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Morris GS1, Brueilly KE2
1Wingate University, Physical Therapy, Wingate, North Carolina, United States, 2Augusta University, Physical Therapy, Augusta, United States
Background: : Chronotropic incompetence (CI) is an inability of the heart to increase its beat rate commensurate with increased functional demand and is thought to reflect underlying autonomic dysfunction. Because aerobic exercise prescriptions are typically predicated on a linear relationship between heart rate and increasing functional demand, the presence of CI limits the utility of this relationship in prescribing exercise intensity. Cancer survivors are known to have autonomic dysfunction and exercise training is an increasingly important therapeutic intervention for this population. As such, it is important to know the incidence of this biomarker of autonomic dysfunction in order to ensure that heart rate-based exercise prescriptions are safe and effective.
Purpose: The purpose of this observational study was to determine the incidence of CI in adults recently diagnosed with abdominal and gastro-intestinal tract cancers.
Methods: 122 subjects (males=91) with a variety of abdominal and digestive tract cancers underwent spirometry (MVV, FEV1, FVC), followed by a standardized ramp bicycle ergometer cardiopulmonary exercise test (CPET) with end-tidal gas analysis (CardiO2/CP system, Medical Graphics Corporation, USA) one week prior to undergoing surgery. The exercise protocol entailed 3 minutes resting on the ergometer, followed by 3 minutes of unloaded cycling, and then performing a ramp protocol to volitional fatigue, followed by 3 minutes of recovery. Ramp rates (5-25 Watts/minute) were chosen to achieve standard test durations of 8-12 minutes per patient. CPET parameters were analyzed by Harbor-UCLA standard methods. Participants who achieved a respiratory exchange ratio (RER) > 1.10 during the CPET were considered to have achieved maximal exercise exertion. CI was defined as an inability to achieve either 1) 85% of age predicted maximum heart rate [age predicted HRmax = 207-(0.7 X age)] during maximal exercise or 2) 80% of predicted heart rate reserve [HRR; (maximum achieved heart rate minus resting heart rate)/(age predicted maximum heart rate minus resting heart rate)]. (Brubaker & Kitzman. Circ. 2011:123:1010).
Results: Subjects (mean age 58.2 + 7.07 yrs.) required on average 10.83 min to reach volitional fatigue (range = 7.55 - 17.50 min). Respiratory exchange ratio (RER) ranged between 1.1 and 1.58, demonstrating that these subjects had achieved a maximal exertional effort. Fifty individuals (41% of the cohort) failed to achieve a HRmax > 85% of age predicted HRmax; 76 individuals (62%) of the cohort failed to achieve a HRR ratio > 80% of predicted HRR and 50 individuals met both criteria for CI.
Conclusion(s): These results 1) suggest that survivors of abdominal and gastro-intestinal cancers are at increased risk of having CI and hence are at risk for incorrect exercise prescriptions, 2) support the need to broadly investigate the incidence of CI in survivors of other cancer diagnoses, because of widespread autonomic dysfunction occurs in this patient population, and 3) provide physiologic support for the current definition of CI.
Implications: These results raise the possibility that prescribed exercise training intensities predicated on age predicted HRmax may result in cancer survivors exercising at greater than intended intensities.
Keywords: Oncology, Chronotropic Incompetence, Exercise Prescription
Funding acknowledgements: This project was unfunded
Purpose: The purpose of this observational study was to determine the incidence of CI in adults recently diagnosed with abdominal and gastro-intestinal tract cancers.
Methods: 122 subjects (males=91) with a variety of abdominal and digestive tract cancers underwent spirometry (MVV, FEV1, FVC), followed by a standardized ramp bicycle ergometer cardiopulmonary exercise test (CPET) with end-tidal gas analysis (CardiO2/CP system, Medical Graphics Corporation, USA) one week prior to undergoing surgery. The exercise protocol entailed 3 minutes resting on the ergometer, followed by 3 minutes of unloaded cycling, and then performing a ramp protocol to volitional fatigue, followed by 3 minutes of recovery. Ramp rates (5-25 Watts/minute) were chosen to achieve standard test durations of 8-12 minutes per patient. CPET parameters were analyzed by Harbor-UCLA standard methods. Participants who achieved a respiratory exchange ratio (RER) > 1.10 during the CPET were considered to have achieved maximal exercise exertion. CI was defined as an inability to achieve either 1) 85% of age predicted maximum heart rate [age predicted HRmax = 207-(0.7 X age)] during maximal exercise or 2) 80% of predicted heart rate reserve [HRR; (maximum achieved heart rate minus resting heart rate)/(age predicted maximum heart rate minus resting heart rate)]. (Brubaker & Kitzman. Circ. 2011:123:1010).
Results: Subjects (mean age 58.2 + 7.07 yrs.) required on average 10.83 min to reach volitional fatigue (range = 7.55 - 17.50 min). Respiratory exchange ratio (RER) ranged between 1.1 and 1.58, demonstrating that these subjects had achieved a maximal exertional effort. Fifty individuals (41% of the cohort) failed to achieve a HRmax > 85% of age predicted HRmax; 76 individuals (62%) of the cohort failed to achieve a HRR ratio > 80% of predicted HRR and 50 individuals met both criteria for CI.
Conclusion(s): These results 1) suggest that survivors of abdominal and gastro-intestinal cancers are at increased risk of having CI and hence are at risk for incorrect exercise prescriptions, 2) support the need to broadly investigate the incidence of CI in survivors of other cancer diagnoses, because of widespread autonomic dysfunction occurs in this patient population, and 3) provide physiologic support for the current definition of CI.
Implications: These results raise the possibility that prescribed exercise training intensities predicated on age predicted HRmax may result in cancer survivors exercising at greater than intended intensities.
Keywords: Oncology, Chronotropic Incompetence, Exercise Prescription
Funding acknowledgements: This project was unfunded
Topic: Oncology, HIV & palliative care; Cardiorespiratory
Ethics approval required: Yes
Institution: Univ. of Texas M.D. Anderson Cancer Center
Ethics committee: Institutional Review Board
Ethics number: Unknown
All authors, affiliations and abstracts have been published as submitted.
