.04) and was accompanied by a decreased V̇O2 only in no-BB (−13% ± 6%, P < 0.001).
Conclusions
The decrease in WR during a 15-min exercise at a fixed HR (slightly higher than that at gas exchange threshold) was attenuated in BB, suggesting a potential role by β-adrenergic stimulation. The phenomenon may represent, also in this population, a sign of impaired exercise tolerance and interferes with aerobic exercise prescription.
Publisher
Ovid Technologies (Wolters Kluwer Health)
Subject
Physical Therapy, Sports Therapy and Rehabilitation,Orthopedics and Sports Medicine